WorldWideScience

Sample records for galaxy group implication

  1. Isolated galaxies, pairs, and groups of galaxies

    International Nuclear Information System (INIS)

    Kuneva, I.; Kalinkov, M.

    1990-01-01

    The authors searched for isolated galaxies, pairs and groups of galaxies in the CfA survey (Huchra et al. 1983). It was assumed that the distances to galaxies are given by R = V/H sub o, where H sub o = 100 km s(exp -1) Mpc(exp -1) and R greater than 6 Mpc. The searching procedure is close to those, applied to find superclusters of galaxies (Kalinkov and Kuneva 1985, 1986). A sphere with fixed radius r (asterisk) is described around each galaxy. The mean spatial density in the sphere is m. Let G 1 be any galaxy and G 2 be its nearest neighbor at a distance R 2 . If R sub 2 exceeds the 95 percent quintile in the distribution of the distances of the second neighbors, then G 1 is an isolated galaxy. Let the midpoint of G 1 and G 2 be O 2 and r 2 =R 2 2. For the volume V 2 , defined with the radius r 2 , the density D 2 less than k mu, the galaxy G 2 is a single one and the procedure for searching for pairs and groups, beginning with this object is over and we have to pass to another object. Here the authors present the groups - isolated and nonisolated - with n greater than 3, found in the CfA survey in the Northern galactic hemisphere. The parameters used are k = 10 and r (asterisk) = 5 Mpc. Table 1 contains: (1) the group number, (2) the galaxy, nearest to the multiplet center, (3) multiplicity n, (4) the brightest galaxy if it is not listed in (2); (5) and (6) are R.A. and Dec. (1950), (7) - mean distance D in Mpc. Further there are the mean density rho (8) of the multiplet (galaxies Mpc (exp -3)), (9) the density rho (asterisk) for r (asterisk) = 5 Mpc and (10) the density rho sub g for the group with its nearest neighbor. The parenthesized digits for densities in the last three columns are powers of ten

  2. Observational properties of compact groups of galaxies

    International Nuclear Information System (INIS)

    Hickson, P.

    1990-01-01

    Compact groups are small, relatively isolated, systems of galaxies with projected separations comparable to the diameters of the galaxies themselves. Two well-known examples are Stephan's Quintet (Stephan, 1877) and Seyfert's Sextet (Seyfert 1948a,b). In groups such as these, the apparent space density of galaxies approaches 10(exp 6) Mpc(sub -3), denser even than the cores of rich clusters. The apparent unlikeliness of the chance occurrence of such tight groupings lead Ambartsumyan (1958, 1975) to conclude that compact groups must be physically dense systems. This view is supported by clear signs of galaxy interactions that are seen in many groups. Spectroscopic observations reveal that typical relative velocities of galaxies in the groups are comparable to their internal stellar velocities. This should be conducive to strong gravitational interactions - more so than in rich clusters, where galaxy velocities are typically much higher. This suggests that compact groups could be excellent laboratories in which to study galaxy interactions and their effects. Compact groups often contain one or more galaxies whose redshift differs greatly from those of the other group members. If these galaxies are at the same distance as the other members, either entire galaxies are being ejected at high velocities from these groups, or some new physical phenomena must be occurring. If their redshifts are cosmological, we must explain why so many discordant galaxies are found in compact groups. In recent years much progress has been made in addressing these questions. Here, the author discusses the current observational data on compact groups and their implications

  3. Diffuse X-ray emission from the NGC 2300 group of galaxies - Implications for dark matter and galaxy evolution in small groups

    Science.gov (United States)

    Mulchaey, John S.; Davis, David S.; Mushotzky, Richard F.; Burstein, David

    1993-01-01

    The discovery of diffuse X-ray emission from the NGC 2300 group of galaxies using the ROSAT Position Sensitive Proportional Counter is reported. The gas distributions is roughly symmetric and extends to a radius of at least 0.2/h(50) Mpc. A Raymond-Smith hot plasma model provides an excellent fit the X-ray spectrum with a best-fit value temperature of 0.9 + -/15 or - 0.14 keV and abundance 0.06 + 0/.12 or - 0.05 solar. The assumption of gravitational confinement leads to a total mass of the group of 3.0 + 0.4 or - 0.5 x 10 exp 13 solar. Baryons can reasonably account for 4 percent of this mass, and errors could push this number not higher than 10-15 percent. This is one of the strongest pieces of evidence that dark matter dominates small groups such as this one. The intragroup medium in this system has the lowest metal abundance yet found in diffuse gas in a group or cluster.

  4. ALIGNMENTS OF GROUP GALAXIES WITH NEIGHBORING GROUPS

    International Nuclear Information System (INIS)

    Wang Yougang; Chen Xuelei; Park, Changbom; Yang Xiaohu; Choi, Yun-Young

    2009-01-01

    Using a sample of galaxy groups found in the Sloan Digital Sky Survey Data Release 4, we measure the following four types of alignment signals: (1) the alignment between the distributions of the satellites of each group relative to the direction of the nearest neighbor group (NNG); (2) the alignment between the major axis direction of the central galaxy of the host group (HG) and the direction of the NNG; (3) the alignment between the major axes of the central galaxies of the HG and the NNG; and (4) the alignment between the major axes of the satellites of the HG and the direction of the NNG. We find strong signal of alignment between the satellite distribution and the orientation of central galaxy relative to the direction of the NNG, even when the NNG is located beyond 3r vir of the host group. The major axis of the central galaxy of the HG is aligned with the direction of the NNG. The alignment signals are more prominent for groups that are more massive and with early-type central galaxies. We also find that there is a preference for the two major axes of the central galaxies of the HG and NNG to be parallel for the system with both early central galaxies, however, not for the systems with both late-type central galaxies. For the orientation of satellite galaxies, we do not find any significant alignment signals relative to the direction of the NNG. From these four types of alignment measurements, we conclude that the large-scale environment traced by the nearby group affects primarily the shape of the host dark matter halo, and hence also affects the distribution of satellite galaxies and the orientation of central galaxies. In addition, the NNG directly affects the distribution of the satellite galaxies by inducing asymmetric alignment signals, and the NNG at very small separation may also contribute a second-order impact on the orientation of the central galaxy in the HG.

  5. Groups and clusters of galaxies

    International Nuclear Information System (INIS)

    Bijleveld, W.

    1984-01-01

    In this thesis, a correlative study is performed with respect to the radio and X-ray parameters of galaxy clusters and groups of galaxies (Msub(v)-Psub(1.4); Msub(v)-Lsub(x); Lsub(x)-Psub(1.4); R-Msub(v) correlations). Special attention is paid to correlations with cD and elliptical galaxies. It is concluded that in rich clusters massive cD galaxies form; massive galaxies are able to bind a large X-ray halo; strong X-ray emitters fuel their central radio sources at a high rate; the total gas content of groups is low, which implies that the contribution of groups to the total matter density in the universe is small. (Auth.)

  6. CHANDRA observations of the NGC 1550 galaxy group: Implication for the temperature and entropy profiles of 1 keV galaxy groups

    DEFF Research Database (Denmark)

    Sun, M.; Forman, W.; Vikhlinin, A.

    2003-01-01

    is remarkably similar to those of two other 1 keV groups with accurate temperature determination. The temperature begins to decline at 0.07r(vir) - 0.1r(vir), while in hot clusters the decline begins at or beyond 0.2rvir. Thus, there are at least some 1 keV groups that have temperature profiles significantly...... different from those of hot clusters, which may reflect the role of nongravitational processes in intracluster medium/intergalactic medium evolution. NGC 1550 has no isentropic core in its entropy pro. le, in contrast to the predictions of "entropy floor'' simulations. We compare the scaled entropy profiles...

  7. The Impact of Star Formation Histories on Stellar Mass Estimation: Implications from the Local Group Dwarf Galaxies

    Science.gov (United States)

    Zhang, Hong-Xin; Puzia, Thomas H.; Weisz, Daniel R.

    2017-11-01

    Building on the relatively accurate star formation histories (SFHs) and metallicity evolution of 40 Local Group (LG) dwarf galaxies derived from resolved color-magnitude diagram modeling, we carried out a comprehensive study of the influence of SFHs, metallicity evolution, and dust extinction on the UV-to-near-IR color-mass-to-light ratio (color-{log}{{{\\Upsilon }}}\\star (λ)) distributions and M ⋆ estimation of local universe galaxies. We find that (1) the LG galaxies follow color-{log}{{{\\Upsilon }}}\\star (λ) relations that fall in between the ones calibrated by previous studies; (2) optical color-{log}{{{\\Upsilon }}}\\star (λ) relations at higher [M/H] are generally broader and steeper; (3) the SFH “concentration” does not significantly affect the color-{log}{{{\\Upsilon }}}\\star (λ) relations; (4) light-weighted ages }λ and metallicities }λ together constrain {log}{{{\\Upsilon }}}\\star (λ) with uncertainties ranging from ≲0.1 dex for the near-IR up to 0.2 dex for the optical passbands; (5) metallicity evolution induces significant uncertainties to the optical but not near-IR {{{\\Upsilon }}}\\star (λ) at a given }λ and }λ ; (6) the V band is the ideal luminance passband for estimating {{{\\Upsilon }}}\\star (λ) from single colors, because the combinations of {{{\\Upsilon }}}\\star (V) and optical colors such as B - V and g - r exhibit the weakest systematic dependences on SFHs, metallicities, and dust extinction; and (7) without any prior assumption on SFHs, M ⋆ is constrained with biases ≲0.3 dex by the optical-to-near-IR SED fitting. Optical passbands alone constrain M ⋆ with biases ≲0.4 dex (or ≲0.6 dex) when dust extinction is fixed (or variable) in SED fitting. SED fitting with monometallic SFH models tends to underestimate M ⋆ of real galaxies. M ⋆ tends to be overestimated (or underestimated) at the youngest (or oldest) }{mass}.

  8. The group environment of Seyfert galaxies. II. Spectrophotometry of galaxies in groups

    International Nuclear Information System (INIS)

    Fricke, K.J.; Kollatschny, W.

    1989-01-01

    Medium-resolution spectrophotometric data of 104 galaxies have been obtained. These galaxies are members of 22 loose groups of < 1 Mpc size. Thirteen of these groups contain Seyfert galaxies. In this paper we present calibrated emission-line data and absolute optical spectra of the individual galaxies as well as plates of each group

  9. Measuring Extinction in Local Group Galaxies Using Background Galaxies

    Science.gov (United States)

    Wyder, T. K.; Hodge, P. W.

    1999-05-01

    Knowledge of the distribution and quantity of dust in galaxies is important for understanding their structure and evolution. The goal of our research is to measure the total extinction through Local Group galaxies using measured properties of background galaxies. Our method relies on the SExtractor software as an objective and automated method of detecting background galaxies. In an initial test, we have explored two WFPC2 fields in the SMC and two in M31 obtained from the HST archives. The two pointings in the SMC are fields around the open clusters L31 and B83 while the two M31 fields target the globular clusters G1 and G170. Except for the G1 observations of M31, the fields chosen are very crowded (even when observed with HST) and we chose them as a particularly stringent test of the method. We performed several experiments using a series of completeness tests that involved superimposing comparison fields, adjusted to the equivalent exposure time, from the HST Medium-Deep and Groth-Westphal surveys. These tests showed that for crowded fields, such as the two in the core of the SMC and the one in the bulge of M31, this automated method of detecting galaxies can be completely dominated by the effects of crowding. For these fields, only a small fraction of the added galaxies was recovered. However, in the outlying G1 field in M31, almost all of the added galaxies were recovered. The numbers of actual background galaxies in this field are consistent with zero extinction. As a follow-up experiment, we used image processing techniques to suppress stellar objects while enhancing objects with non-stellar, more gradual luminosity profiles. This method yielded significant numbers of background galaxies in even the most crowded fields, which we are now analyzing to determine the total extinction and reddening caused by the foreground galaxy.

  10. Clusters and Groups of Galaxies : International Meeting

    CERN Document Server

    Giuricin, G; Mezzetti, M

    1984-01-01

    The large-scale structure of the Universe and systems Clusters, and Groups of galaxies are topics like Superclusters, They fully justify the meeting on "Clusters of great interest. and Groups of Galaxies". The topics covered included the spatial distribution and the clustering of galaxies; the properties of Superclusters, Clusters and Groups of galaxies; radio and X-ray observations; the problem of unseen matter; theories concerning hierarchical clustering, pancakes, cluster and galaxy formation and evolution. The meeting was held at the International Center for Theoretical Physics in Trieste (Italy) from September 13 to September 16, 1983. It was attended by about 150 participants from 22 nations who presented 67 invited lectures (il) and contributed papers (cp), and 45 poster papers (pp). The Scientific Organizing Committee consisted of F. Bertola, P. Biermann, A. Cavaliere, N. Dallaporta, D. Gerba1, M. Hack, J . V . Peach, D. Sciama (Chairman), G. Setti, M. Tarenghi. We are particularly indebted to D. Scia...

  11. Dynamical theory of dense groups of galaxies

    Science.gov (United States)

    Mamon, Gary A.

    1990-01-01

    It is well known that galaxies associate in groups and clusters. Perhaps 40% of all galaxies are found in groups of 4 to 20 galaxies (e.g., Tully 1987). Although most groups appear to be so loose that the galaxy interactions within them ought to be insignificant, the apparently densest groups, known as compact groups appear so dense when seen in projection onto the plane of the sky that their members often overlap. These groups thus appear as dense as the cores of rich clusters. The most popular catalog of compact groups, compiled by Hickson (1982), includes isolation among its selection critera. Therefore, in comparison with the cores of rich clusters, Hickson's compact groups (HCGs) appear to be the densest isolated regions in the Universe (in galaxies per unit volume), and thus provide in principle a clean laboratory for studying the competition of very strong gravitational interactions. The $64,000 question here is then: Are compact groups really bound systems as dense as they appear? If dense groups indeed exist, then one expects that each of the dynamical processes leading to the interaction of their member galaxies should be greatly enhanced. This leads us to the questions: How stable are dense groups? How do they form? And the related question, fascinating to any theorist: What dynamical processes predominate in dense groups of galaxies? If HCGs are not bound dense systems, but instead 1D change alignments (Mamon 1986, 1987; Walke & Mamon 1989) or 3D transient cores (Rose 1979) within larger looser systems of galaxies, then the relevant question is: How frequent are chance configurations within loose groups? Here, the author answers these last four questions after comparing in some detail the methods used and the results obtained in the different studies of dense groups.

  12. Redshift differences of galaxies in nearby groups

    Science.gov (United States)

    Harrison, E. R.

    1975-01-01

    It is reported that galaxies in nearby groups exhibit anomalous nonvelocity redshifts. In this discussion, (1) four classes of nearby groups of galacies are analyzed, and no significant nonvelocity redshift effect is found; and (2) it is pointed out that transverse velocities (i.e., velocities transverse to the line of sight of the main galaxy, or center of mass) contribute components to the redshift measurements of companion galaxies. The redshifts of galaxies in nearby groups of appreciable angular size are considerably affected by these velocity projection effects. The transverse velocity contributions average out in rich, isotropic groups, and also in large samples of irregular groups of low membership, as in the four classes referred to in (1), but can introduce apparent discrepancies in small samples (as studied by Arp) of nearby groups of low membership.

  13. Dynamical properties of compact groups of galaxies

    Science.gov (United States)

    Hickson, Paul; De Oliveira, Claudia M.; Huchra, John P.; Palumbo, Giorgio G.

    1992-01-01

    Radial velocities are presented for 457 galaxies in the 100 Hickson compact groups. More than 84 percent of the galaxies measured have velocities within 1000 km/s of the median velocity in the group. Ninety-two groups have at least three accordant members, and 69 groups have at least four. The radial velocities of these groups range from 1380 to 42,731 km/s with a median of 8889 km/s, corresponding to a median distance of 89/h Mpc. The apparent space density of these systems ranges from 300 to as much as 10 exp 8 sq h/sq Mpc, which exceeds the densities in the centers of rich clusters. The median projected separation between galaxies is 39/h kpc, comparable to the sizes of the galaxies themselves. A significant correlation is found between crossing time and the fraction of gas-rich galaxies in the groups, and a weak anticorrelation is found between crossing time and the luminosity contrast of the first-ranked galaxy.

  14. Galaxies Die in Groups: An IRAC Autopsy

    Science.gov (United States)

    Wilman, D. J.; Pierini, D.; Tyler, K.; McGee, S. L.; Oemler, A., Jr.; Morris, S. L.; Balogh, M. L.; Bower, R. G.; Mulchaey, J. S.

    2008-10-01

    The most massive galaxies in the Universe are also the oldest. To overturn this apparent contradiction with hierarchical growth models, we focus on the group-scale haloes which host most of these galaxies. Our z˜0.4 group sample is selected in redshift space from the CNOC2 redshift survey. A stellar mass selected M_{*} ≲ 2×10^{10}M_{⊙} sample is constructed using IRAC observations. A sensitive Mid InfraRed (MIR) IRAC colour is used to isolate passive galaxies. It produces a bimodal distribution, in which passive galaxies (highlighted by morphological early-types) define a tight MIR colour sequence (Infrared Passive Sequence, IPS). This is due to stellar atmospheric emission from old stellar populations. Significantly offset from the IPS are galaxies where reemission by dust boosts emission at λ_{obs}=8 micron. We term them InfraRed-Excess galaxies whether star formation and/or AGN activity are present. They include all known morphological late-types. The fraction of InfraRed Excess galaxies, f(IRE) drops with M_{*}, such that f(IRE)=0.5 at a ``crossover mass'' of M_{cr}˜ 1.3×10^{11}M_{⊙}. Within our optically-defined group sample there is a strong and consistent deficit in f(IRE) at all masses, but most clearly at M_{*} ≲ 10^{11}M_{⊙}. Suppression of star formation must mainly occur in groups, and the observed trend of f(IRE) with M_{*} can be explained if suppression of M_{*} ≲ 10^{11}M_{⊙} galaxies occurs primarily in the group environment.

  15. Enriched gas in clusters and the dynamics of galaxies and clusters: implications for theories of galaxy formation

    International Nuclear Information System (INIS)

    Binney, J.; Silk, J.

    1978-01-01

    Recent developments in relation to the origin of galaxies are cited: the discovery that the intergalactic medium which seems to pervade rich clusters of galaxies has an iron abundance that lies within an order of magnitude of the solar value; the discovery that elliptical galaxies rotate much more slowly than the models of these galaxies had predicted; and the results of studies of cosmological infall in the context of the formation of galaxies and galaxy clusters, which have shown that the resulting density profile is fairly insensitive to initial conditions. After discussing the implications of these recent observations of X-ray clusters and of the rotation of elliptical galaxies, an attempt is made to construct a picture of the formation of elliptical and spiral galaxies in which galaxies form continuously from redshift z approximately 100 onwards. It is suggested that at a redshift z of roughly 5, a fundamental change occurred in the manner in which the cosmic material fragmented into stellar objects. It seems possible that explanations of a variety of puzzling aspects of galactic evolution, including the formation of Population I disks, the origin of the hot intracluster gas, the mass-to-light ratio stratification of galaxies, and the nature of the galaxy luminosity function, should all be sought in the context of this change of regime. Some remarks are made about gas in poor groups of galaxies and the interaction of disk galaxies with their environments. (U.K.)

  16. Stellar kinematics and structural properties of virgo cluster dwarf early-type galaxies from the SMAKCED project. I. Kinematically decoupled cores and implications for infallen groups in clusters

    Energy Technology Data Exchange (ETDEWEB)

    Toloba, E.; Guhathakurta, P. [UCO/Lick Observatory, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Van de Ven, G. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Boissier, S.; Boselli, A. [Laboratoire d' Astrophysique de Marseille-LAM, Université d' Aix-Marseille and CNRS, UMR 7326, 38 rue F. Joliot-Curie, F-13388 Marseille Cedex 13 (France); Den Brok, M. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Falcón-Barroso, J.; Ryś, A. [Instituto de Astrofísica de Canarias, Vía Láctea s/n, La Laguna, Tenerife (Spain); Hensler, G. [Department of Astrophysics, University of Vienna, Türkenschanzstraße 17, 1180 Vienna (Austria); Janz, J.; Lisker, T. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, D-69120 Heidelberg (Germany); Laurikainen, E.; Salo, H. [Division of Astronomy, Department of Physics, University of Oulu, P.O. Box 3000, FI-90014 Oulu (Finland); Paudel, S. [Laboratoire AIM Paris-Saclay, CNRS/INSU, Université Paris Diderot, CEA/IRFU/SAp, F-91191 Gif-sur-Yvette Cedex (France); Peletier, R. F., E-mail: toloba@ucolick.org [Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen (Netherlands)

    2014-03-10

    We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.''8 (0.14 kpc) and 4.''2 (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC. The frequency of occurrence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation.

  17. Nature of compact groups of galaxies

    International Nuclear Information System (INIS)

    Hickson, P.; Rood, H.J.

    1988-01-01

    Monte Carlo numerical simulation is used to calculate the probability for the chance occurrence of four galaxies projected on the sky satisfying the Hickson isolation criterion within a loose group of eight members. For the models which match most closely the size and galaxy multiplicity function of observed groups, this chance occurrence is found to be smaller by a factor of about 100 than the value obtained previously by Mamom from numerical simulations of dynamical models of groups. This and other direct independent observational results from the literature constitute strong evidence that nearly all of the Hickson compact groups are real physical systems. It is concluded that the tendency for the spiral fraction of a compact group to be larger than the value inferred from the galaxy morphology-group density relation of rich clusters and loose groups is a real physical effect indicating that galaxy morphology depends strongly on a second parameter which, it is suggested, is the velocity dispersion of a system. 21 references

  18. Evolution of dwarf galaxies in the Centaurus A group

    OpenAIRE

    Makarova, L.; Makarov, D.

    2007-01-01

    We consider star formation properties of dwarf galaxies in Cen A group observed within our HST/ACS projects number 9771 and 10235. We model color-magnitude diagrams of the galaxies under consideration and measure star formation rate and metallicity dependence on time. We study environmental dependence of the galaxy evolution and probable origin of the dwarf galaxies in the group.

  19. Dynamics of small groups of galaxies. I. Virialized groups

    International Nuclear Information System (INIS)

    Mamon, G.A.; New York Univ., NY)

    1987-01-01

    The dynamical evolution of small groups of galaxies from an initial virial equilibrium state is investigated by means of numerical simulations. The basic scheme is a gravitational N-body code in which galaxies and diffuse background are treated as single particles with both external parameters and internal structure; collisional and tidal stripping, dynamical friction, mergers, and orbital braking are taken into account. The results are presented in extensive tables and graphs and characterized in detail. Eight-galaxy groups with surface densities like those of compact groups (as defined by Hickson, 1982) are found to be unstable to rapid mergers after 1/30 to 1/8 Hubble time. The effects of dark-matter distribution (in galactic halos or in a common intergalactic background) are considered. 79 references

  20. STATISTICAL TOOLS FOR CLASSIFYING GALAXY GROUP DYNAMICS

    International Nuclear Information System (INIS)

    Hou, Annie; Parker, Laura C.; Harris, William E.; Wilman, David J.

    2009-01-01

    The dynamical state of galaxy groups at intermediate redshifts can provide information about the growth of structure in the universe. We examine three goodness-of-fit tests, the Anderson-Darling (A-D), Kolmogorov, and χ 2 tests, in order to determine which statistical tool is best able to distinguish between groups that are relaxed and those that are dynamically complex. We perform Monte Carlo simulations of these three tests and show that the χ 2 test is profoundly unreliable for groups with fewer than 30 members. Power studies of the Kolmogorov and A-D tests are conducted to test their robustness for various sample sizes. We then apply these tests to a sample of the second Canadian Network for Observational Cosmology Redshift Survey (CNOC2) galaxy groups and find that the A-D test is far more reliable and powerful at detecting real departures from an underlying Gaussian distribution than the more commonly used χ 2 and Kolmogorov tests. We use this statistic to classify a sample of the CNOC2 groups and find that 34 of 106 groups are inconsistent with an underlying Gaussian velocity distribution, and thus do not appear relaxed. In addition, we compute velocity dispersion profiles (VDPs) for all groups with more than 20 members and compare the overall features of the Gaussian and non-Gaussian groups, finding that the VDPs of the non-Gaussian groups are distinct from those classified as Gaussian.

  1. MAGNIFICATION BY GALAXY GROUP DARK MATTER HALOS

    Energy Technology Data Exchange (ETDEWEB)

    Ford, Jes; Hildebrandt, Hendrik; Van Waerbeke, Ludovic [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); Leauthaud, Alexie; Tanaka, Masayuki [Institute for the Physics and Mathematics of the Universe, University of Tokyo, Chiba 277-8582 (Japan); Capak, Peter [NASA Spitzer Science Center, California Institute of Technology, 220-6 Caltech, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Finoguenov, Alexis [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); George, Matthew R. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Rhodes, Jason [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

    2012-08-01

    We report on the detection of gravitational lensing magnification by a population of galaxy groups, at a significance level of 4.9{sigma}. Using X-ray-selected groups in the COSMOS 1.64 deg{sup 2} field, and high-redshift Lyman break galaxies as sources, we measure a lensing-induced angular cross-correlation between the samples. After satisfying consistency checks that demonstrate we have indeed detected a magnification signal, and are not suffering from contamination by physical overlap of samples, we proceed to implement an optimally weighted cross-correlation function to further boost the signal to noise of the measurement. Interpreting this optimally weighted measurement allows us to study properties of the lensing groups. We model the full distribution of group masses using a composite-halo approach, considering both the singular isothermal sphere and Navarro-Frenk-White profiles, and find our best-fit values to be consistent with those recovered using the weak-lensing shear technique. We argue that future weak-lensing studies will need to incorporate magnification along with shear, both to reduce residual systematics and to make full use of all available source information, in an effort to maximize scientific yield of the observations.

  2. Interactions of galaxies outside clusters and massive groups

    Science.gov (United States)

    Yadav, Jaswant K.; Chen, Xuelei

    2018-06-01

    We investigate the dependence of physical properties of galaxies on small- and large-scale density environment. The galaxy population consists of mainly passively evolving galaxies in comparatively low-density regions of Sloan Digital Sky Survey (SDSS). We adopt (i) local density, ρ _{20}, derived using adaptive smoothing kernel, (ii) projected distance, r_p, to the nearest neighbor galaxy and (iii) the morphology of the nearest neighbor galaxy as various definitions of environment parameters of every galaxy in our sample. In order to detect long-range interaction effects, we group galaxy interactions into four cases depending on morphology of the target and neighbor galaxies. This study builds upon an earlier study by Park and Choi (2009) by including improved definitions of target and neighbor galaxies, thus enabling us to better understand the effect of "the nearest neighbor" interaction on the galaxy. We report that the impact of interaction on galaxy properties is detectable at least up to the pair separation corresponding to the virial radius of (the neighbor) galaxies. This turns out to be mostly between 210 and 360 h^{-1}kpc for galaxies included in our study. We report that early type fraction for isolated galaxies with r_p > r_{vir,nei} is almost ignorant of the background density and has a very weak density dependence for closed pairs. Star formation activity of a galaxy is found to be crucially dependent on neighbor galaxy morphology. We find star formation activity parameters and structure parameters of galaxies to be independent of the large-scale background density. We also exhibit that changing the absolute magnitude of the neighbor galaxies does not affect significantly the star formation activity of those target galaxies whose morphology and luminosities are fixed.

  3. EVOLUTION OF GALAXY GROUPS IN THE ILLUSTRIS SIMULATION

    Energy Technology Data Exchange (ETDEWEB)

    Raouf, Mojtaba; Khosroshahi, Habib G. [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), Tehran, 19395-5746 (Iran, Islamic Republic of); Dariush, A., E-mail: m.raouf@ipm.ir [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)

    2016-06-20

    We present the first study of the evolution of galaxy groups in the Illustris simulation. We focus on dynamically relaxed and unrelaxed galaxy groups representing dynamically evolved and evolving galaxy systems, respectively. The evolutionary state of a group is probed from its luminosity gap and separation between the brightest group galaxy and the center of mass of the group members. We find that the Illustris simulation overproduces galaxy systems with a large luminosity gap, known as fossil systems, in comparison to observations and the probed semi-analytical predictions. However, this simulation is just as successful as the probed semi-analytic model in recovering the correlation between luminosity gap and offset of the luminosity centroid. We find evolutionary tracks based on luminosity gap that indicate that a group with a large luminosity gap is rooted in one with a small luminosity gap, regardless of the position of the brightest group galaxy within the halo. This simulation helps to explore, for the first time, the black hole mass and its accretion rate in galaxy groups. For a given stellar mass of the brightest group galaxies, the black hole mass is larger in dynamically relaxed groups with a lower rate of mass accretion. We find this to be consistent with the latest observational studies of radio activity in the brightest group galaxies in fossil groups. We also find that the intragalactic medium in dynamically evolved groups is hotter for a given halo mass than that in evolving groups, again consistent with earlier observational studies.

  4. Galaxy Tagging: photometric redshift refinement and group richness enhancement

    Science.gov (United States)

    Kafle, P. R.; Robotham, A. S. G.; Driver, S. P.; Deeley, S.; Norberg, P.; Drinkwater, M. J.; Davies, L. J.

    2018-06-01

    We present a new scheme, galtag, for refining the photometric redshift measurements of faint galaxies by probabilistically tagging them to observed galaxy groups constructed from a brighter, magnitude-limited spectroscopy survey. First, this method is tested on the DESI light-cone data constructed on the GALFORM galaxy formation model to tests its validity. We then apply it to the photometric observations of galaxies in the Kilo-Degree Imaging Survey (KiDS) over a 1 deg2 region centred at 15h. This region contains Galaxy and Mass Assembly (GAMA) deep spectroscopic observations (i-bandhttps://github.com/pkaf/galtag.git.

  5. INDIVIDUAL AND GROUP GALAXIES IN CNOC1 CLUSTERS

    International Nuclear Information System (INIS)

    Li, I. H.; Yee, H. K. C.; Ellingson, E.

    2009-01-01

    Using wide-field BVR c I imaging for a sample of 16 intermediate redshift (0.17 red ) to infer the evolutionary status of galaxies in clusters, using both individual galaxies and galaxies in groups. We apply the local galaxy density, Σ 5 , derived using the fifth nearest neighbor distance, as a measure of local environment, and the cluster-centric radius, r CL , as a proxy for global cluster environment. Our cluster sample exhibits a Butcher-Oemler effect in both luminosity-selected and stellar-mass-selected samples. We find that f red depends strongly on Σ 5 and r CL , and the Butcher-Oemler effect is observed in all Σ 5 and r CL bins. However, when the cluster galaxies are separated into r CL bins, or into group and nongroup subsamples, the dependence on local galaxy density becomes much weaker. This suggests that the properties of the dark matter halo in which the galaxy resides have a dominant effect on its galaxy population and evolutionary history. We find that our data are consistent with the scenario that cluster galaxies situated in successively richer groups (i.e., more massive dark matter halos) reach a high f red value at earlier redshifts. Associated with this, we observe a clear signature of 'preprocessing', in which cluster galaxies belonging to moderately massive infalling galaxy groups show a much stronger evolution in f red than those classified as nongroup galaxies, especially at the outskirts of the cluster. This result suggests that galaxies in groups infalling into clusters are significant contributors to the Butcher-Oemler effect.

  6. The Evolution of Neutral Hydrogen in Galaxy Groups

    Science.gov (United States)

    Sanderson, Kelly Nicole; Wilcots, Eric; Hess, Kelley M.

    2018-01-01

    The Illustris suite of simulations is held as the standard of large scale gravitational and hydro-dynamical simulations and allows us to make a better comparisons with physical processes at the gaseous level by providing a higher mass resolution than previously available through the Millenium-II simulation. We present a comparison of an analysis on the HI content and distribution of galaxies in groups as a function of their group dark matter halo to the results of a large scale cosmological simulation. From the simulation we select optical group members above a Mr=-18 r-band magnitude and HI group members with HI above 109.5M⊙. We find that 74% of the HI detected galaxies are in groups or clusters and 84% of the optically detected galaxies are in groups or clusters. In the Hess & Wilcots (2013) paper it was found that as group membership, or group dark matter halo mass, increased, the fraction of galaxies detected in HI decreased and the spatial distribution of galaxies in these groups increased. We show the spatial distributions of galaxies, HI and optically detected, in order to reproduce these results. We find that Illustris qualitatively reproduces these trends, however, the simulation seems to be overestimating the mass of HI gas in all of its galaxies as well as the number of galaxies above the 109.5M⊙ limit.

  7. Star formation suppression in compact group galaxies

    DEFF Research Database (Denmark)

    Alatalo, K.; Appleton, P. N.; Lisenfeld, U.

    2015-01-01

    , bars, rings, tidal tails, and possibly nuclear outflows, though the molecular gas morphologies are more consistent with spirals and earlytype galaxies than mergers and interacting systems. Our CO-imaged HCG galaxies, when plotted on the Kennicutt-Schmidt relation, shows star formation (SF) suppression...... color space. This supports the idea that at least some galaxies in HCGs are transitioning objects, where a disruption of the existing molecular gas in the system suppresses SF by inhibiting the molecular gas from collapsing and forming stars efficiently. These observations, combined with recent work...

  8. Motions of galaxies in the neighborhood of the local group

    International Nuclear Information System (INIS)

    Faber, S.M.; Burstein, D.

    1988-01-01

    Two samples of spiral galaxies, as well as elliptical galaxies, are presently used to investigate the velocity field of galaxies relative to the cosmic microwave background to a distance of 3000 km/sec. The velocity-field models optimized include motions due to a spherically-symmetric Great Attractor, a Virgocentric flow, and a Local Anomally of which the Local Group is a part. While the spiral samples are in good agreement with the Great-Attractor-Virgo model for the motion of elliptical galaxies, new observations indicate that the Great Attractor is not spherically symmetric in its inner regions and may require modification of the model. 27 refs

  9. New Members in the Galaxy Group Around Giant Radio Galaxy DA 240

    Science.gov (United States)

    Chen, Ru-Rong; Peng, Bo; Strom, Richard

    2018-05-01

    With new spectroscopic observations of group candidates around the giant radio galaxy DA 240, we have identified five new group members, increasing the number to twenty-five. While all the new members are located some distance from the host galaxy, two of them lie in one of the radio lobes, and the rest are found at a distance from the radio components. The new group members reinforce our earlier conclusion that the distribution of the DA 240 group with respect to the radio lobes is unusual among giant radio galaxy host environments.

  10. THE ORIGIN OF NEUTRAL HYDROGEN CLOUDS IN NEARBY GALAXY GROUPS: EXPLORING THE RANGE OF GALAXY INTERACTIONS

    International Nuclear Information System (INIS)

    Chynoweth, Katie M.; Polisensky, Emil; Holley-Bockelmann, Kelly; Langston, Glen I.

    2011-01-01

    We combine high-resolution N-body simulations with deep observations of neutral hydrogen (H I) in nearby galaxy groups in order to explore two well-known theories of H I cloud formation: H I stripping by galaxy interactions and dark-matter minihalos with embedded H I gas. This paper presents new data from three galaxy groups-Canes Venatici I, NGC 672, and NGC 45-and assembles data from our previous galaxy group campaign to generate a rich H I cloud archive to compare to our simulated data. We find no H I clouds in the Canes Venatici I, NGC 672, or NGC 45 galaxy groups. We conclude that H I clouds in our detection space are most likely to be generated through recent, strong galaxy interactions. We find no evidence of H I clouds associated with dark-matter halos above M HI ∼ 10 6 M sun , within ±700 km s -1 of galaxies, and within 50 kpc projected distance of galaxies.

  11. The DEEP2 Galaxy Redshift Survey: The Voronoi-Delaunay Method Catalog of Galaxy Groups

    Energy Technology Data Exchange (ETDEWEB)

    Gerke, Brian F.; /UC, Berkeley; Newman, Jeffrey A.; /LBNL, NSD; Davis, Marc; /UC, Berkeley /UC, Berkeley, Astron.Dept.; Marinoni, Christian; /Brera Observ.; Yan, Renbin; Coil, Alison L.; Conroy, Charlie; Cooper, Michael C.; /UC, Berkeley, Astron.Dept.; Faber, S.M.; /Lick Observ.; Finkbeiner, Douglas P.; /Princeton U. Observ.; Guhathakurta, Puragra; /Lick Observ.; Kaiser, Nick; /Hawaii U.; Koo, David C.; Phillips, Andrew C.; /Lick Observ.; Weiner, Benjamin J.; /Maryland U.

    2012-02-14

    We use the first 25% of the DEEP2 Galaxy Redshift Survey spectroscopic data to identify groups and clusters of galaxies in redshift space. The data set contains 8370 galaxies with confirmed redshifts in the range 0.7 {<=} z {<=} 1.4, over one square degree on the sky. Groups are identified using an algorithm (the Voronoi-Delaunay Method) that has been shown to accurately reproduce the statistics of groups in simulated DEEP2-like samples. We optimize this algorithm for the DEEP2 survey by applying it to realistic mock galaxy catalogs and assessing the results using a stringent set of criteria for measuring group-finding success, which we develop and describe in detail here. We find in particular that the group-finder can successfully identify {approx}78% of real groups and that {approx}79% of the galaxies that are true members of groups can be identified as such. Conversely, we estimate that {approx}55% of the groups we find can be definitively identified with real groups and that {approx}46% of the galaxies we place into groups are interloper field galaxies. Most importantly, we find that it is possible to measure the distribution of groups in redshift and velocity dispersion, n({sigma}, z), to an accuracy limited by cosmic variance, for dispersions greater than 350 km s{sup -1}. We anticipate that such measurements will allow strong constraints to be placed on the equation of state of the dark energy in the future. Finally, we present the first DEEP2 group catalog, which assigns 32% of the galaxies to 899 distinct groups with two or more members, 153 of which have velocity dispersions above 350 km s{sup -1}. We provide locations, redshifts and properties for this high-dispersion subsample. This catalog represents the largest sample to date of spectroscopically detected groups at z {approx} 1.

  12. The Merger History, AGN and Dwarf Galaxies of Hickson Compact Group 59

    Science.gov (United States)

    Konstantopoulos, I. S.; Gallagher, S. C.; Fedotov, K.; Durrell, P. R.; Tzanavaris, P.; Hill, A. R.; Zabludoff, A. I.; Maier, M. L.; Elmegreen, D. M.; Charlton, J. C.; hide

    2011-01-01

    Compact group galaxies often appear unaffected by their unusually dense environment. Closer examination can, however, reveal the subtle, cumulative effects of multiple galaxy interactions. Hickson Compact Group (HCG) 59 is an excellent example of this situation. We present a photometric study of this group in the optical (HST), infrared (Spitzer) and X-ray (Chandra) regimes aimed at characterizing the star formation and nuclear activity in its constituent galaxies and intra-group medium. We associate five dwarf galaxies with the group and update the velocity dispersion, leading to an increase in the dynamical mass of the group of up to a factor of 10 (to 2.8 x 10(exp 13) Stellar Mass), and a subsequent revision of its evolutionary stage. Star formation is proceeding at a level consistent with the morphological types of the four main galaxies, of which two are star-forming and the other two quiescent. Unlike in some other compact groups, star-forming complexes across HCG 59 closely follow mass-radius scaling relations typical of nearby galaxies. In contrast, the ancient globular cluster populations in galaxies HCG 59A and B show intriguing irregularities, and two extragalactic HII regions are found just west of B. We age-date a faint stellar stream in the intra-group medium at approx. 1 Gyr to examine recent interactions. We detect a likely low-luminosity AGN in HCG 59A by its approx. 10(exp 40) erg/s X-ray emission; the active nucleus rather than star formation can account for the UV+IR SED. We discuss the implications of our findings in the context of galaxy evolution in dense environments.

  13. Properties of Galaxies and Groups: Nature versus Nurture

    Science.gov (United States)

    Niemi, Sami-Matias

    2011-09-01

    Due to the inherently nonlinear nature of gravity cosmological N-body simulations have become an invaluable tool when the growth of structure is being studied and modelled closer to the present epoch. Large simulations with high dynamical range have made it possible to model the formation and growth of cosmic structure with unprecedented accuracy. Moreover, galaxies, the basic building blocks of the Universe, can also be modelled in cosmological context. However, despite all the simulations and successes in recent decades, there are still many unanswered questions in the field of galaxy formation and evolution. One of the longest standing issue being the significance of the formation place and thus initial conditions to a galaxy's evolution in respect to environment, often formulated simply as "nature versus nurture" like in human development and psychology. Unfortunately, our understanding of galaxy evolution in different environments is still limited, albeit, for example, the morphology-density relation has shown that the density of the galaxy's local environment can affect its properties. Consequently, the environment should play a role in galaxy evolution, however despite the efforts, the exact role of the galaxy's local environment to its evolution remains open. This thesis introduction discusses briefly the background cosmology, cosmological N-body simulations and semi-analytical models. The second part is reserved for groups of galaxies, whether they are gravitationally bound, and what this may imply for galaxy evolution. The third part of the thesis concentrates on describing results of a case study of isolated field elliptical galaxies. The final chapter discusses another case study of luminous infra-red galaxies.

  14. Population studies in groups and clusters of galaxies. III. A catalog of galaxies in five nearby groups

    International Nuclear Information System (INIS)

    Ferguson, H.C.; Sandage, A.

    1990-01-01

    Five nearby groups of galaxies have been surveyed using large-scale plates from the 2.5 m duPont Telescope at Las Campanas Observatory. Catalogs of galaxies brighter than B(T) = 20 are presented for the Leo, Dorado, NGC 1400, NGC 5044, and Antlia groups. A total of 1044 galaxies are included, from visual inspection of 14 plates, covering 31 deg square. Galaxies have been classified in the extended Hubble system, and group memberships have been assigned based on velocity (where available) and morphology. About half the galaxies listed are likely members of one of the nearby groups. The catalogs are complete to B(T) = 18, although the completeness limits vary slightly from group to group. Based on King model fits to the surface density profiles, the core radii of the groups range from 0.3 to 1 Mpc, and central densities range from 120 to 1900 galaxies Mpc exp-3 brighter than M(BT) = -12.5. Dynamical analysis indicates that all of the groups are likely to be gravitationally bound. 64 refs

  15. Blooming Trees: Substructures and Surrounding Groups of Galaxy Clusters

    Science.gov (United States)

    Yu, Heng; Diaferio, Antonaldo; Serra, Ana Laura; Baldi, Marco

    2018-06-01

    We develop the Blooming Tree Algorithm, a new technique that uses spectroscopic redshift data alone to identify the substructures and the surrounding groups of galaxy clusters, along with their member galaxies. Based on the estimated binding energy of galaxy pairs, the algorithm builds a binary tree that hierarchically arranges all of the galaxies in the field of view. The algorithm searches for buds, corresponding to gravitational potential minima on the binary tree branches; for each bud, the algorithm combines the number of galaxies, their velocity dispersion, and their average pairwise distance into a parameter that discriminates between the buds that do not correspond to any substructure or group, and thus eventually die, and the buds that correspond to substructures and groups, and thus bloom into the identified structures. We test our new algorithm with a sample of 300 mock redshift surveys of clusters in different dynamical states; the clusters are extracted from a large cosmological N-body simulation of a ΛCDM model. We limit our analysis to substructures and surrounding groups identified in the simulation with mass larger than 1013 h ‑1 M ⊙. With mock redshift surveys with 200 galaxies within 6 h ‑1 Mpc from the cluster center, the technique recovers 80% of the real substructures and 60% of the surrounding groups; in 57% of the identified structures, at least 60% of the member galaxies of the substructures and groups belong to the same real structure. These results improve by roughly a factor of two the performance of the best substructure identification algorithm currently available, the σ plateau algorithm, and suggest that our Blooming Tree Algorithm can be an invaluable tool for detecting substructures of galaxy clusters and investigating their complex dynamics.

  16. CONFIRMATION OF FAINT DWARF GALAXIES IN THE M81 GROUP

    Energy Technology Data Exchange (ETDEWEB)

    Chiboucas, Kristin [Gemini Observatory, 670 North A' ohoku Pl, Hilo, HI 96720 (United States); Jacobs, Bradley A.; Tully, R. Brent [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96821 (United States); Karachentsev, Igor D., E-mail: kchibouc@gemini.edu, E-mail: bjacobs@ifa.hawaii.edu, E-mail: tully@ifa.hawaii.edu, E-mail: ikar@luna.sao.ru [Special Astrophysical Observatory (SAO), Russian Academy of Sciences, Nizhnij Arkhyz, Karachai-Cherkessian Republic 369167 (Russian Federation)

    2013-11-01

    We have followed up on the results of a 65 deg{sup 2} CFHT/MegaCam imaging survey of the nearby M81 Group searching for faint and ultra-faint dwarf galaxies. The original survey turned up 22 faint candidate dwarf members. Based on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as dwarf galaxy members of the group. Distances and stellar population characteristics are discussed for each. To a completeness limit of M{sub r{sup '}}= -10, we find a galaxy luminosity function slope of –1.27 ± 0.04 for the M81 Group. In this region, there are now 36 M81 Group members known, including 4 blue compact dwarfs; 8 other late types including the interacting giants M81, NGC 3077, and M82; 19 early type dwarfs; and at least 5 potential tidal dwarf galaxies. We find that the dSph galaxies in M81 appear to lie in a flattened distribution, similar to that found for the Milky Way and M31. One of the newly discovered dSph galaxies has properties similar to the ultra-faint dwarfs being found in the Local Group with a size R{sub e} ∼ 100 pc and total magnitude estimates M{sub r{sup '}}= -6.8 and M{sub I} ∼ –9.1.

  17. Confirmation of Faint Dwarf Galaxies in the M81 Group

    Science.gov (United States)

    Chiboucas, Kristin; Jacobs, Bradley A.; Tully, R. Brent; Karachentsev, Igor D.

    2013-11-01

    We have followed up on the results of a 65 deg2 CFHT/MegaCam imaging survey of the nearby M81 Group searching for faint and ultra-faint dwarf galaxies. The original survey turned up 22 faint candidate dwarf members. Based on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as dwarf galaxy members of the group. Distances and stellar population characteristics are discussed for each. To a completeness limit of M_{r^{\\prime }} = -10, we find a galaxy luminosity function slope of -1.27 ± 0.04 for the M81 Group. In this region, there are now 36 M81 Group members known, including 4 blue compact dwarfs; 8 other late types including the interacting giants M81, NGC 3077, and M82; 19 early type dwarfs; and at least 5 potential tidal dwarf galaxies. We find that the dSph galaxies in M81 appear to lie in a flattened distribution, similar to that found for the Milky Way and M31. One of the newly discovered dSph galaxies has properties similar to the ultra-faint dwarfs being found in the Local Group with a size Re ~ 100 pc and total magnitude estimates M_{r^{\\prime }} = -6.8 and MI ~ -9.1.

  18. THE DEEP2 GALAXY REDSHIFT SURVEY: THE VORONOI-DELAUNAY METHOD CATALOG OF GALAXY GROUPS

    Energy Technology Data Exchange (ETDEWEB)

    Gerke, Brian F. [KIPAC, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, MS 29, Menlo Park, CA 94725 (United States); Newman, Jeffrey A. [Department of Physics and Astronomy, 3941 O' Hara Street, Pittsburgh, PA 15260 (United States); Davis, Marc [Department of Physics and Department of Astronomy, Campbell Hall, University of California-Berkeley, Berkeley, CA 94720 (United States); Coil, Alison L. [Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Drive, MC 0424, La Jolla, CA 92093 (United States); Cooper, Michael C. [Center for Galaxy Evolution, Department of Physics and Astronomy, University of California-Irvine, Irvine, CA 92697 (United States); Dutton, Aaron A. [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2 (Canada); Faber, S. M.; Guhathakurta, Puragra; Koo, David C.; Phillips, Andrew C. [UCO/Lick Observatory, University of California-Santa Cruz, Santa Cruz, CA 95064 (United States); Konidaris, Nicholas; Lin, Lihwai [Astronomy Department, Caltech 249-17, Pasadena, CA 91125 (United States); Noeske, Kai [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Rosario, David J. [Max Planck Institute for Extraterrestrial Physics, Giessenbachstr. 1, 85748 Garching bei Muenchen (Germany); Weiner, Benjamin J.; Willmer, Christopher N. A. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Yan, Renbin [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada)

    2012-05-20

    We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0 < z < 1.5 and 1295 groups at z > 0.6 in the rest of DEEP2. Twenty-five percent of EGS galaxies and fourteen percent of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay method (VDM) after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). We also confirm that the VDM catalog reconstructs the abundance of galaxy groups with velocity dispersions above {approx}300 km s{sup -1} to an accuracy better than the sample variance, and this successful reconstruction is not strongly dependent on cosmology. This makes the DEEP2 group catalog a promising probe of the growth of cosmic structure that can potentially be used for cosmological tests.

  19. THE DEEP2 GALAXY REDSHIFT SURVEY: THE VORONOI-DELAUNAY METHOD CATALOG OF GALAXY GROUPS

    International Nuclear Information System (INIS)

    Gerke, Brian F.; Newman, Jeffrey A.; Davis, Marc; Coil, Alison L.; Cooper, Michael C.; Dutton, Aaron A.; Faber, S. M.; Guhathakurta, Puragra; Koo, David C.; Phillips, Andrew C.; Konidaris, Nicholas; Lin, Lihwai; Noeske, Kai; Rosario, David J.; Weiner, Benjamin J.; Willmer, Christopher N. A.; Yan, Renbin

    2012-01-01

    We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0 0.6 in the rest of DEEP2. Twenty-five percent of EGS galaxies and fourteen percent of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay method (VDM) after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). We also confirm that the VDM catalog reconstructs the abundance of galaxy groups with velocity dispersions above ∼300 km s –1 to an accuracy better than the sample variance, and this successful reconstruction is not strongly dependent on cosmology. This makes the DEEP2 group catalog a promising probe of the growth of cosmic structure that can potentially be used for cosmological tests.

  20. Mass-to-light ratios of nearby groups of galaxies

    CERN Document Server

    Materne, J

    1980-01-01

    The application of a probability density function gives the possibility of determining groups of galaxies and membership probabilities of the galaxies in a reliable unbiased way. For the five nearest groups so defined, the mean mass-to-light ratio was derived using the concept of negative energy. These groups have a mass-to- light ratio of 16 M/sub (.)//L/sub (.)/. The probability function gives also the possibility of deriving masses of groups in a direct and independent way. (22 refs).

  1. The Origin of the Galaxy and Local Group

    Science.gov (United States)

    Bland-Hawthorn, Joss; Freeman, Ken; Matteucci, Francesca

    This volume contains the updated and expanded lecture notes of the 37th Saas-Fee Advanced Course organised by the Swiss Society for Astrophysics and Astronomy. It offers the most comprehensive and up to date review of one of the hottest research topics in astrophysics - how our Milky Way galaxy formed. Joss Bland-Hawthorn & Ken Freeman lectured on Near Field Cosmology - The Origin of the Galaxy and the Local Group. Francesca Matteucci's chapter is on Chemical evolution of the Milky Way and its Satellites. As designed by the SSAA, books in this series - and this one too - are targeted at graduate and PhD students and young researchers in astronomy, astrophysics and cosmology. Lecturers and researchers entering the field will also benefit from the book. *%K Physics, Astrophysics, Near Field Cosmology, Galaxy, Local Group *%O Milky Way

  2. Galaxy And Mass Assembly (GAMA): the effect of galaxy group environment on active galactic nuclei

    Science.gov (United States)

    Gordon, Yjan A.; Pimbblet, Kevin A.; Owers, Matt S.; Bland-Hawthorn, Joss; Brough, Sarah; Brown, Michael J. I.; Cluver, Michelle E.; Croom, Scott M.; Holwerda, Benne W.; Loveday, Jonathan; Mahajan, Smriti; Wang, Lingyu

    2018-04-01

    In galaxy clusters, efficiently accreting active galactic nuclei (AGNs) are preferentially located in the infall regions of the cluster projected phase-space, and are rarely found in the cluster core. This has been attributed to both an increase in triggering opportunities for infalling galaxies, and a reduction of those mechanisms in the hot, virialized, cluster core. Exploiting the depth and completeness (98 per cent at r 9.9 in 695 groups with 11.53 ≤ log10(M200/M⊙) ≤ 14.56 at z 13.5, AGNs are preferentially found in the infalling galaxy population with 3.6σ confidence. At lower halo masses, we observe no difference in AGN fraction between core and infalling galaxies. These observations support a model where a reduced number of low-speed interactions, ram pressure stripping and intra-group/cluster medium temperature, the dominance of which increase with halo mass, work to inhibit AGN in the cores of groups and clusters with log10(M200/M⊙) > 13.5, but do not significantly affect nuclear activity in cores of less massive structures.

  3. Search for Dark Matter Annihilation in Galaxy Groups.

    Science.gov (United States)

    Lisanti, Mariangela; Mishra-Sharma, Siddharth; Rodd, Nicholas L; Safdi, Benjamin R

    2018-03-09

    We use 413 weeks of publicly available Fermi Pass 8 gamma-ray data combined with recently developed galaxy group catalogs to search for evidence of dark matter annihilation in extragalactic halos. In our study, we use luminosity-based mass estimates and mass-to-concentration relations to infer the J factors and associated uncertainties for hundreds of galaxy groups within a redshift range z≲0.03. We employ a conservative substructure boost factor model, which only enhances the sensitivity by an O(1) factor. No significant evidence for dark matter annihilation is found, and we exclude thermal relic cross sections for dark matter masses below ∼30  GeV to 95% confidence in the bb[over ¯] annihilation channel. These bounds are comparable to those from Milky Way dwarf spheroidal satellite galaxies. The results of our analysis increase the tension but do not rule out the dark matter interpretation of the Galactic Center excess. We provide a catalog of the galaxy groups used in this study and their inferred properties, which can be broadly applied to searches for extragalactic dark matter.

  4. Search for Dark Matter Annihilation in Galaxy Groups

    Science.gov (United States)

    Lisanti, Mariangela; Mishra-Sharma, Siddharth; Rodd, Nicholas L.; Safdi, Benjamin R.

    2018-03-01

    We use 413 weeks of publicly available Fermi Pass 8 gamma-ray data combined with recently developed galaxy group catalogs to search for evidence of dark matter annihilation in extragalactic halos. In our study, we use luminosity-based mass estimates and mass-to-concentration relations to infer the J factors and associated uncertainties for hundreds of galaxy groups within a redshift range z ≲0.03 . We employ a conservative substructure boost factor model, which only enhances the sensitivity by an O (1 ) factor. No significant evidence for dark matter annihilation is found, and we exclude thermal relic cross sections for dark matter masses below ˜30 GeV to 95% confidence in the b b ¯ annihilation channel. These bounds are comparable to those from Milky Way dwarf spheroidal satellite galaxies. The results of our analysis increase the tension but do not rule out the dark matter interpretation of the Galactic Center excess. We provide a catalog of the galaxy groups used in this study and their inferred properties, which can be broadly applied to searches for extragalactic dark matter.

  5. Implications of Galaxy Buildup for Putative IMF Variations in Massive Galaxies

    Science.gov (United States)

    Blancato, Kirsten; Genel, Shy; Bryan, Greg

    2017-08-01

    Recent observational evidence for initial mass function (IMF) variations in massive quiescent galaxies at z = 0 challenges the long-established paradigm of a universal IMF. While a few theoretical models relate the IMF to birth cloud conditions, the physical driver underlying these putative IMF variations is still largely unclear. Here we use post-processing analysis of the Illustris cosmological hydrodynamical simulation to investigate possible physical origins of IMF variability with galactic properties. We do so by tagging stellar particles in the simulation (each representing a stellar population of ≈ {10}6 {M}⊙ ) with individual IMFs that depend on various physical conditions, such as velocity dispersion, metallicity, or star formation rate, at the time and place in which the stars are formed. We then follow the assembly of these populations throughout cosmic time and reconstruct the overall IMF of each z = 0 galaxy from the many distinct IMFs it is composed of. Our main result is that applying the observed relations between IMF and galactic properties to the conditions at the star formation sites does not result in strong enough IMF variations between z = 0 galaxies. Steeper physical IMF relations are required for reproducing the observed IMF trends, and some stellar populations must form with more extreme IMFs than those observed. The origin of this result is the hierarchical nature of massive galaxy assembly, and it has implications for the reliability of the strong observed trends, for the ability of cosmological simulations to capture certain physical conditions in galaxies, and for theories of star formation aiming to explain the physical origin of a variable IMF.

  6. Understanding the unique assembly history of central group galaxies

    International Nuclear Information System (INIS)

    Vulcani, Benedetta; Bundy, Kevin; Lackner, Claire; Leauthaud, Alexie; Treu, Tommaso; Mei, Simona; Coccato, Lodovico; Kneib, Jean Paul; Auger, Matthew; Nipoti, Carlo

    2014-01-01

    Central galaxies (CGs) in massive halos live in unique environments with formation histories closely linked to that of the host halo. In local clusters, they have larger sizes (R e ) and lower velocity dispersions (σ) at fixed stellar mass M * , and much larger R e at a fixed σ than field and satellite galaxies (non-CGs). Using spectroscopic observations of group galaxies selected from the COSMOS survey, we compare the dynamical scaling relations of early-type CGs and non-CGs at z ∼ 0.6 to distinguish possible mechanisms that produce the required evolution. CGs are systematically offset toward larger R e at fixed σ compared to non-CGs with similar M * . The CG R e -M * relation also shows differences, primarily driven by a subpopulation (∼15%) of galaxies with large R e , while the M * -σ relations are indistinguishable. These results are accentuated when double Sérsic profiles, which better fit light in the outer regions of galaxies, are adopted. They suggest that even group-scale CGs can develop extended components by these redshifts that can increase total R e and M * estimates by factors of ∼2. To probe the evolutionary link between our sample and cluster CGs, we also analyze two cluster samples at z ∼ 0.6 and z ∼ 0. We find similar results for the more massive halos at comparable z, but much more distinct CG scaling relations at low-z. Thus, the rapid, late-time accretion of outer components, perhaps via the stripping and accretion of satellites, would appear to be a key feature that distinguishes the evolutionary history of CGs.

  7. Characterizing SL2S galaxy groups using the Einstein radius

    DEFF Research Database (Denmark)

    Verdugo, T.; Motta, V.; Foex, G.

    2014-01-01

    Aims. We aim to study the reliability of RA (the distance from the arcs to the center of the lens) as a measure of the Einstein radius in galaxy groups. In addition, we want to analyze the possibility of using RA as a proxy to characterize some properties of galaxy groups, such as luminosity (L......) and richness (N). Methods. We analyzed the Einstein radius, θE, in our sample of Strong Lensing Legacy Survey (SL2S) galaxy groups, and compared it with RA, using three different approaches: 1) the velocity dispersion obtained from weak lensing assuming a singular isothermal sphere profile (θE,I); 2) a strong.......7 ± 0.2)RA, θE,II = (0.4 ± 1.5) + (1.1 ± 0.4)RA, and θE,III = (0.4 ± 1.5) + (0.9 ± 0.3)RA for each method respectively. We found weak evidence of anti-correlation between RA and z, with Log RA = (0.58 ± 0.06) − (0.04 ± 0.1)z, suggesting a possible evolution of the Einstein radius with z, as reported...

  8. The origin of the galaxy and local group

    CERN Document Server

    2014-01-01

    This volume contains the updated and expanded lecture notes of the 37th Saas-Fee Advanced Course organised by the Swiss Society for Astrophysics and Astronomy. It offers the most comprehensive and up to date review of one of the hottest research topics in astrophysics - how our Milky Way galaxy formed. Joss Bland-Hawthorn & Ken Freeman lectured on Near Field Cosmology - The Origin of the Galaxy and the Local Group. Francesca Matteucci’s chapter is on Chemical evolution of the Milky Way and its Satellites. As designed by the SSAA, books in this series – and this one too – are targeted at graduate and PhD students and young researchers in astronomy, astrophysics and cosmology. Lecturers and researchers entering the field will also benefit from the book.

  9. Groups of galaxies. III. the CfA survey

    International Nuclear Information System (INIS)

    Geller, M.J.; Huchra, J.P.

    1983-01-01

    We present a statistically homogeneous group catalog (CfA) based on the CfA redshift survey (Huchra et al.). Groups in the catalog are all density enhancements in redshift space of a factor greater than 20. Group members are identified according to the procedure described in our previous study (Huchra and Geller) of a shallower whole-sky sample. All groups contain at least three members. Of the 176 groups in the CfA catalog, 102 have been identified in one or more previous studies. Because our algorithm searches for volume rather than surface density enhancements, the groups in a given region generally change only through the addition of fainter members when the magnitude limit of the galaxy catalog increases. In the region of overlap, agreement between our shallow catalog and the CfA catalog is excellent

  10. Groups of galaxies in the Center for Astrophysics redshift survey

    International Nuclear Information System (INIS)

    Ramella, M.; Geller, M.J.; Huchra, J.P.

    1989-01-01

    By applying the Huchra and Geller (1982) objective group identification algorithm to the Center for Astrophysics' redshift survey, a catalog of 128 groups with three or more members is extracted, and 92 of these are used as a statistical sample. A comparison of the distribution of group centers with the distribution of all galaxies in the survey indicates qualitatively that groups trace the large-scale structure of the region. The physical properties of groups may be related to the details of large-scale structure, and it is concluded that differences among group catalogs may be due to the properties of large-scale structures and their location relative to the survey limits. 28 refs

  11. Star formation in globular clusters and dwarf galaxies and implications for the early evolution of galaxies

    Science.gov (United States)

    Lin, Douglas N. C.; Murray, Stephen D.

    1991-01-01

    Based upon the observed properties of globular clusters and dwarf galaxies in the Local Group, we present important theoretical constraints on star formation in these systems. These constraints indicate that protoglobular cluster clouds had long dormant periods and a brief epoch of violent star formation. Collisions between protocluster clouds triggered fragmentation into individual stars. Most protocluster clouds dispersed into the Galactic halo during the star formation epoch. In contrast, the large spread in stellar metallicity in dwarf galaxies suggests that star formation in their pregenitors was self-regulated: we propose the protocluster clouds formed from thermal instability in the protogalactic clouds and show that a population of massive stars is needed to provide sufficient UV flux to prevent the collapsing protogalactic clouds from fragmenting into individual stars. Based upon these constraints, we propose a unified scenario to describe the early epochs of star formation in the Galactic halo as well as the thick and thin components of the Galactic disk.

  12. Galaxies

    International Nuclear Information System (INIS)

    1981-01-01

    Normal galaxies, radio galaxies, and Seyfert galaxies are considered. The large magellanic cloud and the great galaxy in Andromedia are highlighted. Quasars and BL lacertae objects are also discussed and a review of the spectral observations of all of these galaxies and celestial objects is presented

  13. THE COSMOLOGICAL IMPACT OF LUMINOUS TeV BLAZARS. III. IMPLICATIONS FOR GALAXY CLUSTERS AND THE FORMATION OF DWARF GALAXIES

    International Nuclear Information System (INIS)

    Pfrommer, Christoph; Chang, Philip; Broderick, Avery E.

    2012-01-01

    A subset of blazars are powerful TeV emitters, dominating the extragalactic component of the very high energy gamma-ray universe (E ∼> 100 GeV). These TeV gamma rays generate ultrarelativistic electron-positron pairs via pair production with the extragalactic background light. While it has generally been assumed that the kinetic energy of these pairs cascades to GeV gamma rays via inverse Compton scattering, we have argued in Broderick et al. (Paper I in this series) that plasma beam instabilities are capable of dissipating the pairs' energy locally on timescales short in comparison to the inverse Compton cooling time, heating the intergalactic medium (IGM) with a rate that is independent of density. This dramatically increases the entropy of the IGM after redshift z ∼ 2, with a number of important implications for structure formation: (1) this suggests a scenario for the origin of the cool core (CC)/non-cool core (NCC) bimodality in galaxy clusters and groups. Early-forming galaxy groups are unaffected because they can efficiently radiate the additional entropy, developing a CC. However, late-forming groups do not have sufficient time to cool before the entropy is gravitationally reprocessed through successive mergers—counteracting cooling and potentially raising the core entropy further. This may result in a population of X-ray dim groups/clusters, consistent with X-ray stacking analyses of optically selected samples. Hence, blazar heating works differently than feedback by active galactic nuclei, which we show can balance radiative cooling but is unable to transform CC into NCC clusters on the buoyancy timescale due to the weak coupling between the mechanical energy to the cluster gas. (2) We predict a suppression of the Sunyaev-Zel'dovich (SZ) power spectrum template on angular scales smaller than 5' due to the globally reduced central pressure of groups and clusters forming after z ∼ 1. This allows for a larger rms amplitude of the density power

  14. MID-INFRARED EVIDENCE FOR ACCELERATED EVOLUTION IN COMPACT GROUP GALAXIES

    International Nuclear Information System (INIS)

    Walker, Lisa May; Johnson, Kelsey E.; Gallagher, Sarah C.; Hibbard, John E.; Hornschemeier, Ann E.; Tzanavaris, Panayiotis; Charlton, Jane C.; Jarrett, Thomas H.

    2010-01-01

    Compact galaxy groups are at the extremes of the group environment, with high number densities and low velocity dispersions that likely affect member galaxy evolution. To explore the impact of this environment in detail, we examine the distribution in the mid-infrared (MIR) 3.6-8.0 μm color space of 42 galaxies from 12 Hickson compact groups (HCGs) in comparison with several control samples, including the LVL+SINGS galaxies, interacting galaxies, and galaxies from the Coma Cluster. We find that the HCG galaxies are strongly bimodal, with statistically significant evidence for a gap in their distribution. In contrast, none of the other samples show such a marked gap, and only galaxies in the Coma infall region have a distribution that is statistically consistent with the HCGs in this parameter space. To further investigate the cause of the HCG gap, we compare the galaxy morphologies of the HCG and LVL+SINGS galaxies, and also probe the specific star formation rate (SSFR) of the HCG galaxies. While galaxy morphology in HCG galaxies is strongly linked to position with MIR color space, the more fundamental property appears to be the SSFR, or star formation rate normalized by stellar mass. We conclude that the unusual MIR color distribution of HCG galaxies is a direct product of their environment, which is most similar to that of the Coma infall region. In both cases, galaxy densities are high, but gas has not been fully processed or stripped. We speculate that the compact group environment fosters accelerated evolution of galaxies from star-forming and neutral gas-rich to quiescent and neutral gas-poor, leaving few members in the MIR gap at any time.

  15. THE ZURICH ENVIRONMENTAL STUDY OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. I. WHICH ENVIRONMENT AFFECTS GALAXY EVOLUTION?

    Energy Technology Data Exchange (ETDEWEB)

    Carollo, C. Marcella; Cibinel, Anna; Lilly, Simon J.; Miniati, Francesco; Cameron, Ewan; Peng, Yingjie; Pipino, Antonio; Rudick, Craig S. [Institute for Astronomy, ETH Zurich, CH-8093 Zurich (Switzerland); Norberg, Peder [Department of Physics, Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE (United Kingdom); Silverman, John D. [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, The University of Tokyo, Chiba 277-8583 (Japan); Van Gorkom, Jacqueline [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Finoguenov, Alexis, E-mail: marcella@phys.ethz.ch [Max-Planck-Institut für extraterrestrische Physik, D-84571 Garching (Germany)

    2013-10-20

    The Zurich Environmental Study (ZENS) is based on a sample of ∼1500 galaxy members of 141 groups in the mass range ∼10{sup 12.5-14.5} M{sub ☉} within the narrow redshift range 0.05 < z < 0.0585. ZENS adopts novel approaches, described here, to quantify four different galactic environments, namely: (1) the mass of the host group halo; (2) the projected halo-centric distance; (3) the rank of galaxies as central or satellites within their group halos; and (4) the filamentary large-scale structure density. No self-consistent identification of a central galaxy is found in ∼40% of <10{sup 13.5} M{sub ☉} groups, from which we estimate that ∼15% of groups at these masses are dynamically unrelaxed systems. Central galaxies in relaxed and unrelaxed groups generally have similar properties, suggesting that centrals are regulated by their mass and not by their environment. Centrals in relaxed groups have, however, ∼30% larger sizes than in unrelaxed groups, possibly due to accretion of small satellites in virialized group halos. At M > 10{sup 10} M{sub ☉}, satellite galaxies in relaxed and unrelaxed groups have similar size, color, and (specific) star formation rate distributions; at lower galaxy masses, satellites are marginally redder in relaxed relative to unrelaxed groups, suggesting quenching of star formation in low-mass satellites by physical processes active in relaxed halos. Overall, relaxed and unrelaxed groups show similar stellar mass populations, likely indicating similar stellar mass conversion efficiencies. In the enclosed ZENS catalog, we publish all environmental diagnostics as well as the galaxy structural and photometric measurements described in companion ZENS papers II and III.

  16. GALAXIES IN X-RAY GROUPS. III. SATELLITE COLOR AND MORPHOLOGY TRANSFORMATIONS

    Energy Technology Data Exchange (ETDEWEB)

    George, Matthew R.; Ma, Chung-Pei [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Bundy, Kevin; Leauthaud, Alexie; Vulcani, Benedetta [Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa 277-8583 (Japan); Tinker, Jeremy [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Wechsler, Risa H. [Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Finoguenov, Alexis, E-mail: mgeorge@astro.berkeley.edu [Department of Physics, University of Helsinki, Gustaf Haellstroemin katu 2a, FI-00014 Helsinki (Finland)

    2013-06-20

    While the star formation rates and morphologies of galaxies have long been known to correlate with their local environment, the process by which these correlations are generated is not well understood. Galaxy groups are thought to play an important role in shaping the physical properties of galaxies before entering massive clusters at low redshift, and transformations of satellite galaxies likely dominate the buildup of local environmental correlations. To illuminate the physical processes that shape galaxy evolution in dense environments, we study a sample of 116 X-ray selected galaxy groups at z = 0.2-1 with halo masses of 10{sup 13}-10{sup 14} M{sub Sun} and centroids determined with weak lensing. We analyze morphologies based on Hubble Space Telescope imaging and colors determined from 31 photometric bands for a stellar mass-limited population of 923 satellite galaxies and a comparison sample of 16,644 field galaxies. Controlling for variations in stellar mass across environments, we find significant trends in the colors and morphologies of satellite galaxies with group-centric distance and across cosmic time. Specifically at low stellar mass (log (M{sub *}/M{sub Sun }) = 9.8-10.3), the fraction of disk-dominated star-forming galaxies declines from >50% among field galaxies to <20% among satellites near the centers of groups. This decline is accompanied by a rise in quenched galaxies with intermediate bulge+disk morphologies, and only a weak increase in red bulge-dominated systems. These results show that both color and morphology are influenced by a galaxy's location within a group halo. We suggest that strangulation and disk fading alone are insufficient to explain the observed morphological dependence on environment, and that galaxy mergers or close tidal encounters must play a role in building up the population of quenched galaxies with bulges seen in dense environments at low redshift.

  17. GALAXIES IN X-RAY GROUPS. III. SATELLITE COLOR AND MORPHOLOGY TRANSFORMATIONS

    International Nuclear Information System (INIS)

    George, Matthew R.; Ma, Chung-Pei; Bundy, Kevin; Leauthaud, Alexie; Vulcani, Benedetta; Tinker, Jeremy; Wechsler, Risa H.; Finoguenov, Alexis

    2013-01-01

    While the star formation rates and morphologies of galaxies have long been known to correlate with their local environment, the process by which these correlations are generated is not well understood. Galaxy groups are thought to play an important role in shaping the physical properties of galaxies before entering massive clusters at low redshift, and transformations of satellite galaxies likely dominate the buildup of local environmental correlations. To illuminate the physical processes that shape galaxy evolution in dense environments, we study a sample of 116 X-ray selected galaxy groups at z = 0.2-1 with halo masses of 10 13 -10 14 M ☉ and centroids determined with weak lensing. We analyze morphologies based on Hubble Space Telescope imaging and colors determined from 31 photometric bands for a stellar mass-limited population of 923 satellite galaxies and a comparison sample of 16,644 field galaxies. Controlling for variations in stellar mass across environments, we find significant trends in the colors and morphologies of satellite galaxies with group-centric distance and across cosmic time. Specifically at low stellar mass (log (M * /M ☉ ) = 9.8-10.3), the fraction of disk-dominated star-forming galaxies declines from >50% among field galaxies to <20% among satellites near the centers of groups. This decline is accompanied by a rise in quenched galaxies with intermediate bulge+disk morphologies, and only a weak increase in red bulge-dominated systems. These results show that both color and morphology are influenced by a galaxy's location within a group halo. We suggest that strangulation and disk fading alone are insufficient to explain the observed morphological dependence on environment, and that galaxy mergers or close tidal encounters must play a role in building up the population of quenched galaxies with bulges seen in dense environments at low redshift.

  18. X-ray emission from clusters and groups of galaxies

    Science.gov (United States)

    Mushotzky, R.

    1998-01-01

    Recent major advances in x-ray imaging and spectroscopy of clusters have allowed the determination of their mass and mass profile out to approximately 1/2 the virial radius. In rich clusters, most of the baryonic mass is in the gas phase, and the ratio of mass in gas/stars varies by a factor of 2-4. The baryonic fractions vary by a factor of approximately 3 from cluster to cluster and almost always exceed 0.09 h50-[3/2] and thus are in fundamental conflict with the assumption of Omega = 1 and the results of big bang nucleosynthesis. The derived Fe abundances are 0.2-0.45 solar, and the abundances of O and Si for low redshift systems are 0.6-1.0 solar. This distribution is consistent with an origin in pure type II supernova. The amount of light and energy produced by these supernovae is very large, indicating their importance in influencing the formation of clusters and galaxies. The lack of evolution of Fe to a redshift of z approximately 0.4 argues for very early enrichment of the cluster gas. Groups show a wide range of abundances, 0.1-0.5 solar. The results of an x-ray survey indicate that the contribution of groups to the mass density of the universe is likely to be larger than 0.1 h50-2. Many of the very poor groups have large x-ray halos and are filled with small galaxies whose velocity dispersion is a good match to the x-ray temperatures.

  19. TIDAL INTERACTION AS THE ORIGIN OF EARLY-TYPE DWARF GALAXIES IN GROUP ENVIRONMENTS

    International Nuclear Information System (INIS)

    Paudel, Sanjaya; Ree, Chang H.

    2014-01-01

    We present a sample of dwarf galaxies that suffer ongoing disruption by the tidal forces of nearby massive galaxies. By analyzing structural and stellar population properties using the archival imaging and spectroscopic data from the Sloan Digital Sky Survey (SDSS), we find that they are likely a ''smoking gun'' example of the formation through tidal stirring of early-type dwarf galaxies (dEs) in the galaxy group environment. The inner cores of these galaxies are fairly intact and the observed light profiles are well fit by the Sérsic functions while the tidally stretched stellar halos are prominent in the outer parts. They are all located within a sky-projected distance of 50 kpc from the centers of the host galaxies and no dwarf galaxies have relative line-of-sight velocities larger than 205 km s –1 to their hosts. We derive the Composite Stellar Population properties of these galaxies by fitting the SDSS optical spectra to a multiple-burst composite stellar population model. We find that these galaxies accumulate a significant fraction of stellar mass within the last 1 Gyr and contain a majority stellar population with an intermediate age of 2 to 4 Gyr. Based on this evidence, we argue that tidal stirring, particularly through the galaxy-galaxy interaction, might have an important role in the formation and evolution of dEs in the group environment where the influence of other gas stripping mechanism might be limited

  20. The Ultraviolet and Infrared Star Formation Rates of Compact Group Galaxies: An Expanded Sample

    Science.gov (United States)

    Lenkic, Laura; Tzanavaris, Panayiotis; Gallagher, Sarah C.; Desjardins, Tyler D.; Walker, Lisa May; Johnson, Kelsey E.; Fedotov, Konstantin; Charlton, Jane; Cardiff, Ann H.; Durell, Pat R.

    2016-01-01

    Compact groups of galaxies provide insight into the role of low-mass, dense environments in galaxy evolution because the low velocity dispersions and close proximity of galaxy members result in frequent interactions that take place over extended time-scales. We expand the census of star formation in compact group galaxies by Tzanavaris et al. (2010) and collaborators with Swift UVOT, Spitzer IRAC and MIPS 24 m photometry of a sample of 183 galaxies in 46 compact groups. After correcting luminosities for the contribution from old stellar populations, we estimate the dust-unobscured star formation rate (SFRUV) using the UVOT uvw2 photometry. Similarly, we use the MIPS 24 m photometry to estimate the component of the SFR that is obscured by dust (SFRIR). We find that galaxies which are MIR-active (MIR-red), also have bluer UV colours, higher specific SFRs, and tend to lie in Hi-rich groups, while galaxies that are MIR-inactive (MIR-blue) have redder UV colours, lower specific SFRs, and tend to lie in Hi-poor groups. We find the SFRs to be continuously distributed with a peak at about 1 M yr1, indicating this might be the most common value in compact groups. In contrast, the specific SFR distribution is bimodal, and there is a clear distinction between star-forming and quiescent galaxies. Overall, our results suggest that the specific SFR is the best tracer of gas depletion and galaxy evolution in compact groups.

  1. Galaxies

    International Nuclear Information System (INIS)

    1989-01-01

    In studies of the large scale structure of the universe there is a continuing need for extensive galaxy redshift determinations. Optically selected redshift surveys are of particular importance, since flux-limited samples record much higher space densities of galaxies than samples of similar size selected in other wavebands. A considerable amount of the South African Astronomical Observatory (SAAO) observing time is currently being devoted to carrying out a large southern galaxy redshift survey. A recently completed study, the Durham-SAAO redshift survey suggests that the mean density of matter is well below the critical limit for a closed universe and also that the universe may be homogenous at very large scales. Other research conducted by the SAAO include studies on: the distribution of galaxies; Seyfert galaxies; starburst and IRAS galaxies; interacting and compact galaxies; a re-evaluation of the Cepheid distance to NGC 300, and a search for quasars behind galaxies. 1 fig

  2. Galaxies

    International Nuclear Information System (INIS)

    1987-01-01

    The size and nature of any large-scale anisotropy in the three-dimensional distribution of galaxies is still little understood. Recent studies have indicated that large fluctuations in the matter distribution on a scale from tens up to several hundreds of megaparsecs may exist. Work at the South African Astronomical Observatory (SAAO) in recent years has made major contributions to studies of the large scale distribution of galaxies, as well as to solving the problems of the galactic and extragalactic distance scale. Other studies of galaxies undertaken at SAAO include: quasars in the fields of nearby galaxies; dwarf irregular galaxies; IRAS galaxies; Seyfert galaxies; 'hot spot' galaxies; supernovae in NGC 5128 and NGC 1559 and superclusters. 4 figs

  3. Understanding `galaxy groups' as a unique structure in the universe

    Science.gov (United States)

    Paul, S.; John, R. S.; Gupta, P.; Kumar, H.

    2017-10-01

    'Galaxy groups' have hardly been realized as a separate class of objects with specific characteristics in the structural hierarchy. The presumption that the self-similarity of dark matter structures is a valid prescription for the baryonic universe at all scales has rendered smaller structures undetectable by current observational facilities, leading to lesser dedicated studies on them. Some recent reports that indicate a deviation from LX-T scaling in groups compared to clusters have motivated us to study their physical properties in depth. In this article, we report the extensive study on physical properties of groups in comparison to the clusters through cosmological hydrodynamic plus N-body simulations using enzo 2.2 code. As additional physics, radiative cooling, heating due to supernova and star motions, star formation and stellar feedback have been implemented. We have produced a mock sample of 362 objects with mass ranging from 5 × 1012 M⊙ to 2.5 × 1015 M⊙. Strikingly, we have found that objects with mass below ˜8 × 1013 M⊙ do not follow any of the cluster self-similar laws in hydrostatics, not even in thermal and non-thermal energies. Two distinct scaling laws are observed to be followed with breaks at ˜8 × 1013 M⊙ for mass, ˜1 keV for temperature and ˜1 Mpc for radius. This places groups as a distinct entity in the hierarchical structures, well demarcated from clusters. This study reveals that groups are mostly far away from virialization, suggesting the need for formulating new models for deciphering their physical parameters. They are also shown to have high turbulence and more non-thermal energy stored, indicating better visibility in the non-thermal regime.

  4. Understanding 'Galaxy Groups' as a Unique Structure in the Universe

    Science.gov (United States)

    John, Reju Sam; Paul, Surajit; Gupta, Prateek; Kumar, Harish

    2017-07-01

    'Galaxy groups' have hardly been realized as a separate class of objects with specific characteristics in the structural hierarchy of the universe. The presumption that the self-similarity of dark matter structures is a valid prescription for the baryonic universe also at all scales has rendered smaller structures undetectable by current observational facilities, leading to lesser dedicated studies on them. Some recent reports on deviation of {L_x}-T scaling in groups from that of clusters have motivated us to study their physical properties in depth. In this article, we report the extensive study on physical properties of groups in comparison with clusters through cosmological hydrodynamic plus N-body simulations using ENZO 2.2 code. We have included cooling and heating physics and star formation feedback in the simulation. And produced a mock sample of 362 objects with mass ranging from 5×10^{12} M_{⊙} to 2.5×10^{15} M_{⊙}. Strikingly, we have found that objects with a mass below ˜ 8×10^{13} M_{⊙} do not follow any of the cluster self-similar laws in hydrostatics, not even in thermal and non-thermal regimes. Two distinct scaling laws are observed to be followed with breaks at ˜ 6-8× 10^{13} M_{⊙} for mass, ˜1 keV for temperature and ˜1 Mpc for radius. This places groups as a distinct entity in the hierarchical structures, well demarcated from clusters. This study reveals that groups are mostly far away from virialization, suggesting the need for formulating new models for deciphering their physical parameters. They are also shown to have high turbulence and more non-thermal energy stored, indicating better visibility in the non-thermal regime.

  5. A search for extragalactic pulsars in the local group galaxies IC 10 and Barnard’s galaxy

    International Nuclear Information System (INIS)

    Al Noori, H; Roberts, M S E; Champion, D; McLaughlin, M; Ransom, Scott; Ray, P S

    2017-01-01

    As of today, more than 2500 pulsars have been found, nearly all in the Milky Way, with the exception of ∼28 pulsars in the Small and Large Magellanic Clouds. However, there have been few published attempts to search for pulsars deeper in our Galactic neighborhood. Two of the more promising Local Group galaxies are IC 10 and NGC 6822 (also known as Barnard’s Galaxy) due to their relatively high star formation rate and their proximity to our galaxy. IC 10 in particular, holds promise as it is the closest starburst galaxy to us and harbors an unusually high number of Wolf-Rayet stars, implying the presence of many neutron stars. We observed IC 10 and NGC 6822 at 820 MHz with the Green Bank Telescope for ∼15 and 5 hours respectively, and put a strong upper limit of 0.1 mJy on pulsars in either of the two galaxies. We also performed single pulse searches of both galaxies with no firm detections. (paper)

  6. Lost but not forgotten: intracluster light in galaxy groups and clusters

    Science.gov (United States)

    DeMaio, Tahlia; Gonzalez, Anthony H.; Zabludoff, Ann; Zaritsky, Dennis; Connor, Thomas; Donahue, Megan; Mulchaey, John S.

    2018-03-01

    With Hubble Space Telescope imaging, we investigate the progenitor population and formation mechanisms of the intracluster light (ICL) for 23 galaxy groups and clusters at 0.29 ≤ z ≤ 0.89. The colour gradients of the BCG+ICL become bluer with increasing radius out to 53-100 kpc for all but one system, suggesting that violent relaxation after major mergers with the BCG cannot be the dominant source of ICL. The BCG+ICL luminosities and stellar masses are too large for the ICL stars to come from the dissolution of dwarf galaxies alone, given the observed evolution of the faint end of the cluster galaxy luminosity function, implying instead that the ICL grows from the stripping of more massive galaxies. Using the colours of cluster members from the CLASH high-mass sample, we place conservative lower limits on the luminosities of galaxies from which the ICL at r originate via stripping. We find that the ICL at 100 kpc has a colour similar to a 1010.0 M⊙ galaxy and that 75 per cent of the total BCG+ICL luminosity at r originating in galaxies with L > 0.2 L* (log(M★ [M⊙])>10.4), assuming conservatively that these galaxies are completely disrupted. We conclude that the tidal stripping of massive galaxies is the likely source of the intracluster light from 10 to 100 kpc for galaxy groups and clusters.

  7. Simulating The Dynamical Evolution Of Galaxies In Group And Cluster Environments

    Science.gov (United States)

    Vijayaraghavan, Rukmani

    2015-07-01

    Galaxy clusters are harsh environments for their constituent galaxies. A variety of physical processes effective in these dense environments transform gas-rich, spiral, star-forming galaxies to elliptical or spheroidal galaxies with very little gas and therefore minimal star formation. The consequences of these processes are well understood observationally. Galaxies in progressively denser environments have systematically declining star formation rates and gas content. However, a theoretical understanding of of where, when, and how these processes act, and the interplay between the various galaxy transformation mechanisms in clusters remains elusive. In this dissertation, I use numerical simulations of cluster mergers as well as galaxies evolving in quiescent environments to develop a theoretical framework to understand some of the physics of galaxy transformation in cluster environments. Galaxies can be transformed in smaller groups before they are accreted by their eventual massive cluster environments, an effect termed `pre-processing'. Galaxy cluster mergers themselves can accelerate many galaxy transformation mechanisms, including tidal and ram pressure stripping of galaxies and galaxy-galaxy collisions and mergers that result in reassemblies of galaxies' stars and gas. Observationally, cluster mergers have distinct velocity and phase-space signatures depending on the observer's line of sight with respect to the merger direction. Using dark matter only as well as hydrodynamic simulations of cluster mergers with random ensembles of particles tagged with galaxy models, I quantify the effects of cluster mergers on galaxy evolution before, during, and after the mergers. Based on my theoretical predictions of the dynamical signatures of these mergers in combination with galaxy transformation signatures, one can observationally identify remnants of mergers and quantify the effect of the environment on galaxies in dense group and cluster environments. The presence of

  8. Revisiting the Cooling Flow Problem in Galaxies, Groups, and Clusters of Galaxies

    Science.gov (United States)

    McDonald, M.; Gaspari, M.; McNamara, B. R.; Tremblay, G. R.

    2018-05-01

    We present a study of 107 galaxies, groups, and clusters spanning ∼3 orders of magnitude in mass, ∼5 orders of magnitude in central galaxy star formation rate (SFR), ∼4 orders of magnitude in the classical cooling rate ({\\dot{M}}cool}\\equiv {M}gas}(rsample, we measure the ICM cooling rate, {\\dot{M}}cool}, using archival Chandra X-ray data and acquire the SFR and systematic uncertainty in the SFR by combining over 330 estimates from dozens of literature sources. With these data, we estimate the efficiency with which the ICM cools and forms stars, finding {ε }cool}\\equiv {SFR}/{\\dot{M}}cool}=1.4 % +/- 0.4% for systems with {\\dot{M}}cool}> 30 M ⊙ yr‑1. For these systems, we measure a slope in the SFR–{\\dot{M}}cool} relation greater than unity, suggesting that the systems with the strongest cool cores are also cooling more efficiently. We propose that this may be related to, on average, higher black hole accretion rates in the strongest cool cores, which could influence the total amount (saturating near the Eddington rate) and dominant mode (mechanical versus radiative) of feedback. For systems with {\\dot{M}}cool}< 30 M ⊙ yr‑1, we find that the SFR and {\\dot{M}}cool} are uncorrelated and show that this is consistent with star formation being fueled at a low (but dominant) level by recycled ISM gas in these systems. We find an intrinsic log-normal scatter in SFR at a fixed {\\dot{M}}cool} of 0.52 ± 0.06 dex (1σ rms), suggesting that cooling is tightly self-regulated over very long timescales but can vary dramatically on short timescales. There is weak evidence that this scatter may be related to the feedback mechanism, with the scatter being minimized (∼0.4 dex) for systems for which the mechanical feedback power is within a factor of two of the cooling luminosity.

  9. A KiDS weak lensing analysis of assembly bias in GAMA galaxy groups

    Science.gov (United States)

    Dvornik, Andrej; Cacciato, Marcello; Kuijken, Konrad; Viola, Massimo; Hoekstra, Henk; Nakajima, Reiko; van Uitert, Edo; Brouwer, Margot; Choi, Ami; Erben, Thomas; Fenech Conti, Ian; Farrow, Daniel J.; Herbonnet, Ricardo; Heymans, Catherine; Hildebrandt, Hendrik; Hopkins, Andrew M.; McFarland, John; Norberg, Peder; Schneider, Peter; Sifón, Cristóbal; Valentijn, Edwin; Wang, Lingyu

    2017-07-01

    We investigate possible signatures of halo assembly bias for spectroscopically selected galaxy groups from the Galaxy And Mass Assembly (GAMA) survey using weak lensing measurements from the spatially overlapping regions of the deeper, high-imaging-quality photometric Kilo-Degree Survey. We use GAMA groups with an apparent richness larger than 4 to identify samples with comparable mean host halo masses but with a different radial distribution of satellite galaxies, which is a proxy for the formation time of the haloes. We measure the weak lensing signal for groups with a steeper than average and with a shallower than average satellite distribution and find no sign of halo assembly bias, with the bias ratio of 0.85^{+0.37}_{-0.25}, which is consistent with the Λ cold dark matter prediction. Our galaxy groups have typical masses of 1013 M⊙ h-1, naturally complementing previous studies of halo assembly bias on galaxy cluster scales.

  10. Galaxy And Mass Assembly (GAMA): Gas Fueling of Spiral Galaxies in the Local Universe. I. The Effect of the Group Environment on Star Formation in Spiral Galaxies

    Science.gov (United States)

    Grootes, M. W.; Tuffs, R. J.; Popescu, C. C.; Norberg, P.; Robotham, A. S. G.; Liske, J.; Andrae, E.; Baldry, I. K.; Gunawardhana, M.; Kelvin, L. S.; Madore, B. F.; Seibert, M.; Taylor, E. N.; Alpaslan, M.; Brown, M. J. I.; Cluver, M. E.; Driver, S. P.; Bland-Hawthorn, J.; Holwerda, B. W.; Hopkins, A. M.; Lopez-Sanchez, A. R.; Loveday, J.; Rushton, M.

    2017-03-01

    We quantify the effect of the galaxy group environment (for group masses of 1012.5-1014.0 M ⊙) on the current star formation rate (SFR) of a pure, morphologically selected sample of disk-dominated (I.e., late-type spiral) galaxies with redshift ≤0.13. The sample embraces a full representation of quiescent and star-forming disks with stellar mass M * ≥ 109.5 M ⊙. We focus on the effects on SFR of interactions between grouped galaxies and the putative intrahalo medium (IHM) of their host group dark matter halos, isolating these effects from those induced through galaxy-galaxy interactions, and utilizing a radiation transfer analysis to remove the inclination dependence of derived SFRs. The dependence of SFR on M * is controlled for by measuring offsets Δlog(ψ *) of grouped galaxies about a single power-law relation in specific SFR, {\\psi }* \\propto {M}* -0.45+/- 0.01, exhibited by non-grouped “field” galaxies in the sample. While a small minority of the group satellites are strongly quenched, the group centrals and a large majority of satellites exhibit levels of ψ * statistically indistinguishable from their field counterparts, for all M *, albeit with a higher scatter of 0.44 dex about the field reference relation (versus 0.27 dex for the field). Modeling the distributions in Δlog(ψ *), we find that (I) after infall into groups, disk-dominated galaxies continue to be characterized by a similar rapid cycling of gas into and out of their interstellar medium shown prior to infall, with inflows and outflows of ˜1.5-5 x SFR and ˜1-4 x SFR, respectively; and (II) the independence of the continuity of these gas flow cycles on M * appears inconsistent with the required fueling being sourced from gas in the circumgalactic medium on scales of ˜100 kpc. Instead, our data favor ongoing fueling of satellites from the IHM of the host group halo on ˜Mpc scales, I.e., from gas not initially associated with the galaxies upon infall. Consequently, the color

  11. DETECTION OF MOLECULAR GAS IN VOID GALAXIES: IMPLICATIONS FOR STAR FORMATION IN ISOLATED ENVIRONMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Das, M.; Honey, M. [Indian Institute of Astrophysics, Bangalore (India); Saito, T. [Department of Astronomy, Graduate school of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 133-0033 (Japan); Iono, D. [Chile Observatory, NAOJ (Japan); Ramya, S., E-mail: mousumi@iiap.res.in [Shanghai Astronomical Observatory, Shanghai (China)

    2015-12-10

    We present the detection of molecular gas from galaxies located in nearby voids using the CO(1–0) line emission as a tracer. The observations were performed using the 45 m single dish radio telescope of the Nobeyama Radio Observatory. Void galaxies lie in the most underdense parts of our universe and a significant fraction of them are gas rich, late-type spiral galaxies. Although isolated, they have ongoing star formation but appear to be slowly evolving compared to galaxies in denser environments. Not much is known about their star formation properties or cold gas content. In this study, we searched for molecular gas in five void galaxies. The galaxies were selected based on their relatively high IRAS fluxes or Hα line luminosities, both of which signify ongoing star formation. All five galaxies appear to be isolated and two lie within the Bootes void. We detected CO(1–0) emission from four of the five galaxies in our sample and their molecular gas masses lie between 10{sup 8} and 10{sup 9} M{sub ⊙}. We conducted follow-up Hα imaging observations of three detected galaxies using the Himalayan Chandra Telescope and determined their star formation rates (SFRs) from their Hα fluxes. The SFR varies from 0.2 to 1 M{sub ⊙} yr{sup −1}; which is similar to that observed in local galaxies. Our study indicates that although void galaxies reside in underdense regions, their disks contain molecular gas and have SFRs similar to galaxies in denser environments. We discuss the implications of our results.

  12. SHAM beyond clustering: new tests of galaxy–halo abundance matching with galaxy groups

    Energy Technology Data Exchange (ETDEWEB)

    Hearin, Andrew P.; Zentner, Andrew R.; Berlind, Andreas A.; Newman, Jeffrey A.

    2013-05-27

    We construct mock catalogs of galaxy groups using subhalo abundance matching (SHAM) and undertake several new tests of the SHAM prescription for the galaxy-dark matter connection. All SHAM models we studied exhibit significant tension with galaxy groups observed in the Sloan Digital Sky Survey (SDSS). The SHAM prediction for the field galaxy luminosity function (LF) is systematically too dim, and the group galaxy LF systematically too bright, regardless of the details of the SHAM prescription. SHAM models connecting r-band luminosity, Mr, to Vacc, the maximum circular velocity of a subhalo at the time of accretion onto the host, faithfully reproduce galaxy group abundance as a function of richness, g(N). However, SHAM models connecting Mr with Vpeak, the peak value of Vmax over the entire merger history of the halo, over-predict galaxy group abundance. Our results suggest that no SHAM model can simultaneously reproduce the observed g(N) and two-point projected galaxy clustering. Nevertheless, we also report a new success of SHAM: an accurate prediction for Phi(m12), the abundance of galaxy groups as a function of magnitude gap m12, defined as the difference between the r-band absolute magnitude of the two brightest group members. We show that it may be possible to use joint measurements of g(N) and Phi(m12) to tightly constrain the details of the SHAM implementation. Additionally, we show that the hypothesis that the luminosity gap is constructed via random draws from a universal LF provides a poor description of the data, contradicting recent claims in the literature. Finally, we test a common assumption of the Conditional Luminosity Function (CLF) formalism, that the satellite LF need only be conditioned by the brightness of the central galaxy. We find this assumption to be well-supported by the observed Phi(m12).

  13. RADIO GALAXY FEEDBACK IN X-RAY-SELECTED GROUPS FROM COSMOS: THE EFFECT ON THE INTRACLUSTER MEDIUM

    International Nuclear Information System (INIS)

    Giodini, S.; Finoguenov, A.; Boehringer, H.; Pierini, D.; Smolcic, V.; Massey, R.; BIrzan, L.; Zamorani, G.; Oklopcic, A.; Pratt, G. W.; Schinnerer, E.; Koekemoer, A. M.; Salvato, M.; Sanders, D. B.; Kartaltepe, J. S.; Thompson, D.

    2010-01-01

    We quantify the importance of the mechanical energy released by radio galaxies inside galaxy groups. We use scaling relations to estimate the mechanical energy released by 16 radio-active galactic nuclei located inside X-ray-detected galaxy groups in the COSMOS field. By comparing this energy output to the host groups' gravitational binding energy, we find that radio galaxies produce sufficient energy to unbind a significant fraction of the intragroup medium. This unbinding effect is negligible in massive galaxy clusters with deeper potential wells. Our results correctly reproduce the breaking of self-similarity observed in the scaling relation between entropy and temperature for galaxy groups.

  14. METALLICITY DISTRIBUTION FUNCTIONS OF FOUR LOCAL GROUP DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Ross, Teresa L.; Holtzman, Jon [Department of Astronomy, New Mexico State University, P.O. Box 30001, MSC 4500, Las Cruces, NM 88003-8001 (United States); Saha, Abhijit [NOAO, 950 Cherry Avenue, Tucson, AZ 85726-6732 (United States); Anthony-Twarog, Barbara J., E-mail: rosst@nmsu.edu, E-mail: holtz@nmsu.edu, E-mail: bjat@ku.edu [Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045-7582 (United States)

    2015-06-15

    We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry using the Wide Field Camera 3 instrument on board the Hubble Space Telescope. We measured metallicity distribution functions (MDFs) in two ways, (1) matching stars to isochrones in color–color diagrams and (2) solving for the best linear combination of synthetic populations to match the observed color–color diagram. The synthetic technique reduces the effect of photometric scatter and produces MDFs 30%–50% narrower than the MDFs produced from individually matched stars. We fit the synthetic and individual MDFs to analytical chemical evolution models (CEMs) to quantify the enrichment and the effect of gas flows within the galaxies. Additionally, we measure stellar metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not have the radial extent to confirm a metallicity gradient for either galaxy. We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep metal-rich cutoff and an extended metal-poor tail, while Leo II (dwarf spheroidal), Phoenix (dwarf transition), and IC 1613 (dwarf irregular) have wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of our galaxies; therefore we also fit the “Best Accretion Model” of Lynden-Bell. For Leo II, IC 1613, and Phoenix we find similar accretion parameters for the CEM even though they all have different effective yields, masses, star formation histories, and morphologies. We suggest that the dynamical history of a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that have chemically evolved in relative isolation and narrowly peaked MDFs are seen in galaxies that have experienced more complicated dynamical interactions concurrent with their chemical evolution.

  15. X-ray Cavities in Galaxy Groups and Clusters: Central Gas Entropy ...

    Indian Academy of Sciences (India)

    is synchrotron radiation of relativistic electrons, powered by the central AGN, and ... In the X-ray images of galaxies, galaxy groups and clusters, a number of X-ray cavities have been observed. .... 35. Figure 1. Central gas entropy excess K0 vs.

  16. NGC 5291: Implications for the Formation of Dwarf Galaxies

    Science.gov (United States)

    Malphrus, Benjamin K.; Simpson, Caroline E.; Gottesman, S. T.; Hawarden, Timothy G.

    1997-01-01

    The possible formation and evolution of dwarf irregular galaxies from material derived from perturbed evolved galaxies is addressed via an H I study of a likely example, the peculiar system NGC 5291. This system, located in the western outskirts of the cluster Abell 3574, contains the lenticular galaxy NGC 5291 which is in close proximity to a disturbed companion and is flanked by an extensive complex of numerous knots extending roughly 4 min north and 4 min south of the galaxy. In an initial optical and radio study, Longmore et al. (1979, MNRAS, 188, 285) showed that these knots have the spectra of vigorous star-forming regions, and suggested that some may in fact be young dwarf irregular galaxies. High resolution 21-cm line observations taken with the VLA are presented here and reveal that the H I distribution associated with this system encompasses not only the entire N-S complex of optical knots, but also forms an incomplete ring or tail that extends approximately 3 min to the west. The H I associated with NGC 5291 itself shows a high velocity range; the Seashell is not detected. The formation mechanism for this unusual system is unclear and two models - a large, low-luminosity ram-swept disk, and a ram-swept interaction-are discussed. The H I in the system contains numerous concentrations, mostly along the N-S arc of the star-forming complexes, which generally coincide with one or more optical knots; the larger H I features contain several x 10(exp 9) solar mass of gas. Each of the knots is compared to a set of criteria designed to determine if these objects are bound against their own internal kinetic energy and are tidally stable relative to the host galaxy. An analysis of the properties of the H I concentrations surrounding the optical star-forming complexes indicates that at least the largest of these is a bound system; it also possesses a stellar component. It is suggested that this object is a genuinely young dwarf irregular galaxy that has evolved from

  17. Spatially-resolved star formation histories of CALIFA galaxies. Implications for galaxy formation

    Science.gov (United States)

    González Delgado, R. M.; Pérez, E.; Cid Fernandes, R.; García-Benito, R.; López Fernández, R.; Vale Asari, N.; Cortijo-Ferrero, C.; de Amorim, A. L.; Lacerda, E. A. D.; Sánchez, S. F.; Lehnert, M. D.; Walcher, C. J.

    2017-11-01

    This paper presents the spatially resolved star formation history (SFH) of nearby galaxies with the aim of furthering our understanding of the different processes involved in the formation and evolution of galaxies. To this end, we apply the fossil record method of stellar population synthesis to a rich and diverse data set of 436 galaxies observed with integral field spectroscopy in the CALIFA survey. The sample covers a wide range of Hubble types, with stellar masses ranging from M⋆ 109 to 7 × 1011 M⊙. Spectral synthesis techniques are applied to the datacubes to retrieve the spatially resolved time evolution of the star formation rate (SFR), its intensity (ΣSFR), and other descriptors of the 2D SFH in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd) and five bins of stellar mass. Our main results are that (a) galaxies form very fast independently of their current stellar mass, with the peak of star formation at high redshift (z > 2). Subsequent star formation is driven by M⋆ and morphology, with less massive and later type spirals showing more prolonged periods of star formation. (b) At any epoch in the past, the SFR is proportional to M⋆, with most massive galaxies having the highest absolute (but lowest specific) SFRs. (c) While today, the ΣSFR is similar for all spirals and significantly lower in early-type galaxies (ETG), in the past, the ΣSFR scales well with morphology. The central regions of today's ETGs are where the ΣSFR reached the highest values (> 103 M⊙ Gyr-1 pc-2), similar to those measured in high-redshift star-forming galaxies. (d) The evolution of ΣSFR in Sbc systems matches that of models for Milky Way-like galaxies, suggesting that the formation of a thick disk may be a common phase in spirals at early epochs. (e) The SFR and ΣSFR in outer regions of E and S0 galaxies show that they have undergone an extended phase of growth in mass between z = 2 and 0.4. The mass assembled in this phase is in agreement with

  18. Chemical analysis of carbon stars in the local group - l.  The small magnetic cloud and the Sagittarius Dwarf Spheroidal galaxy

    DEFF Research Database (Denmark)

    de Laverny...[], P.; Abia, C.; Dominguez, I

    2006-01-01

    Stars: abundances, stars: carbon, nuclear reactions, nucleosynthesis, abundances, galaxies: Local Group Udgivelsesdato: Feb.......Stars: abundances, stars: carbon, nuclear reactions, nucleosynthesis, abundances, galaxies: Local Group Udgivelsesdato: Feb....

  19. FRESH ACTIVITY IN OLD SYSTEMS: RADIO AGNs IN FOSSIL GROUPS OF GALAXIES

    International Nuclear Information System (INIS)

    Hess, Kelley M.; Wilcots, Eric M.; Hartwick, Victoria L.

    2012-01-01

    We present the first systematic 1.4 GHz Very Large Array radio continuum survey of fossil galaxy group candidates. These are virialized systems believed to have assembled over a gigayear in the past through the merging of galaxy group members into a single, isolated, massive elliptical galaxy and featuring an extended hot X-ray halo. We use new photometric and spectroscopic data from Sloan Digital Sky Survey Data Release 7 to determine that three of the candidates are clearly not fossil groups. Of the remaining 30 candidates, 67% contain a radio-loud (L 1.4GHz > 10 23 W Hz –1 ) active galactic nucleus (AGN) at the center of their dominant elliptical galaxy. We find a weak correlation between the radio luminosity of the AGN and the X-ray luminosity of the halo suggesting that the AGN contributes to energy deposition into the intragroup medium. We only find a correlation between the radio and optical luminosity of the central elliptical galaxy when we include X-ray-selected, elliptically dominated non-fossil groups, indicating a weak relationship between AGN strength and the mass assembly history of the groups. The dominant elliptical galaxy of fossil groups is on average roughly an order of magnitude more luminous than normal group elliptical galaxies in optical, X-ray, and radio luminosities and our findings are consistent with previous results that the radio-loud fraction in elliptical galaxies is linked to the stellar mass of a population. The current level of activity in fossil groups suggests that AGN fueling continues long after the last major merger. We discuss several possibilities for fueling the AGN at the present epoch.

  20. CHEMICAL ABUNDANCES OF SEVEN IRREGULAR AND THREE TIDAL DWARF GALAXIES IN THE M81 GROUP

    International Nuclear Information System (INIS)

    Croxall, Kevin V.; Van Zee, Liese; Lee, Henry; Miller, Bryan W.; Skillman, Evan D.; Lee, Janice C.; Cote, Stephanie; Kennicutt, Robert C.

    2009-01-01

    We have derived nebular abundances for 10 dwarf galaxies belonging to the M81 Group, including several galaxies which do not have abundances previously reported in the literature. For each galaxy, multiple H II regions were observed with GMOS-N at the Gemini Observatory in order to determine abundances of several elements (oxygen, nitrogen, sulfur, neon, and argon). For seven galaxies, at least one H II region had a detection of the temperature sensitive [O III] λ4363 line, allowing a 'direct' determination of the oxygen abundance. No abundance gradients were detected in the targeted galaxies, and the observed oxygen abundances are typically in agreement with the well-known metallicity-luminosity relation. However, three candidate 'tidal dwarf' galaxies lie well off this relation: UGC 5336, Garland, and KDG 61. The nature of these systems suggests that UGC 5336 and Garland are indeed recently formed systems, whereas KDG 61 is most likely a dwarf spheroidal galaxy which lies along the same line of sight as the M81 tidal debris field. We propose that these H II regions formed from previously enriched gas which was stripped from nearby massive galaxies (e.g., NGC 3077 and M81) during a recent tidal interaction.

  1. VLT/UVES abundances in four nearby dwarf spheroidal galaxies. II. Implications for understanding galaxy evolution

    NARCIS (Netherlands)

    Tolstoy, E; Venn, KA; Shetrone, M; Primas, F; Hill, [No Value; Kaufer, A; Szeifert, T

    We have used the Ultraviolet Visual-Echelle Spectrograph (UVES) on Kueyen (UT2) of the Very Large Telescope to take spectra of 15 individual red giant stars in the centers of four nearby dwarf spheroidal galaxies (dSph's) : Sculptor, Fornax, Carina, and Leo I. We measure the abundance variations of

  2. CLASH: EXTREME EMISSION-LINE GALAXIES AND THEIR IMPLICATION ON SELECTION OF HIGH-REDSHIFT GALAXIES

    International Nuclear Information System (INIS)

    Huang, Xingxing; Wang, Junxian; Shu, Xinwen; Zheng, Wei; Ford, Holland; Lemze, Doron; Moustakas, John; Van der Wel, Arjen; Zitrin, Adi; Frye, Brenda L.; Postman, Marc; Bradley, Larry; Coe, Dan; Bartelmann, Matthias; Benítez, Narciso; Broadhurst, Tom; Donahue, Megan; Infante, Leopoldo

    2015-01-01

    We utilize the Cluster Lensing And Supernova survey with Hubble observations of 25 clusters to search for extreme emission-line galaxies (EELGs). The selections are carried out in two central bands: F105W (Y 105 ) and F125W (J 125 ), as the flux of the central bands could be enhanced by the presence of [O III] λλ4959, 5007 at redshifts of ∼0.93-1.14 and 1.57-1.79, respectively. The multiband observations help to constrain the equivalent widths (EWs) of emission lines. Thanks to cluster lensing, we are able to identify 52 candidates down to an intrinsic limiting magnitude of 28.5 and to a rest-frame [O III] λλ4959, 5007 EW of ≅ 3700 Å. Our samples include a number of EELGs at lower luminosities that are missed in other surveys, and the extremely high EW can only be found in such faint galaxies. These EELGs can mimic a dropout feature similar to that of high-redshift galaxies and contaminate the color-color selection of high-redshift galaxies when the signal-to-noise ratio is limited or the band coverage is incomplete

  3. CLASH: EXTREME EMISSION-LINE GALAXIES AND THEIR IMPLICATION ON SELECTION OF HIGH-REDSHIFT GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Xingxing; Wang, Junxian; Shu, Xinwen [CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026 (China); Zheng, Wei; Ford, Holland; Lemze, Doron [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Moustakas, John [Department of Physics and Astronomy, Siena College, 515 Loudon Road, Loudonville, NY 12211 (United States); Van der Wel, Arjen [Max-Planck Institute for Astronomy, Königstuhl 17, D-69117, Heidelberg (Germany); Zitrin, Adi [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MS 249-17, Pasadena, CA 91125 (United States); Frye, Brenda L. [Steward Observatory/Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Postman, Marc; Bradley, Larry; Coe, Dan [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21208 (United States); Bartelmann, Matthias [Leiden Observatory, Leiden University, P. O. Box 9513, 2300 RA Leiden (Netherlands); Benítez, Narciso [Instituto de Astrofísica de Andalucía (CSIC), C/Camino Bajo de Huétor 24, Granada E-18008 (Spain); Broadhurst, Tom [Department of Theoretical Physics, University of Basque Country UPV/EHU E-Bilbao (Spain); Donahue, Megan [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Infante, Leopoldo, E-mail: hxx@mail.ustc.edu.cn [Departamento de Astronoía y Astrofísica, Pontificia Universidad Católica de Chile, V. Mackenna 4860 Santiago 22 (Chile); and others

    2015-03-01

    We utilize the Cluster Lensing And Supernova survey with Hubble observations of 25 clusters to search for extreme emission-line galaxies (EELGs). The selections are carried out in two central bands: F105W (Y {sub 105}) and F125W (J {sub 125}), as the flux of the central bands could be enhanced by the presence of [O III] λλ4959, 5007 at redshifts of ∼0.93-1.14 and 1.57-1.79, respectively. The multiband observations help to constrain the equivalent widths (EWs) of emission lines. Thanks to cluster lensing, we are able to identify 52 candidates down to an intrinsic limiting magnitude of 28.5 and to a rest-frame [O III] λλ4959, 5007 EW of ≅ 3700 Å. Our samples include a number of EELGs at lower luminosities that are missed in other surveys, and the extremely high EW can only be found in such faint galaxies. These EELGs can mimic a dropout feature similar to that of high-redshift galaxies and contaminate the color-color selection of high-redshift galaxies when the signal-to-noise ratio is limited or the band coverage is incomplete.

  4. Implications of the dwarfs spheroidal galaxy mass-metallicity relation

    International Nuclear Information System (INIS)

    Smith, G.H.

    1985-01-01

    The properties of the mass-metallicity relation among dwarf spheroidal galaxies are discussed in terms of a model which assumes that the internal chemical evolution of the dwarf spheroidals was promoted by supernova activity. The model can be used to explain the observed dwarf spheroidal mass-metallicity relation assuming the present mass of these systems M sub s is proportional to their initial masses M as M sub s varies according to a power-law index of exp 7/4. It is inferred from the power-law dependence of M on the proto-cloud radius that the most massive dwarf spheroids were formed from the densest clouds. The observed slope of the mass-metallicity relation for dwarf spheroidal galaxies is found to be significantly different from theoretical estimates of this slope for elliptical galaxies. It is suggested that the difference may imply that spheroidal dwarfs and elliptical galaxies had different formation histories, confirming Kormendy's (1985) observations of differences in the brightness and luminosity trends. 54 references

  5. A COMPACT GROUP OF GALAXIES AT Z = 2.48 HOSTING AN AGN-DRIVEN OUTFLOW

    Energy Technology Data Exchange (ETDEWEB)

    Shih, Hsin-Yi [Gemini Observatory, 670 N Aohoku Place, Hilo, HI 96720 (United States); Stockton, Alan, E-mail: jshih@gemini.edu, E-mail: stockton@ifa.hawaii.edu [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

    2015-12-10

    We present observations of a remarkable compact group of galaxies at z = 2.48. Four galaxies, all within 40 kpc of each other, surround a powerful high-redshift radio source. This group comprises two compact red passive galaxies and a pair of merging galaxies. One of the red galaxies, with an apparent stellar mass of 3.6 × 10{sup 11}M{sub ⊙} and an effective radius of 470 pc, is one of the most extreme examples of a massive quiescent compact galaxy found so far. One of the pair of merging galaxies hosts the active galactic nucleus (AGN) producing the large powerful radio structure. The merger is massive and enriched, consistent with the mass–metallicity relation expected at this redshift. Close to the merging nuclei, the emission lines exhibit broad and asymmetric profiles that suggest outflows powered either by a very young expanding radio jet or by AGN radiation. At ≳50 kpc from the system, we found a fainter extended-emission region that may be a part of a radio-jet-driven outflow.

  6. The Dragonfly Nearby Galaxies Survey. III. The Luminosity Function of the M101 Group

    Science.gov (United States)

    Danieli, Shany; van Dokkum, Pieter; Merritt, Allison; Abraham, Roberto; Zhang, Jielai; Karachentsev, I. D.; Makarova, L. N.

    2017-03-01

    We obtained follow-up HST observations of the seven low surface brightness galaxies discovered with the Dragonfly Telephoto Array in the field of the massive spiral galaxy M101. Out of the seven galaxies, only three were resolved into stars and are potentially associated with the M101 group at D = 7 Mpc. Based on HST ACS photometry in the broad F606W and F814W filters, we use a maximum likelihood algorithm to locate the Tip of the Red Giant Branch in galaxy color-magnitude diagrams. Distances are {6.38}-0.35+0.35,{6.87}-0.30+0.21 and {6.52}-0.27+0.25 {Mpc} and we confirm that they are members of the M101 group. Combining the three confirmed low-luminosity satellites with previous results for brighter group members, we find the M101 galaxy group to be a sparsely populated galaxy group consisting of seven group members, down to M V = -9.2 mag. We compare the M101 cumulative luminosity function to that of the Milky Way and M31. We find that they are remarkably similar; in fact, the cumulative luminosity function of the M101 group gets even flatter for fainter magnitudes, and we show that the M101 group might exhibit the two known small-scale flaws in the ΛCDM model, namely “the missing satellite” problem and the “too big to fail” problem. Kinematic measurements of M101's satellite galaxies are required to determine whether the “too big to fail” problem does in fact exist in the M101 group.

  7. Disk and dwarf spheroidal galaxies kinematics from general relativity with infrared renormalization group effects

    International Nuclear Information System (INIS)

    Rodrigues, Davi C.; Oliveira, Paulo L.C. de; Fabris, Julio C.; Shapiro, Ilya L.

    2011-01-01

    Full text: The running of coupling constants is a well known phenomenon within Quantum Field Theory. It is also known that the renormalization group method can be extended to quantum field theory on curved space time. Nonetheless, although we know that the beta function of QED go to zero in the infrared limit fast enough to lead to constant charge at the classical level (in conformity with both the Appelquist-Carazzone theorem and experimental data), no analogous proof exists for General Relativity. Some authors have proposed that the infrared beta function of General Relativity is not trivial, and as such certain small running of the gravitational coupling might take place at astrophysical scales, leading in particular to changes on the role of dark matter in galaxies. We review and extend our contribution to infrared Renormalization Group (RG) effects to General Relativity in the context of galaxies, an approach we call RGGR. We extend our previous results by analyzing a larger sample of galaxies, now also including elliptical and dwarf spheroidal galaxies, besides disk galaxies (both LSB and HSB). We compare our RGGR results to both standard dark matter profiles (NFW, Isothermal, Burkert) and alternative models of gravity (MOND, MSTG), showing that the RGGR results are similar in quality to the best dark matter profiles (the cored ones, e.g., Isothermal and Burkert), while displaying a better fitting to the data than NFW, MOND or MSTG. To the latter, we evaluated both the shape of the rotation curve and the expected stellar mass-to-light ratios. Dwarf spheroidal (dSph) galaxies are small galaxies believed to be dominated by dark matter, with the highest fraction do dark matter per baryonic matter. These galaxies provide a strong test to any theory that mimics either all or part of the dark matter behavior. In particular, this is the only type of galaxy that MOND seems incapable of fitting the data. (author)

  8. GALAXIES IN X-RAY GROUPS. II. A WEAK LENSING STUDY OF HALO CENTERING

    Energy Technology Data Exchange (ETDEWEB)

    George, Matthew R.; Ma, Chung-Pei [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Leauthaud, Alexie; Bundy, Kevin [Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa 277-8583 (Japan); Finoguenov, Alexis [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany); Rykoff, Eli S. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Tinker, Jeremy L. [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Wechsler, Risa H. [Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Massey, Richard [Department of Physics, University of Durham, South Road, Durham DH1 3LE (United Kingdom); Mei, Simona, E-mail: mgeorge@astro.berkeley.edu [Bureau des Galaxies, Etoiles, Physique, Instrumentation (GEPI), University of Paris Denis Diderot, F-75205 Paris Cedex 13 (France)

    2012-09-20

    Locating the centers of dark matter halos is critical for understanding the mass profiles of halos, as well as the formation and evolution of the massive galaxies that they host. The task is observationally challenging because we cannot observe halos directly, and tracers such as bright galaxies or X-ray emission from hot plasma are imperfect. In this paper, we quantify the consequences of miscentering on the weak lensing signal from a sample of 129 X-ray-selected galaxy groups in the COSMOS field with redshifts 0 < z < 1 and halo masses in the range 10{sup 13}-10{sup 14} M{sub Sun }. By measuring the stacked lensing signal around eight different candidate centers (such as the brightest member galaxy, the mean position of all member galaxies, or the X-ray centroid), we determine which candidates best trace the center of mass in halos. In this sample of groups, we find that massive galaxies near the X-ray centroids trace the center of mass to {approx}< 75 kpc, while the X-ray position and centroids based on the mean position of member galaxies have larger offsets primarily due to the statistical uncertainties in their positions (typically {approx}50-150 kpc). Approximately 30% of groups in our sample have ambiguous centers with multiple bright or massive galaxies, and some of these groups show disturbed mass profiles that are not well fit by standard models, suggesting that they are merging systems. We find that halo mass estimates from stacked weak lensing can be biased low by 5%-30% if inaccurate centers are used and the issue of miscentering is not addressed.

  9. A 17-billion-solar-mass black hole in a group galaxy with a diffuse core.

    Science.gov (United States)

    Thomas, Jens; Ma, Chung-Pei; McConnell, Nicholas J; Greene, Jenny E; Blakeslee, John P; Janish, Ryan

    2016-04-21

    Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day 'dormant' descendants of this population of 'active' black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall--the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600--a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.

  10. Examining the Center: Positions, Dominance, and Star Formation Rates of Most Massive Group Galaxies at Intermediate Redshift

    Science.gov (United States)

    Connelly, Jennifer L.; Parker, Laura C.; McGee, Sean; Mulchaey, John S.; Finoguenov, Alexis; Balogh, Michael; Wilman, David; Group Environment Evolution Collaboration

    2015-01-01

    The group environment is believed to be the stage for many galaxy transformations, helping evolve blue star-forming galaxies to red passive ones. In local studies of galaxy clusters, the central member is usually a single dominant giant galaxy at the center of the potential with little star formation thought to be the result of galaxy mergers. In nearby groups, a range of morphologies and star formation rates are observed and the formation history is less clear. Further, the position and dominance of the central galaxy cannot be assumed in groups, which are less massive and evolved than clusters. To understand the connections between global group properties and properties of the central group galaxy at intermediate redshift, we examine galaxy groups from the Group Environment and Evolution Collaboration (GEEC) catalog, including both optically- and X-ray-selected groups at redshift z~0.4. The sample is diverse, containing a range in overall mass and evolutionary state. The number of groups is significant, membership is notably complete, and measurements span the IR to the UV allowing the properties of the members to be connected to those of the host groups. Having investigated trends in the global group properties previously, including mass and velocity substructure, we turn our attention now to the galaxy populations, focusing on the central regions of these systems. The most massive and second most massive group galaxies are identified by their stellar mass. The positions of the most massive galaxies (MMGs) are determined with respect to both the luminosity-weighted and X-ray center. Star formation rates are used to explore the fraction of passive/quiescent versus star-forming MMGs and the dominance of the MMGs in our group sample is also tested. Determinations of these characteristics and trends constitute the important first steps toward a detailed understanding of the relationships between the properties of host groups and their most massive galaxies and the

  11. Star Formation Histories of Local Group Dwarf Galaxies. (Ludwig Biermann Award Lecture 1996)

    Science.gov (United States)

    Grebel, E. K.

    The star formation histories of dwarf galaxies in the Local Group are reviewed. First the question of Local Group membership is considered based on various criteria. The properties of 31 (36) galaxies are consistent with likely (potential) Local Group membership. To study the star formation histories of these galaxies, a multi-parameter problem needs to be solved: Ages, metallicities, population fractions, and spatial variations must be determined, which depend crucially on the knowledge of reddening and distance. The basic methods for studying resolvable stellar populations are summarized. One method is demonstrated using the Fornax dwarf spheroidal galaxy. A comprehensive compilation of the star formation histories of dwarf irregulars, dwarf ellipticals, and dwarf spheroidals in the Local Group is presented and visualized through Hodge's population boxes. All galaxies appear to have differing fractions of old and intermediate-age populations, and those sufficiently massive and undisturbed to retain and recycle their gas are still forming stars today. Star formation has occurred either in distinct episodes or continuously over long periods of time. Metallicities and enrichment vary widely. Constraints on merger and remnant scenarios are discussed, and a unified picture based on the current knowledge is presented. Primary goals for future observations are: accurate age determinations based on turnoff photometry, detection of subpopulations distinct in age, metallicity, and/or spatial distribution; improved distances; and astrometric studies to derive orbits and constrain past and future interactions.

  12. NGC 741—Mergers and AGN Feedback on a Galaxy-group Scale

    Energy Technology Data Exchange (ETDEWEB)

    Schellenberger, G.; Vrtilek, J. M.; David, L.; O’Sullivan, E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Giacintucci, S. [Naval Research Laboratory, 4555 Overlook Avenue SW, Code 7213, Washington, DC 20375 (United States); Johnston-Hollitt, M.; Duchesne, S. W. [School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, 6140 (New Zealand); Raychaudhury, S., E-mail: gerrit.schellenberger@cfa.harvard.edu [Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007 (India)

    2017-08-10

    Low-mass galaxy cluster systems and groups will play an essential role in upcoming cosmological studies, such as those to be carried out with eROSITA. Though the effects of active galactic nuclei (AGNs) and merging processes are of special importance to quantify biases like selection effects or deviations from hydrostatic equilibrium, they are poorly understood on the galaxy-group scale. We present an analysis of recent deep Chandra and XMM-Newton integrations of NGC 741 that provides an excellent example of a group with multiple concurrent phenomena: both an old central radio galaxy and a spectacular infalling head-tail source, strongly bent jets, a 100-kpc radio trail, intriguing narrow X-ray filaments, and gas-sloshing features. Supported principally by X-ray and radio continuum data, we address the merging history of the group, the nature of the X-ray filaments, the extent of gas-stripping from NGC 742, the character of cavities in the group, and the roles of the central AGN and infalling galaxy in heating the intra-group medium.

  13. HOT AND COLD GALACTIC GAS IN THE NGC 2563 GALAXY GROUP

    Energy Technology Data Exchange (ETDEWEB)

    Rasmussen, Jesper [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Bai, Xue-Ning [Department of Astrophysical Sciences, Peyton Hall, Princeton University, NJ 08544 (United States); Mulchaey, John S. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Van Gorkom, J. H.; Lee, Duane [Department of Astronomy, Columbia University, Mail Code 5246, 550 West 120th Street, New York, NY 10027 (United States); Jeltema, Tesla E. [UCO/Lick Observatories, 1156 High Street, Santa Cruz, CA 95064 (United States); Zabludoff, Ann I. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Wilcots, Eric [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706 (United States); Martini, Paul [Department of Astronomy, 4055 McPherson Laboratory, Ohio State University, 140 West 18th Avenue, Columbus, OH (United States); Roberts, Timothy P., E-mail: jr@dark-cosmology.dk [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)

    2012-03-01

    The role of environmentally induced gas stripping in driving galaxy evolution in groups remains poorly understood. Here we present extensive Chandra and Very Large Array mosaic observations of the hot and cold interstellar medium within the members of the nearby, X-ray bright NGC 2563 group, a prime target for studies of the role of gas stripping and interactions in relatively small host halos. Our observations cover nearly all group members within a projected radius of 1.15 Mpc ({approx}1.4 R{sub vir}) of the group center, down to a limiting X-ray luminosity and H I mass of 3 Multiplication-Sign 10{sup 39} erg s{sup -1} and 2 Multiplication-Sign 10{sup 8} M{sub Sun }, respectively. The X-ray data are consistent with efficient ram pressure stripping of the hot gas halos of early-type galaxies near the group core, but no X-ray tails are seen and the limited statistics preclude strong conclusions. The H I results suggest moderate H I mass loss from the group members when compared to similar field galaxies. Six of the 20 H I-detected group members show H I evidence of ongoing interactions with other galaxies or with the intragroup medium. Suggestive evidence is further seen for galaxies with close neighbors in position-velocity space to show relatively low H I content, consistent with tidal removal of H I. The results thus indicate removal of both hot and cold gas from the group members via a combination of ram pressure stripping and tidal interactions. We also find that 16 of the 20 H I detections occur on one side of the group, reflecting an unusual morphological segregation whose origin remains unclear.

  14. HOT AND COLD GALACTIC GAS IN THE NGC 2563 GALAXY GROUP

    International Nuclear Information System (INIS)

    Rasmussen, Jesper; Bai, Xue-Ning; Mulchaey, John S.; Van Gorkom, J. H.; Lee, Duane; Jeltema, Tesla E.; Zabludoff, Ann I.; Wilcots, Eric; Martini, Paul; Roberts, Timothy P.

    2012-01-01

    The role of environmentally induced gas stripping in driving galaxy evolution in groups remains poorly understood. Here we present extensive Chandra and Very Large Array mosaic observations of the hot and cold interstellar medium within the members of the nearby, X-ray bright NGC 2563 group, a prime target for studies of the role of gas stripping and interactions in relatively small host halos. Our observations cover nearly all group members within a projected radius of 1.15 Mpc (∼1.4 R vir ) of the group center, down to a limiting X-ray luminosity and H I mass of 3 × 10 39 erg s –1 and 2 × 10 8 M ☉ , respectively. The X-ray data are consistent with efficient ram pressure stripping of the hot gas halos of early-type galaxies near the group core, but no X-ray tails are seen and the limited statistics preclude strong conclusions. The H I results suggest moderate H I mass loss from the group members when compared to similar field galaxies. Six of the 20 H I-detected group members show H I evidence of ongoing interactions with other galaxies or with the intragroup medium. Suggestive evidence is further seen for galaxies with close neighbors in position-velocity space to show relatively low H I content, consistent with tidal removal of H I. The results thus indicate removal of both hot and cold gas from the group members via a combination of ram pressure stripping and tidal interactions. We also find that 16 of the 20 H I detections occur on one side of the group, reflecting an unusual morphological segregation whose origin remains unclear.

  15. On the recovery of the local group motion from galaxy redshift surveys

    Energy Technology Data Exchange (ETDEWEB)

    Nusser, Adi [Physics Department and the Asher Space Science Institute-Technion, Haifa 32000 (Israel); Davis, Marc [Departments of Astronomy and Physics, University of California, Berkeley, CA 94720 (United States); Branchini, Enzo, E-mail: adi@physics.technion.ac.il, E-mail: mdavis@berkeley.edu, E-mail: branchin@fis.uniroma3.it [Department of Physics, Università Roma Tre, Via della Vasca Navale 84, I-00146 Rome (Italy)

    2014-06-20

    There is an ∼150 km s{sup –1} discrepancy between the measured motion of the Local Group (LG) of galaxies with respect to the cosmic microwave background and the linear theory prediction based on the gravitational force field of the large-scale structure in full-sky redshift surveys. We perform a variety of tests which show that the LG motion cannot be recovered to better than 150-200 km s{sup –1} in amplitude and within ≈10° in direction. The tests rely on catalogs of mock galaxies identified in the Millennium simulation using semi-analytic galaxy formation models. We compare these results to the K{sub s} = 11.75 Two-Mass Galaxy Redshift Survey, which provides the deepest and most complete all-sky spatial distribution of galaxies with spectroscopic redshifts available thus far. In our analysis, we use a new concise relation for deriving the LG motion and bulk flow from the true distribution of galaxies in redshift space. Our results show that the main source of uncertainty is the small effective depth of surveys like the Two-Mass Redshift Survey (2MRS), which prevents a proper sampling of the large-scale structure beyond ∼100 h {sup –1} Mpc. Deeper redshift surveys are needed to reach the 'convergence scale' of ≈250 h {sup –1} Mpc in a ΛCDM universe. Deeper surveys would also mitigate the impact of the 'Kaiser rocket' which, in a survey like 2MRS, remains a significant source of uncertainty. Thanks to the quiet and moderate density environment of the LG, purely dynamical uncertainties of the linear predictions are subdominant at the level of ∼90 km s{sup –1}. Finally, we show that deviations from linear galaxy biasing and shot noise errors provide a minor contribution to the total error budget.

  16. State-of-the-art multi-wavelength observations of nearby brightest group/cluster galaxies

    Science.gov (United States)

    Gendron-Marsolais, Marie-Lou; Hlavacek-Larrondo, Julie

    2018-01-01

    Nearby galaxy groups and clusters are crucial to our understanding of the impact of nuclear outbursts on the intracluster medium as their proximity allows us to study in detail the processes of feedback from active galactic nuclei in these systems. In this talk, I will present state-of-the-art multi-wavelength observations signatures of this mechanism.I will first show results on multi-configuration 230-470 MHz observations of the Perseus cluster from the Karl G. Jansky Very Large Array, probing the non-thermal emission from the old particle population of the AGN outflows. These observations reveal a multitude of new structures associated with the “mini-halo” and illustrate the high-quality images that can be obtained with the new JVLA at low radio-frequencies.Second, I will present new observations with the optical imaging Fourier transform spectrometer SITELLE (CFHT) of NGC 1275, the Perseus cluster's brightest galaxy. With its wide field of view, it is the only integral field unit spectroscopy instrument able to cover the large emission-line filamentary nebula in NGC 1275. I will present the first detailed velocity map of this nebula in its entirety and tackle the question of its origin (residual cooling flow or dragged gas).Finally, I will present deep Chandra observations of the nearby early-type massive elliptical galaxy NGC 4472, the most optically luminous galaxy in the local Universe, lying on the outskirts of the Virgo cluster. Enhanced X-ray rims around the radio lobes are detected and interpreted as gas uplifted from the core by the buoyant rise of the radio bubbles. We estimate the energy required to lift the gas to constitute a significant fraction of the total outburst energy.I will thus show how these high-fidelity observations of nearby brightest group/cluster galaxies are improving our understanding of the AGN feedback mechanism taking place in galaxy groups and clusters.

  17. Weak Lensing Calibrated M-T Scaling Relation of Galaxy Groups in the COSMOS Field

    NARCIS (Netherlands)

    Kettula, K.; Finoguenov, A.; Massey, R.; Rhodes, J.; Hoekstra, H.; Taylor, J.; Spinelli, P.; Tanaka, M.; Ilbert, O.; Capak, P.; McCracken, H.; Koekemoer, A.

    2013-01-01

    The scaling between X-ray observables and mass for galaxy clusters and groups is instrumental for cluster-based cosmology and an important probe for the thermodynamics of the intracluster gas. We calibrate a scaling relation between the weak lensing mass and X-ray spectroscopic temperature for 10

  18. The connection between galaxy formation and the assembly of stellar halos in the Local Group

    NARCIS (Netherlands)

    Helmi, Amina

    I will review our current understanding of the assembly of stellar halos from a theoretical perspective. I will place particular emphasis on how observations of Local Group galaxies can be used to constrain the assembly history of both their stellar and dark matter halos. Finally I will focus on

  19. ACTIVE GALACTIC NUCLEI IN GROUPS AND CLUSTERS OF GALAXIES: DETECTION AND HOST MORPHOLOGY

    International Nuclear Information System (INIS)

    Arnold, Timothy J.; Martini, Paul; Mulchaey, John S.; Berti, Angela; Jeltema, Tesla E.

    2009-01-01

    The incidence and properties of active galactic nuclei (AGNs) in the field, groups, and clusters can provide new information about how these objects are triggered and fueled, similar to how these environments have been employed to study galaxy evolution. We have obtained new XMM-Newton observations of seven X-ray selected groups and poor clusters with 0.02 -1 ). We find that the X-ray selected AGN fraction increases from f A (L X ≥ 10 41 ; M R ≤ M* R + 1) = 0.047 +0.023 -0.016 in clusters to 0.091 +0.049 -0.034 for the groups (85% significance), or a factor of 2, for AGN above an 0.3-8 keV X-ray luminosity of 10 41 ergs -1 hosted by galaxies more luminous than M* R + 1. The trend is similar, although less significant, for a lower-luminosity host threshold of M R = -20 mag. For many of the groups in the sample, we have also identified AGN via standard emission-line diagnostics and find that these AGNs are nearly disjoint from the X-ray selected AGN. Because there are substantial differences in the morphological mix of galaxies between groups and clusters, we have also measured the AGN fraction for early-type galaxies alone to determine if the differences are directly due to environment, or indirectly due to the change in the morphological mix. We find that the AGN fraction in early-type galaxies is also lower in clusters f A,n≥2.5 (L X ≥ 10 41 ; M R ≤ M* R + 1) = 0.048 +0.028 -0.019 compared to 0.119 +0.064 -0.044 for the groups (92% significance), a result consistent with the hypothesis that the change in AGN fraction is directly connected to environment.

  20. Implications of multiple high-redshift galaxy clusters

    International Nuclear Information System (INIS)

    Hoyle, Ben; Jimenez, Raul; Verde, Licia

    2011-01-01

    To date, 14 high-redshift (z>1.0) galaxy clusters with mass measurements have been observed, spectroscopically confirmed, and are reported in the literature. These objects should be exceedingly rare in the standard Λ cold dark matter (ΛCDM) model. We conservatively approximate the selection functions of these clusters' parent surveys and quantify the tension between the abundances of massive clusters as predicted by the standard ΛCDM model and the observed ones. We alleviate the tension, considering non-Gaussian primordial perturbations of the local type, characterized by the parameter f NL , and derive constraints on f NL arising from the mere existence of these clusters. At the 95% confidence level, f NL >467, with cosmological parameters fixed to their most likely WMAP5 values, or f NL > or approx. 123 (at 95% confidence) if we marginalize over prior WMAP5 parameters. In combination with f NL constraints from cosmic microwave background and halo bias, this determination implies a scale dependence of f NL at ≅3σ. Given the assumptions made in the analysis, we expect any future improvements to the modeling of the non-Gaussian mass function, survey volumes, or selection functions to increase the significance of f NL >0 found here. In order to reconcile these massive, high-z clusters with f NL =0, their masses would need to be systematically lowered by 1.5σ, or the σ 8 parameter should be ∼3σ higher than cosmic microwave background (and large-scale structure) constraints. The existence of these objects is a puzzle: it either represents a challenge to the ΛCDM paradigm or it is an indication that the mass estimates of clusters are dramatically more uncertain than we think.

  1. REVISED MASS-TO-LIGHT RATIOS FOR NEARBY GALAXY GROUPS AND CLUSTERS

    International Nuclear Information System (INIS)

    Shan, Yutong; Courteau, Stéphane; McDonald, Michael

    2015-01-01

    We present a detailed investigation of the cluster stellar mass-to-light (M*/L) ratio and cumulative stellar masses, derived on a galaxy-by-galaxy basis, for 12 massive (M 500 ∼ 10 14 -10 15 M ☉ ), nearby clusters with available optical imaging data from the Sloan Digital Sky Survey Data Release 10 and X-ray data from the Chandra X-ray Observatory. Our method involves a statistical cluster membership using both photometric and spectroscopic redshifts when available to maximize completeness while minimizing contamination effects. We show that different methods of estimating the stellar mass-to-light ratio from observed photometry result in systematic discrepancies in the total stellar masses and average mass-to-light ratios of cluster galaxies. Nonetheless, all conversion methodologies point to a lack of correlation between M*/L i and total cluster mass, even though low-mass groups contain relatively more blue galaxies. We also find no statistically significant correlation between M*/L i and the fraction of blue galaxies (g – i < 0.85). For the mass range covered by our sample, the assumption of a Chabrier initial mass function (IMF) yields an integrated M*/L i ≅ 1.7 ± 0.2 M ☉ /L i, ☉ , a lower value than used in most similar studies, though consistent with the study of low-mass galaxy groups by Leauthaud et al. A light (diet) Salpeter IMF would imply a ∼60% increase in M*/L i

  2. Ultra-compact high velocity clouds in the ALFALFA HI survey: Candidate Local Group galaxies?

    Science.gov (United States)

    Adams, Elizabeth Ann Kovenz

    The increased sensitivity and spatial resolution of the ALFALFA HI survey has resulted in the detection of ultra-compact high velocity clouds (UCHVCs). These objects are good candidates to represent low mass gas-rich galaxies in the Local Group and Local Volume with stellar populations that are too faint to be detected in extant optical surveys. This idea is referred to as the "minihalo hypothesis". We identify the UCHVCs within the ALFALFA dataset via the use of a 3D matched filtering signal identification algorithm. UCHVCs are selected based on a compact size ( 120 km s-1) and isolation. Within the 40% complete ALFALFA survey (alpha.40), 59 UCHVCs are identified; 19 are in a most-isolated subset and are the best galaxy candidates. Due to the presence of large HVC complexes in the fall sky, most notably the Magellanic Stream, the association of UCHVCs with existing structure cannot be ruled out. In the spring sky, the spatial and kinematic distribution of the UCHVCs is consistent with simulations of dark matter halos within the Local Group. In addition, the HI properties of the UCHVCs (if placed at 1 Mpc) are consistent with both theoretical and observational predictions for low mass gas-rich galaxies. Importantly, the HI properties of the UCHVCs are consistent with those of two recently discovered low mass gas-rich galaxies in the Local Group and Local Volume, Leo T and Leo P. Detailed follow-up observations are key for addressing the minihalo hypothesis. High resolution HI observations can constrain the environment of a UCHVC and offer evidence for a hosting dark matter halo through evidence of rotation support and comparison to theoretical models. Observations of one UCHVC at high resolution (15'') reveal the presence of a clumpy HI distribution, similar to both low mass galaxies and circumgalactic compact HVCs. An extended envelope containing ˜50% of the HI flux is resolved out by the array configuration; observations at lower spatial resolution can recover

  3. Collateral Damage: the Implications of Utrecht Star Cluster Astrophysics for Galaxy Evolution

    Science.gov (United States)

    Kruijssen, J. M. D.

    2013-01-01

    Until the early 2000s, the research portfolio of the Astronomical Institute in Utrecht (SIU) did not include galaxy evolution. Somewhat serendipitously, this changed with the advent of the star cluster group. In only a few years, a simple framework was developed to describe and quantify the properties of dynamically evolving star cluster populations. Since then, the ‘Utrecht cluster disruption model’ has shown that the galactic environment plays an important role in setting the evolution of stellar clusters. From this simple result, it follows that cluster populations bear some imprint of the characteristics and histories of their host galaxies, and that star clusters can be used to trace galaxy evolution—an aim for which the Utrecht star cluster models were never designed, but which they are well-capable of fulfilling. I review some of the work in this direction, with a strong emphasis on the contributions from the SIU.

  4. GALAXY INTERACTIONS IN COMPACT GROUPS. I. THE GALACTIC WINDS OF HCG16

    Energy Technology Data Exchange (ETDEWEB)

    Vogt, Frederic P. A.; Dopita, Michael A.; Kewley, Lisa J., E-mail: fvogt@mso.anu.edu.au [Mount Stromlo Observatory, Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611 (Australia)

    2013-05-10

    Using the WiFeS integral field spectrograph, we have undertaken a series of observations of star-forming galaxies in compact groups. In this first paper dedicated to the project, we present the analysis of the spiral galaxy NGC 838, a member of the Hickson Compact Group 16, and of its galactic wind. Our observations reveal that the wind forms an asymmetric, bipolar, rotating structure, powered by a nuclear starburst. Emission line ratio diagnostics indicate that photoionization is the dominant excitation mechanism at the base of the wind. Mixing from slow shocks (up to 20%) increases further out along the outflow axis. The asymmetry of the wind is most likely caused by one of the two lobes of the wind bubble bursting out of its H I envelope, as indicated by line ratios and radial velocity maps. The characteristics of this galactic wind suggest that it is caught early (a few Myr) in the wind evolution sequence. The wind is also quite different from the galactic wind in the partner galaxy NGC 839 which contains a symmetric, shock-excited wind. Assuming that both galaxies have similar interaction histories, the two different winds must be a consequence of the intrinsic properties of NGC 838 and NGC 839 and their starbursts.

  5. Groups of Galaxies in the Nearby Universe Proceedings of the ESO Workshop held at Santiago de Chile

    CERN Document Server

    Saviane, Ivo; Borissova, Jordanka

    2007-01-01

    For every galaxy in the field or in clusters, there are about three galaxies in groups. The Milky Way itself resides in a group, and groups can be found at high redshift. The current generation of 10-m class telescopes and space facilities allows the observation of the members of nearby groups with exquisite detail, and their properties can be correlated with the global properties of their host group. Groups in the local Universe offer us the chance to study galaxies in environments characterized by strong interactions. In the cosmological context, groups trace large-scale structures better than clusters, and the evolution of groups and clusters appears to be related. All these aspects of research on groups of galaxies are summarized in this book written by scientists working in various fields.

  6. Mass of the Local Group from Proper Motions of Distant Dwarf Galaxies

    Science.gov (United States)

    van der Marel, Roeland

    2010-09-01

    The Local Group and its two dominant spirals, the Milky Way and M31, have become the benchmark for testing many aspects of cosmological and galaxy formation theories, due to many exciting new discoveries in the past decade. However, it is difficult to put results in a proper cosmological context, because our knowledge of the mass M of the Local Group remains uncertain by a factor 4. In units of 10^{12} solar masses, a spherical infall model for the zero-velocity surface gives M 1.3; the sum of estimates for the Milky Way and M31 masses gives M 2.6; and the Local Group Timing argument for the M31 orbit gives M 5.6. It is possible to discriminate between the proposed masses by calculating the orbits of galaxies at the edge of the Local Group, which requires knowledge of transverse velocity components. We therefore propose to use ACS/WFC to determine the proper motions of the 4 dwarf galaxies near the edge of the Local Group {Cetus, Leo A, Tucana, Sag DIG} for which deep first epoch data {with 5-7 year time baselines} already exist in the HST Archive. Our team has extensive expertise with HST astrometric science, and our past/ongoing work for, e.g., Omega Cen, LMC/SMC and M31 show that the necessary astrometric accuracy is within the reach of HST's demonstrated capabilities. We have developed, tested, and published a new technique that uses compact background galaxies as astrometric reference sources, and we have already reduced the first epoch data. The final predicted transverse velocity accuracy, 36 km/s when averaged over the sample, will be sufficient to discriminate between each of the proposed Local Group masses at 2-sigma significance {4-sigma between the most extreme values}. Our project will yield the most accurate Local Group mass determination to date, and only HST can achieve the required accuracy.

  7. A Compact Group of Galaxies at z = 2.48 Hosting an AGN-driven Outflow

    Science.gov (United States)

    Shih, Hsin-Yi; Stockton, Alan

    2015-12-01

    We present observations of a remarkable compact group of galaxies at z = 2.48. Four galaxies, all within 40 kpc of each other, surround a powerful high-redshift radio source. This group comprises two compact red passive galaxies and a pair of merging galaxies. One of the red galaxies, with an apparent stellar mass of 3.6 × 1011M⊙ and an effective radius of 470 pc, is one of the most extreme examples of a massive quiescent compact galaxy found so far. One of the pair of merging galaxies hosts the active galactic nucleus (AGN) producing the large powerful radio structure. The merger is massive and enriched, consistent with the mass-metallicity relation expected at this redshift. Close to the merging nuclei, the emission lines exhibit broad and asymmetric profiles that suggest outflows powered either by a very young expanding radio jet or by AGN radiation. At ≳50 kpc from the system, we found a fainter extended-emission region that may be a part of a radio-jet-driven outflow. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The work is also based, in part, on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

  8. Undergraduate ALFALFA Team: Analysis of Spatially-Resolved Star-Formation in Nearby Galaxy Groups and Clusters

    Science.gov (United States)

    Finn, Rose; Collova, Natasha; Spicer, Sandy; Whalen, Kelly; Koopmann, Rebecca A.; Durbala, Adriana; Haynes, Martha P.; Undergraduate ALFALFA Team

    2017-01-01

    As part of the Undergraduate ALFALFA Team, we are conducting a survey of the gas and star-formation properties of galaxies in 36 groups and clusters in the local universe. The galaxies in our sample span a large range of galactic environments, from the centers of galaxy groups and clusters to the surrounding infall regions. One goal of the project is to map the spatial distribution of star-formation; the relative extent of the star-forming and stellar disks provides important information about the internal and external processes that deplete gas and thus drive galaxy evolution. We obtained wide-field H-alpha observations with the WIYN 0.9m telescope at Kitt Peak National Observatory for galaxies in the vicinity of the MKW11 and NRGb004 galaxy groups and the Abell 1367 cluster. We present a preliminary analysis of the relative size of the star-forming and stellar disks as a function of galaxy morphology and local galaxy density, and we calculate gas depletion times using star-formation rates and HI gas mass. We will combine these results with those from other UAT members to determine if and how environmentally-driven gas depletion varies with the mass and X-ray properties of the host group or cluster. This work has supported by NSF grants AST-0847430, AST-1211005 and AST-1637339.

  9. Flocculent and grand design spiral galaxies in groups: time scales for the persistence of grand design spiral structures

    International Nuclear Information System (INIS)

    Elmegreen, B.G.; Elmegreen, D.M.

    1983-01-01

    Spiral arm classifications were made for 261 low-inclination galaxies in groups listed by Huchra and Geller. The fractional occurrence of grand design spiral structure in nonbarred galaxies was found to increase from approx.0.1 to approx.0.6 and then level off as the group crossing rate or galaxy collision rate in a group increases. A simple model is discussed where the random encounters between galaxies of any type and flocculent galaxies induce transient grand design spirals in the flocculent galaxies. If this grand-design stimulation occurs for binary collisions with impact parameters less than αR 25 , were R 25 is the galactic radius at 25 mag arcsec - 2 , and if the induced grand design spirals persist for an average time equal to #betta# galactic rotations, then the quantity α 2 #betta# equals approximately 3 x 10 4 . If binary collisions are responsible for grand design spirals, then this result implies either that the induced spirals last for many galactic rotations (#betta#>15), or that they can be stimulated by very remote encounters (α>45.) Alternatively, grand design spirals may be stimulated by multiple galaxy encounters, which would be the case for such large α, or by interactions with the potential well of the associated group, rather than by simple binary encounters. Weak correlations between the grand design fraction and the galaxy size, or between this fraction and the total number of galaxies in a group, were also found. Spiral structures of barred galaxies show no correlations with group environment

  10. Project Galaxy - Sustianable Resource Supply and Environmental Implications

    Energy Technology Data Exchange (ETDEWEB)

    Downing, Mark [ORNL; Wimmer, Robert [Toyota Motor Corp.

    2012-03-01

    Understanding what it takes to move from a corn-based liquid fuels industry to one that is cellulosic-based requires a complex transition over time. This transition implies, among other things, a shift from annual cropping systems considered under United States Department of Agriculture (USDA) policy as commodity crops, to perennial lignocellulosic crops that are herbaceous and wood-based. Because of changes in land use as well as biomass and other crop supplies, land-based environmental amenities such as water quality, soil health and tilth, air quality, and animal and avian species populations and their diversity change also. Environmental effects are measured as magnitudes (how much they are impacted), and direction of the impact (either positive or negative). By developing a series of quantitative and qualitative metrics, the larger issue of defining relative sustainability may be addressed, and this can be done at a finer detail of regional (scale) and environmental amenity-specific impacts. Although much literature exists about research relevant to specific environmental variables, there is no published, documented, nor research literature on direct application of environmental over-compliance with regards a 'biorefinery.' Our three goals were to (1) understand and quantify bioenergy sustainability and some key environmental effects in a generic set of examples; (2) explain the effort and means to define and quantify specific qualitative environmental measures, and to determine a way to understand changes in these measures over time and what their implications might be; and (3) use these outcomes to evaluate potential sites in any geographic area. This would permit assessment of candidate locations, combined with an understanding of co-production of fuels, chemicals, and electric power, to interpret sustainability measures and the relationship between environmental sustainability and economic sustainability. The process of determining environmental

  11. The First Galaxies and the Likely Discovery of Their Fossils in the Local Group

    Directory of Open Access Journals (Sweden)

    Massimo Ricotti

    2010-01-01

    Full Text Available The lower bound for the mass of a galaxy is unknown, as are the typical luminosity of the smallest galaxies and their numbers. The answers depend on the extent to which star formation in the first population of small mass halos may be suppressed by radiative feedback loops. If early populations of dwarf galaxies did form in significant number before reionization, their “fossils” should be found today in the Local Group. This paper reviews our ongoing efforts to simulate and identify fossil dwarfs in the Local Group. It is widely believed that reionization stopped star formation in fossil dwarfs. However, here we dispute this idea and discuss a physical mechanism whereby recent episodes of star formation would be produced in some fossil dwarfs that, hence, may characterized by a bimodal star formation history. The same mechanism could turn dark halos that failed to form stars before reionization into gas-rich “dark galaxies”. We believe that current observational data supports the thesis that a fraction of the new ultra-faint dwarfs discovered in the Local Group are fossil dwarfs and we predict the existence of a population of ultra-faint dwarfs with lower surface brightness than currently observed.

  12. EVOLUTION IN THE H I GAS CONTENT OF GALAXY GROUPS: PRE-PROCESSING AND MASS ASSEMBLY IN THE CURRENT EPOCH

    Energy Technology Data Exchange (ETDEWEB)

    Hess, Kelley M. [Astrophysics, Cosmology and Gravity Centre (ACGC), Department of Astronomy, University of Cape Town, Rondebosch 7701 (South Africa); Wilcots, Eric M., E-mail: hess@ast.uct.ac.za, E-mail: ewilcots@astro.wisc.edu [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States)

    2013-11-01

    We present an analysis of the neutral hydrogen (H I) content and distribution of galaxies in groups as a function of their parent dark matter halo mass. The Arecibo Legacy Fast ALFA survey α.40 data release allows us, for the first time, to study the H I properties of over 740 galaxy groups in the volume of sky common to the Sloan Digital Sky Survey (SDSS) and ALFALFA surveys. We assigned ALFALFA H I detections a group membership based on an existing magnitude/volume-limited SDSS Data Release 7 group/cluster catalog. Additionally, we assigned group ''proximity' membership to H I detected objects whose optical counterpart falls below the limiting optical magnitude—thereby not contributing substantially to the estimate of the group stellar mass, but significantly to the total group H I mass. We find that only 25% of the H I detected galaxies reside in groups or clusters, in contrast to approximately half of all optically detected galaxies. Further, we plot the relative positions of optical and H I detections in groups as a function of parent dark matter halo mass to reveal strong evidence that H I is being processed in galaxies as a result of the group environment: as optical membership increases, groups become increasingly deficient of H I rich galaxies at their center and the H I distribution of galaxies in the most massive groups starts to resemble the distribution observed in comparatively more extreme cluster environments. We find that the lowest H I mass objects lose their gas first as they are processed in the group environment, and it is evident that the infall of gas rich objects is important to the continuing growth of large scale structure at the present epoch, replenishing the neutral gas supply of groups. Finally, we compare our results to those of cosmological simulations and find that current models cannot simultaneously predict the H I selected halo occupation distribution for both low and high mass halos.

  13. Modelling chemical abundance distributions for dwarf galaxies in the Local Group: the impact of turbulent metal diffusion

    Science.gov (United States)

    Escala, Ivanna; Wetzel, Andrew; Kirby, Evan N.; Hopkins, Philip F.; Ma, Xiangcheng; Wheeler, Coral; Kereš, Dušan; Faucher-Giguère, Claude-André; Quataert, Eliot

    2018-02-01

    We investigate stellar metallicity distribution functions (MDFs), including Fe and α-element abundances, in dwarf galaxies from the Feedback in Realistic Environment (FIRE) project. We examine both isolated dwarf galaxies and those that are satellites of a Milky Way-mass galaxy. In particular, we study the effects of including a sub-grid turbulent model for the diffusion of metals in gas. Simulations that include diffusion have narrower MDFs and abundance ratio distributions, because diffusion drives individual gas and star particles towards the average metallicity. This effect provides significantly better agreement with observed abundance distributions in dwarf galaxies in the Local Group, including small intrinsic scatter in [α/Fe] versus [Fe/H] of ≲0.1 dex. This small intrinsic scatter arises in our simulations because the interstellar medium in dwarf galaxies is well mixed at nearly all cosmic times, such that stars that form at a given time have similar abundances to ≲0.1 dex. Thus, most of the scatter in abundances at z = 0 arises from redshift evolution and not from instantaneous scatter in the ISM. We find similar MDF widths and intrinsic scatter for satellite and isolated dwarf galaxies, which suggests that environmental effects play a minor role compared with internal chemical evolution in our simulations. Overall, with the inclusion of metal diffusion, our simulations reproduce abundance distribution widths of observed low-mass galaxies, enabling detailed studies of chemical evolution in galaxy formation.

  14. The star formation histories of local group dwarf galaxies. II. Searching for signatures of reionization

    Energy Technology Data Exchange (ETDEWEB)

    Weisz, Daniel R. [Department of Astronomy, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Holtzman, Jon [Department of Astronomy, New Mexico State University, Box 30001, 1320 Frenger Street, Las Cruces, NM 88003 (United States); Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F., E-mail: drw@ucsc.edu [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    2014-07-10

    We search for signatures of reionization in the star formation histories (SFHs) of 38 Local Group dwarf galaxies (10{sup 4} < M{sub *} < 10{sup 9} M{sub ☉}). The SFHs are derived from color-magnitude diagrams using archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. Only five quenched galaxies (And V, And VI, And XIII, Leo IV, and Hercules) are consistent with forming the bulk of their stars before reionization, when full uncertainties are considered. Observations of 13 of the predicted 'true fossils' identified by Bovill and Ricotti show that only two (Hercules and Leo IV) indicate star formation quenched by reionization. However, both are within the virial radius of the Milky Way and evidence of tidal disturbance complicates this interpretation. We argue that the late-time gas capture scenario posited by Ricotti for the low mass, gas-rich, and star-forming fossil candidate Leo T is observationally indistinguishable from simple gas retention. Given the ambiguity between environmental effects and reionization, the best reionization fossil candidates are quenched low mass field galaxies (e.g., KKR 25).

  15. Tidal stripping and the structure of dwarf galaxies in the Local Group

    Science.gov (United States)

    Fattahi, Azadeh; Navarro, Julio F.; Frenk, Carlos S.; Oman, Kyle A.; Sawala, Till; Schaller, Matthieu

    2018-05-01

    The shallow faint-end slope of the galaxy mass function is usually reproduced in Λ cold dark matter (ΛCDM) galaxy formation models by assuming that the fraction of baryons that turn into stars drops steeply with decreasing halo mass and essentially vanishes in haloes with maximum circular velocities Vmax value, unless they are small enough to probe only the rising part of the halo circular velocity curve (i.e. half-mass radii, r1/2 ≪ 1 kpc). Many dwarfs have properties in disagreement with this prediction: they are large enough to probe their halo Vmax but their characteristic velocities are well below 20 km s-1. These `cold faint giants' (an extreme example is the recently discovered Crater 2 Milky Way satellite) can only be reconciled with our ΛCDM models if they are the remnants of once massive objects heavily affected by tidal stripping. We examine this possibility using the APOSTLE cosmological hydrodynamical simulations of the Local Group. Assuming that low-velocity-dispersion satellites have been affected by stripping, we infer their progenitor masses, radii, and velocity dispersions, and find them in remarkable agreement with those of isolated dwarfs. Tidal stripping also explains the large scatter in the mass discrepancy-acceleration relation in the dwarf galaxy regime: tides remove preferentially dark matter from satellite galaxies, lowering their accelerations below the amin ˜ 10-11 m s-2 minimum expected for isolated dwarfs. In many cases, the resulting velocity dispersions are inconsistent with the predictions from Modified Newtonian Dynamics, a result that poses a possibly insurmountable challenge to that scenario.

  16. Luminosity function for planetary nebulae and the number of planetary nebulae in local group galaxies

    International Nuclear Information System (INIS)

    Jacoby, G.H.

    1980-01-01

    Identifications of 19 and 34 faint planetary nebulae have been made in the central regions of the SMC and LMC, respectively, using on-line/off-line filter photography at [O III] and Hα. The previously known brighter planetary nebulae in these fields, eight in both the SMC and the LMC, were also identified. On the basis of the ratio of the numbers of faint to bright planetary nebulae in these fields and the numbers of bright planetary nebulae in the surrounding fields, the total numbers of planetary nebulae in the SMC and LMC are estimated to be 285 +- 78 and 996 +- 253, respectively. Corrections have been applied to account for omissions due to crowding confusion in previous surveys, spatial and detectability incompleteness, and obscuration by dust.Equatorial coordinates and finding charts are presented for all the identified planetary nebulae. The coordinates have uncertainties smaller than 0.''6 relative to nearby bright stars, thereby allowing acquisition of the planetary nebulae by bling offsetting.Monochromatic fluxes are derived photographically and used to determine the luminosity function for Magellanic Cloud planetary nebulae as faint as 6 mag below the brightest. The luminosity function is used to estimate the total numbers of planetary nebulae in eight Local Group galaxies in which only bright planetary nebulae have been identified. The dervied luminosity specific number of planetary nebulae per unit luminosity is nearly constant for all eight galaxies, having a value of 6.1 x 10 -7 planetary nebulae L -1 /sub sun/. The mass specific number, based on the three galaxies with well-determined masses, is 2.1 x 10 -7 planetary nebulae M -1 /sub sun/. With estimates for the luminosity and mass of our Galaxy, its total number of planetary nebulae is calculated to be 10,000 +- 4000, in support of the Cudworth distance scale

  17. Are High-redshift Galaxies Hot? Temperature of z > 5 Galaxies and Implications for Their Dust Properties

    International Nuclear Information System (INIS)

    Faisst, Andreas L.; Capak, Peter L.; Masters, Daniel C.; Yan, Lin; Pavesi, Riccardo; Riechers, Dominik A.; Barišić, Ivana; Cooke, Kevin C.; Kartaltepe, Jeyhan S.

    2017-01-01

    Recent studies have found a significant evolution and scatter in the relationship between the UV spectral slope ( β UV ) and the infrared excess (IRX; L IR / L UV ) at z > 4, suggesting different dust properties of these galaxies. The total far-infrared (FIR) luminosity is key for this analysis, but it is poorly constrained in normal (main-sequence) star-forming z > 5 galaxies, where often only one single FIR point is available. To better inform estimates of the FIR luminosity, we construct a sample of local galaxies and three low-redshift analogues of z > 5 systems. The trends in this sample suggest that normal high-redshift galaxies have a warmer infrared (IR) spectral energy distribution (SED) compared to average z < 4 galaxies that are used as priors in these studies. The blueshifted peak and mid-IR excess emission could be explained by a combination of a larger fraction of metal-poor interstellar medium being optically thin to ultraviolet (UV) light and a stronger UV radiation field due to high star formation densities. Assuming a maximally warm IR SED suggests a 0.6 dex increase in total FIR luminosities, which removes some tension between the dust attenuation models and observations of the IRX− β relation at z > 5. Despite this, some galaxies still fall below the minimum IRX− β relation derived with standard dust cloud models. We propose that radiation pressure in these highly star-forming galaxies causes a spatial offset between dust clouds and young star-forming regions within the lifetime of O/B stars. These offsets change the radiation balance and create viewing-angle effects that can change UV colors at fixed IRX. We provide a modified model that can explain the location of these galaxies on the IRX− β diagram.

  18. Are High-redshift Galaxies Hot? Temperature of z > 5 Galaxies and Implications for Their Dust Properties

    Energy Technology Data Exchange (ETDEWEB)

    Faisst, Andreas L.; Capak, Peter L.; Masters, Daniel C. [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Yan, Lin [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Pavesi, Riccardo; Riechers, Dominik A. [Department of Astronomy, Cornell University, Space Sciences Building, Ithaca, NY 14853 (United States); Barišić, Ivana [Max-Planck Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany); Cooke, Kevin C.; Kartaltepe, Jeyhan S., E-mail: afaisst@ipac.caltech.edu [School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623 (United States)

    2017-09-20

    Recent studies have found a significant evolution and scatter in the relationship between the UV spectral slope ( β {sub UV}) and the infrared excess (IRX; L {sub IR}/ L {sub UV}) at z > 4, suggesting different dust properties of these galaxies. The total far-infrared (FIR) luminosity is key for this analysis, but it is poorly constrained in normal (main-sequence) star-forming z > 5 galaxies, where often only one single FIR point is available. To better inform estimates of the FIR luminosity, we construct a sample of local galaxies and three low-redshift analogues of z > 5 systems. The trends in this sample suggest that normal high-redshift galaxies have a warmer infrared (IR) spectral energy distribution (SED) compared to average z < 4 galaxies that are used as priors in these studies. The blueshifted peak and mid-IR excess emission could be explained by a combination of a larger fraction of metal-poor interstellar medium being optically thin to ultraviolet (UV) light and a stronger UV radiation field due to high star formation densities. Assuming a maximally warm IR SED suggests a 0.6 dex increase in total FIR luminosities, which removes some tension between the dust attenuation models and observations of the IRX− β relation at z > 5. Despite this, some galaxies still fall below the minimum IRX− β relation derived with standard dust cloud models. We propose that radiation pressure in these highly star-forming galaxies causes a spatial offset between dust clouds and young star-forming regions within the lifetime of O/B stars. These offsets change the radiation balance and create viewing-angle effects that can change UV colors at fixed IRX. We provide a modified model that can explain the location of these galaxies on the IRX− β diagram.

  19. Galaxy mergers

    International Nuclear Information System (INIS)

    Roos, N.

    1981-01-01

    This thesis contains a series of four papers dealing with the effects of interactions among galaxies during the epoch of cluster formation. Galaxy interactions are investigated and the results incorporated in numerical simulations of the formation of groups and clusters of galaxies. The role of galaxy interactions is analysed in the more general context of simulations of an expanding universe. The evolution of galaxies in rich clusters is discussed. The results of the investigations are presented and their relation to other work done in the field are briefly reviewed and an attempt is made to link galaxy mergers to the occurrence of activity in galactic nuclei. (Auth.)

  20. Optical Observations of M81 Galaxy Group in Narrow Band [SII] and H_alpha Filters: Holmberg IX

    Directory of Open Access Journals (Sweden)

    Arbutina, B.

    2009-12-01

    Full Text Available We present observations of the nearby tidal dwarf galaxy Holmberg IX in M81 galaxy group in narrow band [SII] and H$alpha$ filters, carried out in March and November 2008 with the 2m RCC telescope at NAO Rozhen, Bulgaria. Our search for resident supernova remnants (identified as sources with enhanced [SII] emission relative to their H$alpha$ emission in this galaxy yielded no sources of this kind, besides M&H 10-11 or HoIX X-1. Nevertheless, we found a number of objects with significant H$alpha$ emission that probably represent uncatalogued HII regions.

  1. WISE Discovery of Hyper Luminous Galaxies at z=2-4 and Their Implications for Galaxy and AGN Evolution

    Science.gov (United States)

    Tsai, Chao Wei; Eisenhardt, Peter; Wu, Jingwen; Bridge, Carrie; Assef, Roberto; Benford, Dominic; Blain, Andrew; Cutri, Roc; Griffith, Robert L.; Jarrett, Thomas; hide

    2014-01-01

    On behalf of the WISE Science team, we present the discovery of a class of distant dust-enshrouded galaxies with extremely high luminosity. These galaxies are selected to have extreme red colors in the mid-IR using NASA's Wide-field Infrared Survey Explorer (WISE). They are faint in the optical and near-IR, predominantly at zeta = 2-4, and with IR luminosity > 10(exp 13) Solar Luminosity, making them Hyper-Luminous Infrared Galaxies (HyLIRGs). SEDs incorporating the WISE, Spitzer, and Herschel PACS and SPIRE photometry indicate hot dust dominates the bolometric luminosity, presumably powered by AGN. Preliminary multi-wavelength follow-up suggests that they are different from normal populations in the local M-sigma relation. Their low source density implies that these objects are either intrinsically rare, or a short-lived phase in a more numerous population. If the latter is the case, these hot, dust-enshrouded galaxies may be an early stage in the interplay between AGN and galaxies.

  2. Correlation between the Total Gravitating Mass of Groups and Clusters and the Supermassive Black Hole Mass of Brightest Galaxies

    Science.gov (United States)

    Bogdán, Ákos; Lovisari, Lorenzo; Volonteri, Marta; Dubois, Yohan

    2018-01-01

    Supermassive black holes (BHs) residing in the brightest cluster galaxies are over-massive relative to the stellar bulge mass or central stellar velocity dispersion of their host galaxies. As BHs residing at the bottom of the galaxy cluster’s potential well may undergo physical processes that are driven by the large-scale characteristics of the galaxy clusters, it is possible that the growth of these BHs is (indirectly) governed by the properties of their host clusters. In this work, we explore the connection between the mass of BHs residing in the brightest group/cluster galaxies (BGGs/BCGs) and the virial temperature, and hence total gravitating mass, of galaxy groups/clusters. To this end, we investigate a sample of 17 BGGs/BCGs with dynamical BH mass measurements and utilize XMM-Newton X-ray observations to measure the virial temperatures and infer the {M}500 mass of the galaxy groups/clusters. We find that the {M}{BH}{--}{kT} relation is significantly tighter and exhibits smaller scatter than the {M}{BH}{--}{M}{bulge} relations. The best-fitting power-law relations are {{log}}10({M}{BH}/{10}9 {M}ȯ )=0.20+1.74{{log}}10({kT}/1 {keV}) and {{log}}10({M}{BH}/{10}9 {M}ȯ ) = -0.80+1.72{{log}}10({M}{bulge}/{10}11 {M}ȯ ). Thus, the BH mass of BGGs/BCGs may be set by physical processes that are governed by the properties of the host galaxy group/cluster. These results are confronted with the Horizon-AGN simulation, which reproduces the observed relations well, albeit the simulated relations exhibit notably smaller scatter.

  3. Mergers in galaxy groups. I. Structure and properties of elliptical remnants

    International Nuclear Information System (INIS)

    Taranu, Dan S.; Dubinski, John; Yee, H. K. C.

    2013-01-01

    We present collisionless simulations of dry mergers in groups of 3 to 25 galaxies to test the hypothesis that elliptical galaxies form at the centers of such groups. Mock observations of the central remnants confirm their similarity to ellipticals, despite having no dissipational component. We vary the profile of the original spiral's bulge and find that ellipticals formed from spirals with exponential bulges have too low Sersic indices. Mergers of spirals with de Vaucouleurs (classical) bulges produce remnants with larger Sersic indices correlated with luminosity, as with Sloan Digital Sky Survey ellipticals. Exponential bulge mergers are better fits to faint ellipticals, whereas classical bulge mergers better match luminous ellipticals. Similarly, luminous ellipticals are better reproduced by remnants undergoing many (>5) mergers, and fainter ellipticals by those with fewer mergers. The remnants follow tight size-luminosity and velocity dispersion-luminosity (Faber-Jackson) relations (<0.12 dex scatter), demonstrating that stochastic merging can produce tight scaling relations if the merging galaxies also follow tight scaling relations. The slopes of the size-luminosity and Faber-Jackson relations are close to observations but slightly shallower in the former case. Both relations' intercepts are offset—remnants are too large but have too low dispersions at fixed luminosity. Some remnants show substantial (v/σ > 0.1) rotational support, although most are slow rotators and few are very fast rotators (v/σ > 0.5). These findings contrast with previous studies concluding that dissipation is necessary to produce ellipticals from binary mergers of spirals. Multiple, mostly minor and dry mergers can produce bright ellipticals, whereas significant dissipation could be required to produce faint, rapidly rotating ellipticals.

  4. GMRT HI Observations of the Eridanus Group of Galaxies A. Omar ...

    Indian Academy of Sciences (India)

    The Fornax cluster having the highest galaxy density has the lowest spiral fraction, ... The present GMRT HI observations offer several advantages over studies carried ..... with coarser velocity resolutions for a model galaxy, and determined the ...

  5. Stellar Populations in Compact Galaxy Groups: a Multi-wavelength Study of HCGs 16, 22, and 42, Their Star Clusters, and Dwarf Galaxies

    Science.gov (United States)

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Fedotov, K.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Desjardins, T. D.; Gallagher, S. C.; Walker, L. M.; hide

    2013-01-01

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy.We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 "associates" (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  6. Star-Formation Histories, Abundances, and Kinematics of Dwarf Galaxies in the Local Group

    NARCIS (Netherlands)

    Tolstoy, Eline; Hill, Vanessa; Tosi, Monica; Blandford, R; Kormendy, J; VanDishoeck, E

    2009-01-01

    Within the Local Universe galaxies can be studied in great detail star by star, and here we review the results of quantitative studies in nearby dwarf galaxies. The color-magnitude diagram synthesis method is well established as the most accurate way to determine star-formation histories of galaxies

  7. The Tully–Fisher Relations of the Eridanus Group of Galaxies A ...

    Indian Academy of Sciences (India)

    constant rotation velocity in the outer regions of galaxies is believed to be due to dark matter, and the stellar luminosity directly correlates with the stellar mass, which is the dominant component of the baryonic mass in a galaxy. The cold dark matter mod- els of galaxy formation predict a relation (Mbaryon ∼ V α rot) between ...

  8. A SYSTEMATIC SEARCH FOR X-RAY CAVITIES IN THE HOT GAS OF GALAXY GROUPS

    International Nuclear Information System (INIS)

    Dong Ruobing; Rasmussen, Jesper; Mulchaey, John S.

    2010-01-01

    We have performed a systematic search for X-ray cavities in the hot gas of 51 galaxy groups with Chandra archival data. The cavities are identified based on two methods: subtracting an elliptical β-model fitted to the X-ray surface brightness, and performing unsharp masking. Thirteen groups in the sample (∼25%) are identified as clearly containing cavities, with another 13 systems showing tentative evidence for such structures. We find tight correlations between the radial and tangential radii of the cavities, and between their size and projected distance from the group center, in quantitative agreement with the case for more massive clusters. This suggests that similar physical processes are responsible for cavity evolution and disruption in systems covering a large range in total mass. We see no clear association between the detection of cavities and the current 1.4 GHz radio luminosity of the central brightest group galaxy, but there is a clear tendency for systems with a cool core to be more likely to harbor detectable cavities. To test the efficiency of the adopted cavity detection procedures, we employ a set of mock images designed to mimic typical Chandra data of our sample, and find that the model-fitting approach is generally more reliable than unsharp masking for recovering cavity properties. Finally, we find that the detectability of cavities is strongly influenced by a few factors, particularly the signal-to-noise ratio of the data, and that the real fraction of X-ray groups with prominent cavities could be substantially larger than the 25%-50% suggested by our analysis.

  9. LARGE AREA SURVEY FOR z = 7 GALAXIES IN SDF AND GOODS-N: IMPLICATIONS FOR GALAXY FORMATION AND COSMIC REIONIZATION

    International Nuclear Information System (INIS)

    Ouchi, Masami; Mobasher, Bahram; Shimasaku, Kazuhiro; Ono, Yoshiaki; Nakajima, Kimihiko; Okamura, Sadanori; Ferguson, Henry C.; Fall, S. Michael; Kashikawa, Nobunari; Morokuma, Tomoki; Dickinson, Mark; Giavalisco, Mauro; Ohta, Kouji

    2009-01-01

    We present results of our large area survey for z'-band dropout galaxies at z = 7 in a 1568 arcmin 2 sky area covering the SDF and GOODS-N fields. Combining our ultra-deep Subaru/Suprime-Cam z'- and y-band (λ eff = 1 μm) images with legacy data of Subaru and Hubble Space Telescope, we have identified 22 bright z-dropout galaxies down to y = 26, one of which has a spectroscopic redshift of z = 6.96 determined from Lyα emission. The z = 7 luminosity function yields the best-fit Schechter parameters of φ* = 0.69 +2.62 -0.55 x 10 -3 Mpc -3 , M* UV = -20.10 ± 0.76 mag, and α = -1.72 ± 0.65, and indicates a decrease from z = 6 at a >95% confidence level. This decrease is beyond the cosmic variance in our two fields, which is estimated to be a factor of ∼ 0.2), a lower metallicity, and/or a flatter initial mass function. Our SDF z-dropout galaxies appear to form 60 Mpc long filamentary structures, and the z = 6.96 galaxy with Lyα emission is located at the center of an overdense region consisting of four UV bright dropout candidates, which might suggest an existence of a well-developed ionized bubble at z = 7.

  10. A multi-wavelength study of the evolution of early-type galaxies in groups: the ultraviolet view

    Science.gov (United States)

    Rampazzo, R.; Mazzei, P.; Marino, A.; Bianchi, L.; Plana, H.; Trinchieri, G.; Uslenghi, M.; Wolter, A.

    2018-04-01

    The ultraviolet-optical colour magnitude diagram of rich galaxy groups is characterised by a well developed Red Sequence, a Blue Cloud and the so-called Green Valley. Loose, less evolved groups of galaxies which are probably not virialised yet may lack a well defined Red Sequence. This is actually explained in the framework of galaxy evolution. We are focussing on understanding galaxy migration towards the Red Sequence, checking for signatures of such a transition in their photometric and morphological properties. We report on the ultraviolet properties of a sample of early-type (ellipticals+S0s) galaxies inhabiting the Red Sequence. The analysis of their structures, as derived by fitting a Sérsic law to their ultraviolet luminosity profiles, suggests the presence of an underlying disk. This is the hallmark of dissipation processes that still must have a role to play in the evolution of this class of galaxies. Smooth particle hydrodynamic simulations with chemo-photometric implementations able to match the global properties of our targets are used to derive their evolutionary paths through ultraviolet-optical colour magnitude diagrams, providing some fundamental information such as the crossing time through the Green Valley, which depends on their luminosity. The transition from the Blue Cloud to the Red Sequence takes several Gyrs, being about 3-5 Gyr for the brightest galaxies and longer for fainter ones, if occurring. The photometric study of nearby galaxy structures in the ultraviolet is seriously hampered by either the limited field of view of the cameras (e.g., in Hubble Space Telescope) or by the low spatial resolution of the images (e.g., in the Galaxy Evolution Explorer). Current missions equipped with telescopes and cameras sensitive to ultraviolet wavelengths, such as Swift- UVOT and Astrosat-UVIT, provide a relatively large field of view and a better resolution than the Galaxy Evolution Explorer. More powerful ultraviolet instruments (size, resolution

  11. Westerbork Synthesis Radio Telescope HI Imaging of HI-selected Local Group Galaxy Candidates

    Science.gov (United States)

    Adams, Elizabeth A.; Cannon, J. M.; Oosterloo, T.; Giovanelli, R.; Haynes, M. P.

    2014-01-01

    The paucity of low mass galaxies in the Universe is a long-standing problem. We recently presented a set of isolated ultra-compact high velocity clouds (UCHVCs) identified within the dataset of the Arecibo Legacy Fast ALFA (ALFALFA) HI line survey that are consistent with representing low mass gas-bearing dark matter halos within the Local Group (Adams et al. 2013). At distances of ~1 Mpc, the UCHVCs have HI masses of ~10^5 Msun and indicative dynamical masses of ~10^7 Msun. The HI diameters of the UCHVCs range from 4' to 20', or 1 to 6 kpc at a distance of 1 Mpc. We have selected the most compact and isolated UCHVCs with the highest average column densities as representing the best galaxy candidates. Seven of these systems have been observed with WSRT to enable higher spatial resolution 40-60") studies of the HI distribution. The HI morphology revealed by the WSRT data offers clues to the environment of the UCHVCs, and velocity fields allow the underlying mass distribution to be constrained. The Cornell ALFALFA team is supported by NSF AST-1107390 and by the Brinson Foundation. JMC is supported by NSF grant AST-1211683.

  12. Large Area Survey for z = 7 Galaxies in SDF and GOODS-N: Implications for Galaxy Formation and Cosmic Reionization

    Science.gov (United States)

    Ouchi, Masami; Mobasher, Bahram; Shimasaku, Kazuhiro; Ferguson, Henry C.; Fall, S. Michael; Ono, Yoshiaki; Kashikawa, Nobunari; Morokuma, Tomoki; Nakajima, Kimihiko; Okamura, Sadanori; Dickinson, Mark; Giavalisco, Mauro; Ohta, Kouji

    2009-12-01

    We present results of our large area survey for z'-band dropout galaxies at z = 7 in a 1568 arcmin2 sky area covering the SDF and GOODS-N fields. Combining our ultra-deep Subaru/Suprime-Cam z'- and y-band (λeff = 1 μm) images with legacy data of Subaru and Hubble Space Telescope, we have identified 22 bright z-dropout galaxies down to y = 26, one of which has a spectroscopic redshift of z = 6.96 determined from Lyα emission. The z = 7 luminosity function yields the best-fit Schechter parameters of phi* = 0.69+2.62 -0.55 × 10-3 Mpc-3, M*UV = -20.10 ± 0.76 mag, and α = -1.72 ± 0.65, and indicates a decrease from z = 6 at a >95% confidence level. This decrease is beyond the cosmic variance in our two fields, which is estimated to be a factor of lsim2. We have found that the cosmic star formation rate density drops from the peak at z = 2-3 to z = 7 roughly by a factor of ~10 but not larger than ~100. A comparison with the reionization models suggests either that the universe could not be totally ionized by only galaxies at z = 7, or more likely that properties of galaxies at z = 7 are different from those at low redshifts having, e.g., a larger escape fraction (gsim0.2), a lower metallicity, and/or a flatter initial mass function. Our SDF z-dropout galaxies appear to form 60 Mpc long filamentary structures, and the z = 6.96 galaxy with Lyα emission is located at the center of an overdense region consisting of four UV bright dropout candidates, which might suggest an existence of a well-developed ionized bubble at z = 7. Based on data obtained with the Subaru Telescope, the NASA/ESA Hubble Space Telescope (HST), and Spitzer Space Telescope. The Subaru Telescope is operated by the National Astronomical Observatory of Japan. HST is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology under a

  13. First results from the IllustrisTNG simulations: the stellar mass content of groups and clusters of galaxies

    Science.gov (United States)

    Pillepich, Annalisa; Nelson, Dylan; Hernquist, Lars; Springel, Volker; Pakmor, Rüdiger; Torrey, Paul; Weinberger, Rainer; Genel, Shy; Naiman, Jill P.; Marinacci, Federico; Vogelsberger, Mark

    2018-03-01

    The IllustrisTNG project is a new suite of cosmological magnetohydrodynamical simulations of galaxy formation performed with the AREPO code and updated models for feedback physics. Here, we introduce the first two simulations of the series, TNG100 and TNG300, and quantify the stellar mass content of about 4000 massive galaxy groups and clusters (1013 ≤ M200c/M⊙ ≤ 1015) at recent times (z ≤ 1). The richest clusters have half of their total stellar mass bound to satellite galaxies, with the other half being associated with the central galaxy and the diffuse intracluster light. Haloes more massive than about 5 × 1014 M⊙ have more diffuse stellar mass outside 100 kpc than within 100 kpc, with power-law slopes of the radial mass density distribution as shallow as the dark matter's ( - 3.5 ≲ α3D ≲ -3). Total halo mass is a very good predictor of stellar mass, and vice versa: at z = 0, the 3D stellar mass measured within 30 kpc scales as ∝(M500c)0.49 with a ˜0.12 dex scatter. This is possibly too steep in comparison to the available observational constraints, even though the abundance of The Next Generation less-massive galaxies ( ≲ 1011 M⊙ in stars) is in good agreement with the measured galaxy stellar mass functions at recent epochs. The 3D sizes of massive galaxies fall too on a tight (˜0.16 dex scatter) power-law relation with halo mass, with r^stars_0.5 ∝ (M_200c)^{0.53}. Even more fundamentally, halo mass alone is a good predictor for the whole stellar mass profiles beyond the inner few kiloparsecs, and we show how on average these can be precisely recovered given a single-mass measurement of the galaxy or its halo.

  14. Shaken Snow Globes: Kinematic Tracers of the Multiphase Condensation Cascade in Massive Galaxies, Groups, and Clusters

    Science.gov (United States)

    Gaspari, M.; McDonald, M.; Hamer, S. L.; Brighenti, F.; Temi, P.; Gendron-Marsolais, M.; Hlavacek-Larrondo, J.; Edge, A. C.; Werner, N.; Tozzi, P.; Sun, M.; Stone, J. M.; Tremblay, G. R.; Hogan, M. T.; Eckert, D.; Ettori, S.; Yu, H.; Biffi, V.; Planelles, S.

    2018-02-01

    We propose a novel method to constrain turbulence and bulk motions in massive galaxies, galaxy groups, and clusters, exploring both simulations and observations. As emerged in the recent picture of top-down multiphase condensation, hot gaseous halos are tightly linked to all other phases in terms of cospatiality and thermodynamics. While hot halos (∼107 K) are perturbed by subsonic turbulence, warm (∼104 K) ionized and neutral filaments condense out of the turbulent eddies. The peaks condense into cold molecular clouds (runs, and is corroborated by the combined Hitomi and new Integral Field Unit measurements in the Perseus cluster. The ensemble multiphase gas distributions (from the UV to the radio band) are characterized by substantial spectral line broadening (σ v,los ≈ 100–200 {km} {{{s}}}-1) with a mild line shift. On the other hand, pencil-beam detections (as H I absorption against the AGN backlight) sample the small-scale clouds displaying smaller broadening and significant line shifts of up to several 100 {km} {{{s}}}-1 (for those falling toward the AGN), with increased scatter due to the turbulence intermittency. We present new ensemble σ v,los of the warm Hα+[N II] gas in 72 observed cluster/group cores: the constraints are consistent with the simulations and can be used as robust proxies for the turbulent velocities, in particular for the challenging hot plasma (otherwise requiring extremely long X-ray exposures). Finally, we show that the physically motivated criterion C ≡ t cool/t eddy ≈ 1 best traces the condensation extent region and the presence of multiphase gas in observed clusters and groups. The ensemble method can be applied to many available spectroscopic data sets and can substantially advance our understanding of multiphase halos in light of the next-generation multiwavelength missions.

  15. X-ray emission from clusters and groups of galaxies

    Science.gov (United States)

    Mushotzky, Richard

    1998-01-01

    Recent major advances in x-ray imaging and spectroscopy of clusters have allowed the determination of their mass and mass profile out to ≈1/2 the virial radius. In rich clusters, most of the baryonic mass is in the gas phase, and the ratio of mass in gas/stars varies by a factor of 2–4. The baryonic fractions vary by a factor of ≈3 from cluster to cluster and almost always exceed 0.09 h50−[3/2] and thus are in fundamental conflict with the assumption of Ω = 1 and the results of big bang nucleosynthesis. The derived Fe abundances are 0.2–0.45 solar, and the abundances of O and Si for low redshift systems are 0.6–1.0 solar. This distribution is consistent with an origin in pure type II supernova. The amount of light and energy produced by these supernovae is very large, indicating their importance in influencing the formation of clusters and galaxies. The lack of evolution of Fe to a redshift of z ≈ 0.4 argues for very early enrichment of the cluster gas. Groups show a wide range of abundances, 0.1–0.5 solar. The results of an x-ray survey indicate that the contribution of groups to the mass density of the universe is likely to be larger than 0.1 h50−2. Many of the very poor groups have large x-ray halos and are filled with small galaxies whose velocity dispersion is a good match to the x-ray temperatures. PMID:9419327

  16. Halo ellipticity of GAMA galaxy groups from KiDS weak lensing

    Science.gov (United States)

    van Uitert, Edo; Hoekstra, Henk; Joachimi, Benjamin; Schneider, Peter; Bland-Hawthorn, Joss; Choi, Ami; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Hopkins, Andrew M.; Klaes, Dominik; Kuijken, Konrad; Nakajima, Reiko; Napolitano, Nicola R.; Schrabback, Tim; Valentijn, Edwin; Viola, Massimo

    2017-06-01

    We constrain the average halo ellipticity of ˜2600 galaxy groups from the Galaxy And Mass Assembly (GAMA) survey, using the weak gravitational lensing signal measured from the overlapping Kilo Degree Survey (KiDS). To do so, we quantify the azimuthal dependence of the stacked lensing signal around seven different proxies for the orientation of the dark matter distribution, as it is a priori unknown which one traces the orientation best. On small scales, the major axis of the brightest group/cluster member (BCG) provides the best proxy, leading to a clear detection of an anisotropic signal. In order to relate that to a halo ellipticity, we have to adopt a model density profile. We derive new expressions for the quadrupole moments of the shear field given an elliptical model surface mass density profile. Modelling the signal with an elliptical Navarro-Frenk-White profile on scales R < 250 kpc, and assuming that the BCG is perfectly aligned with the dark matter, we find an average halo ellipticity of ɛh = 0.38 ± 0.12, in fair agreement with results from cold dark matter only simulations. On larger scales, the lensing signal around the BCGs becomes isotropic and the distribution of group satellites provides a better proxy for the halo's orientation instead, leading to a 3σ-4σ detection of a non-zero halo ellipticity at 250 < R < 750 kpc. Our results suggest that the distribution of stars enclosed within a certain radius forms a good proxy for the orientation of the dark matter within that radius, which has also been observed in hydrodynamical simulations.

  17. Galaxy evolution in groups. NGC 3447/NGC 3447A: the odd couple in LGG 225

    Science.gov (United States)

    Mazzei, P.; Marino, A.; Rampazzo, R.; Plana, H.; Rosado, M.; Arias, L.

    2018-02-01

    Context. Local Group (LG) analogs (LGAs) are galaxy associations dominated by a few bright spirals reminiscent of the LG. The NGC 3447/NGC 3447A system is a member of the LGG 225 group, a nearby LGA. This system is considered a physical pair composed of an intermediate-luminosity late-type spiral, NGC 3447 itself, and an irregular companion, NGC 3447A, linked by a faint, short filament of matter. A ring-like structure in the NGC 3447 outskirts has been emphasised by Galaxy Evolution Explorer (GALEX) observations. Aims: This work aims to contribute to the study of galaxy evolution in low-density environments, a favourable habitat to highly effective encounters, shedding light on the evolution of the NGC 3447/NGC 3447A system. Methods: We performed a multi-λ analysis of the surface photometry of this system to derive its spectral energy distribution and structural properties using ultraviolet (UV), Swift UVOT, and optical Sloan Digital Sky Survey (SDSS) images complemented with available far-IR observations. We also characterised the velocity field of the pair using two-dimensional Hα kinematical observations of the system obtained with PUMA Fabry-Perot interferometer at the 2.1 m telescope of San Pedro Mártir (Mexico). All these data are used to constrain smooth particle hydrodynamic simulations with chemo-photometric implementation to shed light on the evolution of this system. Results: The luminosity profiles, from UV to optical wavelengths, are all consistent with the presence of a disc extending and including NGC 3447A. The overall velocity field does not emphasise any significant rotation pattern, rather a small velocity gradient between NGC 3447 and NGC 3447A. Our simulation, detached from a large grid explored to best-fit the global properties of the system, suggests that this arises from an encounter between two halos of equal mass. Conclusions: NGC 3447 and NGC 3447A belong to the same halo, NGC 3447A being a substructure of the same disk including NGC

  18. SPECTROSCOPIC CONFIRMATION OF THE DWARF SPHEROIDAL GALAXY d0994+71 AS A MEMBER OF THE M81 GROUP OF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Toloba, Elisa; Sand, David; Crnojević, Denija [Texas Tech University, Physics Department, Box 41051, Lubbock, TX 79409-1051 (United States); Guhathakurta, Puragra [UCO/Lick Observatory, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Chiboucas, Kristin [Gemini Observatory, 670 North Aohoku Place, Hilo, HI 96720 (United States); Simon, Joshua D., E-mail: toloba@ucolick.org [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

    2016-10-10

    We use Keck/DEIMOS spectroscopy to measure the first velocity and metallicity of a dwarf spheroidal (dSph) galaxy beyond the Local Group using resolved stars. Our target, d0944+71, is a faint dSph found in the halo of the massive spiral galaxy M81 by Chiboucas et al. We coadd the spectra of 27 individual stars and measure a heliocentric radial velocity of −38 ± 10 km s{sup −1}. This velocity is consistent with d0944+71 being gravitationally bound to M81. We coadd the spectra of the 23 stars that are consistent with being red giant branch stars and measure an overall metallicity of [Fe/H] = −1.3 ± 0.3 based on the calcium triplet lines. This metallicity is consistent with d0944+71 following the metallicity−luminosity relation for Local Group dSphs. We investigate several potential sources of observational bias but find that our sample of targeted stars is representative of the metallicity distribution function of d0944+71 and any stellar contamination due to seeing effects is negligible. The low ellipticity of the galaxy and its position in the metallicity−luminosity relation suggest that d0944+71 has not been affected by strong tidal stripping.

  19. Implications for the missing low-mass galaxies (satellites) problem from cosmic shear

    Science.gov (United States)

    Jimenez, Raul; Verde, Licia; Kitching, Thomas D.

    2018-06-01

    The number of observed dwarf galaxies, with dark matter mass ≲ 1011 M⊙ in the Milky Way or the Andromeda galaxy does not agree with predictions from the successful ΛCDM paradigm. To alleviate this problem a suppression of dark matter clustering power on very small scales has been conjectured. However, the abundance of dark matter halos outside our immediate neighbourhood (the Local Group) seem to agree with the ΛCDM-expected abundance. Here we connect these problems to observations of weak lensing cosmic shear, pointing out that cosmic shear can make significant statements about the missing satellites problem in a statistical way. As an example and pedagogical application we use recent constraints on small-scales power suppression from measurements of the CFHTLenS data. We find that, on average, in a region of ˜Gpc3 there is no significant small-scale power suppression. This implies that suppression of small-scale power is not a viable solution to the `missing satellites problem' or, alternatively, that on average in this volume there is no `missing satellites problem' for dark matter masses ≳ 5 × 109 M⊙. Further analysis of current and future weak lensing surveys will probe much smaller scales, k > 10h Mpc-1 corresponding roughly to masses M < 109M⊙.

  20. STELLAR POPULATIONS IN COMPACT GALAXY GROUPS: A MULTI-WAVELENGTH STUDY OF HCGs 16, 22, AND 42, THEIR STAR CLUSTERS, AND DWARF GALAXIES

    International Nuclear Information System (INIS)

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Gronwall, C.; Fedotov, K.; Desjardins, T. D.; Gallagher, S. C.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Walker, L. M.; Johnson, K. E.; Tzanavaris, P.

    2013-01-01

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 ''associates'' (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  1. The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys

    Science.gov (United States)

    Sarbadhicary, Sumit; Badenes, Carles; Chomiuk, Laura; Maldonado, Jessica; Caprioli, Damiano; Heger, Mairead; Huizenga, Daniel

    2018-01-01

    Our understanding of the progenitors of many stellar species, such as supernovae, massive and low-mass He-burning stars, is limited because of many poorly constrained aspects of stellar evolution theory. For my dissertation, I have focused on using Local Group galaxy surveys to constrain stellar evolution scenarios by measuring delay-time distributions (DTD). The DTD is the hypothetical occurrence rate of a stellar object per elapsed time after a brief burst of star formation. It is the measured distribution of timescales on which stars evolve, and therefore serves as a powerful observational constraint on theoretical progenitor models. The DTD can be measured from a survey of stellar objects and a set of star-formation histories of the host galaxy, and is particularly effective in the Local Group, where high-quality star-formation histories are available from resolved stellar populations. I am currently calculating a SN DTD with supernova remnants (SNRs) in order to provide the strongest constraints on the progenitors of thermonuclear and core-collapse supernovae. However, most SNRs do not have reliable age measurements and their evolution depends on the ambient environment. For this reason, I wrote a radio light curve model of an SNR population to extract the visibility times and rates of supernovae - crucial ingredients for the DTD - from an SNR survey. The model uses observational constraints on the local environments from multi-wavelength surveys, accounts for missing SNRs and employs the latest models of shock-driven particle acceleration. The final calculation of the SN DTD in the Local Group is awaiting completion of a systematic SNR catalog from deep radio-continuum images, now in preparation by a group led by Dr. Laura Chomiuk. I have also calculated DTDs for the LMC population of RR Lyrae and Cepheid variables, which serve as important distance calibrators and stellar population tracers. We find that Cepheids can have delay-times between 10 Myrs - 1 Gyr

  2. QUENCHING DEPENDS ON MORPHOLOGIES: IMPLICATIONS FROM THE ULTRAVIOLET-OPTICAL RADIAL COLOR DISTRIBUTIONS IN GREEN VALLEY GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Zhizheng; Lin, Weipeng [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Science, 80 Nandan Road, Shanghai 200030 (China); Li, Jinrong; Kong, Xu [Center of Astrophysics, University of Science and Technology of China, Jinzhai Road 96, Hefei 230026 (China); Wang, Jing, E-mail: panzz@shao.ac.cn, E-mail: linwp@shao.ac.cn [CSIRO Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, NSW 1710 (Australia)

    2014-09-01

    In this Letter, we analyze the radial ultraviolet-optical color distributions in a sample of low redshift green valley galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation is distributed in these galaxies. We find that the dust-corrected u – r colors of early-type galaxies (ETGs) are flat out to R {sub 90}, while the colors monotonously turn blue when r > 0.5 R {sub 50} for late-type galaxies (LTGs). More than half of the ETGs are blue-cored and have remarkable positive NUV – r color gradients, suggesting that their star formations are centrally concentrated. The rest have flat color distributions out to R {sub 90}. The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that ∼50% of the ETGs have EW(Hα) >6.0 Å. Of the LTGs, 95% show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable ''blue-cores'' and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow a general model by which quenching first occurs in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.

  3. QUENCHING DEPENDS ON MORPHOLOGIES: IMPLICATIONS FROM THE ULTRAVIOLET-OPTICAL RADIAL COLOR DISTRIBUTIONS IN GREEN VALLEY GALAXIES

    International Nuclear Information System (INIS)

    Pan, Zhizheng; Lin, Weipeng; Li, Jinrong; Kong, Xu; Wang, Jing

    2014-01-01

    In this Letter, we analyze the radial ultraviolet-optical color distributions in a sample of low redshift green valley galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation is distributed in these galaxies. We find that the dust-corrected u – r colors of early-type galaxies (ETGs) are flat out to R 90 , while the colors monotonously turn blue when r > 0.5 R 50 for late-type galaxies (LTGs). More than half of the ETGs are blue-cored and have remarkable positive NUV – r color gradients, suggesting that their star formations are centrally concentrated. The rest have flat color distributions out to R 90 . The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that ∼50% of the ETGs have EW(Hα) >6.0 Å. Of the LTGs, 95% show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable ''blue-cores'' and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow a general model by which quenching first occurs in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI

  4. Cosmology and galaxy formation

    International Nuclear Information System (INIS)

    Rees, M.J.

    1977-01-01

    Implications of the massive halos and ''missing mass'' for galaxy formation are addressed; it is suggested that this mass consists of ''Population III'' stars that formed before the galaxies did. 19 references

  5. Observations of environmental quenching in groups in the 11 Gyr since z = 2.5: Different quenching for central and satellite galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Tal, Tomer; Illingworth, Garth D.; Magee, Daniel [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Dekel, Avishai [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Oesch, Pascal; Van Dokkum, Pieter G.; Leja, Joel; Momcheva, Ivelina; Nelson, Erica J. [Yale University Astronomy Department, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Muzzin, Adam; Franx, Marijn [Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands); Brammer, Gabriel B. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Marchesini, Danilo [Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States); Patel, Shannon G.; Quadri, Ryan F. [Carnegie Observatories, Pasadena, CA 91101 (United States); Rix, Hans-Walter [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Skelton, Rosalind E. [South African Astronomical Observatory, Observatory Road, Cape Town (South Africa); Wake, David A. [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States); Whitaker, Katherine E., E-mail: tal@ucolick.org [Astrophysics Science Division, Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

    2014-07-10

    We present direct observational evidence for star formation quenching in galaxy groups in the redshift range 0 < z < 2.5. We utilize a large sample of nearly 6000 groups, selected by fixed cumulative number density from three photometric catalogs, to follow the evolving quiescent fractions of central and satellite galaxies over roughly 11 Gyr. At z ∼ 0, central galaxies in our sample range in stellar mass from Milky Way/M31 analogs (M{sub *}/M{sub ☉} = 6.5 × 10{sup 10}) to nearby massive ellipticals (M{sub *}/M{sub ☉} = 1.5 × 10{sup 11}). Satellite galaxies in the same groups reach masses as low as twice that of the Large Magellanic Cloud (M{sub *}/M{sub ☉} = 6.5 × 10{sup 9}). Using statistical background subtraction, we measure the average rest-frame colors of galaxies in our groups and calculate the evolving quiescent fractions of centrals and satellites over seven redshift bins. Our analysis shows clear evidence for star formation quenching in group halos, with a different quenching onset for centrals and their satellite galaxies. Using halo mass estimates for our central galaxies, we find that star formation shuts off in centrals when typical halo masses reach between 10{sup 12} and 10{sup 13} M{sub ☉}, consistent with predictions from the halo quenching model. In contrast, satellite galaxies in the same groups most likely undergo quenching by environmental processes, whose onset is delayed with respect to their central galaxy. Although star formation is suppressed in all galaxies over time, the processes that govern quenching are different for centrals and satellites. While mass plays an important role in determining the star formation activity of central galaxies, quenching in satellite galaxies is dominated by the environment in which they reside.

  6. Observations of environmental quenching in groups in the 11 Gyr since z = 2.5: Different quenching for central and satellite galaxies

    International Nuclear Information System (INIS)

    Tal, Tomer; Illingworth, Garth D.; Magee, Daniel; Dekel, Avishai; Oesch, Pascal; Van Dokkum, Pieter G.; Leja, Joel; Momcheva, Ivelina; Nelson, Erica J.; Muzzin, Adam; Franx, Marijn; Brammer, Gabriel B.; Marchesini, Danilo; Patel, Shannon G.; Quadri, Ryan F.; Rix, Hans-Walter; Skelton, Rosalind E.; Wake, David A.; Whitaker, Katherine E.

    2014-01-01

    We present direct observational evidence for star formation quenching in galaxy groups in the redshift range 0 < z < 2.5. We utilize a large sample of nearly 6000 groups, selected by fixed cumulative number density from three photometric catalogs, to follow the evolving quiescent fractions of central and satellite galaxies over roughly 11 Gyr. At z ∼ 0, central galaxies in our sample range in stellar mass from Milky Way/M31 analogs (M * /M ☉ = 6.5 × 10 10 ) to nearby massive ellipticals (M * /M ☉ = 1.5 × 10 11 ). Satellite galaxies in the same groups reach masses as low as twice that of the Large Magellanic Cloud (M * /M ☉ = 6.5 × 10 9 ). Using statistical background subtraction, we measure the average rest-frame colors of galaxies in our groups and calculate the evolving quiescent fractions of centrals and satellites over seven redshift bins. Our analysis shows clear evidence for star formation quenching in group halos, with a different quenching onset for centrals and their satellite galaxies. Using halo mass estimates for our central galaxies, we find that star formation shuts off in centrals when typical halo masses reach between 10 12 and 10 13 M ☉ , consistent with predictions from the halo quenching model. In contrast, satellite galaxies in the same groups most likely undergo quenching by environmental processes, whose onset is delayed with respect to their central galaxy. Although star formation is suppressed in all galaxies over time, the processes that govern quenching are different for centrals and satellites. While mass plays an important role in determining the star formation activity of central galaxies, quenching in satellite galaxies is dominated by the environment in which they reside.

  7. Eight luminous early-type galaxies in nearby pairs and sparse groups. I. Stellar populations spatially analysed

    Science.gov (United States)

    Rosa, D. A.; Milone, A. C.; Krabbe, A. C.; Rodrigues, I.

    2018-06-01

    We present a detailed spatial analysis of stellar populations based on long-slit optical spectra in a sample of eight luminous early-type galaxies selected from nearby sparse groups and pairs, three of them may have interaction with another galaxy of similar mass. We have spatially measured luminosity-weighted averages of age, [M/H], [Fe/H], and [α /Fe] in the sample galaxies to add empirical data relative to the influence of galaxy mass, environment, interaction, and AGN feedback in their formation and evolution. The stellar population of the individual galaxies were determined through the well-established stellar population synthesis code starlight using semi-empirical simple stellar population models. Radial variations of luminosity- weighted means of age, [M/H], [Fe/H], and [α /Fe] were quantified up to half of the effective radius of each galaxy. We found trends between representative values of age, [M/H], [α /Fe], and the nuclear stellar velocity dispersion. There are also relations between the metallicity/age gradients and the velocity dispersion. Contributions of 1-4 Gyr old stellar populations were quantified in IC 5328 and NGC 6758 as well as 4-8 Gyr old ones in NGC 5812. Extended gas is present in IC 5328, NGC 1052, NGC 1209, and NGC 6758, and the presence of a LINER is identified in all these galaxies. The regions up to one effective radius of all galaxies are basically dominated by α -enhanced metal-rich old stellar populations likely due to rapid star formation episodes that induced efficient chemical enrichment. On average, the age and [α /Fe] gradients are null and the [M/H] gradients are negative, although discordant cases were found. We found no correlation between the stellar population properties and the LINER presence as well as between the stellar properties and environment or gravitational interaction, suggesting that the influence of progenitor mass cannot be discarded in the formation and evolution of early-type galaxies.

  8. CAN AGN FEEDBACK BREAK THE SELF-SIMILARITY OF GALAXIES, GROUPS, AND CLUSTERS?

    Energy Technology Data Exchange (ETDEWEB)

    Gaspari, M. [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, D-85741 Garching (Germany); Brighenti, F. [Astronomy Department, University of Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Temi, P. [Astrophysics Branch, NASA/Ames Research Center, MS 245-6, Moffett Field, CA 94035 (United States); Ettori, S., E-mail: mgaspari@mpa-garching.mpg.de [INAF, Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy)

    2014-03-01

    It is commonly thought that active galactic nucleus (AGN) feedback can break the self-similar scaling relations of galaxies, groups, and clusters. Using high-resolution three-dimensional hydrodynamic simulations, we isolate the impact of AGN feedback on the L {sub x}-T {sub x} relation, testing the two archetypal and common regimes, self-regulated mechanical feedback and a quasar thermal blast. We find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R {sub 500}, while the central cooling times are inversely proportional to the core density. Breaking self-similarity thus implies breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can break the core-included L {sub x}-T {sub x} at T {sub 500} ≲ 1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmological simulations. Even with partial evacuation, massive systems remain overheated. We show that the action of purely AGN feedback is to lower the luminosity and heat the gas, perpendicular to the fit.

  9. CAN AGN FEEDBACK BREAK THE SELF-SIMILARITY OF GALAXIES, GROUPS, AND CLUSTERS?

    International Nuclear Information System (INIS)

    Gaspari, M.; Brighenti, F.; Temi, P.; Ettori, S.

    2014-01-01

    It is commonly thought that active galactic nucleus (AGN) feedback can break the self-similar scaling relations of galaxies, groups, and clusters. Using high-resolution three-dimensional hydrodynamic simulations, we isolate the impact of AGN feedback on the L x -T x relation, testing the two archetypal and common regimes, self-regulated mechanical feedback and a quasar thermal blast. We find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R 500 , while the central cooling times are inversely proportional to the core density. Breaking self-similarity thus implies breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can break the core-included L x -T x at T 500 ≲ 1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmological simulations. Even with partial evacuation, massive systems remain overheated. We show that the action of purely AGN feedback is to lower the luminosity and heat the gas, perpendicular to the fit

  10. Dwarf spheroidal galaxies: Keystones of galaxy evolution

    Science.gov (United States)

    Gallagher, John S., III; Wyse, Rosemary F. G.

    1994-01-01

    Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark-matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

  11. A direct measurement of the baryonic mass function of galaxies & implications for the galactic baryon fraction

    NARCIS (Netherlands)

    Papastergis, Emmanouil; Cattaneo, Andrea; Huang, Shan; Giovanelli, Riccardo; Haynes, Martha P.

    2012-01-01

    We use both an HI-selected and an optically-selected galaxy sample to directly measure the abundance of galaxies as a function of their "baryonic" mass (stars + atomic gas). Stellar masses are calculated based on optical data from the Sloan Digital Sky Survey (SDSS) and atomic gas masses are

  12. Gas Sloshing and Radio Galaxy Dynamics in the Core of the 3C 449 Group

    Science.gov (United States)

    Lal, Dharam V.; Kraft, Ralph P.; Randall, Scott W.; Forman, William R.; Nulsen, Paul E.; Roediger, Elke; ZuHone, John A.; Hardcastle, Martin J.; Jones, Christine; Croston, Judith H.

    2013-01-01

    We present results from a 140 ks Chandra/ACIS-S observation of the hot gas around the canonical FR I radio galaxy 3C 449. An earlier, shorter 30 ks Chandra observation of the group gas showed an unusual entropy distribution and a surface brightness edge in the gas that could be a strong shock around the inner radio lobes. In our deeper data we find no evidence for a temperature increase inside of the brightness edge, but a temperature decrease across part of the edge. This suggests that the edge is a "sloshing" cold front due to a merger within the last 1.3-1.6 Gyr. Both the northern and southern inner jets are bent slightly to the west in projection as they enter their respective lobes, suggesting that the sloshing core is moving to the east. The straight inner jet flares at approximately the position where it crosses the contact edge, suggesting that the jet is entraining and thermalizing some of the hot gas as it crosses the edge.We also detect filaments of X-ray emission around the southern inner radio jet and lobe which we attribute to low entropy entrained gas. The lobe flaring and gas entrainment were originally predicted in simulations of Loken et al. and are confirmed in our deep observation.

  13. Multiple attachments and group psychotherapy: implications for college counseling centers.

    Science.gov (United States)

    Marmarosh, Cheri L

    2009-10-01

    A large body of literature has supported the application of attachment theory to the understanding of college student development and the process of individual psychotherapy. Despite group treatment being one of the major methods of intervention in college counseling centers, there has been very little research guided by attachment theory that has been applied to the area of group psychotherapy. Many current assessment instruments used in college counseling centers can be supported with attachment theory, and many group therapy interventions are aimed at facilitating secure working models of self, other, and groups. This paper explores the importance of personal and group attachments in group psychotherapy and specifically addresses implications for clinical training and research in university counseling centers.

  14. Some implications of excess soft X-ray emission from Seyfert 1 galaxies

    International Nuclear Information System (INIS)

    Fabian, A.C.; Guilbert, P.W.; Arnaud, K.A.; Shafer, R.A.; Tennant, A.F.; Ward, M.J.

    1986-01-01

    The X-ray spectrum of Seyfert 1 galaxies is characterized by a hard power-law spectrum. It is often postulated that this maintains a Compton-heated two-phase Broad-Line Region (BLR) around the central source. It is shown here that the strong excess soft X-ray emission observed in MKN 841 and other Seyfert galaxies invalidates this model if the BLR is spherically symmetric. Alternatives are proposed. (author)

  15. Absorption-line detections of 105-106 K gas in spiral-rich groups of galaxies

    International Nuclear Information System (INIS)

    Stocke, John T.; Keeney, Brian A.; Danforth, Charles W.; Syphers, David; Yamamoto, H.; Shull, J. Michael; Green, James C.; Froning, Cynthia; Savage, Blair D.; Wakker, Bart; Kim, Tae-Sun; Ryan-Weber, Emma V.; Kacprzak, Glenn G.

    2014-01-01

    Using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope, the COS Science Team has conducted a high signal-to-noise survey of 14 bright QSOs. In a previous paper, these far-UV spectra were used to discover 14 'warm' (T ≥ 10 5 K) absorbers using a combination of broad Lyα and broad O VI absorptions. A reanalysis of a few of this new class of absorbers using slightly relaxed fitting criteria finds as many as 20 warm absorbers could be present in this sample. A shallow, wide spectroscopic galaxy redshift survey has been conducted around these sight lines to investigate the warm absorber environment, which is found to be spiral-rich groups or cluster outskirts with radial velocity dispersions σ = 250-750 km s –1 . While 2σ evidence is presented favoring the hypothesis that these absorptions are associated with the galaxy groups and not with the individual, nearest galaxies, this evidence has considerable systematic uncertainties and is based on a small sample size so it is not entirely conclusive. If the associations are with galaxy groups, the observed frequency of warm absorbers (dN/dz = 3.5-5 per unit redshift) requires them to be very extended as an ensemble on the sky (∼1 Mpc in radius at high covering factor). Most likely these warm absorbers are interface gas clouds whose presence implies the existence of a hotter (T ∼ 10 6.5 K), diffuse, and probably very massive (>10 11 M ☉ ) intra-group medium which has yet to be detected directly.

  16. The star formation histories of local group dwarf galaxies. I. Hubble space telescope/wide field planetary camera 2 observations

    Energy Technology Data Exchange (ETDEWEB)

    Weisz, Daniel R. [Department of Astronomy, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Holtzman, Jon [Department of Astronomy, New Mexico State University, Box 30001, 1320 Frenger Street, Las Cruces, NM 88003 (United States); Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F., E-mail: drw@ucsc.edu [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    2014-07-10

    We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with τ ∼ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH (τ ∼ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M < 10{sup 5} M{sub ☉} to 30% for galaxies with M > 10{sup 7} M{sub ☉}) and is largely explained by environment; (5) the distinction between 'ultra-faint' and 'classical' dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.

  17. The star formation histories of local group dwarf galaxies. I. Hubble space telescope/wide field planetary camera 2 observations

    International Nuclear Information System (INIS)

    Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; Holtzman, Jon; Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F.

    2014-01-01

    We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with τ ∼ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH (τ ∼ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M < 10 5 M ☉ to 30% for galaxies with M > 10 7 M ☉ ) and is largely explained by environment; (5) the distinction between 'ultra-faint' and 'classical' dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.

  18. A challenge to dSph formation models: are the most isolated Local Group dSph galaxies truly old?

    Science.gov (United States)

    Monelli, Matteo

    2017-08-01

    What is the origin of the different dwarf galaxy types? The classification into dwarf irregular (dIrr), spheroidal (dSph), and transition (dT) types is based on their present-day properties. However, star formation histories (SFHs) reconstructed from deep color-magnitude diagrams (CMDs) provide details on the early evolution of galaxies of all these types, and indicate only two basic evolutionary paths. One is characterized by a vigorous but brief initial star-forming event, and little or no star formation thereafter (fast evolution), and the other one by roughly continuous star formation until (nearly) the present time (slow evolution). These two paths do not map directly onto the dIrr, dT and dSph types. Thus, the present galaxy properties do not reflect their lifetime evolution. Since there are some indications that slow dwarfs were assembled in lower-density environments than fast dwarfs, Gallart et al (2015) proposed that the distinction between fast and slow dwarfs reflects the characteristic density of the environment where they formed. This scenario, and more generally scenarios where dSph galaxies formed through the interaction with a massive galaxy, are challenged by a small sample of extremely isolated dSph/dT in the outer fringes of the Local Group. This proposal targets two of these objects (VV124, KKR25) for which we will infer their SFH - through a novel technique that combines the information from their RR Lyrae stars and deep CMDs sampling the intermediate-age population - in order to test these scenarios. This is much less demanding on observing time than classical SFH derivation using full depth CMDs.

  19. Mass-invariance of the iron enrichment in the hot haloes of massive ellipticals, groups, and clusters of galaxies

    Science.gov (United States)

    Mernier, F.; de Plaa, J.; Werner, N.; Kaastra, J. S.; Raassen, A. J. J.; Gu, L.; Mao, J.; Urdampilleta, I.; Truong, N.; Simionescu, A.

    2018-05-01

    X-ray measurements find systematically lower Fe abundances in the X-ray emitting haloes pervading groups (kT ≲ 1.7 keV) than in clusters of galaxies. These results have been difficult to reconcile with theoretical predictions. However, models using incomplete atomic data or the assumption of isothermal plasmas may have biased the best fit Fe abundance in groups and giant elliptical galaxies low. In this work, we take advantage of a major update of the atomic code in the spectral fitting package SPEX to re-evaluate the Fe abundance in 43 clusters, groups, and elliptical galaxies (the CHEERS sample) in a self-consistent analysis and within a common radius of 0.1r500. For the first time, we report a remarkably similar average Fe enrichment in all these systems. Unlike previous results, this strongly suggests that metals are synthesised and transported in these haloes with the same average efficiency across two orders of magnitude in total mass. We show that the previous metallicity measurements in low temperature systems were biased low due to incomplete atomic data in the spectral fitting codes. The reasons for such a code-related Fe bias, also implying previously unconsidered biases in the emission measure and temperature structure, are discussed.

  20. Physically detached 'compact groups'

    Science.gov (United States)

    Hernquist, Lars; Katz, Neal; Weinberg, David H.

    1995-01-01

    A small fraction of galaxies appear to reside in dense compact groups, whose inferred crossing times are much shorter than a Hubble time. These short crossing times have led to considerable disagreement among researchers attempting to deduce the dynamical state of these systems. In this paper, we suggest that many of the observed groups are not physically bound but are chance projections of galaxies well separated along the line of sight. Unlike earlier similar proposals, ours does not require that the galaxies in the compact group be members of a more diffuse, but physically bound entity. The probability of physically separated galaxies projecting into an apparent compact group is nonnegligible if most galaxies are distributed in thin filaments. We illustrate this general point with a specific example: a simulation of a cold dark matter universe, in which hydrodynamic effects are included to identify galaxies. The simulated galaxy distribution is filamentary and end-on views of these filaments produce apparent galaxy associations that have sizes and velocity dispersions similar to those of observed compact groups. The frequency of such projections is sufficient, in principle, to explain the observed space density of groups in the Hickson catalog. We discuss the implications of our proposal for the formation and evolution of groups and elliptical galaxies. The proposal can be tested by using redshift-independent distance estimators to measure the line-of-sight spatial extent of nearby compact groups.

  1. The Faint Optical Afterglow and Host Galaxy of GRB 020124: Implications for the Nature of Dark Gamma-Ray Bursts

    Science.gov (United States)

    Berger, E.; Kulkarni, S. R.; Bloom, J. S.; Price, P. A.; Fox, D. W.; Frail, D. A.; Axelrod, T. S.; Chevalier, R. A.; Colbert, E.; Costa, E.; Djorgovski, S. G.; Frontera, F.; Galama, T. J.; Halpern, J. P.; Harrison, F. A.; Holtzman, J.; Hurley, K.; Kimble, R. A.; McCarthy, P. J.; Piro, L.; Reichart, D.; Ricker, G. R.; Sari, R.; Schmidt, B. P.; Wheeler, J. C.; Vanderppek, R.; Yost, S. A.

    2002-12-01

    We present ground-based optical observations of GRB 020124 starting 1.6 hr after the burst, as well as subsequent Very Large Array and Hubble Space Telescope (HST) observations. The optical afterglow of GRB 020124 is one of the faintest afterglows detected to date, and it exhibits a relatively rapid decay, Fν~t-1.60+/-0.04, followed by further steepening. In addition, a weak radio source was found coincident with the optical afterglow. The HST observations reveal that a positionally coincident host galaxy must be the faintest host to date, R>~29.5 mag. The afterglow observations can be explained by several models requiring little or no extinction within the host galaxy, AhostV~0-0.9 mag. These observations have significant implications for the interpretation of the so-called dark bursts (bursts for which no optical afterglow is detected), which are usually attributed to dust extinction within the host galaxy. The faintness and relatively rapid decay of the afterglow of GRB 020124, combined with the low inferred extinction, indicate that some dark bursts are intrinsically dim and not dust obscured. Thus, the diversity in the underlying properties of optical afterglows must be observationally determined before substantive inferences can be drawn from the statistics of dark bursts.

  2. Formation of galaxies

    International Nuclear Information System (INIS)

    Szalay, A.S.

    1984-12-01

    The present theories of galaxy formation are reviewed. The relation between peculiar velocities and the correlation function of galaxies points to the possibility that galaxies do not form uniformly everywhere. Scale invariant properties of the cluster-cluster correlations are discussed. Comparing the correlation functions in a dimensionless way, galaxies appear to be stronger clustered, in contrast with the comparison of the dimensional amplitudes of the correlation functions. Theoretical implications of several observations as Lyman-α clouds, correlations of faint galaxies are discussed. None of the present theories of galaxy formation can account for all facts in a natural way. 29 references

  3. A comparison of galaxy group luminosity functions from semi-analytic models

    NARCIS (Netherlands)

    Snaith, Owain N.; Gibson, Brad K.; Brook, Chris B.; Courty, Stéphanie; Sánchez-Blázquez, Patricia; Kawata, Daisuke; Knebe, Alexander; Sales, Laura V.

    Semi-analytic models (SAMs) are currently one of the primary tools with which we model statistically significant ensembles of galaxies. The underlying physical prescriptions inherent to each SAM are, in many cases, different from one another. Several SAMs have been applied to the dark matter merger

  4. Monitoring survey of pulsating giant stars in the Local Group galaxies: survey description, science goals, target selection

    International Nuclear Information System (INIS)

    Saremi, E; Abedi, A; Javadi, A; Khosroshahi, H; Molaei Nezhad, A; Van Loon, J Th; Bamber, J; Hashemi, S A; Nikzat, F

    2017-01-01

    The population of nearby dwarf galaxies in the Local Group constitutes a complete galactic environment, perfect suited for studying the connection between stellar populations and galaxy evolution. In this study, we are conducting an optical monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify long period variable stars (LPVs). These stars are at the end points of their evolution and therefore their luminosity can be directly translated into their birth masses; this enables us to reconstruct the star formation history. By the end of the monitoring survey, we will have performed observations over ten epochs, spaced approximately three months apart, and identified long-period, dust-producing AGB stars; five epochs of data have been obtained already. LPVs are also the main source of dust; in combination with Spitzer Space Telescope images at mid-IR wavelengths we will quantify the mass loss, and provide a detailed map of the mass feedback into the interstellar medium. We will also use the amplitudes in different optical passbands to determine the radius variations of the stars, and relate this to their mass loss. (paper)

  5. Monitoring survey of pulsating giant stars in the Local Group galaxies: survey description, science goals, target selection

    Science.gov (United States)

    Saremi, E.; Javadi, A.; van Loon, J. Th; Khosroshahi, H.; Abedi, A.; Bamber, J.; Hashemi, S. A.; Nikzat, F.; Molaei Nezhad, A.

    2017-06-01

    The population of nearby dwarf galaxies in the Local Group constitutes a complete galactic environment, perfect suited for studying the connection between stellar populations and galaxy evolution. In this study, we are conducting an optical monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify long period variable stars (LPVs). These stars are at the end points of their evolution and therefore their luminosity can be directly translated into their birth masses; this enables us to reconstruct the star formation history. By the end of the monitoring survey, we will have performed observations over ten epochs, spaced approximately three months apart, and identified long-period, dust-producing AGB stars; five epochs of data have been obtained already. LPVs are also the main source of dust; in combination with Spitzer Space Telescope images at mid-IR wavelengths we will quantify the mass loss, and provide a detailed map of the mass feedback into the interstellar medium. We will also use the amplitudes in different optical passbands to determine the radius variations of the stars, and relate this to their mass loss.

  6. Evolved stars in the Local Group galaxies - II. AGB, RSG stars and dust production in IC10

    Science.gov (United States)

    Dell'Agli, F.; Di Criscienzo, M.; Ventura, P.; Limongi, M.; García-Hernández, D. A.; Marini, E.; Rossi, C.

    2018-06-01

    We study the evolved stellar population of the Local Group galaxy IC10, with the aim of characterizing the individual sources observed and to derive global information on the galaxy, primarily the star formation history and the dust production rate. To this aim, we use evolutionary sequences of low- and intermediate-mass (M account for 40% of the sources brighter than the tip of the red giant branch. Most of these stars descend from ˜1.1 - 1.3 M⊙ progenitors, formed during the major epoch of star formation, which occurred ˜2.5 Gyr ago. The presence of a significant number of bright stars indicates that IC10 has been site of significant star formation in recent epochs and currently hosts a group of massive stars in the core helium-burning phase. Dust production in this galaxy is largely dominated by carbon stars; the overall dust production rate estimated is 7 × 10-6 M⊙/yr.

  7. The Araucaria Project. The distance to the Sculptor group galaxy NGC 7793 from near-infrared photometry of Cepheid variables

    Directory of Open Access Journals (Sweden)

    Zgirski Bartlomiej

    2017-01-01

    Full Text Available We performed deep near-infrared J and K photometry of a field in the Sculptor Group spiral galaxy NGC 7793 using ESO VLT and HAWK-I instrument. We produced a sample of 14 Cepheids whose locations and periods of pulsation were known from our previous paper on distance determination to this galaxy based on V and I bands. We determined mean J and K magnitudes based on measurements from two nights and produced period-luminosity relations for both filters. Using those near-infrared dependencies together with relations for bands V and I obtained before, we were able to obtain true distance modulus for NGC 7793. We also calculated the mean reddening affecting our Cepheids.

  8. Task Type and Group Motivation: Implications for a Behavioral Approach to Leadership in Small Groups.

    Science.gov (United States)

    Latham, Van M.

    1987-01-01

    Discusses a theory of leadership effectiveness in small discussion/decision making groups developed to facilitate discussion and goal efficacy. Develops four leadership styles (coordinator, inventor, enthusiast, and director) focusing on two critical questions the leader must address. Discusses implications of the model for leadership training and…

  9. EARLY-TYPE GALAXIES AT z = 1.3. I. THE LYNX SUPERCLUSTER: CLUSTER AND GROUPS AT z = 1.3. MORPHOLOGY AND COLOR-MAGNITUDE RELATION

    International Nuclear Information System (INIS)

    Mei, Simona; Raichoor, Anand; Huertas-Company, Marc; Adam Stanford, S.; Rettura, Alessandro; Jee, Myungkook J.; Holden, Brad P.; Illingworth, Garth D.; Postman, Marc; Nakata, Fumiaki; Kodama, Tadayuki; Finoguenov, Alexis; Ford, Holland C.; Rosati, Piero; Tanaka, Masayuki; Koyama, Yusei; Shankar, Francesco; Carrasco, Eleazar R.; Demarco, Ricardo; Eisenhardt, Peter

    2012-01-01

    We confirm the detection of three groups in the Lynx supercluster, at z ≈ 1.3, through spectroscopic follow-up and X-ray imaging, and we give estimates for their redshifts and masses. We study the properties of the group galaxies compared to the two central clusters, RX J0849+4452 and RX J0848+4453. Using spectroscopic follow-up and multi-wavelength photometric redshifts, we select 89 galaxies in the clusters, of which 41 are spectroscopically confirmed, and 74 galaxies in the groups, of which 25 are spectroscopically confirmed. We morphologically classify galaxies by visual inspection, noting that our early-type galaxy (ETG) sample would have been contaminated at the 30%-40% level by simple automated classification methods (e.g., based on Sérsic index). In luminosity-selected samples, both clusters and groups show high fractions of bulge-dominated galaxies with a diffuse component that we visually identified as a disk and which we classified as bulge-dominated spirals, e.g., Sas. The ETG fractions never rise above ≈50% in the clusters, which is low compared to the fractions observed in other massive clusters at z ≈ 1. In the groups, ETG fractions never exceed ≈25%. However, overall bulge-dominated galaxy fractions (ETG plus Sas) are similar to those observed for ETGs in clusters at z ∼ 1. Bulge-dominated galaxies visually classified as spirals might also be ETGs with tidal features or merger remnants. They are mainly red and passive, and span a large range in luminosity. Their star formation seems to have been quenched before experiencing a morphological transformation. Because their fraction is smaller at lower redshifts, they might be the spiral population that evolves into ETGs. For mass-selected samples of galaxies with masses M > 10 10.6 M ☉ within Σ > 500 Mpc –2 , the ETG and overall bulge-dominated galaxy fractions show no significant evolution with respect to local clusters, suggesting that morphological transformations might occur at lower

  10. The Star Formation History of the Local Group Dwarf Galaxy Leo I

    Science.gov (United States)

    Gallart, Carme; Freedman, Wendy L.; Aparicio, Antonio; Bertelli, Giampaolo; Chiosi, Cesare

    1999-11-01

    We present a quantitative analysis of the star formation history (SFH) of the Local Group dSph galaxy Leo I, from the information in its Hubble Space Telescope [(V-I),I] color-magnitude diagram (CMD). It reaches the level of the oldest main-sequence turnoffs, and this allows us to retrieve the SFH in considerable detail. The method we use is based on comparing, via synthetic CMDs, the expected distribution of stars in the CMD for different evolutionary scenarios with the observed distribution. We consider the SFH to be composed by the SFR(t), the chemical enrichment law Z(t), the initial mass function (IMF), and a function β(f,q) controlling the fraction f and mass ratio distribution q of binary stars. We analyze a set of ~=50 combinations of four Z(t), three IMFs, and more than four β(f,q). For each of them, the best SFR(t) is searched for among ~=6x107 models. The comparison between the observed CMD and the model CMDs is done through χ2ν minimization of the differences in the number of stars in a set of regions of the CMD, chosen to sample stars of different ages or in specific stellar evolutionary phases. We empirically determine the range of χ2ν values that indicate acceptable models for our set of data using tests with models with known SFHs. Our solution for the SFH of Leo I defines a minimum of χ2ν in a well-defined position of the parameter space, and the derived SFR(t) is robust, in the sense that its main characteristics are unchanged for different combinations of the remaining parameters. However, only a narrow range of assumptions for Z(t), IMF, and β(f,q) result in a good agreement between the data and the models, namely, Z=0.0004, a IMF Kroupa et al. or slightly steeper, and a relatively large fraction of binary stars, with f=0.3-0.6, q>0.6, and an approximately flat IMF for the secondaries, or particular combinations of these parameters that would produce a like fraction of similar mass binaries. Most star formation activity (70% to 80

  11. The Araucaria Project. The Distance to the Sculptor Group Galaxy NGC 7793 from Near-infrared Photometry of Cepheid Variables

    Energy Technology Data Exchange (ETDEWEB)

    Zgirski, Bartlomiej; Pietrzyński, Grzegorz; Wielgorski, Piotr; Narloch, Weronika; Graczyk, Dariusz [Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw (Poland); Gieren, Wolfgang; Gorski, Marek [Universidad de Concepcion, Departamento de Astronomia, Casilla 160-C, Concepcion (Chile); Karczmarek, Paulina [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478, Warsaw (Poland); Kudritzki, Rolf-Peter; Bresolin, Fabio, E-mail: bzgirski@camk.edu.pl, E-mail: pietrzyn@camk.edu.pl, E-mail: pwielgor@camk.edu.pl, E-mail: wnarloch@camk.edu.pl, E-mail: darek@astro-udec.cl, E-mail: mgorski@astrouw.edu.pl, E-mail: wgieren@astro-udec.cl, E-mail: pkarczmarek@astrouw.edu.pl, E-mail: kud@ifa.hawaii.edu, E-mail: bresolin@ifa.hawaii.edu [Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Drive, Honolulu HI 96822 (United States)

    2017-10-01

    Following the earlier discovery of classical Cepheid variables in the Sculptor Group spiral galaxy NGC 7793 from an optical wide-field imaging survey, we have performed deep near-infrared J - and K -band follow-up photometry of a subsample of these Cepheids to derive the distance to this galaxy with a higher accuracy than what was possible from optical photometry alone, by minimizing the effects of reddening and metallicity on the distance result. Combining our new near-infrared period–luminosity relations with previous optical photometry, we obtain a true distance modulus to NGC 7793 of (27.66 ± 0.04) mag (statistical) ±0.07 mag (systematic), i.e., a distance of (3.40 ± 0.17) Mpc. We also determine the mean reddening affecting the Cepheids to be E(B − V) = (0.08 ± 0.02) mag, demonstrating that there is significant dust extinction intrinsic to the galaxy in addition to the small foreground extinction. A comparison of the new, improved Cepheid distance to earlier distance determinations of NGC 7793 from the Tully–Fisher and TRGB methods is in agreement within the reported uncertainties of these previous measurements.

  12. Galaxy And Mass Assembly (GAMA): A “No Smoking” Zone for Giant Elliptical Galaxies?

    International Nuclear Information System (INIS)

    Khosroshahi, Habib G.; Raouf, Mojtaba; Miraghaei, Halime; Brough, Sarah; Croton, Darren J.; Graham, Alister; Driver, Simon; Baldry, Ivan; Brown, Michael; Prescott, Matt; Wang, Lingyu

    2017-01-01

    We study the radio emission of the most massive galaxies in a sample of dynamically relaxed and unrelaxed galaxy groups from the Galaxy and Mass Assembly survey. The dynamical state of the group is defined by the stellar dominance of the brightest group galaxy (BGG), e.g., the luminosity gap between the two most luminous members, and the offset between the position of the BGG and the luminosity centroid of the group. We find that the radio luminosity of the largest galaxy in the group strongly depends on its environment, such that the BGGs in dynamically young (evolving) groups are an order of magnitude more luminous in the radio than those with a similar stellar mass but residing in dynamically old (relaxed) groups. This observation has been successfully reproduced by a newly developed semi-analytic model that allows us to explore the various causes of these findings. We find that the fraction of radio-loud BGGs in the observed dynamically young groups is ∼2 times that of the dynamically old groups. We discuss the implications of this observational constraint on the central galaxy properties in the context of galaxy mergers and the super massive black hole accretion rate.

  13. Galaxy And Mass Assembly (GAMA): A “No Smoking” Zone for Giant Elliptical Galaxies?

    Energy Technology Data Exchange (ETDEWEB)

    Khosroshahi, Habib G.; Raouf, Mojtaba; Miraghaei, Halime [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), Tehran, 19395-5746 (Iran, Islamic Republic of); Brough, Sarah [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia); Croton, Darren J.; Graham, Alister [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122 (Australia); Driver, Simon [International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Baldry, Ivan [Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Brown, Michael [School of Physics, Monash University, Clayton, VIC 3800 (Australia); Prescott, Matt [Astrophysics Group, The University of Western Cape, Robert Sobukwe Road, Bellville 7530 (South Africa); Wang, Lingyu, E-mail: habib@ipm.ir [SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD, Groningen (Netherlands)

    2017-06-20

    We study the radio emission of the most massive galaxies in a sample of dynamically relaxed and unrelaxed galaxy groups from the Galaxy and Mass Assembly survey. The dynamical state of the group is defined by the stellar dominance of the brightest group galaxy (BGG), e.g., the luminosity gap between the two most luminous members, and the offset between the position of the BGG and the luminosity centroid of the group. We find that the radio luminosity of the largest galaxy in the group strongly depends on its environment, such that the BGGs in dynamically young (evolving) groups are an order of magnitude more luminous in the radio than those with a similar stellar mass but residing in dynamically old (relaxed) groups. This observation has been successfully reproduced by a newly developed semi-analytic model that allows us to explore the various causes of these findings. We find that the fraction of radio-loud BGGs in the observed dynamically young groups is ∼2 times that of the dynamically old groups. We discuss the implications of this observational constraint on the central galaxy properties in the context of galaxy mergers and the super massive black hole accretion rate.

  14. The masses of local group dwarf spheroidal galaxies: The death of the universal mass profile

    International Nuclear Information System (INIS)

    Collins, Michelle L. M.; Martin, Nicolas F.; Chapman, Scott C.; Irwin, Michael J.; Rich, R. M.; Ibata, Rodrigo A.; Bate, Nicholas F.; Lewis, Geraint F.; Peñarrubia, Jorge; Arimoto, Nobuo; Casey, Caitlin M.; Ferguson, Annette M. N.; Koch, Andreas; McConnachie, Alan W.; Tanvir, Nial

    2014-01-01

    We investigate the claim that all dwarf spheroidal galaxies (dSphs) reside within halos that share a common, universal mass profile as has been derived for dSphs of the galaxy. By folding in kinematic information for 25 Andromeda dSphs, more than doubling the previous sample size, we find that a singular mass profile cannot be found to fit all of the observations well. Further, the best-fit dark matter density profile measured solely for the Milky Way dSphs is marginally discrepant with that of the Andromeda dSphs (at just beyond the 1σ level), where a profile with lower maximum circular velocity, and hence mass, is preferred. The agreement is significantly better when three extreme Andromeda outliers, And XIX, XXI, and XXV, all of which have large half-light radii (≳ 600 pc) and low-velocity dispersions (σ v < 5 km s –1 ), are omitted from the sample. We argue that the unusual properties of these outliers are likely caused by tidal interactions with the host galaxy.

  15. The masses of local group dwarf spheroidal galaxies: The death of the universal mass profile

    Energy Technology Data Exchange (ETDEWEB)

    Collins, Michelle L. M.; Martin, Nicolas F. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Chapman, Scott C.; Irwin, Michael J. [Institute of Astronomy, Madingley Rise, Cambridge, CB3 0HA (United Kingdom); Rich, R. M. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States); Ibata, Rodrigo A. [Observatoire de Strasbourg, 11 rue de l' Université, F-67000, Strasbourg (France); Bate, Nicholas F.; Lewis, Geraint F. [Sydney Institute for Astronomy, School of Physics, A28, University of Sydney, NSW 2006 (Australia); Peñarrubia, Jorge [Instituto de Astrofísica de Andalucia-CSIC, Glorieta de la Astronomía s/n, E-18008, Granada (Spain); Arimoto, Nobuo [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A' ohoku Place, Hilo, HI 96720 (United States); Casey, Caitlin M. [Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822-1839 (United States); Ferguson, Annette M. N. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Koch, Andreas [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); McConnachie, Alan W. [NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, British Columbia, Victoria V9E 2E7 (Canada); Tanvir, Nial [Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)

    2014-03-01

    We investigate the claim that all dwarf spheroidal galaxies (dSphs) reside within halos that share a common, universal mass profile as has been derived for dSphs of the galaxy. By folding in kinematic information for 25 Andromeda dSphs, more than doubling the previous sample size, we find that a singular mass profile cannot be found to fit all of the observations well. Further, the best-fit dark matter density profile measured solely for the Milky Way dSphs is marginally discrepant with that of the Andromeda dSphs (at just beyond the 1σ level), where a profile with lower maximum circular velocity, and hence mass, is preferred. The agreement is significantly better when three extreme Andromeda outliers, And XIX, XXI, and XXV, all of which have large half-light radii (≳ 600 pc) and low-velocity dispersions (σ {sub v} < 5 km s{sup –1}), are omitted from the sample. We argue that the unusual properties of these outliers are likely caused by tidal interactions with the host galaxy.

  16. THE HALO MERGER RATE IN THE MILLENNIUM SIMULATION AND IMPLICATIONS FOR OBSERVED GALAXY MERGER FRACTIONS

    International Nuclear Information System (INIS)

    Genel, Shy; Genzel, Reinhard; Bouche, Nicolas; Naab, Thorsten; Sternberg, Amiel

    2009-01-01

    We have developed a new method to extract halo merger rates from the Millennium Simulation. First, by removing superfluous mergers that are artifacts of the standard friends-of-friends (FOF) halo identification algorithm, we find a lower merger rate compared to previous work. The reductions are more significant at lower redshifts and lower halo masses, and especially for minor mergers. Our new approach results in a better agreement with predictions from the extended Press-Schechter model. Second, we find that the FOF halo finder overestimates the halo mass by up to 50% for halos that are about to merge, which leads to an additional ∼20% overestimate of the merger rate. Therefore, we define halo masses by including only particles that are gravitationally bound to their FOF groups. We provide new best-fitting parameters for a global formula to account for these improvements. In addition, we extract the merger rate per progenitor halo, as well as per descendant halo. The merger rate per progenitor halo is the quantity that should be related to observed galaxy merger fractions when they are measured via pair counting. At low-mass/redshift, the merger rate increases moderately with mass and steeply with redshift. At high enough mass/redshift (for the rarest halos with masses a few times the 'knee' of the mass function), these trends break down, and the merger rate per progenitor halo decreases with mass and increases only moderately with redshift. Defining the merger rate per progenitor halo also allows us to quantify the rate at which halos are being accreted onto larger halos, in addition to the minor and major merger rates. We provide an analytic formula that converts any given merger rate per descendant halo into a merger rate per progenitor halo. Finally, we perform a direct comparison between observed merger fractions and the fraction of halos in the Millennium Simulation that have undergone a major merger during the recent dynamical friction time, and find a

  17. ALMA Observations of Molecular Clouds in Three Group-centered Elliptical Galaxies: NGC 5846, NGC 4636, and NGC 5044

    Science.gov (United States)

    Temi, Pasquale; Amblard, Alexandre; Gitti, Myriam; Brighenti, Fabrizio; Gaspari, Massimo; Mathews, William G.; David, Laurence

    2018-05-01

    We present new ALMA CO(2–1) observations of two well-studied group-centered elliptical galaxies: NGC 4636 and NGC 5846. In addition, we include a revised analysis of Cycle 0 ALMA observations of the central galaxy in the NGC 5044 group. We find evidence that molecular gas is a common presence in bright group-centered galaxies (BGG). CO line widths are broader than Galactic molecular clouds, and using the reference Milky Way X CO, the total molecular mass ranges from 2.6 × 105 M ⊙ in NGC 4636 to 6.1 × 107 M ⊙ in NGC 5044. Complementary observations using the ALMA Compact Array do not exhibit any detection of a CO diffuse component at the sensitivity level achieved by current exposures. The origin of the detected molecular features is still uncertain, but these ALMA observations suggest that they are the end product of the hot gas cooling process and not the result of merger events. Some of the molecular clouds are associated with dust features as revealed by HST dust extinction maps, suggesting that these clouds formed from dust-enhanced cooling. The global nonlinear condensation may be triggered via the chaotic turbulent field or buoyant uplift. The large virial parameter of the molecular structures and correlation with the warm ({10}3{--}{10}5 {{K}})/hot (≥106) phase velocity dispersion provide evidence that they are unbound giant molecular associations drifting in the turbulent field, consistent with numerical predictions of the chaotic cold accretion process. Alternatively, the observed large CO line widths may be generated by molecular gas flowing out from cloud surfaces due to heating by the local hot gas atmosphere.

  18. Cosmological implication of wide field Sunyaev-Zel'dovich galaxy clusters survey: exploration by simulation

    International Nuclear Information System (INIS)

    Juin, Jean-Baptiste

    2005-01-01

    The goal of my Phd research is to prepare the data analysis of the near future wide-field observations of galaxy clusters detected by Sunyaev Zel'dovitch effect. I set up a complete chain of original tools to carry out this study. These tools allow me to highlight critical and important points of selection effects that has to be taken into account in future analysis. Analysis chain is composed by: a simulation of observed millimeter sky, state-of-the-art algorithms of SZ galaxy clusters extraction from observed maps, a statistical model of selection effects of the whole detection chain and, finally, tools to constrain, from detected SZ sources catalog, the cosmological parameters. I focus myself on multi-channel experiments equipped with large bolometer camera. I use these tools for a prospecting on Olimpo experiment. (author) [fr

  19. The active galactic nucleus population in X-ray-selected galaxy groups at 0.5 < Z < 1.1

    International Nuclear Information System (INIS)

    Oh, Semyeong; Woo, Jong-Hak; Matsuoka, Kenta; Mulchaey, John S.; Finoguenov, Alexis; Tanaka, Masayuki; Cooper, Michael C.; Ziparo, Felicia; Bauer, Franz E.

    2014-01-01

    We use Chandra data to study the incidence and properties of active galactic nuclei (AGNs) in 16 intermediate redshift (0.5 < z < 1.1) X-ray-selected galaxy groups in the Chandra Deep Field-South. We measure an AGN fraction of f(L X,H >10 42 ;M R <−20)=8.0 −2.3 +3.0 % at z-bar ∼0.74, approximately a factor of two higher than the AGN fraction found for rich clusters at comparable redshift. This extends the trend found at low redshift for groups to have higher AGN fractions than clusters. Our estimate of the AGN fraction is also more than a factor of three higher than that of low redshift X-ray-selected groups. Using optical spectra from various surveys, we also constrain the properties of emission-line selected AGNs in these groups. In contrast to the large population of X-ray AGNs (N(L X, H > 10 41 erg s –1 ) = 25), we find only four emission-line AGNs, three of which are also X-ray bright. Furthermore, most of the X-ray AGNs in our groups are optically dull (i.e., lack strong emission-lines), similar to those found in low redshift X-ray groups and clusters of galaxies. This contrasts with the AGN population found in low redshift optically selected groups which are dominated by emission-line AGNs. The differences between the optically and X-ray-selected AGNs populations in groups are consistent with a scenario where most AGNs in the densest environments are currently in a low accretion state.

  20. Implications of Stellar Feedback for Dynamical Modeling of the Milky Way and Dwarf Galaxies

    Science.gov (United States)

    Wetzel, Andrew

    2018-04-01

    I will present recent results on dynamical modeling of stellar populations from the FIRE cosmological zoom-in baryonic simulations of Milky Way-like and dwarf galaxies. First, I will discuss the dynamical formation of the Milky Way, including the origin of thin+thick stellar disk morphology. I also will discuss the curious origin of metal-rich stars on halo-like orbits near the Sun, as recently measured by Gaia, with new insights from FIRE simulations on stellar radial migration/heating. Next, I will discuss role of stellar feedback in generating non-equilibrium fluctuations of the gravitational potential in low-mass 'dwarf' galaxies, which can explain the origin of cores in their dark-matter density profiles. In particular, we predict significant observable effects on stellar dynamics, including radial migration, size fluctuations, and population gradients, which can provide observational tests of feedback-driven core formation. Finally, this scenario can explain the formation of newly discovered 'ultra-diffuse' galaxies.

  1. TESTING STRICT HYDROSTATIC EQUILIBRIUM IN SIMULATED CLUSTERS OF GALAXIES: IMPLICATIONS FOR A1689

    International Nuclear Information System (INIS)

    Molnar, S. M.; Umetsu, K.; Chiu, I.-N.; Chen, P.; Hearn, N.; Broadhurst, T.; Bryan, G.; Shang, C.

    2010-01-01

    Accurate mass determination of clusters of galaxies is crucial if they are to be used as cosmological probes. However, there are some discrepancies between cluster masses determined based on gravitational lensing and X-ray observations assuming strict hydrostatic equilibrium (i.e., the equilibrium gas pressure is provided entirely by thermal pressure). Cosmological simulations suggest that turbulent gas motions remaining from hierarchical structure formation may provide a significant contribution to the equilibrium pressure in clusters. We analyze a sample of massive clusters of galaxies drawn from high-resolution cosmological simulations and find a significant contribution (20%-45%) from non-thermal pressure near the center of relaxed clusters, and, in accord with previous studies, a minimum contribution at about 0.1 R vir , growing to about 30%-45% at the virial radius, R vir . Our results strongly suggest that relaxed clusters should have significant non-thermal support in their core region. As an example, we test the validity of strict hydrostatic equilibrium in the well-studied massive galaxy cluster A1689 using the latest high-resolution gravitational lensing and X-ray observations. We find a contribution of about 40% from non-thermal pressure within the core region of A1689, suggesting an alternate explanation for the mass discrepancy: the strict hydrostatic equilibrium is not valid in this region.

  2. Chemical evolution of Local Group dwarf galaxies in a cosmological context - I. A new modelling approach and its application to the Sculptor dwarf spheroidal galaxy

    Science.gov (United States)

    Romano, Donatella; Starkenburg, Else

    2013-09-01

    We present a new approach for chemical evolution modelling, specifically designed to investigate the chemical properties of dwarf galaxies in a full cosmological framework. In particular, we focus on the Sculptor dwarf spheroidal galaxy, for which a wealth of observational data exists, as a test bed for our model. We select four candidate Sculptor-like galaxies from the satellite galaxy catalogue generated by implementation of a version of the Munich semi-analytic model for galaxy formation on the level 2 Aquarius dark matter simulations and use the mass assembly and star formation histories predicted for these four systems as an input for the chemical evolution code. We follow explicitly the evolution of several chemical elements, both in the cold gas out of which the stars form and in the hot medium residing in the halo. We take into account in detail the lifetimes of stars of different initial masses, the distribution of the delay times for Type Ia supernova explosions and the dependence of the stellar yields from the initial metallicity of the stars. We allow large fractions of metals to be deposited into the hot phase, either directly as stars die or through reheated gas flows powered by supernova explosions. We find that, in order to reproduce both the observed metallicity distribution function and the observed abundance ratios of long-lived stars of Sculptor, large fractions of the reheated metals must never re-enter regions of active star formation. With this prescription, all the four analogues to the Sculptor dwarf spheroidal galaxy extracted from the simulated satellites catalogue on the basis of luminosity and stellar population ages are found to reasonably match the detailed chemical properties of real Sculptor stars. However, all model galaxies do severely underestimate the fraction of very metal poor stars observed in Sculptor. Our analysis thus sets further constraints on the semi-analytical models and, at large, on possible metal enrichment

  3. The Oldest Stars of the Extremely Metal-Poor Local Group Dwarf Irregular Galaxy Leo A

    Science.gov (United States)

    Schulte-Ladbeck, Regina E.; Hopp, Ulrich; Drozdovsky, Igor O.; Greggio, Laura; Crone, Mary M.

    2002-08-01

    We present deep Hubble Space Telescope (HST) single-star photometry of Leo A in B, V, and I. Our new field of view is offset from the centrally located field observed by Tolstoy et al. in order to expose the halo population of this galaxy. We report the detection of metal-poor red horizontal branch stars, which demonstrate that Leo A is not a young galaxy. In fact, Leo A is as least as old as metal-poor Galactic Globular Clusters that exhibit red horizontal branches and are considered to have a minimum age of about 9 Gyr. We discuss the distance to Leo A and perform an extensive comparison of the data with stellar isochrones. For a distance modulus of 24.5, the data are better than 50% complete down to absolute magnitudes of 2 or more. We can easily identify stars with metallicities between 0.0001 and 0.0004, and ages between about 5 and 10 Gyr, in their post-main-sequence phases, but we lack the detection of main-sequence turnoffs that would provide unambiguous proof of ancient (>10 Gyr) stellar generations. Blue horizontal branch stars are above the detection limits but difficult to distinguish from young stars with similar colors and magnitudes. Synthetic color-magnitude diagrams show it is possible to populate the blue horizontal branch in the halo of Leo A. The models also suggest ~50% of the total astrated mass in our pointing to be attributed to an ancient (>10 Gyr) stellar population. We conclude that Leo A started to form stars at least about 9 Gyr ago. Leo A exhibits an extremely low oxygen abundance, only 3% of solar, in its ionized interstellar medium. The existence of old stars in this very oxygen-deficient galaxy illustrates that a low oxygen abundance does not preclude a history of early star formation. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  4. Clusters of Galaxies

    Science.gov (United States)

    Huchtmeier, W. K.; Richter, O. G.; Materne, J.

    1981-09-01

    The large-scale structure of the universe is dominated by clustering. Most galaxies seem to be members of pairs, groups, clusters, and superclusters. To that degree we are able to recognize a hierarchical structure of the universe. Our local group of galaxies (LG) is centred on two large spiral galaxies: the Andromeda nebula and our own galaxy. Three sr:naller galaxies - like M 33 - and at least 23 dwarf galaxies (KraanKorteweg and Tammann, 1979, Astronomische Nachrichten, 300, 181) can be found in the evironment of these two large galaxies. Neighbouring groups have comparable sizes (about 1 Mpc in extent) and comparable numbers of bright members. Small dwarf galaxies cannot at present be observed at great distances.

  5. Globular clusters in high-redshift dwarf galaxies: a case study from the Local Group

    Science.gov (United States)

    Zick, Tom O.; Weisz, Daniel R.; Boylan-Kolchin, Michael

    2018-06-01

    We present the reconstructed evolution of rest-frame ultraviolet (UV) luminosities of the most massive Milky Way dwarf spheroidal satellite galaxy, Fornax, and its five globular clusters (GCs) across redshift, based on analysis of the stellar fossil record and stellar population synthesis modelling. We find that (1) Fornax's (proto-)GCs can generate 10-100 times more UV flux than the field population, despite comprising 3. (3) GC formation can introduce order-of-magnitude errors in abundance matching. We also find that some compact HFF objects are consistent with the reconstructed properties of Fornax's GCs at the same redshifts (e.g. surface brightness, star formation rate), suggesting we may have already detected proto-GCs in the early Universe. Finally, we discuss the prospects for improving the connections between local GCs and proto-GCs detected in the early Universe.

  6. STELLAR POPULATION GRADIENTS IN ULTRALUMINOUS INFRARED GALAXIES: IMPLICATIONS FOR GAS INFLOW TIMESCALES

    International Nuclear Information System (INIS)

    Soto, Kurt T.; Martin, Crystal L.

    2010-01-01

    Using longslit, optical spectra of ultraluminous infrared galaxies, we measure the evolution in the star formation intensity during galactic mergers. In individual galaxies, we resolve kiloparsec scales allowing comparison of the nucleus, inner disk, and outer disk. We find that the strength of the Hβ absorption line increases with the projected distance from the center of the merger, typically reaching about 9 A around 10 kpc. At these radii, the star formation intensity must have rapidly decreased about 300-400 Myr ago; only stellar populations deficient in stars more massive than Type A produce such strong Balmer absorption. In contrast, we find the star formation history in the central kiloparsec consistent with continuous star formation. Our measurements indicate that gas depletion occurs from the outer disk inward during major mergers. This result is consistent with merger-induced gas inflow and empirically constrains the gas inflow timescale. Numerical simulations accurately calculate the total amount of infalling gas but often assume the timescale for infall. These new measurements are therefore central to modeling merger-induced star formation and active galactic nucleus activity.

  7. VERY STRONG EMISSION-LINE GALAXIES IN THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY AND IMPLICATIONS FOR HIGH-REDSHIFT GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Atek, H.; Colbert, J.; Shim, H. [Spitzer Science Center, Caltech, Pasadena, CA 91125 (United States); Siana, B.; Bridge, C. [Department of Astronomy, Caltech, Pasadena, CA 91125 (United States); Scarlata, C. [Department of Astronomy, University of Minnesota-Twin Cities, Minneapolis, MN 55455 (United States); Malkan, M.; Ross, N. R. [Department of Physics and Astronomy, University of California, Los Angeles, CA (United States); McCarthy, P.; Dressler, A.; Hathi, N. P. [Observatories of the Carnegie Institution for Science, Pasadena, CA 91101 (United States); Teplitz, H. [Infrared Processing and Analysis Center, Caltech, Pasadena, CA 91125 (United States); Henry, A.; Martin, C. [Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Bunker, A. J. [Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Fosbury, R. A. E. [Space Telescope-European Coordinating Facility, Garching bei Muenchen (Germany)

    2011-12-20

    The WFC3 Infrared Spectroscopic Parallel Survey uses the Hubble Space Telescope (HST) infrared grism capabilities to obtain slitless spectra of thousands of galaxies over a wide redshift range including the peak of star formation history of the universe. We select a population of very strong emission-line galaxies with rest-frame equivalent widths (EWs) higher than 200 A. A total of 176 objects are found over the redshift range 0.35 < z < 2.3 in the 180 arcmin{sup 2} area that we have analyzed so far. This population consists of young and low-mass starbursts with high specific star formation rates (sSFR). After spectroscopic follow-up of one of these galaxies with Keck/Low Resolution Imaging Spectrometer, we report the detection at z = 0.7 of an extremely metal-poor galaxy with 12 + log(O/H) =7.47 {+-} 0.11. After estimating the active galactic nucleus fraction in the sample, we show that the high-EW galaxies have higher sSFR than normal star-forming galaxies at any redshift. We find that the nebular emission lines can substantially affect the total broadband flux density with a median brightening of 0.3 mag, with some examples of line contamination producing brightening of up to 1 mag. We show that the presence of strong emission lines in low-z galaxies can mimic the color-selection criteria used in the z {approx} 8 dropout surveys. In order to effectively remove low-redshift interlopers, deep optical imaging is needed, at least 1 mag deeper than the bands in which the objects are detected. Without deep optical data, most of the interlopers cannot be ruled out in the wide shallow HST imaging surveys. Finally, we empirically demonstrate that strong nebular lines can lead to an overestimation of the mass and the age of galaxies derived from fitting of their spectral energy distribution (SED). Without removing emission lines, the age and the stellar mass estimates are overestimated by a factor of 2 on average and up to a factor of 10 for the high-EW galaxies

  8. J0454-0309: evidence of a strong lensing fossil group falling into a poor galaxy cluster

    Science.gov (United States)

    Schirmer, M.; Suyu, S.; Schrabback, T.; Hildebrandt, H.; Erben, T.; Halkola, A.

    2010-05-01

    Aims: We have discovered a strong lensing fossil group (J0454) projected near the well-studied cluster MS0451-0305. Using the large amount of available archival data, we compare J0454 to normal groups and clusters. A highly asymmetric image configuration of the strong lens enables us to study the substructure of the system. Methods: We used multicolour Subaru/Suprime-Cam and CFHT/Megaprime imaging, together with Keck spectroscopy to identify member galaxies. A VLT/FORS2 spectrum was taken to determine the redshifts of the brightest elliptical and the lensed arc. Using HST/ACS images, we determined the group's weak lensing signal and modelled the strong lens system. This is the first time that a fossil group is analysed with lensing methods. The X-ray luminosity and temperature were derived from XMM-Newton data. Results: J0454 is located at z = 0.26, with a gap of 2.5 mag between the brightest and second brightest galaxies within half the virial radius. Outside a radius of 1.5 Mpc, we find two filaments extending over 4 Mpc, and within we identify 31 members spectroscopically and 33 via the red sequence with i systems, a sparse cluster and an infalling fossil group, where the latter seeds the brightest cluster galaxy. An alternative to the sparse cluster could be a filament projected along the line of sight mimicking a cluster, with galaxies streaming towards the fossil group. This work is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii; based on observations made with ESO Telescopes at the La Silla and Paranal Observatories, Chile (ESO DDT

  9. Some Like it Hot: Linking Diffuse X-Ray Luminosity, Baryonic Mass, and Star Formation Rate in Compact Groups of Galaxies

    Science.gov (United States)

    Desjardins, Tyler D.; Gallagher, Sarah C.; Hornschemeier, Ann E.; Mulchaey, John S.; Walker, Lisa May; Brandt, Willian N.; Charlton, Jane C.; Johnson, Kelsey E.; Tzanavaris, Panayiotis

    2014-01-01

    We present an analysis of the diffuse X-ray emission in 19 compact groups (CGs) of galaxies observed with Chandra. The hottest, most X-ray luminous CGs agree well with the galaxy cluster X-ray scaling relations in L(x-T) and (L(x-sigma), even in CGs where the hot gas is associated with only the brightest galaxy. Using Spitzer photometry, we compute stellar masses and classify Hickson CGs 19, 22, 40, and 42, and RSCGs 32, 44, and 86 as fossil groups using a new definition for fossil systems that includes a broader range of masses. We find that CGs with total stellar and Hi masses are great than or equal to 10(sup (11.3) solar mass are often X-ray luminous, while lower-mass CGs only sometimes exhibit faint, localized X-ray emission. Additionally, we compare the diffuse X-ray luminosity against both the total UV and 24 micron star formation rates of each CG and optical colors of the most massive galaxy in each of the CGs. The most X-ray luminous CGs have the lowest star formation rates, likely because there is no cold gas available for star formation, either because the majority of the baryons in these CGs are in stars or the X-ray halo, or due togas stripping from the galaxies in CGs with hot halos. Finally, the optical colors that trace recent star formation histories of the most massive group galaxies do not correlate with the X-ray luminosities of the CGs, indicating that perhaps the current state of the X-ray halos is independent of the recent history of stellar mass assembly in the most massive galaxies.

  10. Brightest group galaxies - II: the relative contribution of BGGs to the total baryon content of groups at z < 1.3

    Science.gov (United States)

    Gozaliasl, Ghassem; Finoguenov, Alexis; Khosroshahi, Habib G.; Henriques, Bruno M. B.; Tanaka, Masayuki; Ilbert, Olivier; Wuyts, Stijn; McCracken, Henry J.; Montanari, Francesco

    2018-04-01

    We performed a detailed study of the evolution of the star formation rate (SFR) and stellar mass of the brightest group galaxies (BGGs) and their relative contribution to the total baryon budget within R200 (f^{BGG}_{b,200}). The sample comprises 407 BGGs selected from X-ray groups (M200 = 1012.8-1014 M⊙) out to z ˜ 1.3 identified in the Cosmic Evolution Survey (COSMOS), XMM Large-Scale Structure survey (XMM-LSS), and the All-Wavelength Extended Groth strip International Survey (AEGIS) fields. We find that BGGs constitute two distinct populations of quiescent and star-forming galaxies and their mean SFR is ˜2 dex higher than the median SFR at z 2 dex. We take into account the halo mass growth of groups in selecting the sample of BGGs and find that the mean (median) stellar mass of BGGs has grown by 0.3 dex since z = 1.3 to the present day. We show that up to ˜ 45 per cent of the stellar mass growth in a star-forming BGG can be due to its star formation activity. With respect to f^{BGG}_{b,200}, we find it to increase with decreasing redshift by ˜0.35 dex, while decreasing with halo mass in a redshift-dependent manner. We show that the slope of the relation between f^{BGG}_{b,200} and halo mass increases negatively with decreasing redshift. This trend is driven by an insufficient star formation in BGGs, compared to the halo growth rate. We separately show the BGGs with the 20 per cent highest f^{BGG}_{b,200} are generally non-star-forming galaxies and grow in mass by processes not related to star formation (e.g. dry mergers and tidal striping). We present the M⋆-Mh and M⋆/Mh-Mh relations and compare them with semi-analytic model predictions and a number of results from the literature. We quantify the intrinsic scatter in stellar mass of BGGs at fixed halo mass (σ _{log M_{\\star}}) and find that σ _{{log }M_{\\star}} increases from 0.3 dex at z ˜ 0.2-0.5 dex at z ˜ 1.0 due to the bimodal distribution of stellar mass.

  11. CLUSTERING OF SLOAN DIGITAL SKY SURVEY III PHOTOMETRIC LUMINOUS GALAXIES: THE MEASUREMENT, SYSTEMATICS, AND COSMOLOGICAL IMPLICATIONS

    International Nuclear Information System (INIS)

    Ho, Shirley; White, Martin; Schlegel, David J.; Seljak, Uros; Reid, Beth; Cuesta, Antonio; Padmanabhan, Nikhil; Seo, Hee-Jong; De Putter, Roland; Ross, Ashley J.; Percival, Will J.; Saito, Shun; Schlafly, Eddie; Hernández-Monteagudo, Carlos; Sánchez, Ariel G.; Blanton, Michael; Skibba, Ramin; Schneider, Don; Mena, Olga; Viel, Matteo

    2012-01-01

    The Sloan Digital Sky Survey (SDSS) surveyed 14,555 deg 2 , and delivered over a trillion pixels of imaging data. We present a study of galaxy clustering using 900,000 luminous galaxies with photometric redshifts, spanning between z = 0.45 and z = 0.65, constructed from the SDSS using methods described in Ross et al. This data set spans 11,000 deg 2 and probes a volume of 3 h –3 Gpc 3 , making it the largest volume ever used for galaxy clustering measurements. We describe in detail the construction of the survey window function and various systematics affecting our measurement. With such a large volume, high-precision cosmological constraints can be obtained given careful control and understanding of the observational systematics. We present a novel treatment of the observational systematics and its applications to the clustering signals from the data set. In this paper, we measure the angular clustering using an optimal quadratic estimator at four redshift slices with an accuracy of ∼15%, with a bin size of δ l = 10 on scales of the baryon acoustic oscillations (BAOs; at l ∼ 40-400). We also apply corrections to the power spectra due to systematics and derive cosmological constraints using the full shape of the power spectra. For a flat ΛCDM model, when combined with cosmic microwave background Wilkinson Microwave Anisotropy Probe 7 (WMAP7) and H 0 constraints from using 600 Cepheids observed by Wide Field Camera 3 (WFC3; HST), we find Ω Λ = 0.73 ± 0.019 and H 0 to be 70.5 ± 1.6 s –1 Mpc –1 km. For an open ΛCDM model, when combined with WMAP7 + HST, we find Ω K = 0.0035 ± 0.0054, improved over WMAP7+HST alone by 40%. For a wCDM model, when combined with WMAP7+HST+SN, we find w = –1.071 ± 0.078, and H 0 to be 71.3 ± 1.7 s –1 Mpc –1 km, which is competitive with the latest large-scale structure constraints from large spectroscopic surveys such as the SDSS Data Release 7 (DR7) and WiggleZ. We also find that systematic-corrected power

  12. CLUSTERING OF SLOAN DIGITAL SKY SURVEY III PHOTOMETRIC LUMINOUS GALAXIES: THE MEASUREMENT, SYSTEMATICS, AND COSMOLOGICAL IMPLICATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Ho, Shirley; White, Martin; Schlegel, David J.; Seljak, Uros; Reid, Beth [Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, MS 50R-5045, Berkeley, CA 94720 (United States); Cuesta, Antonio; Padmanabhan, Nikhil [Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT 06511 (United States); Seo, Hee-Jong [Berkeley Center for Cosmological Physics, LBL and Department of Physics, University of California, Berkeley, CA 94720 (United States); De Putter, Roland [ICC, University of Barcelona (IEEC-UB), Marti i Franques 1, E-08028 Barcelona (Spain); Ross, Ashley J.; Percival, Will J. [Institute of Cosmology and Gravitation, Dennis Sciama Building, University of Portsmouth, Portsmouth PO1 3FX (United Kingdom); Saito, Shun [Department of Astronomy, University of California Berkeley, CA (United States); Schlafly, Eddie [Department of Astronomy, Harvard University, 60 Garden St. MS 20, Cambridge, MA 02138 (United States); Hernandez-Monteagudo, Carlos [Centro de Estudios de Fisica del Cosmos de Aragon (CEFCA), Plaza de San Juan 1, planta 2, E-44001 Teruel (Spain); Sanchez, Ariel G. [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Blanton, Michael [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Skibba, Ramin [Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Schneider, Don [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Mena, Olga [Instituto de Fisica Corpuscular, Universidad de Valencia-CSIC (Spain); Viel, Matteo, E-mail: cwho@lbl.gov [INAF-Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I-34131 Trieste (Italy); and others

    2012-12-10

    The Sloan Digital Sky Survey (SDSS) surveyed 14,555 deg{sup 2}, and delivered over a trillion pixels of imaging data. We present a study of galaxy clustering using 900,000 luminous galaxies with photometric redshifts, spanning between z = 0.45 and z = 0.65, constructed from the SDSS using methods described in Ross et al. This data set spans 11,000 deg{sup 2} and probes a volume of 3 h {sup -3} Gpc{sup 3}, making it the largest volume ever used for galaxy clustering measurements. We describe in detail the construction of the survey window function and various systematics affecting our measurement. With such a large volume, high-precision cosmological constraints can be obtained given careful control and understanding of the observational systematics. We present a novel treatment of the observational systematics and its applications to the clustering signals from the data set. In this paper, we measure the angular clustering using an optimal quadratic estimator at four redshift slices with an accuracy of {approx}15%, with a bin size of {delta}{sub l} = 10 on scales of the baryon acoustic oscillations (BAOs; at l {approx} 40-400). We also apply corrections to the power spectra due to systematics and derive cosmological constraints using the full shape of the power spectra. For a flat {Lambda}CDM model, when combined with cosmic microwave background Wilkinson Microwave Anisotropy Probe 7 (WMAP7) and H{sub 0} constraints from using 600 Cepheids observed by Wide Field Camera 3 (WFC3; HST), we find {Omega}{sub {Lambda}} = 0.73 {+-} 0.019 and H{sub 0} to be 70.5 {+-} 1.6 s{sup -1} Mpc{sup -1} km. For an open {Lambda}CDM model, when combined with WMAP7 + HST, we find {Omega}{sub K} = 0.0035 {+-} 0.0054, improved over WMAP7+HST alone by 40%. For a wCDM model, when combined with WMAP7+HST+SN, we find w = -1.071 {+-} 0.078, and H{sub 0} to be 71.3 {+-} 1.7 s{sup -1} Mpc{sup -1} km, which is competitive with the latest large-scale structure constraints from large spectroscopic

  13. Stable hydrostatic equilibrium configurations of the galaxy and implications for its halo

    International Nuclear Information System (INIS)

    Bloemen, J.B.G.M.

    1987-01-01

    Using a variety of observations, it is shown that the gaseous, magnetic field, and cosmic-ray components in the local region of the Galaxy may be in a large-scale hydrostatic equilibrium that is stable against Parker-type instabilities. Lower limits for the density of the halo are derived as a function of its scale height. The temperature of the hot medium in the disk and at large distances from the plane is found to be typically about a million K in a stable equilibrium, whereas around z roughly 1-3 kpc the temperature could be only 200,000-300,000 K. The scale height of the sum of cosmic-ray and magnetic field pressures in a stable hydrostatic equilibrium state is found to be only weakly dependent on the scale height of the gaseous halo. 109 references

  14. A Radio Study of the Seyfert Galaxy Markarian 6: Implications for Seyfert Life Cycles

    Science.gov (United States)

    Kharb, P.; O'Dea, C. P.; Baum, S. A.; Colbert, E. J. M.; Xu, C.

    2006-11-01

    We have carried out an extensive radio study with the Very Large Array on the Seyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structure in the source. The radio emission occurs on three different spatial scales: ~7.5 kpc bubbles, ~1.5 kpc bubbles lying nearly orthogonal to them, and a ~1 kpc radio jet lying orthogonal to the kiloparsec-scale bubble. To explain the complex morphology, we first consider a scenario in which the radio structures are the result of superwinds ejected by a nuclear starburst. However, recent Spitzer observations of Mrk 6 provide an upper limit to the star formation rate (SFR) of ~5.5 Msolar yr-1, an estimate much lower than the SFR of ~33 Msolar yr-1 derived assuming that the bubbles are a result of starburst winds energized by supernova explosions. Thus, a starburst alone cannot meet the energy requirements for the creation of the bubbles in Mrk 6. We then present an energetically plausible model wherein the bubbles are a result of energy deposited by the kiloparsec-scale jet as it plows into the interstellar medium. Finally, we consider a model in which the complex radio structure is a result of an episodically powered precessing jet that changes its orientation. This model is the most attractive as it can naturally explain the complex radio morphology and is consistent with the energetics, the spectral index, and the polarization structure. Radio emission in this scenario is a short-lived phenomenon in the lifetime of a Seyfert galaxy, which results from an accretion event.

  15. SERENDIPITOUS DISCOVERY OF A MASSIVE cD GALAXY AT z = 1.096: IMPLICATIONS FOR THE EARLY FORMATION AND LATE EVOLUTION OF cD GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Liu, F. S. [College of Physical Science and Technology, Shenyang Normal University, Shenyang 110034 (China); Guo Yicheng; Koo, David C.; Trump, Jonathan R.; Barro, Guillermo; Yesuf, Hassen; Faber, S. M.; Cheung, Edmond [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Giavalisco, M. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Cassata, P. [Aix Marseille Universite, CNRS, LAM-Laboratoire d' Astrophysique de Marseille, F-13388 Marseille (France); Koekemoer, A. M.; Grogin, Norman A. [Space Telescope Science Institute, 3700 San Martin Boulevard, Baltimore, MD 21218 (United States); Pentericci, L.; Castellano, M. [INAF Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monteporzio (RM) (Italy); Mao, Shude [National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Beijing 100012 (China); Xia, X. Y. [Tianjin Astrophysics Center, Tianjin Normal University, Tianjin 300387 (China); Hathi, Nimish P. [Observatories of the Carnegie Institution for Science, Pasadena, CA 91101 (United States); Huang, Kuang-Han [Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Kocevski, Dale [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055 (United States); McGrath, Elizabeth J., E-mail: fengshan@ucolick.org [Department of Physics and Astronomy, Colby College, Mayflower Hill Drive, Waterville, ME 0490 (United States); and others

    2013-06-01

    We have made a serendipitous discovery of a massive ({approx}5 Multiplication-Sign 10{sup 11} M{sub Sun }) cD galaxy at z = 1.096 in a candidate-rich cluster in the Hubble Ultra Deep Field (HUDF) area of GOODS-South. This brightest cluster galaxy (BCG) is the most distant cD galaxy confirmed to date. Ultra-deep HST/WFC3 images reveal an extended envelope starting from {approx}10 kpc and reaching {approx}70 kpc in radius along the semimajor axis. The spectral energy distributions indicate that both its inner component and outer envelope are composed of an old, passively evolving (specific star formation rate <10{sup -4} Gyr{sup -1}) stellar population. The cD galaxy lies on the same mass-size relation as the bulk of quiescent galaxies at similar redshifts. The cD galaxy has a higher stellar mass surface density ({approx}M{sub *}/R{sub 50}{sup 2}) but a similar velocity dispersion ({approx}{radical}(M{sub *}/R{sub 50})) to those of more massive, nearby cDs. If the cD galaxy is one of the progenitors of today's more massive cDs, its size (R{sub 50}) and stellar mass have had to increase on average by factors of 3.4 {+-} 1.1 and 3.3 {+-} 1.3 over the past {approx}8 Gyr, respectively. Such increases in size and stellar mass without being accompanied by significant increases in velocity dispersion are consistent with evolutionary scenarios driven by both major and minor dissipationless (dry) mergers. If such cD envelopes originate from dry mergers, our discovery of even one example proves that some BCGs entered the dry merger phase at epochs earlier than z = 1. Our data match theoretical models which predict that the continuance of dry mergers at z < 1 can result in structures similar to those of massive cD galaxies seen today. Moreover, our discovery is a surprise given that the extreme depth of the HUDF is essential to reveal such an extended cD envelope at z > 1 and, yet, the HUDF covers only a minuscule region of sky ({approx}3.1 Multiplication-Sign 10{sup -8

  16. Galaxy formation and physical bias

    Science.gov (United States)

    Cen, Renyue; Ostriker, Jeremiah P.

    1992-01-01

    We have supplemented our code, which computes the evolution of the physical state of a representative piece of the universe to include, not only the dynamics of dark matter (with a standard PM code), and the hydrodynamics of the gaseous component (including detailed collisional and radiative processes), but also galaxy formation on a heuristic but plausible basis. If, within a cell the gas is Jeans' unstable, collapsing, and cooling rapidly, it is transformed to galaxy subunits, which are then followed with a collisionless code. After grouping them into galaxies, we estimate the relative distributions of galaxies and dark matter and the relative velocities of galaxies and dark matter. In a large scale CDM run of 80/h Mpc size with 8 x 10 exp 6 cells and dark matter particles, we find that physical bias b is on the 8/h Mpc scale is about 1.6 and increases towards smaller scales, and that velocity bias is about 0.8 on the same scale. The comparable HDM simulation is highly biased with b = 2.7 on the 8/h Mpc scale. Implications of these results are discussed in the light of the COBE observations which provide an accurate normalization for the initial power spectrum. CDM can be ruled out on the basis of too large a predicted small scale velocity dispersion at greater than 95 percent confidence level.

  17. Host galaxy properties of mergers of stellar binary black holes and their implications for advanced LIGO gravitational wave sources

    Science.gov (United States)

    Cao, Liang; Lu, Youjun; Zhao, Yuetong

    2018-03-01

    Understanding the host galaxy properties of stellar binary black hole (SBBH) mergers is important for revealing the origin of the SBBH gravitational wave sources detected by advanced LIGO and helpful for identifying their electromagnetic counterparts. Here, we present a comprehensive analysis of the host galaxy properties of SBBHs by implementing semi-analytical recipes for SBBH formation and merger into cosmological galaxy formation model. If the time delay between SBBH formation and merger ranges from ≲ Gyr to the Hubble time, SBBH mergers at redshift z ≲ 0.3 occur preferentially in big galaxies with stellar mass M* ≳ 2 × 1010 M⊙ and metallicities Z peaking at ˜0.6 Z⊙. However, the host galaxy stellar mass distribution of heavy SBBH mergers (M•• ≳ 50 M⊙) is bimodal with one peak at ˜109 M⊙ and the other peak at ˜2 × 1010 M⊙. The contribution fraction from host galaxies with Z ≲ 0.2 Z⊙ to heavy mergers is much larger than that to less heavy mergers. If SBBHs were formed in the early Universe (e.g. z > 6), their mergers detected at z ≲ 0.3 occur preferentially in even more massive galaxies with M* > 3 × 1010 M⊙ and in galaxies with metallicities mostly ≳ 0.2 Z⊙ and peaking at Z ˜ 0.6 Z⊙, due to later cosmic assembly and enrichment of their host galaxies. SBBH mergers at z ≲ 0.3 mainly occur in spiral galaxies, but the fraction of SBBH mergers that occur in elliptical galaxies can be significant if those SBBHs were formed in the early Universe; and about two-thirds of those mergers occur in the central galaxies of dark matter haloes. We also present results on the host galaxy properties of SBBH mergers at higher redshift.

  18. TURBULENCE AND DYNAMO IN GALAXY CLUSTER MEDIUM: IMPLICATIONS ON THE ORIGIN OF CLUSTER MAGNETIC FIELDS

    International Nuclear Information System (INIS)

    Xu Hao; Collins, David C.; Norman, Michael L.; Li Hui; Li Shengtai

    2009-01-01

    We present self-consistent cosmological magnetohydrodynamic (MHD) simulations that simultaneously follow the formation of a galaxy cluster and the magnetic field ejection by an active galactic nucleus (AGN). We find that the magnetic fields ejected by the AGNs, though initially distributed in relatively small volumes, can be transported throughout the cluster and be further amplified by the intracluster medium (ICM) turbulence during the cluster formation process. The ICM turbulence is shown to be generated and sustained by the frequent mergers of smaller halos. Furthermore, a cluster-wide dynamo process is shown to exist in the ICM and amplify the magnetic field energy and flux. The total magnetic energy in the cluster can reach ∼10 61 erg while micro Gauss (μG) fields can distribute over ∼ Mpc scales throughout the whole cluster. This finding shows that magnetic fields from AGNs, being further amplified by the ICM turbulence through small-scale dynamo processes, can be the origin of cluster-wide magnetic fields.

  19. ENTROPY AT THE OUTSKIRTS OF GALAXY CLUSTERS AS IMPLICATIONS FOR COSMOLOGICAL COSMIC-RAY ACCELERATION

    International Nuclear Information System (INIS)

    Fujita, Yutaka; Ohira, Yutaka; Yamazaki, Ryo

    2013-01-01

    Recently, gas entropy at the outskirts of galaxy clusters has attracted much attention. We propose that the entropy profiles could be used to study cosmic-ray (CR) acceleration around the clusters. If the CRs are effectively accelerated at the formation of clusters, the kinetic energy of infalling gas is consumed by the acceleration and the gas entropy should decrease. As a result, the entropy profiles become flat at the outskirts. If the acceleration is not efficient, the entropy should continue to increase outward. By comparing model predictions with X-ray observations with Suzaku, which show flat entropy profiles, we find that the CRs have carried ∼< 7% of the kinetic energy of the gas away from the clusters. Moreover, the CR pressure at the outskirts can be ∼< 40% of the total pressure. On the other hand, if the entropy profiles are not flat at the outskirts, as indicated by combined Plank and ROSAT observations, the carried energy and the CR pressure should be much smaller than the above estimations.

  20. Confining hot spots in 3C 196 - implications for QSO-companion galaxies

    International Nuclear Information System (INIS)

    Brown, R.L.; Broderick, J.J.; Mitchell, K.J.; Virginia Polytechnic Institute and State Univ., Blacksburg; NASA, Goddard Space Flight Center, Greenbelt, MD)

    1986-01-01

    VLBI observations of the extremely compact hot spot in the northern radio lobe of the QSO 3C 196 reveal the angular size of its smallest substructure to be 0.065 arcsec x 0.045 arcsec or about 300 pc at the redshift distance. The morphology of the hot spot and its orientation relative to the more diffuse radio emission suggest that it is formed by an oblique interaction between the nuclear QSO jet and circum-QSO cloud. The inferred density in this cloud, together with its apparent size, imply that the cloud contains a galactic mass, greater than a billion solar masses of gas. The effect of the jet will be to hasten gravitational collapse of the cloud. If many QSOs such as 3C 196 are formed or found in gas-rich environments, the QSO radio phase may commonly stimulate the metamorphosis of circum-QSO gas to QSO-companion galaxies or it may play a significant part in catalyzing star formation in existing companions. 30 references

  1. The signal of weak gravitational lensing from galaxy groups and clusters

    Science.gov (United States)

    Markert, Sean

    2017-02-01

    The weak gravitational lensing of galaxy clusters is a valuable tool. The deflection of light around a lens is solely dependent on the underlying distribution of foreground mass, and independent of tracers of mass such as the mass to light ratio and kinematics. As a direct probe of mass, weak lensing serves as an independent calibration of mass-observable relationships. These massive clusters are objects of great interest to astronomers, as their abundance is dependent on the conditions of the early universe, and accurate counts of clusters serve as a test of cosmological model. Upcoming surveys, such as LSST and DES, promise to push the limit of observable weak lensing, detecting clusters and sources at higher redshift than has ever been detected before. This makes accurate counts of clusters of a given mass and redshift, and proper calibration of mass-observable relationships, vital to cosmological studies. We used M> 1013.5 h-1M ⊙ halos from the MultiDark Planck simulation at z 0.5 to study the behavior of the reduced shear in clusters. We generated 2D maps of convergence and shear the halos using the GLAMER lensing library. Using these maps, we simulated observations of randomly placed background sources, and generate azimuthal averages of the shear. This reduced shear profile, and the true reduced shear profile of the halo, is fit using analytical solutions for shear of the NFW, Einasto, and truncated NFW density profile. The masses of these density profiles are then compared to the total halo masses from the halo catalogs. We find that fits to the reduced shear for halos extending past ≈ 2 h-1Mpc are fits to the noise of large scale structure along the line of sight. This noise is largely in the 45° rotated component to the reduced tangential shear, and is a breakdown in the approximation of gtan ≈ gnot required for density profile fitting of clusters. If fits are constrained to a projected radii of < 2 h-1Mpc, we see massively improved fits

  2. Constraining the Nature of Dark Matter with the Star-formation History of the Faintest Local Group Dwarf Galaxy Satellites

    International Nuclear Information System (INIS)

    Chau, Alice; Mayer, Lucio; Governato, Fabio

    2017-01-01

    Λ warm dark matter (ΛWDM), realized by collisionless particles of 1–3 keV, has been proposed as an alternative scenario to Λ-Cold-Dark Matter (ΛCDM) for the dwarf galaxy scale discrepancies. We present an approach to test the viability of such WDM models using star-formation histories (SFHs) of the dwarf spheroidal galaxies (dSphs) in the Local Group. We compare their high-time-resolution SFHs with the collapse redshift of their dark halos in CDM and WDM. Collapse redshift is inferred after determining the subhalo infall mass. This is based on the dwarf current mass inferred from stellar kinematics, combined with cosmological simulation results on subhalo evolution. WDM subhalos close to the filtering mass scale, forming significantly later than CDM, are the most difficult to reconcile with early truncation of star formation ( z ≥ 3). The ultra-faint dwarfs (UFDs) provide the most stringent constraints. Using six UFDs and eight classical dSphs, we show that a 1 keV particle is strongly disfavored, consistently with other reported methods. Excluding other models is only hinted for a few UFDs. Other UFDs for which the lack of robust constraints on halo mass prevents us from carrying out our analysis rigorously, show a very early onset of star formation that will strengthen the constraints delivered by our method in the future. We discuss the various caveats, notably the low number of dwarfs with accurately determined SFHs and the uncertainties when determining the subhalo infall mass, most notably the baryonic physics. Our preliminary analysis may serve as a pathfinder for future investigations that will combine accurate SFHs for local dwarfs with direct analysis of WDM simulations with baryons.

  3. Constraining the Nature of Dark Matter with the Star-formation History of the Faintest Local Group Dwarf Galaxy Satellites

    Energy Technology Data Exchange (ETDEWEB)

    Chau, Alice; Mayer, Lucio [Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, CH-8057 Zürich (Switzerland); Governato, Fabio [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States)

    2017-08-10

    Λ warm dark matter (ΛWDM), realized by collisionless particles of 1–3 keV, has been proposed as an alternative scenario to Λ-Cold-Dark Matter (ΛCDM) for the dwarf galaxy scale discrepancies. We present an approach to test the viability of such WDM models using star-formation histories (SFHs) of the dwarf spheroidal galaxies (dSphs) in the Local Group. We compare their high-time-resolution SFHs with the collapse redshift of their dark halos in CDM and WDM. Collapse redshift is inferred after determining the subhalo infall mass. This is based on the dwarf current mass inferred from stellar kinematics, combined with cosmological simulation results on subhalo evolution. WDM subhalos close to the filtering mass scale, forming significantly later than CDM, are the most difficult to reconcile with early truncation of star formation ( z ≥ 3). The ultra-faint dwarfs (UFDs) provide the most stringent constraints. Using six UFDs and eight classical dSphs, we show that a 1 keV particle is strongly disfavored, consistently with other reported methods. Excluding other models is only hinted for a few UFDs. Other UFDs for which the lack of robust constraints on halo mass prevents us from carrying out our analysis rigorously, show a very early onset of star formation that will strengthen the constraints delivered by our method in the future. We discuss the various caveats, notably the low number of dwarfs with accurately determined SFHs and the uncertainties when determining the subhalo infall mass, most notably the baryonic physics. Our preliminary analysis may serve as a pathfinder for future investigations that will combine accurate SFHs for local dwarfs with direct analysis of WDM simulations with baryons.

  4. A CATALOG OF ULTRA-COMPACT HIGH VELOCITY CLOUDS FROM THE ALFALFA SURVEY: LOCAL GROUP GALAXY CANDIDATES?

    International Nuclear Information System (INIS)

    Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P.

    2013-01-01

    We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34 Jy km s –1 , median angular diameters of 10', and median velocity widths of 23 km s –1 . We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of ∼1 Mpc, the UCHVCs have neutral hydrogen (H I) masses of ∼10 5 -10 6 M ☉ , H I diameters of ∼2-3 kpc, and indicative dynamical masses within the H I extent of ∼10 7 -10 8 M ☉ , similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.

  5. A CATALOG OF ULTRA-COMPACT HIGH VELOCITY CLOUDS FROM THE ALFALFA SURVEY: LOCAL GROUP GALAXY CANDIDATES?

    Energy Technology Data Exchange (ETDEWEB)

    Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P., E-mail: betsey@astro.cornell.edu, E-mail: riccardo@astro.cornell.edu, E-mail: haynes@astro.cornell.edu [Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States)

    2013-05-01

    We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34 Jy km s{sup -1}, median angular diameters of 10', and median velocity widths of 23 km s{sup -1}. We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of {approx}1 Mpc, the UCHVCs have neutral hydrogen (H I) masses of {approx}10{sup 5}-10{sup 6} M{sub Sun }, H I diameters of {approx}2-3 kpc, and indicative dynamical masses within the H I extent of {approx}10{sup 7}-10{sup 8} M{sub Sun }, similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.

  6. SERENDIPITOUS DISCOVERY OF A MASSIVE cD GALAXY AT z = 1.096: IMPLICATIONS FOR THE EARLY FORMATION AND LATE EVOLUTION OF cD GALAXIES

    International Nuclear Information System (INIS)

    Liu, F. S.; Guo Yicheng; Koo, David C.; Trump, Jonathan R.; Barro, Guillermo; Yesuf, Hassen; Faber, S. M.; Cheung, Edmond; Giavalisco, M.; Cassata, P.; Koekemoer, A. M.; Grogin, Norman A.; Pentericci, L.; Castellano, M.; Mao, Shude; Xia, X. Y.; Hathi, Nimish P.; Huang, Kuang-Han; Kocevski, Dale; McGrath, Elizabeth J.

    2013-01-01

    We have made a serendipitous discovery of a massive (∼5 × 10 11 M ☉ ) cD galaxy at z = 1.096 in a candidate-rich cluster in the Hubble Ultra Deep Field (HUDF) area of GOODS-South. This brightest cluster galaxy (BCG) is the most distant cD galaxy confirmed to date. Ultra-deep HST/WFC3 images reveal an extended envelope starting from ∼10 kpc and reaching ∼70 kpc in radius along the semimajor axis. The spectral energy distributions indicate that both its inner component and outer envelope are composed of an old, passively evolving (specific star formation rate –4 Gyr –1 ) stellar population. The cD galaxy lies on the same mass-size relation as the bulk of quiescent galaxies at similar redshifts. The cD galaxy has a higher stellar mass surface density (∼M * /R 50 2 ) but a similar velocity dispersion (∼√(M * /R 50 )) to those of more massive, nearby cDs. If the cD galaxy is one of the progenitors of today's more massive cDs, its size (R 50 ) and stellar mass have had to increase on average by factors of 3.4 ± 1.1 and 3.3 ± 1.3 over the past ∼8 Gyr, respectively. Such increases in size and stellar mass without being accompanied by significant increases in velocity dispersion are consistent with evolutionary scenarios driven by both major and minor dissipationless (dry) mergers. If such cD envelopes originate from dry mergers, our discovery of even one example proves that some BCGs entered the dry merger phase at epochs earlier than z = 1. Our data match theoretical models which predict that the continuance of dry mergers at z 1 and, yet, the HUDF covers only a minuscule region of sky (∼3.1 × 10 –8 ). Adding that cDs are rare, our serendipitous discovery hints that such cDs may be more common than expected, perhaps even ubiquitous. Images reaching HUDF depths of more area (especially with cluster BCGs at z > 1) are needed to confirm this conjecture.

  7. Ionised gas structure of 100 kpc in an over-dense region of the galaxy group COSMOS-Gr30 at z 0.7

    Science.gov (United States)

    Epinat, B.; Contini, T.; Finley, H.; Boogaard, L. A.; Guérou, A.; Brinchmann, J.; Carton, D.; Michel-Dansac, L.; Bacon, R.; Cantalupo, S.; Carollo, M.; Hamer, S.; Kollatschny, W.; Krajnović, D.; Marino, R. A.; Richard, J.; Soucail, G.; Weilbacher, P. M.; Wisotzki, L.

    2018-01-01

    We report the discovery of a 104 kpc2 gaseous structure detected in [O II]λλ3727, 3729 in an over-dense region of the COSMOS-Gr30 galaxy group at z 0.725 with deep MUSE Guaranteed Time Observations. We estimate the total amount of diffuse ionised gas to be of the order of ( 5 ± 3) × 1010 M⊙ and explore its physical properties to understand its origin and the source(s) of the ionisation. The MUSE data allow the identification of a dozen group members that are embedded in this structure through emission and absorption lines. We extracted spectra from small apertures defined for both the diffuse ionised gas and the galaxies. We investigated the kinematics and ionisation properties of the various galaxies and extended gas regions through line diagnostics (R23, O32, and [O III]/Hβ) that are available within the MUSE wavelength range. We compared these diagnostics to photo-ionisation models and shock models. The structure is divided into two kinematically distinct sub-structures. The most extended sub-structure of ionised gas is likely rotating around a massive galaxy and displays filamentary patterns that link some galaxies. The second sub-structure links another massive galaxy that hosts an active galactic nucleus (AGN) to a low-mass galaxy, but it also extends orthogonally to the AGN host disc over 35 kpc. This extent is likely ionised by the AGN itself. The location of small diffuse regions in the R23 vs. O32 diagram is compatible with photo-ionisation. However, the location of three of these regions in this diagram (low O32, high R23) can also be explained by shocks, which is supported by their high velocity dispersions. One edge-on galaxy shares the same properties and may be a source of shocks. Regardless of the hypothesis, the extended gas seems to be non-primordial. We favour a scenario where the gas has been extracted from galaxies by tidal forces and AGN triggered by interactions between at least the two sub-structures. Based on observations made with

  8. A revised catalog of CfA galaxy groups in the Virgo/Great Attractor flow field

    Science.gov (United States)

    Nolthenius, Richard

    1993-01-01

    A new identification of groups and clusters in the CfAl Catalog of Huchra, et al. (1983) is presented, using a percolation algorithm to identify density enhancements. The procedure differs from that of the original Geller and Huchra (1983; GH) catalog in several important respects; galaxy distances are calculated from the Virgo-Great Attractor flow model of Faber and Burnstein (1988), the adopted distance linkage criteria is only approx. 1/4 as large as in the Geller and Huchra catalog, the sky link relation is taken from Nolthenius and White (1987), correction for interstellar extinction is included, and 'by-hand' adjustments to group memberships are made in the complex regions of Virgo/Coma I/Ursa Major and Coma/A1367 (to allow for varying group velocity dispersions and to trim unphysical 'spider arms'). Since flow model distances are poorly determined in these same regions, available distances from the IR Tully-Fisher planetary nebula luminosity function and surface brightness resolution methods are adopted if possible.

  9. The Unexpected Past of a Dwarf Galaxy

    Science.gov (United States)

    1996-08-01

    understood by Knut Lundmark and P.J. Melotte. The designation WLM is shorthand of Wolf-Lundmark-Melotte. More recent investigations have fixed its distance at about 2.9 million light years, somewhat farther away than the Andromeda galaxy (2 million light years) and placing it at the very edge of the region occupied by the Local Group. WLM is one of the most isolated members; its nearest neighbour dwarf galaxy, IC 1613, is more 1 million light years away. A halo around WLM The ESO astronomers recently obtained deep CCD images of WLM with the 3.5-m ESO New Technology Telescope (NTT) and the ESO Multi-Mode Instrument (EMMI). With the excellent imaging capabilities of this facility, they were able to see large numbers of individual stars in this galaxy. A mosaic of two of these images is reproduced as ESO Press Photo 34/96 that accompanies this Press Release. WLM appears to be quite elongated, and surprisingly, its largest extension is about 8000 light years or more than twice as large as thought before. Nevertheless, this is still 12 times smaller than the Milky Way galaxy. There is a clear excess of very faint stars that extends to the edge of the sky field covered by the NTT exposures. Some of these are probably foreground stars inside the Milky Way, but there are many more than expected, and their numbers increase closer to WLM . These stars look quite different from the ones in the central region of that galaxy: they are much redder and relatively faint; this is a strong indication that they are much older. The distant stars thus appear to belong to an old halo around this dwarf galaxy. This shows that WLM must be very old, perhaps as old as the Milky Way, and in any case much older than indicated by the ages of the stars near its centre. The present discovery furthermore proves that a halo may also form around a dwarf galaxy, and it is not a feature exclusively reserved for large spiral galaxies. Implications of this discovery WLM is so isolated that it has most probably

  10. Statistical analysis of the spatial distribution of galaxies and clusters

    International Nuclear Information System (INIS)

    Cappi, Alberto

    1993-01-01

    This thesis deals with the analysis of the distribution of galaxies and clusters, describing some observational problems and statistical results. First chapter gives a theoretical introduction, aiming to describe the framework of the formation of structures, tracing the history of the Universe from the Planck time, t_p = 10"-"4"3 sec and temperature corresponding to 10"1"9 GeV, to the present epoch. The most usual statistical tools and models of the galaxy distribution, with their advantages and limitations, are described in chapter two. A study of the main observed properties of galaxy clustering, together with a detailed statistical analysis of the effects of selecting galaxies according to apparent magnitude or diameter, is reported in chapter three. Chapter four delineates some properties of groups of galaxies, explaining the reasons of discrepant results on group distributions. Chapter five is a study of the distribution of galaxy clusters, with different statistical tools, like correlations, percolation, void probability function and counts in cells; it is found the same scaling-invariant behaviour of galaxies. Chapter six describes our finding that rich galaxy clusters too belong to the fundamental plane of elliptical galaxies, and gives a discussion of its possible implications. Finally chapter seven reviews the possibilities offered by multi-slit and multi-fibre spectrographs, and I present some observational work on nearby and distant galaxy clusters. In particular, I show the opportunities offered by ongoing surveys of galaxies coupled with multi-object fibre spectrographs, focusing on the ESO Key Programme A galaxy redshift survey in the south galactic pole region to which I collaborate and on MEFOS, a multi-fibre instrument with automatic positioning. Published papers related to the work described in this thesis are reported in the last appendix. (author) [fr

  11. Einstein observations of the Hydra A cluster and the efficiency of galaxy formation in groups and clusters

    Science.gov (United States)

    David, L. P.; Arnaud, K. A.; Forman, W.; Jones, C.

    1990-01-01

    The Einstein imaging proportional counter observations of the poor cluster of galaxies centered on the radio galaxy Hydra A are examined. From the surface brightness profile, it is found that the X-ray-emitting gas in the Hydra A cluster must be condensing out of the intracluster medium at a rate of 600 solar masses/yr. This is one of the largest mass deposition rates observed in a cluster of galaxies. The ratio of gas mass to stellar mass is compared for a variety of systems, showing that this ratio correlates with the gas temperature.

  12. VizieR Online Data Catalog: Ccompact group galaxies UV and IR SFR (Lenkic+, 2016)

    Science.gov (United States)

    Lenkic, L.; Tzanavaris, P.; Gallagher, S. C.; Desjardins, T. D.; Walker, L. M.; Johnson, K. E.; Fedotov, K.; Charlton, J.; Hornschemeier, A. E.; Durrell, P. R.; Gronwall, C.

    2017-07-01

    The sample of CGs studied here is the same sample studied by Walker et al. (2012AJ....143...69W) of 49 CGs: 33 Hickson Compact Groups and 16 Redshift Survey Compact Groups (RSCGs). The RSCG catalogue of 89 CGs was constructed by Barton et al. (1996AJ....112..871B). The data used in this study originated from 'fill-in' observations with UVOT's three UV filters (uvw2, uvm2, uvw1) as well as the bluest optical filter (u). All UV data (PI: Tzanavaris) were downloaded from the Swift archive. The Spitzer Infrared Array Camera images for our sample of CGs are archival data presented by Walker et al. (2012AJ....143...69W) Spitzer MIPS (24um) data were obtained from the Spitzer Heritage Archive. (4 data files).

  13. A new measurement of the baryonic fraction using the sparse NGC 3258 group of galaxies

    DEFF Research Database (Denmark)

    Pedersen, Kristian; Yoshii, Y.; Sommer-Larsen, J.

    1997-01-01

    )(-1) kpc is found to be 0.065(-0.020)(+0.051) for h(50) = 1, where h(50) = H-0/50 km s(-1) Mpc(-1), in good agreement with the universal value of 0.05 +/- 0.01 predicted by standard big bang nucleosynthesis for a universe with Omega(0) = 1 and h(50) = 1. Since the deep potential of the NGC 3258 group...

  14. The Spitzer-IRAC/MIPS Extragalactic Survey (SIMES). II. Enhanced Nuclear Accretion Rate in Galaxy Groups at z ∼ 0.2

    Science.gov (United States)

    Baronchelli, I.; Rodighiero, G.; Teplitz, H. I.; Scarlata, C. M.; Franceschini, A.; Berta, S.; Barrufet, L.; Vaccari, M.; Bonato, M.; Ciesla, L.; Zanella, A.; Carraro, R.; Mancini, C.; Puglisi, A.; Malkan, M.; Mei, S.; Marchetti, L.; Colbert, J.; Sedgwick, C.; Serjeant, S.; Pearson, C.; Radovich, M.; Grado, A.; Limatola, L.; Covone, G.

    2018-04-01

    For a sample of star-forming galaxies in the redshift interval 0.15 < z < 0.3, we study how both the relative strength of the active galactic nucleus (AGN) infrared emission, compared to that due to the star formation (SF), and the numerical fraction of AGNs change as a function of the total stellar mass of the hosting galaxy group ({M}group}* ) between 1010.25 and 1011.9 M ⊙. Using a multicomponent spectral energy distribution SED fitting analysis, we separate the contribution of stars, AGN torus, and star formation to the total emission at different wavelengths. This technique is applied to a new multiwavelength data set in the SIMES field (23 not-redundant photometric bands), spanning the wavelength range from the UV (GALEX) to the far-IR (Herschel) and including crucial AKARI and WISE mid-IR observations (4.5 μm < λ < 24 μm), where the black hole thermal emission is stronger. This new photometric catalog, which includes our best photo-z estimates, is released through the NASA/IPAC Infrared Science Archive (IRSA). Groups are identified through a friends-of-friends algorithm (∼62% purity, ∼51% completeness). We identified a total of 45 galaxies requiring an AGN emission component, 35 of which are in groups and 10 in the field. We find the black hole accretion rate (BHAR) ∝ ({M}group}* {)}1.21+/- 0.27 and (BHAR/SFR) ∝ ({M}group}* {)}1.04+/- 0.24, while, in the same range of {M}group}* , we do not observe any sensible change in the numerical fraction of AGNs. Our results indicate that the nuclear activity (i.e., the BHAR and the BHAR/SFR ratio) is enhanced when galaxies are located in more massive and richer groups.

  15. Focus Group Evidence: Implications for Design and Analysis

    Science.gov (United States)

    Ryan, Katherine E.; Gandha, Tysza; Culbertson, Michael J.; Carlson, Crystal

    2014-01-01

    In evaluation and applied social research, focus groups may be used to gather different kinds of evidence (e.g., opinion, tacit knowledge). In this article, we argue that making focus group design choices explicitly in relation to the type of evidence required would enhance the empirical value and rigor associated with focus group utilization. We…

  16. Exploratory Study of Children's Task Groups: Instructional Implications.

    Science.gov (United States)

    Keyton, Joann; Dodson, Nancy L.

    Despite the increasing popularity of cooperative learning techniques in elementary instruction, many educators believe that children do not possess effective group interaction skills and advocate that children be taught the group communication skills necessary for group interaction as a separate instructional component. Unfortunately,…

  17. Evolution of Hot Gas in Elliptical Galaxies

    Science.gov (United States)

    Mathews, William G.

    2004-01-01

    This theory grant was awarded to study the curious nature, origin and evolution of hot gas in elliptical galaxies and their surrounding groups. Understanding the properties of this X-ray emitting gas has profound implications over the broad landscape of modern astrophysics: cosmology, galaxy formation, star formation, cosmic metal enrichment, galactic structure and dynamics, and the physics of hot gases containing dust and magnetic fields. One of our principal specific objectives was to interpret the marvelous new observations from the XMM and Chandru satellite X-ray telescopes.

  18. KINEMATIC CLASSIFICATIONS OF LOCAL INTERACTING GALAXIES: IMPLICATIONS FOR THE MERGER/DISK CLASSIFICATIONS AT HIGH-z

    International Nuclear Information System (INIS)

    Hung, Chao-Ling; Larson, Kirsten L.; Sanders, D. B.; Rich, Jeffrey A.; Yuan, Tiantian; Kewley, Lisa J.; Casey, Caitlin M.; Smith, Howard A.; Hayward, Christopher C.

    2015-01-01

    The classification of galaxy mergers and isolated disks is key for understanding the relative importance of galaxy interactions and secular evolution during the assembly of galaxies. Galaxy kinematics as traced by emission lines have been used to suggest the existence of a significant population of high-z star-forming galaxies consistent with isolated rotating disks. However, recent studies have cautioned that post-coalescence mergers may also display disk-like kinematics. To further investigate the robustness of merger/disk classifications based on kinematic properties, we carry out a systematic classification of 24 local (U)LIRGs spanning a range of morphologies: from isolated spiral galaxies, ongoing interacting systems, to fully merged remnants. We artificially redshift the Wide Field Spectrograph observations of these local (U)LIRGs to z = 1.5 to make a realistic comparison with observations at high-z, and also to ensure that all galaxies have the same spatial sampling of ∼900 pc. Using both kinemetry-based and visual classifications, we find that the reliability of kinematic classification shows a strong trend with the interaction stage of galaxies. Mergers with two nuclei and tidal tails have the most distinct kinematics compared to isolated disks, whereas a significant population of the interacting disks and merger remnants are indistinguishable from isolated disks. The high fraction of mergers displaying disk-like kinematics reflects the complexity of the dynamics during galaxy interactions. Additional merger indicators such as morphological properties traced by stars or molecular gas are required to further constrain the merger/disk classifications at high-z

  19. Ratio of extinction to reddening for interstellar matter using galaxies. I. A limit on the neutral extinction from photometry of the 3C 129 group

    International Nuclear Information System (INIS)

    Sandage, A.

    1975-01-01

    The ratio of total extinction to reddening of interstellar matter has been determined by a new method applied to galaxies in the highly obscured 3C 129 and 3C 129.1 group (l = 160 0 , b = 0 0 ). The difference between the observed magnitude of the first-ranked group member and the magnitude calculated from the redshift-apparent magnitude (Hubble) diagram (at the known redshift of the group) is the total extinction A/sub v/ to within the sigma(M/sub v/) that applies to the first-ranked cluster member. Comparison of the observed color with the known intrinsic color of giant E galaxies gives E(B--V), and therefore R. Photometry of the 3C 129 group gives R identical with A/sub v//E(B--V) = 3.72 +- 0.32(sigma). Correction for the finite bandwidth of the BV system gives R (O star base) = 3.35 +- 0.29 (sigma). Comparison with R determined from the color-difference method gives a limit for the fraction of neutral-to-selective extinction of f = A/sub v/ (neutral)/A/sub v/ (selective) = 0.10 +- 0.15(sigma) which is a null result (f = 0) to within the statistics. Hence, no neutral extinction has been detected at the 1 sigma level of the experiment. Use of the method on many additional groups of galaxies is expected to substantially reduce the error of this limit

  20. Absorption-line detections of 10{sup 5}-10{sup 6} K gas in spiral-rich groups of galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Stocke, John T.; Keeney, Brian A.; Danforth, Charles W.; Syphers, David; Yamamoto, H.; Shull, J. Michael; Green, James C.; Froning, Cynthia [Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309 (United States); Savage, Blair D.; Wakker, Bart; Kim, Tae-Sun [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States); Ryan-Weber, Emma V.; Kacprzak, Glenn G., E-mail: john.stocke@colorado.edu [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, VIC 3122 (Australia)

    2014-08-20

    Using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope, the COS Science Team has conducted a high signal-to-noise survey of 14 bright QSOs. In a previous paper, these far-UV spectra were used to discover 14 'warm' (T ≥ 10{sup 5} K) absorbers using a combination of broad Lyα and broad O VI absorptions. A reanalysis of a few of this new class of absorbers using slightly relaxed fitting criteria finds as many as 20 warm absorbers could be present in this sample. A shallow, wide spectroscopic galaxy redshift survey has been conducted around these sight lines to investigate the warm absorber environment, which is found to be spiral-rich groups or cluster outskirts with radial velocity dispersions σ = 250-750 km s{sup –1}. While 2σ evidence is presented favoring the hypothesis that these absorptions are associated with the galaxy groups and not with the individual, nearest galaxies, this evidence has considerable systematic uncertainties and is based on a small sample size so it is not entirely conclusive. If the associations are with galaxy groups, the observed frequency of warm absorbers (dN/dz = 3.5-5 per unit redshift) requires them to be very extended as an ensemble on the sky (∼1 Mpc in radius at high covering factor). Most likely these warm absorbers are interface gas clouds whose presence implies the existence of a hotter (T ∼ 10{sup 6.5} K), diffuse, and probably very massive (>10{sup 11} M {sub ☉}) intra-group medium which has yet to be detected directly.

  1. Obligations to High Priority Target Groups: Philosophical Implications.

    Science.gov (United States)

    Christmas, June Jackson

    Community mental health center services must be most plentiful where the need is greatest and must be appropriate and available to meet these needs. The first high priority group, according to statistics on juvenile delinquency, and narcotics, is the black inner city. Socio-psychiatric services, numerous enough in quantity to begin to meet needs…

  2. Statistical measures of galaxy clustering

    International Nuclear Information System (INIS)

    Porter, D.H.

    1988-01-01

    Consideration is given to the large-scale distribution of galaxies and ways in which this distribution may be statistically measured. Galaxy clustering is hierarchical in nature, so that the positions of clusters of galaxies are themselves spatially clustered. A simple identification of groups of galaxies would be an inadequate description of the true richness of galaxy clustering. Current observations of the large-scale structure of the universe and modern theories of cosmology may be studied with a statistical description of the spatial and velocity distributions of galaxies. 8 refs

  3. Evolution of public cooperation in a monitored society with implicated punishment and within-group enforcement

    Science.gov (United States)

    Chen, Xiaojie; Sasaki, Tatsuya; Perc, Matjaž

    2015-11-01

    Monitoring with implicated punishment is common in human societies to avert freeriding on common goods. But is it effective in promoting public cooperation? We show that the introduction of monitoring and implicated punishment is indeed effective, as it transforms the public goods game to a coordination game, thus rendering cooperation viable in infinite and finite well-mixed populations. We also show that the addition of within-group enforcement further promotes the evolution of public cooperation. However, although the group size in this context has nonlinear effects on collective action, an intermediate group size is least conductive to cooperative behaviour. This contradicts recent field observations, where an intermediate group size was declared optimal with the conjecture that group-size effects and within-group enforcement are responsible. Our theoretical research thus clarifies key aspects of monitoring with implicated punishment in human societies, and additionally, it reveals fundamental group-size effects that facilitate prosocial collective action.

  4. Age groups and spread of influenza: implications for vaccination strategy

    Directory of Open Access Journals (Sweden)

    Hsieh Ying-Hen

    2010-04-01

    Full Text Available Abstract Background The unpredictable nature of the potentially devastating impact of 2009 pH1N1 influenza pandemic highlights the need for pandemic preparedness planning, where modeling studies could be most useful for simulations of possible future scenarios. Methods A compartmental model with pre-symptomatic and asymptomatic influenza infections is proposed which incorporates age groups as well as intervention measures such as age-specific vaccination, in order to study spread of influenza in a community. Results We derive the basic reproduction number and other effective reproduction numbers under various intervention measures. For illustration, we make use of the Pneumonia and Influenza (P&I mortality data and vaccination data of the very young (age 0-2 and the very old (age >64 during 2004-2005 Taiwan winter influenza season to fit our model and to compute the relevant reproduction numbers. The reproduction number for this winter flu season is estimated to be slightly above one (~1.0001. Conclusions Comparatively large errors in fitting the P&I mortality data of the elderly (>64 were observed shortly after winter school closings in January, which may indicate the impact of younger, more active age groups transmitting influenza to other age groups outside of the school settings; in particular, to the elderly in the households. Pre-symptomatic infections seemed to have little effect on the model fit, while asymptomatic infection by asymptomatic infectives has a more pronounced impact on the model fit for the elderly mortality, perhaps indicating a larger role in disease transmission by asymptomatic infection. Simulations indicate that the impact of vaccination on the disease incidence might not be fully revealed in the change (or the lack thereof in the effective reproduction number with interventions, but could still be substantial. The estimated per contact transmission probability for susceptible elderly is significantly higher than that

  5. Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

    Energy Technology Data Exchange (ETDEWEB)

    Deason, Alis [Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, CA (United States); Wetzel, Andrew [TAPIR, California Institute of Technology, Pasadena, CA (United States); Garrison-Kimmel, Shea, E-mail: alis@ucolick.org [Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, CA (United States)

    2014-10-20

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M {sub star} > 10{sup 6} M {sub ☉} that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.

  6. Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

    International Nuclear Information System (INIS)

    Deason, Alis; Wetzel, Andrew; Garrison-Kimmel, Shea

    2014-01-01

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M star > 10 6 M ☉ that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.

  7. Group Decisions in Biodiversity Conservation: Implications from Game Theory

    OpenAIRE

    Frank, David M.; Sarkar, Sahotra

    2010-01-01

    Background Decision analysis and game theory [1], [2] have proved useful tools in various biodiversity conservation planning and modeling contexts [3]?[5]. This paper shows how game theory may be used to inform group decisions in biodiversity conservation scenarios by modeling conflicts between stakeholders to identify Pareto?inefficient Nash equilibria. These are cases in which each agent pursuing individual self?interest leads to a worse outcome for all, relative to other feasible outcomes....

  8. THE ORIGIN OF DUST IN EARLY-TYPE GALAXIES AND IMPLICATIONS FOR ACCRETION ONTO SUPERMASSIVE BLACK HOLES

    Energy Technology Data Exchange (ETDEWEB)

    Martini, Paul [Department of Astronomy and Center for Cosmology and Astroparticle Physics, The Ohio State University, Columbus, OH 43210 (United States); Dicken, Daniel [Institut de Astrophysique Spatiale, Paris (France); Storchi-Bergmann, Thaisa [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, Caixa Postal 15051, 91501-970 Porto Alegre, RS (Brazil)

    2013-04-01

    We have conducted an archival Spitzer study of 38 early-type galaxies in order to determine the origin of the dust in approximately half of this population. Our sample galaxies generally have good wavelength coverage from 3.6 {mu}m to 160 {mu}m, as well as visible-wavelength Hubble Space Telescope (HST) images. We use the Spitzer data to estimate dust masses, or establish upper limits, and find that all of the early-type galaxies with dust lanes in the HST data are detected in all of the Spitzer bands and have dust masses of {approx}10{sup 5}-10{sup 6.5} M{sub Sun }, while galaxies without dust lanes are not detected at 70 {mu}m and 160 {mu}m and typically have <10{sup 5} M{sub Sun} of dust. The apparently dust-free galaxies do have 24 {mu}m emission that scales with the shorter-wavelength flux, yet substantially exceeds the expectations of photospheric emission by approximately a factor of three. We conclude this emission is dominated by hot, circumstellar dust around evolved stars that does not survive to form a substantial interstellar component. The order-of-magnitude variations in dust masses between galaxies with similar stellar populations rule out a substantial contribution from continual, internal production in spite of the clear evidence for circumstellar dust. We demonstrate that the interstellar dust is not due to purely external accretion, unless the product of the merger rate of dusty satellites and the dust lifetime is at least an order of magnitude higher than expected. We propose that dust in early-type galaxies is seeded by external accretion, yet the accreted dust is maintained by continued growth in externally accreted cold gas beyond the nominal lifetime of individual grains. The several Gyr depletion time of the cold gas is long enough to reconcile the fraction of dusty early-type galaxies with the merger rate of gas-rich satellites. As the majority of dusty early-type galaxies are also low-luminosity active galactic nuclei and likely fueled

  9. Group decisions in biodiversity conservation: implications from game theory.

    Science.gov (United States)

    Frank, David M; Sarkar, Sahotra

    2010-05-27

    Decision analysis and game theory have proved useful tools in various biodiversity conservation planning and modeling contexts. This paper shows how game theory may be used to inform group decisions in biodiversity conservation scenarios by modeling conflicts between stakeholders to identify Pareto-inefficient Nash equilibria. These are cases in which each agent pursuing individual self-interest leads to a worse outcome for all, relative to other feasible outcomes. Three case studies from biodiversity conservation contexts showing this feature are modeled to demonstrate how game-theoretical representation can inform group decision-making. The mathematical theory of games is used to model three biodiversity conservation scenarios with Pareto-inefficient Nash equilibria: (i) a two-agent case involving wild dogs in South Africa; (ii) a three-agent raptor and grouse conservation scenario from the United Kingdom; and (iii) an n-agent fish and coral conservation scenario from the Philippines. In each case there is reason to believe that traditional mechanism-design solutions that appeal to material incentives may be inadequate, and the game-theoretical analysis recommends a resumption of further deliberation between agents and the initiation of trust--and confidence--building measures. Game theory can and should be used as a normative tool in biodiversity conservation contexts: identifying scenarios with Pareto-inefficient Nash equilibria enables constructive action in order to achieve (closer to) optimal conservation outcomes, whether by policy solutions based on mechanism design or otherwise. However, there is mounting evidence that formal mechanism-design solutions may backfire in certain cases. Such scenarios demand a return to group deliberation and the creation of reciprocal relationships of trust.

  10. Group decisions in biodiversity conservation: implications from game theory.

    Directory of Open Access Journals (Sweden)

    David M Frank

    Full Text Available BACKGROUND: Decision analysis and game theory have proved useful tools in various biodiversity conservation planning and modeling contexts. This paper shows how game theory may be used to inform group decisions in biodiversity conservation scenarios by modeling conflicts between stakeholders to identify Pareto-inefficient Nash equilibria. These are cases in which each agent pursuing individual self-interest leads to a worse outcome for all, relative to other feasible outcomes. Three case studies from biodiversity conservation contexts showing this feature are modeled to demonstrate how game-theoretical representation can inform group decision-making. METHODOLOGY AND PRINCIPAL FINDINGS: The mathematical theory of games is used to model three biodiversity conservation scenarios with Pareto-inefficient Nash equilibria: (i a two-agent case involving wild dogs in South Africa; (ii a three-agent raptor and grouse conservation scenario from the United Kingdom; and (iii an n-agent fish and coral conservation scenario from the Philippines. In each case there is reason to believe that traditional mechanism-design solutions that appeal to material incentives may be inadequate, and the game-theoretical analysis recommends a resumption of further deliberation between agents and the initiation of trust--and confidence--building measures. CONCLUSIONS AND SIGNIFICANCE: Game theory can and should be used as a normative tool in biodiversity conservation contexts: identifying scenarios with Pareto-inefficient Nash equilibria enables constructive action in order to achieve (closer to optimal conservation outcomes, whether by policy solutions based on mechanism design or otherwise. However, there is mounting evidence that formal mechanism-design solutions may backfire in certain cases. Such scenarios demand a return to group deliberation and the creation of reciprocal relationships of trust.

  11. Studies in the X-Ray Emission of Clusters of Galaxies and Other Topics

    Science.gov (United States)

    Vrtilek, Jan; Thronson, Harley (Technical Monitor)

    2001-01-01

    The paper discusses the following: (1) X-ray study of groups of galaxies with Chandra and XMM. (2) X-ray properties of point sources in Chandra deep fields. (3) Study of cluster substructure using wavelet techniques. (4) Combined study of galaxy clusters with X-ray and the S-Z effect. Groups of galaxies are the fundamental building blocks of large scale structure in the Universe. X-ray study of the intragroup medium offers a powerful approach to addressing some of the major questions that still remain about almost all aspects of groups: their ages, origins, importance of composition of various galaxy types, relations to clusters, and origin and enrichment of the intragroup gas. Long exposures with Chandra have opened new opportunities for the study of X-ray background. The presence of substructure within clusters of galaxies has substantial implications for our understanding of cluster evolution as well as fundamental questions in cosmology.

  12. THE COLORS OF CENTRAL AND SATELLITE GALAXIES IN zCOSMOS OUT TO z ≅ 0.8 AND IMPLICATIONS FOR QUENCHING

    International Nuclear Information System (INIS)

    Knobel, C.; Lilly, S. J.; Kovač, K.; Peng, Y.; Bschorr, T. J.; Carollo, C. M.; Caputi, K.; Contini, T.; Kneib, J.-P.; Le Fevre, O.; Mainieri, V.; Renzini, A.; Scodeggio, M.; Zamorani, G.; Bardelli, S.; Bolzonella, M.; Bongiorno, A.; Cucciati, O.; De la Torre, S.; De Ravel, L.

    2013-01-01

    We examine the red fraction of central and satellite galaxies in the large zCOSMOS group catalog out to z ≅ 0.8, correcting for both the incompleteness in stellar mass and for the less than perfect purities of the central and satellite samples. We show that at all masses and at all redshifts, the fraction of satellite galaxies that have been quenched, i.e., that are red, is systematically higher than that of centrals, as seen locally in the Sloan Digital Sky Survey (SDSS). The satellite quenching efficiency, which is the probability that a satellite is quenched because it is a satellite rather than a central, is, as locally, independent of stellar mass. Furthermore, the average value is about 0.5, which is also very similar to that seen in the SDSS. We also construct the mass functions of blue and red centrals and satellites and show that these broadly follow the predictions of the Peng et al. analysis of the SDSS groups. Together, these results indicate that the effect of the group environment in quenching satellite galaxies was very similar to what it is today when the universe was about half its present age.

  13. Group Leader Reflections on Their Training and Experience: Implications for Group Counselor Educators and Supervisors

    Science.gov (United States)

    Ohrt, Jonathan H.; Ener, Elizabeth; Porter, Jessica; Young, Tabitha L.

    2014-01-01

    Effective group leaders possess specialized counseling skills and abilities; however, attention to group leadership training appears to be lagging behind that of individual counseling. In this phenomenological study we explored group leaders' perceptions of their training and experience. Twenty-two professional counselors participated in…

  14. Interactions between intergalactic medium and galaxies

    International Nuclear Information System (INIS)

    Einasto, J.; Saar, E.

    1977-01-01

    The interaction of galaxies with the environmental gas both in clusters and in small groups of galaxies is investigated. Interaction between galaxies and the ambient medium can be considered simply as final touches in the process of galaxy formation. Large relative velocities of galaxies in their clusters and of the intercluster gas result in a loss of the intergalactic gas, that in its turn affects the morphology of cluster galaxies. Interaction between the coronal clouds and the gas in the disk of spiral galaxies may result in regular patterns of star formation and in the bending of planes of galaxies

  15. Galaxy collisions

    International Nuclear Information System (INIS)

    Combes, F.

    1987-01-01

    Galaxies are not isolated systems of stars and gas, ''independent universes'' as believed by astronomers about ten years ago, but galaxies are formed and evolve by interaction with their environment, and in particular with their nearest neighbors. Gravitational interactions produce enormous tides in the disk of spiral galaxies, generate spiral arms and trigger bursts of star formation. Around elliptical galaxies, the collision with a small companion produces a series of waves, or shells. A galaxy interaction leads, in most cases, to the coalescence of the two coliders; therefore all galaxies are not formed just after the Big-Bang, when matter recombines: second generation galaxies are still forming now by galaxy mergers, essentially elliptical galaxies, but also compact dwarfs. Collisions between galaxies could also trigger activity in nuclei for radiogalaxies and quasars [fr

  16. Isolated galaxies

    International Nuclear Information System (INIS)

    Einasto, Maret

    1990-01-01

    To test for the possible presence of really isolated galaxies, which form a randomly distributed population in voids, we compare the distribution of most isolated galaxies in an observed sample with distributions of the same number of random points using the nearest neighbour test. The results show that the random population of really isolated galaxies does not exist - even the most isolated galaxies are connected with systems of galaxies, forming their outlying parts. (author)

  17. MOND implications for spectral line profiles of shell galaxies: shell formation history and mass-velocity scaling relations

    Czech Academy of Sciences Publication Activity Database

    Bílek, Michal; Jungwiert, Bruno; Ebrová, Ivana; Bartošková, Kateřina

    2015-01-01

    Roč. 575, March (2015), A29/1-A29/8 ISSN 0004-6361 Institutional support: RVO:67985815 Keywords : galaxies * gravitation * kinematics and dynamic Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  18. The Atacama Cosmology Telescope: Detection or Sunyaev-Zel'Dovich Decrement in Groups and Clusters Associated with Luminous Red Galaxies

    Science.gov (United States)

    Hand, Nick; Appel, John William; Battaglia, Nick; Bond, J. Richard; Das, Sudeep; Devlin, Mark J.; Dunkley, Joanna; Dunner, Rolando; Essinger-Hileman, Thomas; Fowler, Joseph W.; hide

    2010-01-01

    We present a detection of the Sunyaev-Zel'dovich (SZ) decrement associated with the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey. The SZ data come from 148 GHz maps of the equatorial region made by the Atacama Cosmology Telescope (ACT). The LRG sample is divided by luminosity into four bins, and estimates for the central Sunyaev-Zel'dovich temperature decrement are calculated through a stacking process. We detect and account for a bias of the SZ signal due to weak radio sources. We use numerical simulations to relate the observed decrement to Y(sub 200) and clustering properties to relate the galaxy luminosity bins to mass. We also use a relation between BCG luminosity and cluster mass based on stacked gravitational lensing measurements to estimate the characteristic halo masses. The masses are found to be in the range approx.10(exp 13) - 10(exp 14)/h Stellar Mass, a lower range than has been previously probed.

  19. Hot Gas Halos in Galaxies

    Science.gov (United States)

    Mulchaey, John

    Most galaxy formation models predict that massive low-redshift disk galaxies are embedded in extended hot halos of externally accreted gas. Such gas appears necessary to maintain ongoing star formation in isolated spirals like the Milky Way. To explain the large population of red galaxies in rich groups and clusters, most galaxy evolution models assume that these hot gas halos are stripped completely when a galaxy enters a denser environment. This simple model has been remarkably successful at reproducing many observed properties of galaxies. Although theoretical arguments suggest hot gas halos are an important component in galaxies, we know very little about this gas from an observational standpoint. In fact, previous observations have failed to detect soft X-ray emission from such halos in disk galaxies. Furthermore, the assumption that hot gas halos are stripped completely when a galaxy enters a group or cluster has not been verified. We propose to combine proprietary and archival XMM-Newton observations of galaxies in the field, groups and clusters to study how hot gas halos are impacted by environment. Our proposed program has three components: 1) The deepest search to date for a hot gas halo in a quiescent spiral galaxy. A detection will confirm a basic tenet of disk galaxy formation models, whereas a non-detection will seriously challenge these models and impose new constraints on the growth mode and feedback history of disk galaxies. 2) A detailed study of the hot gas halos properties of field early-type galaxies. As environmental processes such as stripping are not expected to be important in the field, a study of hot gas halos in this environment will allow us to better understand how feedback and other internal processes impact hot gas halos. 3) A study of hot gas halos in the outskirts of groups and clusters. By comparing observations with our suite of simulations we can begin to understand what role the stripping of hot gas halos plays in galaxy

  20. Mental Health Support Groups, Stigma, and Self-Esteem : Positive and Negative Implications of Group Identification

    NARCIS (Netherlands)

    Crabtree, Jason W.; Haslam, S. Alexander; Postmes, Tom; Haslam, Catherine

    2010-01-01

    Research into the relationship between stigmatization and well-being suggests that identification with a stigmatized group can buffer individuals from the adverse effects of stigma. In part, this is because social identification is hypothesized to provide a basis for social support which increases

  1. Non-linear corrections to the cosmological matter power spectrum and scale-dependent galaxy bias: implications for parameter estimation

    International Nuclear Information System (INIS)

    Hamann, Jan; Hannestad, Steen; Melchiorri, Alessandro; Wong, Yvonne Y Y

    2008-01-01

    We explore and compare the performances of two non-linear correction and scale-dependent biasing models for the extraction of cosmological information from galaxy power spectrum data, especially in the context of beyond-ΛCDM (CDM: cold dark matter) cosmologies. The first model is the well known Q model, first applied in the analysis of Two-degree Field Galaxy Redshift Survey data. The second, the P model, is inspired by the halo model, in which non-linear evolution and scale-dependent biasing are encapsulated in a single non-Poisson shot noise term. We find that while the two models perform equally well in providing adequate correction for a range of galaxy clustering data in standard ΛCDM cosmology and in extensions with massive neutrinos, the Q model can give unphysical results in cosmologies containing a subdominant free-streaming dark matter whose temperature depends on the particle mass, e.g., relic thermal axions, unless a suitable prior is imposed on the correction parameter. This last case also exposes the danger of analytic marginalization, a technique sometimes used in the marginalization of nuisance parameters. In contrast, the P model suffers no undesirable effects, and is the recommended non-linear correction model also because of its physical transparency

  2. Non-linear corrections to the cosmological matter power spectrum and scale-dependent galaxy bias: implications for parameter estimation

    Science.gov (United States)

    Hamann, Jan; Hannestad, Steen; Melchiorri, Alessandro; Wong, Yvonne Y. Y.

    2008-07-01

    We explore and compare the performances of two non-linear correction and scale-dependent biasing models for the extraction of cosmological information from galaxy power spectrum data, especially in the context of beyond-ΛCDM (CDM: cold dark matter) cosmologies. The first model is the well known Q model, first applied in the analysis of Two-degree Field Galaxy Redshift Survey data. The second, the P model, is inspired by the halo model, in which non-linear evolution and scale-dependent biasing are encapsulated in a single non-Poisson shot noise term. We find that while the two models perform equally well in providing adequate correction for a range of galaxy clustering data in standard ΛCDM cosmology and in extensions with massive neutrinos, the Q model can give unphysical results in cosmologies containing a subdominant free-streaming dark matter whose temperature depends on the particle mass, e.g., relic thermal axions, unless a suitable prior is imposed on the correction parameter. This last case also exposes the danger of analytic marginalization, a technique sometimes used in the marginalization of nuisance parameters. In contrast, the P model suffers no undesirable effects, and is the recommended non-linear correction model also because of its physical transparency.

  3. Galaxy Formation

    DEFF Research Database (Denmark)

    Sparre, Martin

    Galaxy formation is an enormously complex discipline due to the many physical processes that play a role in shaping galaxies. The objective of this thesis is to study galaxy formation with two different approaches: First, numerical simulations are used to study the structure of dark matter and how...... galaxies form stars throughout the history of the Universe, and secondly it is shown that observations of gamma-ray bursts (GRBs) can be used to probe galaxies with active star formation in the early Universe. A conclusion from the hydrodynamical simulations is that the galaxies from the stateof...... is important, since it helps constraining chemical evolution models at high redshift. A new project studying how the population of galaxies hosting GRBs relate to other galaxy population is outlined in the conclusion of this thesis. The core of this project will be to quantify how the stellar mass function...

  4. THE FORNAX DWARF GALAXY AS A REMNANT OF RECENT DWARF-DWARF MERGING IN THE LOCAL GROUP

    International Nuclear Information System (INIS)

    Yozin, C.; Bekki, K.

    2012-01-01

    We present results from the first numerical analysis to support the hypothesis, first proposed in Coleman et al., that the Fornax dwarf galaxy was formed from the minor merging of two dwarfs about 2 Gyr ago. Using orbits for the Fornax dwarf that are consistent with the latest proper motion measurements, our dynamical evolution models show that the observed asymmetric shell-like substructures can be formed from the remnant of a smaller dwarf during minor merging. These models also predict the formation of diffuse stellar streams. We discuss how these stellar substructures depend on model parameters of dwarf-dwarf merging, and how the intermediate-age subpopulations found in the vicinity of these substructures may be formed from gas accretion in past merger events. We also suggest that one of Fornax's globular clusters originates from a merged dwarf companion, and demonstrate where as yet undetected tidal streams or H I gas formed from the dwarf merging may be found in the outer halo of the Galaxy.

  5. EVOLUTION OF THE GALAXY-DARK MATTER CONNECTION AND THE ASSEMBLY OF GALAXIES IN DARK MATTER HALOS

    Energy Technology Data Exchange (ETDEWEB)

    Yang Xiaohu; Zhang Youcai; Han Jiaxin [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Nandan Road 80, Shanghai 200030 (China); Mo, H. J. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305 (United States); Van den Bosch, Frank C., E-mail: xhyang@shao.ac.cn [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States)

    2012-06-10

    We present a new model to describe the galaxy-dark matter connection across cosmic time, which unlike the popular subhalo abundance-matching technique is self-consistent in that it takes account of the facts that (1) subhalos are accreted at different times and (2) the properties of satellite galaxies may evolve after accretion. Using observations of galaxy stellar mass functions (SMFs) out to z {approx} 4, the conditional SMF at z {approx} 0.1 obtained from Sloan Digital Sky Survey galaxy group catalogs, and the two-point correlation function (2PCF) of galaxies at z {approx} 0.1 as a function of stellar mass, we constrain the relation between galaxies and dark matter halos over the entire cosmic history from z {approx} 4 to the present. This relation is then used to predict the median assembly histories of different stellar mass components within dark matter halos (central galaxies, satellite galaxies, and halo stars). We also make predictions for the 2PCFs of high-z galaxies as function of stellar mass. Our main findings are the following: (1) Our model reasonably fits all data within the observational uncertainties, indicating that the {Lambda}CDM concordance cosmology is consistent with a wide variety of data regarding the galaxy population across cosmic time. (2) At low-z, the stellar mass of central galaxies increases with halo mass as M{sup 0.3} and M{sup {approx}>4.0} at the massive and low-mass ends, respectively. The ratio M{sub *,c}/M reveals a maximum of {approx}0.03 at a halo mass M {approx} 10{sup 11.8} h{sup -1} M{sub Sun }, much lower than the universal baryon fraction ({approx}0.17). At higher redshifts the maximum in M{sub *,c}/M remains close to {approx}0.03, but shifts to higher halo mass. (3) The inferred timescale for the disruption of satellite galaxies is about the same as the dynamical friction timescale of their subhalos. (4) The stellar mass assembly history of central galaxies is completely decoupled from the assembly history of its host

  6. Redshift distributions of galaxies in the Dark Energy Survey Science Verification shear catalogue and implications for weak lensing

    Energy Technology Data Exchange (ETDEWEB)

    Bonnett, C.; Troxel, M. A.; Hartley, W.; Amara, A.; Leistedt, B.; Becker, M. R.; Bernstein, G. M.; Bridle, S. L.; Bruderer, C.; Busha, M. T.; Carrasco Kind, M.; Childress, M. J.; Castander, F. J.; Chang, C.; Crocce, M.; Davis, T. M.; Eifler, T. F.; Frieman, J.; Gangkofner, C.; Gaztanaga, E.; Glazebrook, K.; Gruen, D.; Kacprzak, T.; King, A.; Kwan, J.; Lahav, O.; Lewis, G.; Lidman, C.; Lin, H.; MacCrann, N.; Miquel, R.; O’Neill, C. R.; Palmese, A.; Peiris, H. V.; Refregier, A.; Rozo, E.; Rykoff, E. S.; Sadeh, I.; Sánchez, C.; Sheldon, E.; Uddin, S.; Wechsler, R. H.; Zuntz, J.; Abbott, T.; Abdalla, F. B.; Allam, S.; Armstrong, R.; Banerji, M.; Bauer, A. H.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carretero, J.; Cunha, C. E.; D’Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Fausti Neto, A.; Fernandez, E.; Flaugher, B.; Fosalba, P.; Gerdes, D. W.; Gruendl, R. A.; Honscheid, K.; Jain, B.; James, D. J.; Jarvis, M.; Kim, A. G.; Kuehn, K.; Kuropatkin, N.; Li, T. S.; Lima, M.; Maia, M. A. G.; March, M.; Marshall, J. L.; Martini, P.; Melchior, P.; Miller, C. J.; Neilsen, E.; Nichol, R. C.; Nord, B.; Ogando, R.; Plazas, A. A.; Reil, K.; Romer, A. K.; Roodman, A.; Sako, M.; Sanchez, E.; Santiago, B.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, D.; Vikram, V.; Walker, A. R.

    2016-08-01

    We present photometric redshift estimates for galaxies used in the weak lensing analysis of the Dark Energy Survey Science Verification (DES SV) data. Four model- or machine learning-based photometric redshift methods { annz2, bpz calibrated against BCC-U fig simulations, skynet, and tpz { are analysed. For training, calibration, and testing of these methods, we also construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evalu-ated against the matched spectroscopic catalogue, focusing on metrics relevant for weak lensing analyses, with additional validation against COSMOS photo-zs. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72 ±0.01 over the range 0:3 < z < 1:3, we construct three tomographic bins with means of z = {0.45; 0.67,1.00g}. These bins each have systematic uncertainties δz ≲ 0.05 in the mean of the fiducial skynet photo-z n(z). We propagate the errors in the redshift distributions through to their impact on cosmological parameters estimated with cosmic shear, and find that they cause shifts in the value of σ8 of approx. 3%. This shift is within the one sigma statistical errors on σ8 for the DES SV shear catalog. We also found that further study of the potential impact of systematic differences on the critical surface density, Σcrit, contained levels of bias safely less than the statistical power of DES SV data. We recommend a final Gaussian prior for the photo-z bias in the mean of n(z) of width 0:05 for each of the three tomographic bins, and show that this is a sufficient bias model for the corresponding cosmology analysis.

  7. THE SELF-SIMILARITY OF THE CIRCUMGALACTIC MEDIUM WITH GALAXY VIRIAL MASS: IMPLICATIONS FOR COLD-MODE ACCRETION

    Energy Technology Data Exchange (ETDEWEB)

    Churchill, Christopher W.; Nielsen, Nikole M.; Trujillo-Gomez, Sebastian [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); Kacprzak, Glenn G. [Center for Astrophysics and Supercomputing, Swinburne University of Technology, Victoria 3122 (Australia)

    2013-02-01

    We apply halo abundance matching to obtain galaxy virial masses, M{sub h}, and radii, R{sub vir}, for 183 'isolated' galaxies from the 'Mg II Absorber-Galaxy Catalog'. All galaxies have spectroscopic redshifts (0.07 {<=} z {<=} 1.12) and their circumgalactic medium (CGM) is probed in Mg II absorption within projected galactocentric distances D {<=} 200 kpc. We examine the behavior of equivalent width, W{sub r} (2796), and covering fraction, f{sub c} , as a function of D, D/R{sub vir}, and M{sub h}. Bifurcating the sample at the median mass log M{sub h}/M{sub Sun} = 12, we find (1) systematic segregation of M{sub h} on the W{sub r} (2796)-D plane (4.0{sigma}); high-mass halos are found at higher D with larger W{sub r} (2796) compared to low-mass halos. On the W{sub r} (2796)-D/R{sub vir} plane, mass segregation vanishes and we find W{sub r} (2796){proportional_to}(D/R{sub vir}){sup -2} (8.9{sigma}). (2) High-mass halos have larger f{sub c} at a given D, whereas f{sub c} is independent of M{sub h} at all D/R{sub vir}. (3) f{sub c} is constant with M{sub h} over the range 10.7 {<=} log M{sub h}/M{sub Sun} {<=} 13.9 within a given D or D/R{sub vir}. The combined results suggest the Mg II absorbing CGM is self-similar with halo mass, even above log M{sub h}/M{sub Sun} {approx_equal} 12, where cold mode accretion is predicted to be quenched. If theory is correct, either outflows or sub-halos must contribute to absorption in high-mass halos such that low- and high-mass halos are observationally indistinguishable using Mg II absorption strength once impact parameter is scaled by halo mass. Alternatively, the data may indicate predictions of a universal shut down of cold-mode accretion in high-mass halos may require revision.

  8. Low mass X-ray binaries in the Inner Galaxy: implications for millisecond pulsars and the GeV excess

    Energy Technology Data Exchange (ETDEWEB)

    Haggard, Daryl; Heinke, Craig; Hooper, Dan; Linden, Tim

    2017-05-01

    If millisecond pulsars (MSPs) are responsible for the excess gamma-ray emission observed from the region surrounding the Galactic Center, the same region should also contain a large population of low-mass X-ray binaries (LMXBs). In this study, we compile and utilize a sizable catalog of LMXBs observed in the the Milky Way's globular cluster system and in the Inner Galaxy, as well as the gamma-ray emission observed from globular clusters, to estimate the flux of gamma rays predicted from MSPs in the Inner Galaxy. From this comparison, we conclude that only up to $\\sim$4-23% of the observed gamma-ray excess is likely to originate from MSPs. This result is consistent with, and more robust than, previous estimates which utilized smaller samples of both globular clusters and LMXBs. If MSPs had been responsible for the entirety of the observed excess, INTEGRAL should have detected $\\sim$$10^3$ LMXBs from within a $10^{\\circ}$ radius around the Galactic Center, whereas only 42 LMXBs (and 46 additional LMXB candidates) have been observed.

  9. The dynamics of aggregates of galaxies as related to their main galaxies

    International Nuclear Information System (INIS)

    Einasto, J.; Joeveer, M.; Kaasik, A.; Vennik, J.

    1976-01-01

    The dynamics of the aggregates of galaxies is compared with the dynamics of their member galaxies. It is demonstrated that within a factor 1.5-2 the dispersion of relative line-of-sight velocities is constant from the nuclei of main galaxies to the periphery of an aggregate. This isothermality of aggregates of galaxies is observed in all aggregates studied so far, from poor groups to rich clusters. The fact that the velocity dispersion of stars in galaxies is equal to that of galaxies in aggregates applies only to main galaxies. The stars in all companion galaxies have a smaller velocity dispersion of stars. The dynamical evolution of both galaxies and aggregates of galaxies is very slow. Thus the above data suggest that galaxies and their aggregates were formed together. (orig.) [de

  10. Reference group theory with implications for information studies: a theoretical essay

    Directory of Open Access Journals (Sweden)

    E. Murell Dawson

    2001-01-01

    Full Text Available This article explores the role and implications of reference group theory in relation to the field of library and information science. Reference group theory is based upon the principle that people take the standards of significant others as a basis for making self-appraisals, comparisons, and choices regarding need and use of information. Research that applies concepts of reference group theory to various sectors of library and information studies can provide data useful in enhancing areas such as information-seeking research, special populations, and uses of information. Implications are promising that knowledge gained from like research can be beneficial in helping information professionals better understand the role theory plays in examining ways in which people manage their information and social worlds.

  11. Implications for Primordial Non-Gaussianity ($f_{NL}$) from weak lensing masses of high-z galaxy clusters

    CERN Document Server

    Jimenez, Raul

    2009-01-01

    The recent weak lensing measurement of the dark matter mass of the high-redshift galaxy cluster XMMUJ2235.3-2557 of (8.5 +- 1.7) x 10^{14} Msun at z=1.4, indicates that, if the cluster is assumed to be the result of the collapse of dark matter in a primordial gaussian field in the standard LCDM model, then its abundance should be 3-10 if the non-Gaussianity parameter f^local_NL is in the range 150-200. This value is comparable to the limit for f_NL obtained by current constraints from the CMB. We conclude that mass determination of high-redshift, massive clusters can offer a complementary probe of primordial non-gaussianity.

  12. Galaxy formation

    International Nuclear Information System (INIS)

    Gribbin, J.

    1979-01-01

    The current debate on the origin and evolution of galaxies is reviewed and evidence to support the so-called 'isothermal' and 'adiabatic' fluctuation models considered. It is shown that new theories have to explain the formation of both spiral and elliptical galaxies and the reason for their differences. It is stated that of the most recent models the best indicates that rotating spiral galaxies are formed naturally when gas concentrates in the centre of a great halo and forms stars while ellipticals are explained by later interactions between spiral galaxies and merging, which can cancel out the rotation while producing an elliptical galaxy in which the stars, coming from two original galaxies, follow very elliptical, anisotropic orbits. (UK)

  13. The Pan-STARRS1 medium-deep survey: The role of galaxy group environment in the star formation rate versus stellar mass relation and quiescent fraction out to z ∼ 0.8

    International Nuclear Information System (INIS)

    Lin, Lihwai; Chen, Chin-Wei; Coupon, Jean; Hsieh, Bau-Ching; Jian, Hung-Yu; Foucaud, Sebastien; Norberg, Peder; Bower, R. G.; Cole, Shaun; Arnalte-Mur, Pablo; Draper, P.; Heinis, Sebastien; Phleps, Stefanie; Chen, Wen-Ping; Lee, Chien-Hsiu; Burgett, William; Chambers, K. C.; Denneau, L.; Flewelling, H.; Hodapp, K. W.

    2014-01-01

    Using a large optically selected sample of field and group galaxies drawn from the Pan-STARRS1 Medium-Deep Survey (PS1/MDS), we present a detailed analysis of the specific star formation rate (SSFR)—stellar mass (M * ) relation, as well as the quiescent fraction versus M * relation in different environments. While both the SSFR and the quiescent fraction depend strongly on stellar mass, the environment also plays an important role. Using this large galaxy sample, we confirm that the fraction of quiescent galaxies is strongly dependent on environment at a fixed stellar mass, but that the amplitude and the slope of the star-forming sequence is similar between the field and groups: in other words, the SSFR-density relation at a fixed stellar mass is primarily driven by the change in the star-forming and quiescent fractions between different environments rather than a global suppression in the star formation rate for the star-forming population. However, when we restrict our sample to the cluster-scale environments (M > 10 14 M ☉ ), we find a global reduction in the SSFR of the star-forming sequence of 17% at 4σ confidence as opposed to its field counterpart. After removing the stellar mass dependence of the quiescent fraction seen in field galaxies, the excess in the quiescent fraction due to the environment quenching in groups and clusters is found to increase with stellar mass, although deeper and larger data from the full PS1/MDS will be required to draw firm conclusions. We argue that these results are in favor of galaxy mergers to be the primary environment quenching mechanism operating in galaxy groups whereas strangulation is able to reproduce the observed trend in the environment quenching efficiency and stellar mass relation seen in clusters. Our results also suggest that the relative importance between mass quenching and environment quenching depends on stellar mass—the mass quenching plays a dominant role in producing quiescent galaxies for more

  14. The Pan-STARRS1 medium-deep survey: The role of galaxy group environment in the star formation rate versus stellar mass relation and quiescent fraction out to z ∼ 0.8

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Lihwai; Chen, Chin-Wei; Coupon, Jean; Hsieh, Bau-Ching [Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan, R.O.C. (China); Jian, Hung-Yu [Department of Physics, National Taiwan University, Taipei 106, Taiwan, R.O.C. (China); Foucaud, Sebastien [Department of Earth Sciences, National Taiwan Normal University, N°88, Tingzhou Road, Sec. 4, Taipei 11677, Taiwan, R.O.C. (China); Norberg, Peder; Bower, R. G.; Cole, Shaun; Arnalte-Mur, Pablo; Draper, P. [Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Heinis, Sebastien [Department of Astronomy, University of Maryland, MD 20742 (United States); Phleps, Stefanie [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, D-85748 Garching (Germany); Chen, Wen-Ping [Graduate Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan, R.O.C. (China); Lee, Chien-Hsiu [University Observatory Munich, Scheinerstrasse 1, D-81679 Munich (Germany); Burgett, William; Chambers, K. C.; Denneau, L.; Flewelling, H.; Hodapp, K. W., E-mail: lihwailin@asiaa.sinica.edu.tw [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); and others

    2014-02-10

    Using a large optically selected sample of field and group galaxies drawn from the Pan-STARRS1 Medium-Deep Survey (PS1/MDS), we present a detailed analysis of the specific star formation rate (SSFR)—stellar mass (M {sub *}) relation, as well as the quiescent fraction versus M {sub *} relation in different environments. While both the SSFR and the quiescent fraction depend strongly on stellar mass, the environment also plays an important role. Using this large galaxy sample, we confirm that the fraction of quiescent galaxies is strongly dependent on environment at a fixed stellar mass, but that the amplitude and the slope of the star-forming sequence is similar between the field and groups: in other words, the SSFR-density relation at a fixed stellar mass is primarily driven by the change in the star-forming and quiescent fractions between different environments rather than a global suppression in the star formation rate for the star-forming population. However, when we restrict our sample to the cluster-scale environments (M > 10{sup 14} M {sub ☉}), we find a global reduction in the SSFR of the star-forming sequence of 17% at 4σ confidence as opposed to its field counterpart. After removing the stellar mass dependence of the quiescent fraction seen in field galaxies, the excess in the quiescent fraction due to the environment quenching in groups and clusters is found to increase with stellar mass, although deeper and larger data from the full PS1/MDS will be required to draw firm conclusions. We argue that these results are in favor of galaxy mergers to be the primary environment quenching mechanism operating in galaxy groups whereas strangulation is able to reproduce the observed trend in the environment quenching efficiency and stellar mass relation seen in clusters. Our results also suggest that the relative importance between mass quenching and environment quenching depends on stellar mass—the mass quenching plays a dominant role in producing quiescent

  15. Galaxies in x-ray selected clusters and groups in Dark Energy Survey Data I: Stellar mass growth of bright central galaxies since Z similar to 1.2

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Y.; Miller, C.; McKay, T.; Rooney, P.; Evrard, A. E.; Romer, A. K.; Perfecto, R.; Song, J; Desai, S.; Mohr, J. J.; Vikram, V.

    2016-01-10

    Using the science verification data of the Dark Energy Survey for a new sample of 106 X-ray selected clusters and groups, we study the stellar mass growth of bright central galaxies (BCGs) since redshift z similar to 1.2. Compared with the expectation in a semi-analytical model applied to the Millennium Simulation, the observed BCGs become under-massive/under-luminous with decreasing redshift. We incorporate the uncertainties associated with cluster mass, redshift, and BCG stellar mass measurements into an analysis of a redshift-dependent BCG-cluster mass relation, m(*) proportional to (M-200/1.5 x 10(14)M(circle dot))(0.24 +/- 0.08)(1+z)(-0.19 +/- 0.34), and compare the observed relation to the model prediction. We estimate the average growth rate since z = 1.0 for BCGs hosted by clusters of M-200,M-z = 10(13.8)M(circle dot); at z = 1.0: m(*, BCG) appears to have grown by 0.13 +/- 0.11 dex, in tension at the similar to 2.5 sigma significance level with the 0.40 dex growth rate expected from the semi-analytic model. We show that the build-up of extended intracluster light after z = 1.0 may alleviate this tension in BCG growth rates.

  16. Comparative Genomics of the Bacterial Genus Streptococcus Illuminates Evolutionary Implications of Species Groups

    Science.gov (United States)

    Gao, Xiao-Yang; Zhi, Xiao-Yang; Li, Hong-Wei; Klenk, Hans-Peter; Li, Wen-Jun

    2014-01-01

    Members of the genus Streptococcus within the phylum Firmicutes are among the most diverse and significant zoonotic pathogens. This genus has gone through considerable taxonomic revision due to increasing improvements of chemotaxonomic approaches, DNA hybridization and 16S rRNA gene sequencing. It is proposed to place the majority of streptococci into “species groups”. However, the evolutionary implications of species groups are not clear presently. We use comparative genomic approaches to yield a better understanding of the evolution of Streptococcus through genome dynamics, population structure, phylogenies and virulence factor distribution of species groups. Genome dynamics analyses indicate that the pan-genome size increases with the addition of newly sequenced strains, while the core genome size decreases with sequential addition at the genus level and species group level. Population structure analysis reveals two distinct lineages, one including Pyogenic, Bovis, Mutans and Salivarius groups, and the other including Mitis, Anginosus and Unknown groups. Phylogenetic dendrograms show that species within the same species group cluster together, and infer two main clades in accordance with population structure analysis. Distribution of streptococcal virulence factors has no obvious patterns among the species groups; however, the evolution of some common virulence factors is congruous with the evolution of species groups, according to phylogenetic inference. We suggest that the proposed streptococcal species groups are reasonable from the viewpoints of comparative genomics; evolution of the genus is congruent with the individual evolutionary trajectories of different species groups. PMID:24977706

  17. A SPECTROSCOPICALLY CONFIRMED EXCESS OF 24 μm SOURCES IN A SUPER GALAXY GROUP AT z = 0.37: ENHANCED DUSTY STAR FORMATION RELATIVE TO THE CLUSTER AND FIELD ENVIRONMENT

    International Nuclear Information System (INIS)

    Tran, Kim-Vy H.; Saintonge, Amelie; Moustakas, John; Bai, Lei; Zaritsky, Dennis; Gonzalez, Anthony H.; Kautsch, Stefan J.; Holden, Bradford P.

    2009-01-01

    To trace how dust-obscured star formation varies with environment, we compare the fraction of 24 μm sources in a super galaxy group to the field and a rich galaxy cluster at z ∼ 0.35. We draw on multi-wavelength observations 9 Based on observations made with (1) The ESO telescopes at Paranal Observatories under program IDs 072.A-0367, 076.B-0362, 078.B-0409; (2) the NASA/ESA Hubble Space Telescope (GO-10499); STScI is operated by the association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555; (3) the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA; support for this work was provided by NASA through an award issued by JPL/Caltech (GO-20683); (4) the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060; and (5) the Magellan 6.5 m telescope operated by OCIW. that combine Hubble, Chandra, and Spitzer imaging with extensive optical spectroscopy (>1800 redshifts) to isolate galaxies in each environment and thus ensure a uniform analysis. We focus on the four galaxy groups (σ 1D = 303-580 km s -1 ) in supergroup 1120-12 that will merge to form a galaxy cluster comparable in mass to Coma. We find that (1) the fraction of supergroup galaxies with SFR IR ≥ 3 M sun yr -1 is 4 times higher than in the cluster (32% ± 5% versus 7% ± 2%); (2) the supergroup's infrared luminosity function confirms that it has a higher density of IR members compared to the cluster and includes bright IR sources (log(L IR )[erg s -1 ] >45) not found in galaxy clusters at z ∼ * )[M sun ] IR ≥ 3 M sun yr -1 members that are outside the group cores (R proj ≥ 0.5 Mpc); once their star formation is quenched, most will evolve into faint red galaxies. Our analysis indicates that the supergroup's 24 μm population also differs from

  18. The (Biological or Cultural) Essence of Essentialism: Implications for Policy Support among Dominant and Subordinated Groups.

    Science.gov (United States)

    Soylu Yalcinkaya, Nur; Estrada-Villalta, Sara; Adams, Glenn

    2017-01-01

    Most research links (racial) essentialism to negative intergroup outcomes. We propose that this conclusion reflects both a narrow conceptual focus on biological/genetic essence and a narrow research focus from the perspective of racially dominant groups. We distinguished between beliefs in biological and cultural essences, and we investigated the implications of this distinction for support of social justice policies (e.g., affirmative action) among people with dominant (White) and subordinated (e.g., Black, Latino) racial identities in the United States. Whereas, endorsement of biological essentialism may have similarly negative implications for social justice policies across racial categories, we investigated the hypothesis that endorsement of cultural essentialism would have different implications across racial categories. In Studies 1a and 1b, we assessed the properties of a cultural essentialism measure we developed using two samples with different racial/ethnic compositions. In Study 2, we collected data from 170 participants using an online questionnaire to test the implications of essentialist beliefs for policy support. Consistent with previous research, we found that belief in biological essentialism was negatively related to policy support for participants from both dominant and subordinated categories. In contrast, the relationship between cultural essentialism and policy support varied across identity categories in the hypothesized way: negative for participants from the dominant category but positive for participants from subordinated categories. Results suggest that cultural essentialism may provide a way of identification that subordinated communities use to mobilize support for social justice.

  19. The (Biological or Cultural Essence of Essentialism: Implications for Policy Support among Dominant and Subordinated Groups

    Directory of Open Access Journals (Sweden)

    Nur Soylu Yalcinkaya

    2017-05-01

    Full Text Available Most research links (racial essentialism to negative intergroup outcomes. We propose that this conclusion reflects both a narrow conceptual focus on biological/genetic essence and a narrow research focus from the perspective of racially dominant groups. We distinguished between beliefs in biological and cultural essences, and we investigated the implications of this distinction for support of social justice policies (e.g., affirmative action among people with dominant (White and subordinated (e.g., Black, Latino racial identities in the United States. Whereas, endorsement of biological essentialism may have similarly negative implications for social justice policies across racial categories, we investigated the hypothesis that endorsement of cultural essentialism would have different implications across racial categories. In Studies 1a and 1b, we assessed the properties of a cultural essentialism measure we developed using two samples with different racial/ethnic compositions. In Study 2, we collected data from 170 participants using an online questionnaire to test the implications of essentialist beliefs for policy support. Consistent with previous research, we found that belief in biological essentialism was negatively related to policy support for participants from both dominant and subordinated categories. In contrast, the relationship between cultural essentialism and policy support varied across identity categories in the hypothesized way: negative for participants from the dominant category but positive for participants from subordinated categories. Results suggest that cultural essentialism may provide a way of identification that subordinated communities use to mobilize support for social justice.

  20. Nature vs. nurture in the low-density environment: structure and evolution of early-type dwarf galaxies in poor groups

    Science.gov (United States)

    Annibali, F.; Grützbauch, R.; Rampazzo, R.; Bressan, A.; Zeilinger, W. W.

    2011-04-01

    We present the stellar population properties of 13 dwarf galaxies residing in poor groups (low-density environment, LDE) observed with VIMOS at VLT. Ages, metallicities, and [α/Fe] ratios were derived within an r < re/2 aperture from the Lick indices Hβ, Mgb, Fe5270, and Fe5335 through comparison with our simple stellar population (SSP) models that account for variable [α/Fe] ratios. For a fiducial subsample of 10 early-type dwarfs, we derived median values and scatters around the medians of 5.7 ± 4.4 Gyr, -0.26 ± 0.28, and -0.04 ± 0.33 for age, log Z/Z⊙, and [α/Fe] , respectively. For a selection of bright early-type galaxies (ETGs) from an earlier sample residing in a comparable environment, we derive median values of 9.8 ± 4.1 Gyr, 0.06 ± 0.16, and 0.18 ± 0.13 for the same stellar population parameters. It follows that dwarfs are on average younger, less metal rich, and less enhanced in the α-elements than giants, in agreement with the extrapolation to the low-mass regime of the scaling relations derived for giant ETGs. From the total (dwarf + giant) sample, we find that age ∝ σ0.39 ± 0.22, Z ∝ σ0.80 ± 0.16, and α/Fe ∝ σ0.42 ± 0.22. We also find correlations with morphology, in the sense that the metallicity and the [α/Fe] ratio increase with the Sersic index n or with the bulge-to-total light fraction B/T. The presence of a strong morphology-[α/Fe] relation appears to contradict the possible evolution along the Hubble sequence from low B/T (low n) to high B/T (high n) galaxies. We also investigate the role played by environment by comparing the properties of our LDE dwarfs with those of Coma red passive dwarfs from the literature. We find possible evidence that LDE dwarfs experienced more prolonged star formations than Coma dwarfs, however larger data samples are needed to draw firmer conclusions. Based on observations obtained at the European Southern Observatory, La Silla, Chile.

  1. Interstellar matter within elliptical galaxies

    Science.gov (United States)

    Jura, Michael

    1988-01-01

    Multiwavelength observations of elliptical galaxies are reviewed, with an emphasis on their implications for theoretical models proposed to explain the origin and evolution of the interstellar matter. Particular attention is given to interstellar matter at T less than 100 K (atomic and molecular gas and dust), gas at T = about 10,000 K, and gas at T = 10 to the 6th K or greater. The data are shown to confirm the occurrence of mass loss from evolved stars, significant accretion from companion galaxies, and cooling inflows; no evidence is found for large mass outflow from elliptical galaxies.

  2. Galaxy formation

    International Nuclear Information System (INIS)

    Silk, J.; Di Cintio, A.; Dvorkin, I.

    2014-01-01

    Galaxy formation is at the forefront of observation and theory in cosmology. An improved understanding is essential for improving our knowledge both of the cosmological parameters, of the contents of the universe, and of our origins. In these lectures intended for graduate students, galaxy formation theory is reviewed and confronted with recent observational issues. In lecture 1, the following topics are presented: star formation considerations, including IMF, star formation efficiency and star formation rate, the origin of the galaxy luminosity function, and feedback in dwarf galaxies. In lecture 2, we describe formation of disks and massive spheroids, including the growth of supermassive black holes, negative feedback in spheroids, the AGN-star formation connection, star formation rates at high redshift and the baryon fraction in galaxies.

  3. The Milky Way galaxy

    International Nuclear Information System (INIS)

    Woerden, H. van; Allen, R.J.; Burton, W.B.

    1985-01-01

    IAU Symposium 106, held at the Kapteyn Institute in Groningen, presents an overview of all major aspects of galactic astronomy. The vast subject is covered in 20 authoritative review papers and 22 invited papers, each with discussion, plus 81 shorter contributions. The book opens with 4 reviews by historians of science, outlining the history of galactic research. Part 2 deals with (i) galactic rotation, (ii) the large-scale distributions of matter, of both old and young stellar populations, and of the atomic, molecular and high-energy components of the interstellar medium, (iii) small-scale structure in the gas, (iv) the galactic nucleus, (v) the high-velocity clouds. Part 3 discusses the dynamics of the local group of Galaxies and of the Milky Way-Magellanic clouds system, the dynamical and chemical evolution of the Galaxy and of its disk and halo components and the formation of the Galaxy. The controversial subject of spiral structure and star formation is analyzed in several extensive reviews and lively discussions, featuring both observational and theoretical developments. Results of extragalactic research are blended with studies of our Galaxy throughout the book, and there is a separate comparison between Andromeda and Milky Way Galaxies. The Symposium featured the first maps produced by IRAS, and results from most major telescopes in a variety of wavebands. Many review papers present material not published elsewhere. The book closes with a lecture on life in the Galaxy and with an imaginative symposium summary. (orig.)

  4. THE DISTRIBUTION OF FAINT SATELLITES AROUND CENTRAL GALAXIES IN THE CANADA-FRANCE-HAWAII TELESCOPE LEGACY SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, C. Y.; Jing, Y. P.; Li, Cheng [Key Laboratory for Research in Galaxies and Cosmology of Chinese Academy of Sciences, Shanghai Astronomical Observatory, Nandan Road 80, Shanghai 200030 (China)

    2012-11-20

    We investigate the radial number density profile and the abundance distribution of faint satellites around central galaxies in the low-redshift universe using the Canada-France-Hawaii Telescope (CFHT) Legacy Survey. We consider three samples of central galaxies with magnitudes of M {sub r} = -21, -22, and -23 selected from the Sloan Digital Sky Survey group catalog of Yang et al. The satellite distribution around these central galaxies is obtained by cross-correlating these galaxies with the photometric catalog of the CFHT Legacy Survey. The projected radial number density of the satellites obeys a power-law form with the best-fit logarithmic slope of -1.05, independent of both the central galaxy luminosity and the satellite luminosity. The projected cross-correlation function between central and satellite galaxies exhibits a non-monotonic trend with satellite luminosity. It is most pronounced for central galaxies with M {sub r} = -21, where the decreasing trend of clustering amplitude with satellite luminosity is reversed when satellites are fainter than central galaxies by more than 2 mag. A comparison with the satellite luminosity functions in the Milky Way (MW) and M31 shows that the MW/M31 system has about twice as many satellites as around a typical central galaxy of similar luminosity. The implications for theoretical models are briefly discussed.

  5. Growing Galaxies Gently

    Science.gov (United States)

    2010-10-01

    New observations from ESO's Very Large Telescope have, for the first time, provided direct evidence that young galaxies can grow by sucking in the cool gas around them and using it as fuel for the formation of many new stars. In the first few billion years after the Big Bang the mass of a typical galaxy increased dramatically and understanding why this happened is one of the hottest problems in modern astrophysics. The results appear in the 14 October issue of the journal Nature. The first galaxies formed well before the Universe was one billion years old and were much smaller than the giant systems - including the Milky Way - that we see today. So somehow the average galaxy size has increased as the Universe has evolved. Galaxies often collide and then merge to form larger systems and this process is certainly an important growth mechanism. However, an additional, gentler way has been proposed. A European team of astronomers has used ESO's Very Large Telescope to test this very different idea - that young galaxies can also grow by sucking in cool streams of the hydrogen and helium gas that filled the early Universe and forming new stars from this primitive material. Just as a commercial company can expand either by merging with other companies, or by hiring more staff, young galaxies could perhaps also grow in two different ways - by merging with other galaxies or by accreting material. The team leader, Giovanni Cresci (Osservatorio Astrofisico di Arcetri) says: "The new results from the VLT are the first direct evidence that the accretion of pristine gas really happened and was enough to fuel vigorous star formation and the growth of massive galaxies in the young Universe." The discovery will have a major impact on our understanding of the evolution of the Universe from the Big Bang to the present day. Theories of galaxy formation and evolution may have to be re-written. The group began by selecting three very distant galaxies to see if they could find evidence

  6. ELEMENTAL ABUNDANCES AND THEIR IMPLICATIONS FOR THE CHEMICAL ENRICHMENT OF THE BOOeTES I ULTRAFAINT GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Gilmore, Gerard [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Norris, John E.; Yong, David [Research School of Astronomy and Astrophysics, The Australian National University, Weston, ACT 2611 (Australia); Monaco, Lorenzo [European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19 (Chile); Wyse, Rosemary F. G. [Department of Physics and Astronomy, The Johns Hopkins University, 3900 North Charles Street, Baltimore, MD 21218 (United States); Geisler, D., E-mail: gil@ast.cam.ac.uk, E-mail: jen@mso.anu.edu.au, E-mail: yong@mso.anu.edu.au, E-mail: lmonaco@eso.org, E-mail: wyse@pha.jhu.edu, E-mail: dgeisler@astro-udec.cl [Departamento de Astronomia, Universidad de Concepcion (Chile)

    2013-01-20

    We present a double-blind analysis of high-dispersion spectra of seven red giant members of the Booetes I ultrafaint dwarf spheroidal galaxy, complemented with re-analysis of a similar spectrum of an eighth-member star. The stars cover [Fe/H] from -3.7 to -1.9 and include a CEMP-no star with [Fe/H] = -3.33. We conclude from our chemical abundance data that Booetes I has evolved as a self-enriching star-forming system, from essentially primordial initial abundances. This allows us uniquely to investigate the place of CEMP-no stars in a chemically evolving system, in addition to limiting the timescale of star formation. The elemental abundances are formally consistent with a halo-like distribution, with enhanced mean [{alpha}/Fe] and small scatter about the mean. This is in accord with the high-mass stellar initial mass function in this low-stellar-density, low-metallicity system being indistinguishable from the present-day solar neighborhood value. There is a non-significant hint of a decline in [{alpha}/Fe] with [Fe/H]; together with the low scatter, this requires low star formation rates, allowing time for supernova ejecta to be mixed over the large spatial scales of interest. One star has very high [Ti/Fe], but we do not confirm a previously published high value of [Mg/Fe] for another star. We discuss the existence of CEMP-no stars, and the absence of any stars with lower CEMP-no enhancements at higher [Fe/H], a situation that is consistent with knowledge of CEMP-no stars in the Galactic field. We show that this observation requires there be two enrichment paths at very low metallicities: CEMP-no and 'carbon-normal'.

  7. ELEMENTAL ABUNDANCES AND THEIR IMPLICATIONS FOR THE CHEMICAL ENRICHMENT OF THE BOÖTES I ULTRAFAINT GALAXY

    International Nuclear Information System (INIS)

    Gilmore, Gerard; Norris, John E.; Yong, David; Monaco, Lorenzo; Wyse, Rosemary F. G.; Geisler, D.

    2013-01-01

    We present a double-blind analysis of high-dispersion spectra of seven red giant members of the Boötes I ultrafaint dwarf spheroidal galaxy, complemented with re-analysis of a similar spectrum of an eighth-member star. The stars cover [Fe/H] from –3.7 to –1.9 and include a CEMP-no star with [Fe/H] = –3.33. We conclude from our chemical abundance data that Boötes I has evolved as a self-enriching star-forming system, from essentially primordial initial abundances. This allows us uniquely to investigate the place of CEMP-no stars in a chemically evolving system, in addition to limiting the timescale of star formation. The elemental abundances are formally consistent with a halo-like distribution, with enhanced mean [α/Fe] and small scatter about the mean. This is in accord with the high-mass stellar initial mass function in this low-stellar-density, low-metallicity system being indistinguishable from the present-day solar neighborhood value. There is a non-significant hint of a decline in [α/Fe] with [Fe/H]; together with the low scatter, this requires low star formation rates, allowing time for supernova ejecta to be mixed over the large spatial scales of interest. One star has very high [Ti/Fe], but we do not confirm a previously published high value of [Mg/Fe] for another star. We discuss the existence of CEMP-no stars, and the absence of any stars with lower CEMP-no enhancements at higher [Fe/H], a situation that is consistent with knowledge of CEMP-no stars in the Galactic field. We show that this observation requires there be two enrichment paths at very low metallicities: CEMP-no and 'carbon-normal'.

  8. Stars at Low Metallicity in Dwarf Galaxies

    NARCIS (Netherlands)

    Tolstoy, Eline; Battaglia, Giuseppina; Cole, Andrew; Hunt, LK; Madden, S; Schneider, R

    2008-01-01

    Dwarf galaxies offer an opportunity to understand the properties of low metallicity star formation both today and at the earliest times at the, epoch of the formation of the first stars. Here we concentrate on two galaxies in the Local Group: the dwarf irregular galaxy Leo A, which has been the

  9. A MINUET OF GALAXIES

    Science.gov (United States)

    2002-01-01

    This troupe of four galaxies, known as Hickson Compact Group 87 (HCG 87), is performing an intricate dance orchestrated by the mutual gravitational forces acting between them. The dance is a slow, graceful minuet, occurring over a time span of hundreds of millions of years. The Wide Field and Planetary Camera 2 on NASA's Hubble Space Telescope (HST) provides a striking improvement in resolution over previous ground-based imaging. In particular, this image reveals complex details in the dust lanes of the group's largest galaxy member (HCG 87a), which is actually disk-shaped, but tilted so that we see it nearly edge-on. Both 87a and its elliptically shaped nearest neighbor (87b) have active galactic nuclei which are believed to harbor black holes that are consuming gas. A third group member, the nearby spiral galaxy 87c, may be undergoing a burst of active star formation. Gas flows within galaxies can be intensified by the gravitational tidal forces between interacting galaxies. So interactions can provide fresh fuel for both active nuclei and starburst phenomena. These three galaxies are so close to each other that gravitational forces disrupt their structure and alter their evolution. From the analysis of its spectra, the small spiral near the center of the group could either be a fourth member or perhaps an unrelated background object. The HST image was made by combining images taken in four different color filters in order to create a three-color picture. Regions of active star formation are blue (hot stars) and also pinkish if hot hydrogen gas is present. The complex dark bands across the large edge-on disk galaxy are due to interstellar dust silhouetted against the galaxy's background starlight. A faint tidal bridge of stars can be seen between the edge-on and elliptical galaxies. HCG 87 was selected for Hubble imaging by members of the public who visited the Hubble Heritage website (http://heritage.stsci.edu) during the month of May and registered their votes

  10. The Next Generation Virgo Cluster Survey. VII. The Intrinsic Shapes of Low-luminosity Galaxies in the Core of the Virgo Cluster, and a Comparison with the Local Group

    Science.gov (United States)

    Sánchez-Janssen, Rubén; Ferrarese, Laura; MacArthur, Lauren A.; Côté, Patrick; Blakeslee, John P.; Cuillandre, Jean-Charles; Duc, Pierre-Alain; Durrell, Patrick; Gwyn, Stephen; McConnacchie, Alan W.; Boselli, Alessandro; Courteau, Stéphane; Emsellem, Eric; Mei, Simona; Peng, Eric; Puzia, Thomas H.; Roediger, Joel; Simard, Luc; Boyer, Fred; Santos, Matthew

    2016-03-01

    We investigate the intrinsic shapes of low-luminosity galaxies in the central 300 kpc of the Virgo Cluster using deep imaging obtained as part of the Next Generation Virgo Cluster Survey (NGVS). We build a sample of nearly 300 red-sequence cluster members in the yet-unexplored -14 families of triaxial models with normally distributed intrinsic ellipticities, E = 1 - C/A, and triaxialities, T = (A2 - B2)/(A2 - C2). We develop a Bayesian framework to explore the posterior distribution of the model parameters, which allows us to work directly on discrete data, and to account for individual, surface-brightness-dependent axis ratio uncertainties. For this population we infer a mean intrinsic ellipticity \\bar{E} = {0.43}-0.02+0.02 and a mean triaxiality \\bar{T} = {0.16}-0.06+0.07. This implies that faint Virgo galaxies are best described as a family of thick, nearly oblate spheroids with mean intrinsic axis ratios 1:0.94:0.57. The core of Virgo lacks highly elongated low-luminosity galaxies, with 95% of the population having q > 0.45. We additionally attempt a study of the intrinsic shapes of Local Group (LG) satellites of similar luminosities. For the LG population we infer a slightly larger mean intrinsic ellipticity \\bar{E} = {0.51}-0.06+0.07, and the paucity of objects with round apparent shapes translates into more triaxial mean shapes, 1:0.76:0.49. Numerical studies that follow the tidal evolution of satellites within LG-sized halos are in good agreement with the inferred shape distributions, but the mismatch for faint galaxies in Virgo highlights the need for more adequate simulations of this population in the cluster environment. We finally compare the intrinsic shapes of NGVS low-mass galaxies with samples of more massive quiescent systems, and with field, star-forming galaxies of similar luminosities. We find that the intrinsic flattening in this low-luminosity regime is almost independent of the environment in which the galaxy resides, but there is a hint

  11. How groups co-ordinate their concepts and terminology: implications for medical informatics.

    Science.gov (United States)

    Garrod, S

    1998-11-01

    Conceptual and terminological systems are established and maintained by the communities who use them. This paper reports experiments which investigate the role of communication and interaction in the process. The experiments show that isolated pairs of communicators and virtual communities of interacting pairs naturally converge on their own conceptual and terminological systems when confronted with a common task. The results also indicate that the system converged on is optimal for that particular group engaged in that particular task. These findings are discussed in relation to the increasing use of tightly coordinated medical teams and its implications for getting them to adopt standardized medical terminologies.

  12. THE SUPERNOVA DELAY TIME DISTRIBUTION IN GALAXY CLUSTERS AND IMPLICATIONS FOR TYPE-Ia PROGENITORS AND METAL ENRICHMENT

    International Nuclear Information System (INIS)

    Maoz, Dan; Sharon, Keren; Avishay Gal-Yam

    2010-01-01

    Knowledge of the supernova (SN) delay time distribution (DTD)-the SN rate versus time that would follow a hypothetical brief burst of star formation-can shed light on SN progenitors and physics, as well as on the timescales of chemical enrichment in different environments. We compile recent measurements of the Type-Ia SN (SN Ia) rate in galaxy clusters at redshifts from z = 0 out to z = 1.45, just 2 Gyr after cluster star formation at z ∼ 3. We review the plausible range for the observed total iron-to-stellar mass ratio in clusters, based on the latest data and analyses, and use it to constrain the time-integrated number of SN Ia events in clusters. With these data, we recover the DTD of SNe Ia in cluster environments. The DTD is sharply peaked at the shortest time-delay interval we probe, 0Gyr -1.2±0.3 from t = 400 Myr to a Hubble time can satisfy both constraints. Shallower power laws such as t -1/2 cannot, assuming a single DTD, and a single star formation burst (either brief or extended) at high z. This implies that 50%-85% of SNe Ia explode within 1 Gyr of star formation. DTDs from double-degenerate (DD) models, which generically have ∼t -1 shapes over a wide range of timescales, match the data, but only if their predictions are scaled up by factors of 5-10. Single-degenerate (SD) DTDs always give poor fits to the data, due to a lack of delayed SNe and overall low numbers of SNe. The observations can also be reproduced with a combination of two SN Ia populations-a prompt SD population of SNe Ia that explodes within a few Gyr of star formation, and produces about 60% of the iron mass in clusters, and a DD population that contributes the events seen at z < 1.5. An alternative scenario of a single, prompt, SN Ia population, but a composite star formation history in clusters, consisting of a burst at high z, followed by a constant star formation rate, can reproduce the SN rates, but is at odds with direct measurements of star formation in clusters at 0 < z

  13. Elemental Abundances and their Implications for the Chemical Enrichment of the Boötes I Ultrafaint Galaxy

    Science.gov (United States)

    Gilmore, Gerard; Norris, John E.; Monaco, Lorenzo; Yong, David; Wyse, Rosemary F. G.; Geisler, D.

    2013-01-01

    We present a double-blind analysis of high-dispersion spectra of seven red giant members of the Boötes I ultrafaint dwarf spheroidal galaxy, complemented with re-analysis of a similar spectrum of an eighth-member star. The stars cover [Fe/H] from -3.7 to -1.9 and include a CEMP-no star with [Fe/H] = -3.33. We conclude from our chemical abundance data that Boötes I has evolved as a self-enriching star-forming system, from essentially primordial initial abundances. This allows us uniquely to investigate the place of CEMP-no stars in a chemically evolving system, in addition to limiting the timescale of star formation. The elemental abundances are formally consistent with a halo-like distribution, with enhanced mean [α/Fe] and small scatter about the mean. This is in accord with the high-mass stellar initial mass function in this low-stellar-density, low-metallicity system being indistinguishable from the present-day solar neighborhood value. There is a non-significant hint of a decline in [α/Fe] with [Fe/H]; together with the low scatter, this requires low star formation rates, allowing time for supernova ejecta to be mixed over the large spatial scales of interest. One star has very high [Ti/Fe], but we do not confirm a previously published high value of [Mg/Fe] for another star. We discuss the existence of CEMP-no stars, and the absence of any stars with lower CEMP-no enhancements at higher [Fe/H], a situation that is consistent with knowledge of CEMP-no stars in the Galactic field. We show that this observation requires there be two enrichment paths at very low metallicities: CEMP-no and "carbon-normal." Based on observations collected at the European Southern Observatory, Paranal, Chile (Proposal P82.182.B-0372, PI: G. Gilmore).

  14. SUZAKU MONITORING OF THE SEYFERT 1 GALAXY NGC 5548: WARM ABSORBER LOCATION AND ITS IMPLICATION FOR COSMIC FEEDBACK

    International Nuclear Information System (INIS)

    Krongold, Y.; Andrade-Velazquez, M.; Binette, L.; Jimenez-Bailon, E.; Elvis, M.; Nicastro, F.; Brickhouse, N. S.; Liu, Y.; Wilkes, B.; Mathur, S.; Reeves, J. N.; Grupe, D.; McHardy, I. M.; Minezaki, T.; Yoshii, Y.

    2010-01-01

    We present a 2 month Suzaku X-ray monitoring of the Seyfert 1 galaxy NGC 5548. The campaign consists of seven observations (with exposure time of ∼30 ks each), separated by ∼1 week. This paper focus on the X-ray Imaging Spectrometer data of NGC 5548. We analyze the response in the opacity of the gas that forms the well-known ionized absorber in this source for ionizing flux variations. Despite variations by a factor of ∼4 in the impinging continuum, the soft X-ray spectra of the source show little spectral variations, suggesting no response from the ionized absorber. A detailed time modeling of the spectra confirms the lack of opacity variations for an absorbing component with high ionization (U X ∼ -0.85), and high outflow velocity (v out ∼ 1040 km s -1 ), as the ionization parameter was found to be consistent with a constant value during the whole campaign. Instead, the models suggest that the ionization parameter of a low ionization (U X ∼ -2.8), low velocity (v out ∼ 590 km s -1 ) absorbing component might be changing linearly with the ionizing flux, as expected for gas in photoionization equilibrium. However, given the lack of spectral variations among observations, we consider the variations in this component as tentative. Using the lack of variations, we set an upper limit of n e 7 cm -3 for the electron density of the gas forming the high ionization, high velocity component. This implies a large distance from the continuum source (R>0.033 pc; R>5000R S ). If the variations in the low ionization, low velocity component are real, they imply n e >9.8 x 10 4 cm -3 and R 1.2 x 10 56 erg) can be enough to disrupt the interstellar medium, possibly quenching or regulating large-scale star formation. However, the total mass and energy ejected by the wind may still be lower than the one required for cosmic feedback, even when extrapolated to quasar luminosities. Such feedback would require that we are observing the wind before it is fully accelerated.

  15. Phylogenetic continuum indicates "galaxies" in the protein universe: preliminary results on the natural group structures of proteins.

    Science.gov (United States)

    Ladunga, I

    1992-04-01

    The markedly nonuniform, even systematic distribution of sequences in the protein "universe" has been analyzed by methods of protein taxonomy. Mapping of the natural hierarchical system of proteins has revealed some dense cores, i.e., well-defined clusterings of proteins that seem to be natural structural groupings, possibly seeds for a future protein taxonomy. The aim was not to force proteins into more or less man-made categories by discriminant analysis, but to find structurally similar groups, possibly of common evolutionary origin. Single-valued distance measures between pairs of superfamilies from the Protein Identification Resource were defined by two chi 2-like methods on tripeptide frequencies and the variable-length subsequence identity method derived from dot-matrix comparisons. Distance matrices were processed by several methods of cluster analysis to detect phylogenetic continuum between highly divergent proteins. Only well-defined clusters characterized by relatively unique structural, intracellular environmental, organismal, and functional attribute states were selected as major protein groups, including subsets of viral and Escherichia coli proteins, hormones, inhibitors, plant, ribosomal, serum and structural proteins, amino acid synthases, and clusters dominated by certain oxidoreductases and apolar and DNA-associated enzymes. The limited repertoire of functional patterns due to small genome size, the high rate of recombination, specific features of the bacterial membranes, or of the virus cycle canalize certain proteins of viruses and Gram-negative bacteria, respectively, to organismal groups.

  16. Deficiency of normal galaxies among Markaryan galaxies

    International Nuclear Information System (INIS)

    Iyeveer, M.M.

    1986-01-01

    Comparison of the morphological types of Markaryan galaxies and other galaxies in the Uppsala catalog indicates a strong deficiency of normal ellipticals among the Markaryan galaxies, for which the fraction of type E galaxies is ≤ 1% against 10% among the remaining galaxies. Among the Markaryan galaxies, an excess of barred galaxies is observed - among the Markaryan galaxies with types Sa-Scd, approximately half or more have bars, whereas among the remaining galaxies of the same types bars are found in about 1/3

  17. Galaxy Formation

    CERN Document Server

    Longair, Malcolm S

    2008-01-01

    This second edition of Galaxy Formation is an up-to-date text on astrophysical cosmology, expounding the structure of the classical cosmological models from a contemporary viewpoint. This forms the background to a detailed study of the origin of structure and galaxies in the Universe. The derivations of many of the most important results are derived by simple physical arguments which illuminate the results of more advanced treatments. A very wide range of observational data is brought to bear upon these problems, including the most recent results from WMAP, the Hubble Space Telescope, galaxy surveys like the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey, studies of Type 1a supernovae, and many other observations.

  18. The Galaxy Evolution Probe

    Science.gov (United States)

    Glenn, Jason; Galaxy Evolution Probe Team

    2018-01-01

    The Galaxy Evolution Probe (GEP) is a concept for a far-infrared observatory to survey large regions of sky for star-forming galaxies from z = 0 to beyond z = 3. Our knowledge of galaxy formation is incomplete and requires uniform surveys over a large range of redshifts and environments to accurately describe mass assembly, star formation, supermassive black hole growth, interactions between these processes, and what led to their decline from z ~ 2 to the present day. Infrared observations are sensitive to dusty, star-forming galaxies, which have bright polycyclic aromatic hydrocarbon (PAH) emission features and warm dust continuum in the rest-frame mid infrared and cooler thermal dust emission in the far infrared. Unlike previous far-infrared continuum surveys, the GEP will measure photometric redshifts commensurate with galaxy detections from PAH emission and Si absorption features, without the need for obtaining spectroscopic redshifts of faint counterparts at other wavelengths.The GEP design includes a 2 m diameter telescope actively cooled to 4 K and two instruments: (1) An imager covering 10 to 300 um with 25 spectral resolution R ~ 8 bands (with lower R at the longest wavelengths) to detect star-forming galaxies and measure their redshifts photometrically. (2) A 23 – 190 um, R ~ 250 dispersive spectrometer for redshift confirmation and identification of obscured AGN using atomic fine-structure lines. Lines including [Ne V], [O IV], [O III], [O I], and [C II] will probe gas physical conditions, radiation field hardness, and metallicity. Notionally, the GEP will have a two-year mission: galaxy surveys with photometric redshifts in the first year and a second year devoted to follow-up spectroscopy. A comprehensive picture of star formation in galaxies over the last 10 billion years will be assembled from cosmologically relevant volumes, spanning environments from field galaxies and groups, to protoclusters, to dense galaxy clusters.Commissioned by NASA, the

  19. Physics Implications of Flat Directions in Free Fermionic Superstring Models; 2, Renormalization Group Analysis

    CERN Document Server

    Cleaver, G.; Espinosa, J.R.; Everett, L.L.; Langacker, P.; Wang, J.

    1999-01-01

    We continue the investigation of the physics implications of a class of flat directions for a prototype quasi-realistic free fermionic string model (CHL5), building upon the results of the previous paper in which the complete mass spectrum and effective trilinear couplings of the observable sector were calculated to all orders in the superpotential. We introduce soft supersymmetry breaking mass parameters into the model, and investigate the gauge symmetry breaking patterns and the renormalization group analysis for two representative flat directions, which leave an additional $U(1)'$ as well as the SM gauge group unbroken at the string scale. We study symmetry breaking patterns that lead to a phenomenologically acceptable $Z-Z'$ hierarchy, $M_{Z^{'}} \\sim {\\cal O}(1~{\\rm TeV})$ and $ 10^{12}~{\\rm GeV}$ for electroweak and intermediate scale $U(1)^{'}$ symmetry breaking, respectively, and the associated mass spectra after electroweak symmetry breaking. The fermion mass spectrum exhibits unrealistic features, i...

  20. Gas-rich dwarfs and accretion phenomena in early-type galaxies

    International Nuclear Information System (INIS)

    Silk, J.; Norman, C.

    1979-01-01

    Recent constraints on intergalactic H I clouds suggest that allowable accretion rates by several luminous early-type galaxies are too low to account for their observed H I content. We have therefore developed an alternative model, wherein gas-rich dwarf galaxies are accreted into galactic halos. This process is significant in groups of galaxies only when a sufficiently high density of gas-rich dwarfs (approx.30 Mpc -3 ) is present. The dwarf galaxy gas content plays a crucial role in enabling the galaxy to be trapped in the halo by interaction with a galactic wind or extensive gaseous corona. Gas stripping occurs, resulting in the formation of dwarf spheroidal systems that populate the outer halos of massive galaxies and in the injection of a system of clouds into the halo. If the clouds are initially confined by the pressure of the ambient halo medium, dissipation and continuing infall enable the clouds to accrete into the central regions of galaxies before becoming gravitationally unstable and presumably forming stars. Consequences of this scenario include the production of a radial abundance gradient and infall of adequate amounts of neutral gas to account for the observations of H I in early-type galaxies. This gas accretion rate is also sufficient to feed active nuclei and radio sources. An important cosmological implication of our model is that, because the characteristic time scale of a gas-rich dwarf galaxy to be accreted and lose its gas is comparable to a Hubble time, there many have been a far more extensive primordial distribution of such systems at earlier epochs. This implies that accretion rates were greatly enhanced at relatively recent epochs (z> or approx. =0.5) and could account both for the rapid cosmological evolution inferred for radio galaxies and quasars, and for the observed frequency of occurrence of quasar absorption-line systems

  1. Chandra Finds Surprising Black Hole Activity In Galaxy Cluster

    Science.gov (United States)

    2002-09-01

    Scientists at the Carnegie Observatories in Pasadena, California, have uncovered six times the expected number of active, supermassive black holes in a single viewing of a cluster of galaxies, a finding that has profound implications for theories as to how old galaxies fuel the growth of their central black holes. The finding suggests that voracious, central black holes might be as common in old, red galaxies as they are in younger, blue galaxies, a surprise to many astronomers. The team made this discovery with NASA'S Chandra X-ray Observatory. They also used Carnegie's 6.5-meter Walter Baade Telescope at the Las Campanas Observatory in Chile for follow-up optical observations. "This changes our view of galaxy clusters as the retirement homes for old and quiet black holes," said Dr. Paul Martini, lead author on a paper describing the results that appears in the September 10 issue of The Astrophysical Journal Letters. "The question now is, how do these black holes produce bright X-ray sources, similar to what we see from much younger galaxies?" Typical of the black hole phenomenon, the cores of these active galaxies are luminous in X-ray radiation. Yet, they are obscured, and thus essentially undetectable in the radio, infrared and optical wavebands. "X rays can penetrate obscuring gas and dust as easily as they penetrate the soft tissue of the human body to look for broken bones," said co-author Dr. Dan Kelson. "So, with Chandra, we can peer through the dust and we have found that even ancient galaxies with 10-billion-year-old stars can have central black holes still actively pulling in copious amounts of interstellar gas. This activity has simply been hidden from us all this time. This means these galaxies aren't over the hill after all and our theories need to be revised." Scientists say that supermassive black holes -- having the mass of millions to billions of suns squeezed into a region about the size of our Solar System -- are the engines in the cores of

  2. A dichotomy in satellite quenching around L* galaxies

    Science.gov (United States)

    Phillips, John I.; Wheeler, Coral; Boylan-Kolchin, Michael; Bullock, James S.; Cooper, Michael C.; Tollerud, Erik J.

    2014-01-01

    We examine the star formation properties of bright (˜0.1 L*) satellites around isolated ˜L* hosts in the local Universe using spectroscopically confirmed systems in the Sloan Digital Sky Survey Data Release 7. Our selection method is carefully designed with the aid of N-body simulations to avoid groups and clusters. We find that satellites are significantly more likely to be quenched than a stellar mass-matched sample of isolated galaxies. Remarkably, this quenching occurs only for satellites of hosts that are themselves quenched: while star formation is unaffected in the satellites of star-forming hosts, satellites around quiescent hosts are more than twice as likely to be quenched than stellar-mass-matched field samples. One implication of this is that whatever shuts down star formation in isolated, passive L* galaxies also play at least an indirect role in quenching star formation in their bright satellites. The previously reported tendency for `galactic conformity' in colour/morphology may be a by-product of this host-specific quenching dichotomy. The Sérsic indices of quenched satellites are statistically identical to those of field galaxies with the same specific star formation rates, suggesting that environmental and secular quenching give rise to the same morphological structure. By studying the distribution of pairwise velocities between the hosts and satellites, we find dynamical evidence that passive host galaxies reside in dark matter haloes that are ˜45 per cent more massive than those of star-forming host galaxies of the same stellar mass. We emphasize that even around passive hosts, the mere fact that galaxies become satellites does not typically result in star formation quenching: we find that only ˜30 per cent of ˜0.1L* galaxies that fall in from the field are quenched around passive hosts, compared with ˜0 per cent around star-forming hosts.

  3. Flocculent and grand design spiral arm structure in cluster galaxies

    International Nuclear Information System (INIS)

    Elmegreen, D.M.

    1982-01-01

    A total of 829 spiral galaxies in 22 clusters having redshifts between z = 0.02 and 0.06 were classified according to the appearance of their spiral arm structures. The fraction of galaxies that have a grand design spiral structure was found to be higher among barred galaxies than among non-barred galaxies (at z = 0.02, 95 per cent of strongly barred galaxies have a grand design, compared with 67 per cent of non-barred or weakly barred galaxies). Cluster galaxies and distant non-cluster galaxies have the same fraction of grand design galaxies when resolution effects are considered. The grand design fraction among cluster galaxies is also similar to the fraction observed among nearby galaxies in binary systems and in groups. (author)

  4. Tidal streams in the local group and beyond observations and implications

    CERN Document Server

    Carlin, Jeffrey

    2016-01-01

    This volume is written by leading scientists in the field, who review the current state of our knowledge of tidal streams in the Milky Way, the Andromeda galaxy, and in other nearby galaxies.  The cosmological origins of dwarf galaxies and the physical processes by which they are tidally disrupted into streams and incorporated into galaxy halos are discussed. The techniques that have been used to identify tidal streams are presented, and will be useful to researchers who would like to find substructures in the next generation of optical sky surveys, including Pan-STARRS and LSST.  The methods that are currently under development to constrain both large scale distribution of dark matter in the Milky Way and the (small scale) lumpiness of the dark matter distribution are also explained.  The authors also provide motivation for future spectroscopic surveys of Milky Way halo stars, which will aid both in the identification of tidal streams and the constraint of dark matter properties.This volume is aimed at g...

  5. Lopsided spiral galaxies

    International Nuclear Information System (INIS)

    Jog, Chanda J.; Combes, Francoise

    2009-01-01

    The light distribution in the disks of many galaxies is 'lopsided' with a spatial extent much larger along one half of a galaxy than the other, as seen in M101. Recent observations show that the stellar disk in a typical spiral galaxy is significantly lopsided, indicating asymmetry in the disk mass distribution. The mean amplitude of lopsidedness is 0.1, measured as the Fourier amplitude of the m=1 component normalized to the average value. Thus, lopsidedness is common, and hence it is important to understand its origin and dynamics. This is a new and exciting area in galactic structure and dynamics, in contrast to the topic of bars and two-armed spirals (m=2) which has been extensively studied in the literature. Lopsidedness is ubiquitous and occurs in a variety of settings and tracers. It is seen in both stars and gas, in the outer disk and the central region, in the field and the group galaxies. The lopsided amplitude is higher by a factor of two for galaxies in a group. The lopsidedness has a strong impact on the dynamics of the galaxy, its evolution, the star formation in it, and on the growth of the central black hole and on the nuclear fuelling. We present here an overview of the observations that measure the lopsided distribution, as well as the theoretical progress made so far to understand its origin and properties. The physical mechanisms studied for its origin include tidal encounters, gas accretion and a global gravitational instability. The related open, challenging problems in this emerging area are discussed

  6. How dead are dead galaxies? Mid-infrared fluxes of quiescent galaxies at redshift 0.3 < z < 2.5: implications for star formation rates and dust heating

    Energy Technology Data Exchange (ETDEWEB)

    Fumagalli, Mattia; Labbé, Ivo; Patel, Shannon G.; Franx, Marijn [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Van Dokkum, Pieter; Momcheva, Ivelina; Nelson, Erica [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Brammer, Gabriel [European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago (Chile); Da Cunha, Elisabete; Rix, Hans-Walter; Maseda, Michael [Max Planck Institute for Astronomy (MPIA), Konigstuhl 17, D-69117 Heidelberg (Germany); Schreiber, Natascha M. Förster [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany); Kriek, Mariska [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Quadri, Ryan [Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States); Wake, David; Lundgren, Britt [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States); Whitaker, Katherine E. [Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Marchesini, Danilo [Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States); Pacifici, Camilla [Yonsei University Observatory, Yonsei University, Seoul 120-749 (Korea, Republic of); Skelton, Rosalind E. [South African Astronomical Observatory, Observatory Road, Cape Town (South Africa)

    2014-11-20

    We investigate star formation rates (SFRs) of quiescent galaxies at high redshift (0.3 < z < 2.5) using 3D-HST WFC3 grism spectroscopy and Spitzer mid-infrared data. We select quiescent galaxies on the basis of the widely used UVJ color-color criteria. Spectral energy distribution (SED) fitting (rest-frame optical and near-IR) indicates very low SFRs for quiescent galaxies (sSFR ∼ 10{sup –12} yr{sup –1}). However, SED fitting can miss star formation if it is hidden behind high dust obscuration and ionizing radiation is re-emitted in the mid-infrared. It is therefore fundamental to measure the dust-obscured SFRs with a mid-IR indicator. We stack the MIPS 24 μm images of quiescent objects in five redshift bins centered on z = 0.5, 0.9, 1.2, 1.7, 2.2 and perform aperture photometry. Including direct 24 μm detections, we find sSFR ∼ 10{sup –11.9} × (1 + z){sup 4} yr{sup –1}. These values are higher than those indicated by SED fitting, but at each redshift they are 20-40 times lower than those of typical star-forming galaxies. The true SFRs of quiescent galaxies might be even lower, as we show that the mid-IR fluxes can be due to processes unrelated to ongoing star formation, such as cirrus dust heated by old stellar populations and circumstellar dust. Our measurements show that star formation quenching is very efficient at every redshift. The measured SFR values are at z > 1.5 marginally consistent with the ones expected from gas recycling (assuming that mass loss from evolved stars refuels star formation) and well below that at lower redshifts.

  7. How dead are dead galaxies? Mid-infrared fluxes of quiescent galaxies at redshift 0.3 < z < 2.5: implications for star formation rates and dust heating

    International Nuclear Information System (INIS)

    Fumagalli, Mattia; Labbé, Ivo; Patel, Shannon G.; Franx, Marijn; Van Dokkum, Pieter; Momcheva, Ivelina; Nelson, Erica; Brammer, Gabriel; Da Cunha, Elisabete; Rix, Hans-Walter; Maseda, Michael; Schreiber, Natascha M. Förster; Kriek, Mariska; Quadri, Ryan; Wake, David; Lundgren, Britt; Whitaker, Katherine E.; Marchesini, Danilo; Pacifici, Camilla; Skelton, Rosalind E.

    2014-01-01

    We investigate star formation rates (SFRs) of quiescent galaxies at high redshift (0.3 < z < 2.5) using 3D-HST WFC3 grism spectroscopy and Spitzer mid-infrared data. We select quiescent galaxies on the basis of the widely used UVJ color-color criteria. Spectral energy distribution (SED) fitting (rest-frame optical and near-IR) indicates very low SFRs for quiescent galaxies (sSFR ∼ 10 –12 yr –1 ). However, SED fitting can miss star formation if it is hidden behind high dust obscuration and ionizing radiation is re-emitted in the mid-infrared. It is therefore fundamental to measure the dust-obscured SFRs with a mid-IR indicator. We stack the MIPS 24 μm images of quiescent objects in five redshift bins centered on z = 0.5, 0.9, 1.2, 1.7, 2.2 and perform aperture photometry. Including direct 24 μm detections, we find sSFR ∼ 10 –11.9 × (1 + z) 4 yr –1 . These values are higher than those indicated by SED fitting, but at each redshift they are 20-40 times lower than those of typical star-forming galaxies. The true SFRs of quiescent galaxies might be even lower, as we show that the mid-IR fluxes can be due to processes unrelated to ongoing star formation, such as cirrus dust heated by old stellar populations and circumstellar dust. Our measurements show that star formation quenching is very efficient at every redshift. The measured SFR values are at z > 1.5 marginally consistent with the ones expected from gas recycling (assuming that mass loss from evolved stars refuels star formation) and well below that at lower redshifts.

  8. Quasars in galaxy cluster environments

    International Nuclear Information System (INIS)

    Ellingson, E.

    1989-01-01

    The evolution of radio loud quasars is found to be strongly dependent upon their galaxy cluster environment. Previous studies have shown that bright quasars are found in rich clusters, while high luminosity quasars are found only in poorer environments. The analysis of low luminosity radio quiet quasars indicate that they are never found in rich environments, suggesting that they are a physically different class of objects. Properties of the quasar environment are investigated to determine constraints on the physical mechanisms of quasar formation and evolution. The optical cluster morphology indicates that the cluster cores have smaller radii and higher galaxy densities than are typical for low redshift clusters of similar richness. Radio morphologies may indicate that the formation of a dense intra-cluster medium is associated with the quasars' fading at these epochs. Galaxy colors appear to be normal, but there may be a tendency for clusters associated with high luminosity quasars to contain a higher fraction of gas-rich galaxies than those associated with low luminosity quasars. Multislit spectroscopic observations of galaxies associated with high luminosity quasars indicate that quasars are preferentially located in regions of low relative velocity dispersion, either in rich clusters of abnormally low dispersion, or in poor groups which are dynamically normal. This suggests that galaxy-galaxy interactions may play a role in quasar formation and sustenanace. Virialization of rich clusters and the subsequent increase in galaxy velocities may therefore be responsible for the fading of quasars in rich environments

  9. Neutral hydrogen in elliptical and IO galaxies

    International Nuclear Information System (INIS)

    Bottinelli, L.; Gouguenheim, L.

    1979-01-01

    New HI detections have been obtained using the Nancay radiotelescope for NGC 2974 and 3962. These results and the large scale distribution obtained for NGC 3962 indicate that the HI-rich elliptical galaxies exhibit common properties which are not easily explained by accretion of an intergalactic cloud. The field aroud NGC 1052 has been mapped and there is an HI connection with the neighbouring galaxies. The HI content of several IO galaxies indicates that the galaxies which are members of groups are relatively HI-rich; this could be produced by additional HI coming from companion galaxies [fr

  10. Direct Measurement of Dust Attenuation in z approx. 1.5 Star-Forming Galaxies from 3D-HST: Implications for Dust Geometry and Star Formation Rates

    Science.gov (United States)

    Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B; Conroy, Charlie; Schreiber, Natascha M. Foerster; Franx, Marijn; Fumagalli, Mattia; Lundren, Britt; Momcheva, Ivelina; Nelson, Erica J.; hide

    2013-01-01

    The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust towards star-forming regions (measured using Balmer decrements) and the integrated dust properties (derived by comparing spectral energy distributions [SEDs] with stellar population and dust models) for a statistically significant sample of distant galaxies. We select a sample of 163 galaxies between 1.36 or = 5 and measure Balmer decrements from stacked spectra. First, we stack spectra in bins of integrated stellar dust attenuation, and find that there is extra dust extinction towards star-forming regions (AV,HII is 1.81 times the integrated AV, star), though slightly lower than found for low-redshift starburst galaxies. Next, we stack spectra in bins of specific star formation rate (log sSFR), star formation rate (log SFR), and stellar mass (logM*). We find that on average AV,HII increases with SFR and mass, but decreases with increasing sSFR. The amount of extra extinction also decreases with increasing sSFR and decreasing stellar mass. Our results are consistent with the two-phase dust model - in which galaxies contain both a diffuse and a stellar birth cloud dust component - as the extra extinction will increase once older stars outside the star-forming regions become more dominant. Finally, using our Balmer decrements we derive dust-corrected H(alpha) SFRs, and find evidence that SED fitting produces incorrect SFRs if very rapidly declining SFHs are included in the explored parameter space. Subject headings: dust, extinction- galaxies: evolution- galaxies: high-redshift

  11. The visibility of high-redshift galaxies

    International Nuclear Information System (INIS)

    Phillipps, S.; Davies, J.I.; Disney, M.J.

    1990-01-01

    The most visible galaxies - that is, those which have the largest apparent sizes and isophotal luminosities when seen at a given distance - are those with a particular observed surface brightness. Extending this argument to high-redshift galaxies, it is clear that this optimum surface brightness moves progressively to brighter intrinsic surface brightnesses, so as to counteract the effect of K-corrections and cosmological dimming. Thus the galaxies appearing in faint surveys will be from a population distinctly different from those 'normal' galaxies observed nearby. Galaxies in deep surveys are more likely to be spirals and to be of high surface brightness. This has very important implications for observational studies of galaxy evolution. (author)

  12. Superclusters and galaxy formation

    International Nuclear Information System (INIS)

    Einasto, J.; Joeveer, M.; Saar, E.

    1979-01-01

    The spatial distribution of Galaxies and Galaxy congestions in the southern galactic hemisphere is studied. The rich galaxy congestions, containing many elliptic Galaxies and radiogalaxies, are linked with each other by chains of scanty congestions with moderate content of elliptic Galaxies and radiogalaxies. The flat formation, linking the density pikes and the intermediate chains, can reasonably be called supercongestion. In the central region of supercongestions there is a thin layer of Galaxies consisting of only spiral Galaxies. The neighbouring supercongestions touch each other, while the intersupercongestion space contains no Galaxy congestions and almost no Galaxies. It is shown that such a structure was, apparently, formed before the formation of Galaxies

  13. Ellipticities of Elliptical Galaxies in Different Environments

    Science.gov (United States)

    Chen, Cheng-Yu; Hwang, Chorng-Yuan; Ko, Chung-Ming

    2016-10-01

    We studied the ellipticity distributions of elliptical galaxies in different environments. From the ninth data release of the Sloan Digital Sky Survey, we selected galaxies with absolute {r}\\prime -band magnitudes between -21 and -22. We used the volume number densities of galaxies as the criterion for selecting the environments of the galaxies. Our samples were divided into three groups with different volume number densities. The ellipticity distributions of the elliptical galaxies differed considerably in these three groups of different density regions. We deprojected the observed 2D ellipticity distributions into intrinsic 3D shape distributions, and the result showed that the shapes of the elliptical galaxies were relatively spherically symmetric in the high density region (HDR) and that relatively more flat galaxies were present in the low density region (LDR). This suggests that the ellipticals in the HDRs and LDRs have different origins or that different mechanisms might be involved. The elliptical galaxies in the LDR are likely to have evolved from mergers in relatively anisotropic structures, such as filaments and webs, and might contain information on the anisotropic spatial distribution of their parent mergers. By contrast, elliptical galaxies in the HDR might be formed in more isotropic structures, such as galaxy clusters, or they might encounter more torqueing effects compared with galaxies in LDRs, thereby becoming rounder.

  14. The Greater Impact of Mergers on the Growth of Massive Galaxies: Implications for Mass Assembly and Evolution since z sime 1

    Science.gov (United States)

    Bundy, Kevin; Fukugita, Masataka; Ellis, Richard S.; Targett, Thomas A.; Belli, Sirio; Kodama, Tadayuki

    2009-06-01

    Using deep infrared observations conducted with the MOIRCS imager on the Subaru Telescope in the northern GOODS field combined with public surveys in GOODS-S, we investigate the dependence on stellar mass, M *, and galaxy type of the close pair fraction (5 h -1 kpc implied merger rate. In terms of combined depth and survey area, our publicly available mass-limited sample represents a significant improvement over earlier infrared surveys used for this purpose. In common with some recent studies, we find that the fraction of paired systems that could result in major mergers is low (~4%) and does not increase significantly with redshift to z ≈ 1.2, with vprop(1 + z)1.6±1.6. Our key finding is that massive galaxies with M *>1011 M sun are more likely to host merging companions than less massive systems (M * ~ 1010 M sun). We find evidence for a higher pair fraction for red, spheroidal hosts compared to blue, late-type systems, in line with expectations based on clustering at small scales. The so-called "dry" mergers between early-type galaxies devoid of star formation (SF) represent nearly 50% of close pairs with M *>3 × 1010 M sun at z ~ 0.5, but less than 30% at z ~ 1. This result can be explained by the increasing abundance of red, early-type galaxies at these masses. We compare the volumetric merger rate of galaxies with different masses to mass-dependent trends in galaxy evolution. Our results reaffirm the conclusion of Bundy et al. that major mergers do not fully account for the formation of spheroidal galaxies since z ~ 1. In terms of mass assembly, major mergers contribute little to galaxy growth below M * ~ 3 × 1010 M sun but play a more significant role among galaxies with M * gsim 1011 M sun ~ 30% of which have undergone mostly dry mergers over the observed redshift range. Overall, the relatively rapid and recent coalescence of high-mass galaxies mirrors the expected hierarchical growth of halos and is consistent with recent model predictions, even if

  15. Living with a carbon allowance: The experiences of Carbon Rationing Action Groups and implications for policy

    International Nuclear Information System (INIS)

    Howell, Rachel A.

    2012-01-01

    Carbon Rationing Action Groups (CRAGs) are grassroots voluntary groups of citizens concerned about climate change, who set themselves a carbon allowance each year and provide support to members seeking to reduce their direct carbon emissions from household energy use and personal transport. Some groups have a financial penalty for carbon emitted in excess of the ration, and systems whereby under-emitters are rewarded using the monies collected from over-emitters. CRAGs therefore operate the nearest scheme in existence to the proposed policy of Personal Carbon Trading (PCT). This paper reports the findings of a study of the opinions and experiences of individuals involved in CRAGs (‘CRAGgers’). In general, interviewees have made significant behavioural changes and emissions reductions, but many would be unwilling to sell spare carbon allowances within a national PCT system. The choices made by CRAGgers with respect to the design and operation of their ‘carbon accounting’, their experiences of reducing fossil fuel energy use, and their views on personal carbon trading at CRAG and national level are discussed. Some possible implications for PCT and other policies are considered, as well as the limitations of CRAGs in informing an understanding of the potential impacts and operation of PCT. - Highlights: ► Reports opinions and experiences of members of Carbon Rationing Action Groups (CRAGs). ► Many interviewees have made significant reductions to their carbon footprint. ► CRAGs offer insights into individuals' experiences of living with a carbon allowance. ► Most CRAGs involve highly motivated individuals and avoid trading. ► They nonetheless offer some insights into Personal Carbon Trading and other policies.

  16. S0 galaxies in Formax

    DEFF Research Database (Denmark)

    Bedregal...[], A. G.; Aragón-Salamanca, A.; Merrifield, M. R.

    2006-01-01

    Galaxies: elliptical and lenticular, cD: galaxies: kinematics and dynamics Udgivelsesdato: Oct.1......Galaxies: elliptical and lenticular, cD: galaxies: kinematics and dynamics Udgivelsesdato: Oct.1...

  17. THE ASSEMBLY OF GALAXY CLUSTERS

    International Nuclear Information System (INIS)

    Berrier, Joel C.; Stewart, Kyle R.; Bullock, James S.; Purcell, Chris W.; Barton, Elizabeth J.; Wechsler, Risa H.

    2009-01-01

    We study the formation of 53 galaxy cluster-size dark matter halos (M = 10 14.0-14.76 M sun ) formed within a pair of cosmological Λ cold dark matter N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host ∼0.3 L * galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no 'preprocessing' in the group environment prior to their accretion into the cluster. On average, 70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; less than 12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past (∼<6 Gyr) than a field halo of the same mass. These results suggest that local cluster processes such as ram pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between cluster and field populations at a fixed stellar mass, and that pre-evolution or past merging in the group environment is of secondary importance for setting cluster galaxy properties for most clusters. The accretion times for z = 0 cluster members are quite extended, with ∼20% incorporated into the cluster halo more than 7 Gyr ago and ∼20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate timescale for late-type to early-type transformation within the cluster environment to be ∼6 Gyr.

  18. Exploring Group Composition among Young, Urban Women of Color in Prenatal Care: Implications for Satisfaction, Engagement, and Group Attendance.

    Science.gov (United States)

    Earnshaw, Valerie A; Rosenthal, Lisa; Cunningham, Shayna D; Kershaw, Trace; Lewis, Jessica; Rising, Sharon Schindler; Stasko, Emily; Tobin, Jonathan; Ickovics, Jeannette R

    2016-01-01

    Group models of prenatal care continue to grow in popularity. However, little is known about how group composition (similarity or diversity between members of groups) relates to care-related outcomes. The current investigation aimed to explore associations between prenatal care group composition with patient satisfaction, engagement, and group attendance among young, urban women of color. Data were drawn from two studies conducted in New Haven and Atlanta (2001-2004; n = 557) and New York City (2008-2011; n = 375) designed to evaluate group prenatal care among young, urban women of color. Women aged 14 to 25 were assigned to group prenatal care and completed surveys during their second and third trimesters of pregnancy. Group attendance was recorded. Data were merged and analyzed guided by the Group Actor-Partner Interdependence Model using multilevel regression. Analyses explored composition in terms of age, race, ethnicity, and language. Women in groups with others more diverse in age reported greater patient engagement and, in turn, attended more group sessions, b(se) = -0.01(0.01); p = .04. The composition of prenatal care groups seems to be associated with young women's engagement in care, ultimately relating to the number of group prenatal care sessions they attend. Creating groups diverse in age may be particularly beneficial for young, urban women of color, who have unique pregnancy needs and experiences. Future research is needed to test the generalizability of these exploratory findings. Copyright © 2016 Jacobs Institute of Women's Health. Published by Elsevier Inc. All rights reserved.

  19. Physics implications of flat directions in free fermionic superstring models. II. Renormalization group analysis

    International Nuclear Information System (INIS)

    Cleaver, G.; Cvetic, M.; Everett, L.; Langacker, P.; Wang, J.; Espinosa, J.R.; Everett, L.

    1999-01-01

    We continue the investigation of the physics implications of a class of flat directions for a prototype quasi-realistic free fermionic string model (CHL5), building upon the results of a previous paper in which the complete mass spectrum and effective trilinear couplings of the observable sector were calculated to all orders in the superpotential. We introduce soft supersymmetry breaking mass parameters into the model, and investigate the gauge symmetry breaking patterns and the renormalization group analysis for two representative flat directions, which leave an additional U(1) ' as well as the SM gauge group unbroken at the string scale. We study symmetry breaking patterns that lead to a phenomenologically acceptable Z-Z ' hierarchy, M Z ' ∼O(1 TeV) and 10 12 GeV for electroweak and intermediate scale U(1) ' symmetry breaking, respectively, and the associated mass spectra after electroweak symmetry breaking. The fermion mass spectrum exhibits unrealistic features, including massless exotic fermions, but has an interesting d-quark hierarchy and associated CKM matrix in one case. There are (some) non-canonical effective μ terms, which lead to a non-minimal Higgs sector with more than two Higgs doublets involved in the symmetry breaking, and a rich structure of Higgs particles, charginos, and neutralinos, some of which, however, are massless or ultralight. In the electroweak scale cases the scale of supersymmetry breaking is set by the Z ' mass, with the sparticle masses in the several TeV range. copyright 1999 The American Physical Society

  20. THE CONTRIBUTION OF TP-AGB AND RHeB STARS TO THE NEAR-IR LUMINOSITY OF LOCAL GALAXIES: IMPLICATIONS FOR STELLAR MASS MEASUREMENTS OF HIGH-REDSHIFT GALAXIES

    International Nuclear Information System (INIS)

    Melbourne, J.; Williams, Benjamin F.; Dalcanton, Julianne J.; Rosenfield, Philip; Weisz, D.

    2012-01-01

    Using high spatial resolution Hubble Space Telescope WFC3 and Advanced Camera for Surveys imaging of resolved stellar populations, we constrain the contribution of thermally pulsing asymptotic giant branch (TP-AGB) stars and red helium burning (RHeB) stars to the 1.6 μm near-infrared (NIR) luminosities of 23 nearby galaxies, including dwarfs and spirals. The TP-AGB phase contributes as much as 17% of the integrated F160W flux, even when the red giant branch is well populated. The RHeB population contribution can match or even exceed the TP-AGB contribution, providing as much as 21% (18% after a statistical correction for foreground) of the integrated F160W light. We estimate that these two short-lived phases may account for up to 70% of the rest-frame NIR flux at higher redshift. The NIR mass-to-light (M/L) ratio should therefore be expected to vary significantly due to fluctuations in the star formation rate (SFR) over timescales from 25 Myr to several Gyr, an effect that may be responsible for some of the lingering scatter in NIR galaxy scaling relations such as the Tully-Fisher and metallicity-luminosity relations. We compare our observational results to predictions based on optically derived star formation histories and stellar population synthesis (SPS) models, including models based on the 2008 Padova isochrones (used in popular SPS programs) and the updated 2010 Padova isochrones, which shorten the lifetimes of low-mass (old) low-metallicity TP-AGB populations. The updated (2010) SPS models generally reproduce the expected numbers of TP-AGB stars in the sample; indeed, for 65% of the galaxies, the discrepancy between modeled and observed numbers is smaller than the measurement uncertainties. The weighted mean model/data number ratio for TP-AGB stars is 1.5 (1.4 with outliers removed) with a standard deviation of 0.5. The same SPS models, however, give a larger discrepancy in the F160W flux contribution from the TP-AGB stars, overpredicting the flux by a

  1. Cross sections in 25 groups obtained from ENDF/B-IV and ENDL/78 libraries, processed with GALAXY and NJOY computer codes

    International Nuclear Information System (INIS)

    Chalhoub, E.S.; Corcuera, R.P.

    1982-01-01

    The discrepancies existing between ENDF/B-IV and ENDL/78 libraries, in diferent energy regions are identified, and the order of the differences in multigroup sections are determined, when GALAXY or NJOY computer codes are used. (E.G.) [pt

  2. Crashing galaxies, cosmic fireworks

    International Nuclear Information System (INIS)

    Keel, W.C.

    1989-01-01

    The study of binary systems is reviewed. The history of the study of interacting galaxies, the behavior of gas in binary systems, studies to identify the processes that occur when galaxies interact, and the relationship of Seyfert galaxies and quasars to binary systems are discussed. The development of an atlas of peculiar galaxies (Arp, 1966) and methods for modeling galaxy interactions are examined

  3. Spherical galaxies.

    Science.gov (United States)

    Telles, J. E.; de Souza, R. E.; Penereiro, J. C.

    1990-11-01

    RESUMEN. Presentamos fotometria fotografica de 8 objetos y espectrosco- pla para 3 galaxias, las cuales son buenos candidatos para galaxias esfericas. Los resultados fotometricos se presentan en la forma de iso- fotas y de perfiles radiales promedlo, de los cuales se derivan para- metros estructurales. Estas observaciones combinadas con parametros di- namicos obtenidos de observaciones espectrosc6picas, son consistentes con el plano fundamental derivado por Djorgovski y Davis (1987). ABSTRACT. We present photographic surface photometry for 8 objects and spectroscopy for 3 galaxies which are good candidates for spherical galaxies. Photometric results are presented in the form of isophotes and mean radial profiles from which we derived structural parameters. These observations combined with dynamical parameters obtained from spectroscopic observations are consistent with the fundamental plane derived by Djorgovski and Davis (1987). Keq wo : CALAXIES-ELLIPTICAL

  4. The rotation of galaxies: clues to their formation

    International Nuclear Information System (INIS)

    Fall, S.M.

    1982-01-01

    The rotation of galaxies of different morphological types is closely linked with their structural features and therefore with the processes by which they formed. In this context, the most important distinction is between galaxies that are dominated by a spheroid or bulge component - the ellipticals and some lenticulars - and galaxies that are dominated by a disk component - some lenticulars, the spirals and some irregulars. As the result of improvements in spectroscopic techniques, we now have reliable kinematic data for galaxies of most types in a wide range of masses and sizes. The author discusses the observational results and their implications for several views of the origin and evolution of galaxies. (Auth.)

  5. Direct Measurements of Dust Attenuation in z ~ 1.5 Star-forming Galaxies from 3D-HST: Implications for Dust Geometry and Star Formation Rates

    Science.gov (United States)

    Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B.; Conroy, Charlie; Förster Schreiber, Natascha M.; Franx, Marijn; Fumagalli, Mattia; Lundgren, Britt; Momcheva, Ivelina; Nelson, Erica J.; Skelton, Rosalind E.; van Dokkum, Pieter G.; Whitaker, Katherine E.; Wuyts, Stijn

    2014-06-01

    The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust around star-forming regions (A V, H II ) and the integrated dust content (A V, star). We select a sample of 163 galaxies between 1.36 =5 and measure Balmer decrements from stacked spectra to calculate A V, H II . First, we stack spectra in bins of A V, star, and find that A V, H II = 1.86 A V, star, with a significance of σ = 1.7. Our result is consistent with the two-component dust model, in which galaxies contain both diffuse and stellar birth cloud dust. Next, we stack spectra in bins of specific star formation rate (log SSFR), star formation rate (log SFR), and stellar mass (log M *). We find that on average A V, H II increases with SFR and mass, but decreases with increasing SSFR. Interestingly, the data hint that the amount of extra attenuation decreases with increasing SSFR. This trend is expected from the two-component model, as the extra attenuation will increase once older stars outside the star-forming regions become more dominant in the galaxy spectrum. Finally, using Balmer decrements we derive dust-corrected Hα SFRs, and find that stellar population modeling produces incorrect SFRs if rapidly declining star formation histories are included in the explored parameter space.

  6. Direct measurements of dust attenuation in z ∼ 1.5 star-forming galaxies from 3D-HST: Implications for dust geometry and star formation rates

    International Nuclear Information System (INIS)

    Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B.; Conroy, Charlie; Schreiber, Natascha M. Förster; Wuyts, Stijn; Franx, Marijn; Fumagalli, Mattia; Lundgren, Britt; Momcheva, Ivelina; Nelson, Erica J.; Van Dokkum, Pieter G.; Skelton, Rosalind E.; Whitaker, Katherine E.

    2014-01-01

    The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust around star-forming regions (A V, H II ) and the integrated dust content (A V, star ). We select a sample of 163 galaxies between 1.36 ≤ z ≤ 1.5 with Hα signal-to-noise ratio ≥5 and measure Balmer decrements from stacked spectra to calculate A V, H II . First, we stack spectra in bins of A V, star , and find that A V, H II = 1.86 A V, star , with a significance of σ = 1.7. Our result is consistent with the two-component dust model, in which galaxies contain both diffuse and stellar birth cloud dust. Next, we stack spectra in bins of specific star formation rate (log SSFR), star formation rate (log SFR), and stellar mass (log M * ). We find that on average A V, H II increases with SFR and mass, but decreases with increasing SSFR. Interestingly, the data hint that the amount of extra attenuation decreases with increasing SSFR. This trend is expected from the two-component model, as the extra attenuation will increase once older stars outside the star-forming regions become more dominant in the galaxy spectrum. Finally, using Balmer decrements we derive dust-corrected Hα SFRs, and find that stellar population modeling produces incorrect SFRs if rapidly declining star formation histories are included in the explored parameter space.

  7. HOT GAS HALOS IN EARLY-TYPE FIELD GALAXIES

    International Nuclear Information System (INIS)

    Mulchaey, John S.; Jeltema, Tesla E.

    2010-01-01

    We use Chandra and XMM-Newton to study the hot gas content in a sample of field early-type galaxies. We find that the L X -L K relationship is steeper for field galaxies than for comparable galaxies in groups and clusters. The low hot gas content of field galaxies with L K ∼ * suggests that internal processes such as supernovae-driven winds or active galactic nucleus feedback expel hot gas from low-mass galaxies. Such mechanisms may be less effective in groups and clusters where the presence of an intragroup or intracluster medium can confine outflowing material. In addition, galaxies in groups and clusters may be able to accrete gas from the ambient medium. While there is a population of L K ∼ * galaxies in groups and clusters that retain hot gas halos, some galaxies in these rich environments, including brighter galaxies, are largely devoid of hot gas. In these cases, the hot gas halos have likely been removed via ram pressure stripping. This suggests a very complex interplay between the intragroup/intracluster medium and hot gas halos of galaxies in rich environments, with the ambient medium helping to confine or even enhance the halos in some cases and acting to remove gas in others. In contrast, the hot gas content of more isolated galaxies is largely a function of the mass of the galaxy, with more massive galaxies able to maintain their halos, while in lower mass systems the hot gas escapes in outflowing winds.

  8. Predicting galaxy star formation rates via the co-evolution of galaxies and haloes

    Science.gov (United States)

    Watson, Douglas F.; Hearin, Andrew P.; Berlind, Andreas A.; Becker, Matthew R.; Behroozi, Peter S.; Skibba, Ramin A.; Reyes, Reinabelle; Zentner, Andrew R.; van den Bosch, Frank C.

    2015-01-01

    In this paper, we test the age matching hypothesis that the star formation rate (SFR) of a galaxy of fixed stellar mass is determined by its dark matter halo formation history, e.g. more quiescent galaxies reside in older haloes. We present new Sloan Digital Sky Survey measurements of the galaxy two-point correlation function and galaxy-galaxy lensing as a function of stellar mass and SFR, separated into quenched and star-forming galaxy samples to test this simple model. We find that our age matching model is in excellent agreement with these new measurements. We also find that our model is able to predict: (1) the relative SFRs of central and satellite galaxies, (2) the SFR dependence of the radial distribution of satellite galaxy populations within galaxy groups, rich groups, and clusters and their surrounding larger scale environments, and (3) the interesting feature that the satellite quenched fraction as a function of projected radial distance from the central galaxy exhibits an ˜r-.15 slope, independent of environment. These accurate predictions are intriguing given that we do not explicitly model satellite-specific processes after infall, and that in our model the virial radius does not mark a special transition region in the evolution of a satellite. The success of the model suggests that present-day galaxy SFR is strongly correlated with halo mass assembly history.

  9. Chemical evolution of galaxies

    International Nuclear Information System (INIS)

    Vigroux, Laurent

    1979-01-01

    This research thesis addresses theories on the chemical evolution of galaxies which aim at explaining abundances of different elements in galaxies, and more particularly aims at improving the model by modifying hypotheses. After a description of the simple model and of its uncertainties, the author shows how it is possible to understand the evolution of the main elements. Predictions obtained with this model are then compared with the present knowledge on galaxies by considering them according to an increasing complexity: Sun's neighbourhood, our galaxy, other spiral galaxies, elliptical galaxies, and finally galaxy clusters. A specific attention is given to irregular galaxies which are the simplest systems [fr

  10. Secular Evolution in Disk Galaxies

    Science.gov (United States)

    Kormendy, John

    2013-10-01

    bulges because the latter retain a `memory' of their disky origin. That is, they have one or more characteristics of disks: (1) flatter shapes than those of classical bulges, (2) correspondingly large ratios of ordered to random velocities, (3) small velocity dispersions with respect to the Faber-Jackson correlation between velocity dispersion and bulge luminosity, (4) spiral structure or nuclear bars in the `bulge' part of the light profile, (5) nearly exponential brightness profiles and (6) starbursts. So the cleanest examples of pseudobulges are recognisable. However, pseudo and classical bulges can coexist in the same galaxy. I review two important implications of secular evolution: (1) The existence of pseudobulges highlights a problem with our theory of galaxy formation by hierarchical clustering. We cannot explain galaxies that are completely bulgeless. Galaxy mergers are expected to happen often enough so that every giant galaxy should have a classical bulge. But we observe that bulgeless giant galaxies are common in field environments. We now realise that many dense centres of galaxies that we used to think are bulges were not made by mergers; they were grown out of disks. So the challenge gets more difficult. This is the biggest problem faced by our theory of galaxy formation. (2) Pseudobulges are observed to contain supermassive black holes (BHs), but they do not show the well-known, tight correlations between BH mass and the mass and velocity dispersion of the host bulge. This leads to the suggestion that there are two fundamentally different BH feeding processes. Rapid global inward gas transport in galaxy mergers leads to giant BHs that correlate with host ellipticals and classical bulges, whereas local and more stochastic feeding of small BHs in largely bulgeless galaxies evidently involves too little energy feedback to result in BH-host coevolution. It is an important success of the secular evolution picture that morphological differences can be used to

  11. Galaxy Collisions Forging New Worlds from Cosmic Crashes

    CERN Document Server

    Struck, Curtis

    2011-01-01

    Galaxy collisions are the key process in building galaxies, triggering the formation of stars and the build-up of heavy elements that allow the formation of planets and solar systems. This book presents the revolutionary research advances achieved in the last decade and lucidly explains the underlying dynamical processes. Galaxy Collisions takes a comprehensive trip through the visually spectacular world of galaxy collisions; investigates the interactions of stars, gas clouds, and dark matter in galaxy collisions; uses analogies and metaphors to help comprehend the bizarre world of galaxies; presents recent research results to enhance the understanding of galaxy formation and evolution; includes discoveries of minor collisions within our own group of galaxies; shows how a galaxy collision might affect a solar system, or a planet like ours.

  12. The Road to Galaxy Formation

    CERN Document Server

    Keel, William C

    2007-01-01

    The formation of galaxies is one of the greatest puzzles in astronomy, the solution is shrouded in the depths of space and time, but has profound implications for the universe we observe today. The book discusses the beginnings of the process from cosmological observations and calculations, considers the broad features of galaxies that we need to explain and what we know of their later history. The author compares the competing theories for galaxy formation and considers the progress expected from new generations of powerful telescopes both on earth and in space. In this second edition the author has retained the observationally-based approach of the first edition, a feature which was particularly well-reviewed: Writing in Nature, Carlton Baugh noted in February 2003 that “It is refreshing, in a market dominated by theorists, to come across a book on galaxy formation written from an observational perspective. The Road to Galaxy Formation should prove to be a handy primer on observations for graduate student...

  13. X-ray emssion from normal galaxies

    International Nuclear Information System (INIS)

    Speybroeck, L. van; Bechtold, J.

    1981-01-01

    A summary of results obtained with the Einstein Observatory is presented. There are two general categories of normal galaxy investigation being pursued - detailed studies of nearby galaxies where individual sources can be detected and possibly correlated with galactic morphology, and shorter observations of many more distant objects to determine the total luminosity distribution of normal galaxies. The principal examples of the first type are the CFA study of M31 and the Columbia study of the Large Magellanic Cloud. The Columbia normal galaxy survey is the principal example of the second type, although there also are smaller CFA programs concentrating on early galaxies and peculiar galaxies, and MIT has observed some members of the local group. (Auth.)

  14. Reconstructing galaxy histories from globular clusters.

    Science.gov (United States)

    West, Michael J; Côté, Patrick; Marzke, Ronald O; Jordán, Andrés

    2004-01-01

    Nearly a century after the true nature of galaxies as distant 'island universes' was established, their origin and evolution remain great unsolved problems of modern astrophysics. One of the most promising ways to investigate galaxy formation is to study the ubiquitous globular star clusters that surround most galaxies. Globular clusters are compact groups of up to a few million stars. They generally formed early in the history of the Universe, but have survived the interactions and mergers that alter substantially their parent galaxies. Recent advances in our understanding of the globular cluster systems of the Milky Way and other galaxies point to a complex picture of galaxy genesis driven by cannibalism, collisions, bursts of star formation and other tumultuous events.

  15. The rotation of galaxy clusters

    International Nuclear Information System (INIS)

    Tovmassian, H.M.

    2015-01-01

    The method for detection of the galaxy cluster rotation based on the study of distribution of member galaxies with velocities lower and higher of the cluster mean velocity over the cluster image is proposed. The search for rotation is made for flat clusters with a/b> 1.8 and BMI type clusters which are expected to be rotating. For comparison there were studied also round clusters and clusters of NBMI type, the second by brightness galaxy in which does not differ significantly from the cluster cD galaxy. Seventeen out of studied 65 clusters are found to be rotating. It was found that the detection rate is sufficiently high for flat clusters, over 60 per cent, and clusters of BMI type with dominant cD galaxy, ≈ 35 per cent. The obtained results show that clusters were formed from the huge primordial gas clouds and preserved the rotation of the primordial clouds, unless they did not have mergings with other clusters and groups of galaxies, in the result of which the rotation has been prevented

  16. The physical properties of giant molecular cloud complexes in the outer Galaxy - Implications for the ratio of H2 column density to (C-12)O intensity

    Science.gov (United States)

    Sodroski, T. J.

    1991-01-01

    The physical properties of 35 giant molecular cloud complexes in the outer Galaxy were derived from the Goddard-Columbia surveys of the Galactic plane region (Dame et al., 1987). The spatial and radial velocity boundaries for the individual cloud complexes were estimated by analyzing the spatial and velocity structure of emission features in the (C-12)O surveys, and the distance to each cmplex was determined kinematically on the assumption of a flat rotation curve. The ratio of the H2 column density to the (C-12)O intensity for the outer Galaxy complexes was found to be about 6.0 x 10 to the 20th molecules/sq cm K per km/sec, which is by a factor of 2-3 greater than the value derived by other auhtors for the inner Galaxy complexes. This increase in the H2 column density/(C-12)O intensity with the distance from with the Galactic center is consistent with predictions of the optically thick cloudlet model of giant molecular cloud complexes.

  17. Application of Focal Conflict Theory to Psychoeducational Groups: Implications for Process, Content, and Leadership

    Science.gov (United States)

    Champe, Julia; Rubel, Deborah J.

    2012-01-01

    Group psychoeducation is a common group type used for a range of purposes. The literature presents balancing content and process as a challenge for psychoeducational group leaders. While the significance of group psychoeducation is supported, practitioners are given little direction for addressing process in these groups. Focal Conflict Theory…

  18. The Blue Compact Dwarf Galaxy IZw18

    NARCIS (Netherlands)

    Musella, I.; Marconi, M.; Fiorentino, G.; Clementini, G.; Aloisi, A.; Annibali, F.; Contreras, R.; Saha, A.; Tosi, M.; van der Marel, R. P.

    2012-01-01

    We present the results obtained for the Blue compact galaxy IZw18 on the basis of ACS HST data obtained from our group. In particular, we discuss the stellar population and the variable stars content of this galaxy to get information about its star formation history and distance.

  19. The Hyperluminous Infrared Quasar 3C 318 and Its Implications for Interpreting Sub-MM Detections of High-Redshift Radio Galaxies

    Science.gov (United States)

    Willott, Chris J.; Rawlings, Steve; Jarvis, Matt J.

    1999-01-01

    We present near-infrared spectroscopy and imaging of the compact steep-spectrum radio source 3C 318 which shows it to be a quasar at redshift z = 1.574 (the z = 0.752 value previously reported is incorrect). 3C 318 is an IRAS, ISO and SCUBA source so its new redshift makes it the most intrinsically luminous far-infrared (FIR) source in the 3C catalogue (there is no evidence of strong gravitational lensing effects). Its bolometric luminosity greatly exceeds the 10(exp 13) solar luminosity level above which an object is said to be hyperluminous. Its spectral energy distribution (SED) requires that the quasar heats the dust responsible for the FIR flux, as is believed to be the case in other hyperluminous galaxies, and contributes (at the greater than 10% level) to the heating of the CIA dust responsible for the sub-mm emission. We cannot determine whether a starburst makes an important contribution to the heating of the coolest dust, so evidence for a high star-formation rate is circumstantial being based on the high dust, and hence gas, C-1 mass required by its sub-mm detection. We show that the current sub-mm and FIR data available for the highest-redshift radio galaxies are consistent with SEDs similar to that of 3C 318. This indicates that at least some of this population may be detected in the sub-mm because of dust heated by the quasar nucleus, and that interpreting sub-mm detection as evidence for very high (approx. less than 1000 solar mass/yr) star-formation rates may not always be valid. We show that the 3C318 quasar is slightly reddened (A(sub v) approx. = 0.5), the most likely cause of which is SMC-type dust in the host galaxy. If very distant radio galaxies are reddened in a similar way then we show that only slightly greater amounts of dust could obscure the quasars in these sources. We speculate that the low fraction of quasars amongst the very high redshift (z approx. greater than 3) objects in low-frequency radio-selected samples is the result of

  20. Do Galaxies Follow Darwinian Evolution?

    Science.gov (United States)

    2006-12-01

    , France, who coordinates the VIMOS VLT Deep Survey team that made the discovery. "They suggest that galaxies as we see them today are the product of their inherent genetic information, evolved over time, as well as complex interactions with their environments, such as mergers." Scientists have known for several decades that galaxies in the Universe's past look different to those in the present-day Universe, local to the Milky Way [3]. Today, galaxies can be roughly classified as red, when few or no new stars are being born, or blue, where star formation is still ongoing. Moreover, a strong correlation exists between a galaxy's colour and the environment it resides in: the more sociable types found in dense clusters are more likely to be red than the more isolated ones. By looking back at a wide range of galaxies of a variety of ages, the astronomers were aiming to study how this peculiar correlation has evolved over time. "Using VIMOS, we were able to use the largest sample of galaxies currently available for this type of study, and because of the instrument's ability to study many objects at a time we obtained many more measurements than previously possible," said Angela Iovino, from the Brera Astronomical Observatory, Italy, another member of the team. The team's discovery of a marked variation in the 'colour-density' relationship, depending on whether a galaxy is found in a cluster or alone, and on its luminosity, has many potential implications. The findings suggest for example that being located in a cluster quenches a galaxy's ability to form stars more quickly compared with those in isolation. Luminous galaxies also run out of star-forming material at an earlier time than fainter ones. They conclude that the connection between galaxies' colour, luminosity and their local environment is not merely a result of primordial conditions 'imprinted' during their formation - but just as for humans, galaxies' relationship and interactions can have a profound impact on their

  1. Evidence for AGN feedback in low-mass galaxies

    Science.gov (United States)

    Masters, Karen; Penny, Sam; Smethurst, Rebecca; Krawczyk, Coleman; Nichol, Bob; SDSS-IV MaNGA

    2018-01-01

    Despite being the dominant galaxy population by number in groups and clusters, the formation and quenching mechanism of dwarf galaxies remains unknown. We present evidence for AGN feedback in a subset of 69 quenched low-mass galaxies (M* less than 5e9 Msun, fainter than Mr = -19) selected from the first two years of the MaNGA survey. The majority (85 per cent) of these quenched galaxies appear to reside in a group environment. We find 6 galaxies in our sample that appear to have an active AGN that is preventing on-going star-formation; this is the first time such a feedback mechanism has been observed in this mass range. Interestingly, five of these six galaxies have an ionised gas component that is kinematically offset from their stellar component, suggesting the gas is either recently accreted or outflowing. We hypothesise these six galaxies are low-mass equivalents to the “red geysers” observed in more massive galaxies. Of the other 62 galaxies in the sample, we find 8 do appear to have some low-level, residual star formation, or emission from hot, evolved stars. The remaining galaxies in our sample have no detectable ionised gas emission throughout their structures, consistent with them being quenched. I will show that despite being the "simplest" galaxies in our current models of galaxy formation, these quenched dwarf galaxies are a diverse population.

  2. Functional groups show distinct differences in nitrogen cycling during early stand development: implications for forest management

    Science.gov (United States)

    Doug P. Aubrey; David R. Coyle; Mark D. Coleman

    2012-01-01

    Background and aims Nutrient acquisition of forest stands is controlled by soil resource availability and belowground production, but tree species are rarely compared in this regard. Here, we examine ecological and management implications of nitrogen (N) dynamics during early forest stand development in productive commercial tree species with narrow (Populus...

  3. Review: Prevalence and co-occurrence of addictions in US ethnic/racial groups: Implications for genetic research.

    Science.gov (United States)

    Luczak, Susan E; Khoddam, Rubin; Yu, Sheila; Wall, Tamara L; Schwartz, Anna; Sussman, Steve

    2017-08-01

    We conducted a review of the prevalence and co-occurrence of 12 types of addictions in US ethnic/racial groups and discuss the implications of the results for genetic research on addictions. We utilized MEDLINE and PsycINFO databases to review the literature on alcohol, tobacco, marijuana, illicit drugs, gambling, eating/food, internet, sex, love, exercise, work, and shopping. We present results for each addiction based on total US prevalence, prevalence within ethnic groups, and co-occurrence of addictions among ethnic groups when available. This review indicates very little research has examined the interrelationships of addictive behaviors among US ethnic groups. The studies that exist have focused nearly exclusively on comorbidity of substances and gambling behaviors. Overall findings suggest differences among US ethnic groups in prevalence of addictions and in prevalence of addiction among those who use substances or engage in gambling. Almost no ethnic group comparisons of other addictive behaviors including eating/food, internet, love, sex, exercise, work, and shopping were identified in the literature. Despite large-scale research efforts to examine alcohol and substance use disorders in the United States, few studies have been published that examine these addictive behaviors among ethnic groups, and even fewer examine co-occurrence and comorbidity with other addictions. Even with the limited studies, these findings have implications for genetic research on addictive behaviors. We include a discussion of these implications, including issues of population stratification, disaggregation, admixture, and the interplay between genetic and environmental factors in understanding the etiology and treatment of addictions. (Am J Addict 2017;26:424-436). © 2016 American Academy of Addiction Psychiatry.

  4. Investigations of Galaxy Clusters Using Gravitational Lensing

    Energy Technology Data Exchange (ETDEWEB)

    Wiesner, Matthew P. [Northern Illinois Univ., DeKalb, IL (United States)

    2014-08-01

    In this dissertation, we discuss the properties of galaxy clusters that have been determined using strong and weak gravitational lensing. A galaxy cluster is a collection of galaxies that are bound together by the force of gravity, while gravitational lensing is the bending of light by gravity. Strong lensing is the formation of arcs or rings of light surrounding clusters and weak lensing is a change in the apparent shapes of many galaxies. In this work we examine the properties of several samples of galaxy clusters using gravitational lensing. In Chapter 1 we introduce astrophysical theory of galaxy clusters and gravitational lensing. In Chapter 2 we examine evidence from our data that galaxy clusters are more concentrated than cosmology would predict. In Chapter 3 we investigate whether our assumptions about the number of galaxies in our clusters was valid by examining new data. In Chapter 4 we describe a determination of a relationship between mass and number of galaxies in a cluster at higher redshift than has been found before. In Chapter 5 we describe a model of the mass distribution in one of the ten lensing systems discovered by our group at Fermilab. Finally in Chapter 6 we summarize our conclusions.

  5. Analysis of Sunyaev-Zel'dovich effect mass-observable relations using South Pole Telescope observations of an X-ray selected sample of low-mass galaxy clusters and groups

    Energy Technology Data Exchange (ETDEWEB)

    Liu, J.; Mohr, J.; Saro, A.; Aird, K. A.; Ashby, M. L. N.; Bautz, M.; Bayliss, M.; Benson, B. A.; Bleem, L. E.; Bocquet, S.; Brodwin, M.; Carlstrom, J. E.; Chang, C. L.; Chiu, I.; Cho, H. M.; Clocchiatti, A.; Crawford, T. M.; Crites, A. T.; de Haan, T.; Desai, S.; Dietrich, J. P.; Dobbs, M. A.; Foley, R. J.; Gangkofner, D.; George, E. M.; Gladders, M. D.; Gonzalez, A. H.; Halverson, N. W.; Hennig, C.; Hlavacek-Larrondo, J.; Holder, G. P.; Holzapfel, W. L.; Hrubes, J. D.; Jones, C.; Keisler, R.; Lee, A. T.; Leitch, E. M.; Lueker, M.; Luong-Van, D.; McDonald, M.; McMahon, J. J.; Meyer, S. S.; Mocanu, L.; Murray, S. S.; Padin, S.; Pryke, C.; Reichardt, C. L.; Rest, A.; Ruel, J.; Ruhl, J. E.; Saliwanchik, B. R.; Sayre, J. T.; Schaffer, K. K.; Shirokoff, E.; Spieler, H. G.; Stalder, B.; Staniszewski, Z.; Stark, A. A.; Story, K.;  uhada, R.; Vanderlinde, K.; Vieira, J. D.; Vikhlinin, A.; Williamson, R.; Zahn, O.; Zenteno, A.

    2015-02-25

    We use microwave observations from the South Pole Telescope (SPT) to examine the Sunyaev–Zel'dovich effect (SZE) signatures of a sample of 46 X-ray selected groups and clusters drawn from ~6 deg2 of the XMM–Newton Blanco Cosmology Survey. These systems extend to redshift z = 1.02 and probe the SZE signal to the lowest X-ray luminosities (≥1042 erg s-1) yet; these sample characteristics make this analysis complementary to previous studies. We develop an analysis tool, using X-ray luminosity as a mass proxy, to extract selection-bias-corrected constraints on the SZE significance and Y_500 mass relations. The former is in good agreement with an extrapolation of the relation obtained from high-mass clusters. However, the latter, at low masses, while in good agreement with the extrapolation from the high-mass SPT clusters, is in tension at 2.8σ with the Planck constraints, indicating the low-mass systems exhibit lower SZE signatures in the SPT data. We also present an analysis of potential sources of contamination. For the radio galaxy point source population, we find 18 of our systems have 843 MHz Sydney University Molonglo Sky Survey sources within 2 arcmin of the X-ray centre, and three of these are also detected at significance >4 by SPT. Of these three, two are associated with the group brightest cluster galaxies, and the third is likely an unassociated quasar candidate. We examine the impact of these point sources on our SZE scaling relation analyses and find no evidence of biases. We also examine the impact of dusty galaxies using constraints from the 220 GHz data. The stacked sample provides 2.8σ significant evidence of dusty galaxy flux, which would correspond to an average underestimate of the SPT Y_500 signal that is (17 ± 9)per cent in this sample of low-mass systems. Finally, we explore the impact of future data from SPTpol and XMM-XXL, showing that it will lead to a factor of 4 to 5 tighter

  6. The Local Group: Our Galactic Neighborhood.

    Science.gov (United States)

    Hodge, Paul

    1987-01-01

    Presents information on the properties and largest spirals of the Local Group galaxies. Explains the three categories of galaxies, identifies the brightest members of the Local Group, and discusses recent discoveries within the group. (ML)

  7. Report of the Nuclear Energy Agency expert group on gut transfer factors: implications for dose per unit intake

    International Nuclear Information System (INIS)

    1988-01-01

    This note describes the gut transfer factors recommended by an Expert Group of the Nuclear Energy Agency for intakes of certain important elements in food and drinking water. The evidence behind the recommendations is discussed and their implications for dose per unit intake is investigated. It is found that in many cases the dose per unit intake calculated using the gut uptake factor recommended by the Expert Group is similar to that calculated using the recommendations of ICRP Publication 30. However, in some cases there are substantial increases in dose per unit intake. The largest increases are by a factor of fifty for intakes of certain thorium isotopes by infants. (author)

  8. Distributional pattern of benthic foraminiferal morpho-groups in the shelf region off Mangalore: Environmental implications

    Digital Repository Service at National Institute of Oceanography (India)

    Khare, N.; Sinha, R.; Rai, A.K.; Nigam, R.

    , the population was further placed into two broad morpho-groups namely, angular-asymmetrical and rounded-symmetrical. The surficial distribution of these groups revealed that angular-asymmetrical forms are abundant in relatively deeper region whereas rounded...

  9. GALAXY ENVIRONMENTS OVER COSMIC TIME: THE NON-EVOLVING RADIAL GALAXY DISTRIBUTIONS AROUND MASSIVE GALAXIES SINCE z = 1.6

    International Nuclear Information System (INIS)

    Tal, Tomer; Van Dokkum, Pieter G.; Leja, Joel; Franx, Marijn; Wake, David A.; Whitaker, Katherine E.

    2013-01-01

    We present a statistical study of the environments of massive galaxies in four redshift bins between z = 0.04 and z = 1.6, using data from the Sloan Digital Sky Survey and the NEWFIRM Medium Band Survey. We measure the projected radial distribution of galaxies in cylinders around a constant number density selected sample of massive galaxies and utilize a statistical subtraction of contaminating sources. Our analysis shows that massive primary galaxies typically live in group halos and are surrounded by 2-3 satellites with masses more than one-tenth of the primary galaxy mass. The cumulative stellar mass in these satellites roughly equals the mass of the primary galaxy itself. We further find that the radial number density profile of galaxies around massive primaries has not evolved significantly in either slope or overall normalization in the past 9.5 Gyr. A simplistic interpretation of this result can be taken as evidence for a lack of mergers in the studied groups and as support for a static evolution model of halos containing massive primaries. Alternatively, there exists a tight balance between mergers and accretion of new satellites such that the overall distribution of galaxies in and around the halo is preserved. The latter interpretation is supported by a comparison to a semi-analytic model, which shows a similar constant average satellite distribution over the same redshift range.

  10. Systematically evaluating the impact of diagnosis-related groups (DRGs) on health care delivery: a matrix of ethical implications.

    Science.gov (United States)

    Fourie, Carina; Biller-Andorno, Nikola; Wild, Verina

    2014-04-01

    Swiss hospitals were required to implement a prospective payment system for reimbursement using a diagnosis-related groups (DRGs) classification system by the beginning of 2012. Reforms to a health care system should be assessed for their impact, including their impact on ethically relevant factors. Over a number of years and in a number of countries, questions have been raised in the literature about the ethical implications of the implementation of DRGs. However, despite this, researchers have not attempted to identify the major ethical issues associated with DRGs systematically. To address this gap in the literature, we have developed a matrix for identifying the ethical implications of the implementation of DRGs. It was developed using a literature review, and empirical studies on DRGs, as well as a review and analysis of existing ethics frameworks. The matrix consists of the ethically relevant parameters of health care systems on which DRGs are likely to have an impact; the ethical values underlying these parameters; and examples of specific research questions associated with DRGs to illustrate how the matrix can be applied. While the matrix has been developed in light of the Swiss health care reform, it could be used as a basis for identifying the ethical implications of DRG-based systems worldwide and for highlighting the ethical implications of other kinds of provider payment systems (PPS). Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

  11. The Achieving Success Everyday Group Counseling Model: Implications for Professional School Counselors

    Science.gov (United States)

    Steen, Sam; Henfield, Malik S.; Booker, Beverly

    2014-01-01

    This article presents the Achieving Success Everyday (ASE) group counseling model, which is designed to help school counselors integrate students' academic and personal-social development into their group work. We first describe this group model in detail and then offer one case example of a middle school counselor using the ASE model to conduct a…

  12. Implications of Boy Scout group use of public lands for natural resource managers: a regional comparison

    Science.gov (United States)

    Gail A. Vander Stoep

    1992-01-01

    Resource managers can apply group-specific rather than generic communications and management strategies to different public land user groups. This study compares use patterns of one user group, Boy Scout troops, from two regions of the United States. It identifies their public land use patterns, activities, needs, and motivations. Results can be used by resource...

  13. Dark Galaxies and Lost Baryons (IAU S244)

    Science.gov (United States)

    Davies, Jonathan I.; Disney, Michael J.

    2008-05-01

    Preface; Conference prelims; The HI that barked in the night M. J. Disney; The detection of dark galaxies in blind HI surveys J. I. Davies; Red haloes of galaxies - reservoirs of baryonic dark matter? E. Zackrisson, N. Bergvall, C. Flynn, G. Ostlin, G. Micheva and B. Baldwell; Constraints on dark and visible mass in galaxies from strong gravitational lensing S. Dye and S. Warren; Lost baryons at low redshift S. Mathur, F. Nicastro and R. Williams; Observed properties of dark matter on small spatial scales R. Wyse and G. Gilmore; The mass distribution in spiral galaxies P. Salucci; Connecting lost baryons and dark galaxies via QSO absorption lines T. Tripp; ALFALFA: HI cosmology in the local universe R. Giovanelli; The ALFALFA search for (almost) dark galaxies across the HI mass function M. Haynes; HI clouds detected towards Virgo with the Arecibo Legacy Fast ALFA Survey B. Kent; Cosmic variance in the HI mass function S. Schneider; The Arecibo Galaxy Environments Survey - potential for finding dark galaxies and results so far R. Minchin et al.; Free-floating HI clouds in the M81 group E. Brinks, F. Walter and E. Skillman; Where are the stars in dark galaxies J. Rosenberg, J. Salzer and J. Cannon; The halo by halo missing baryon problem S. McGaugh; The local void is really empty R. Tully; Voids in the local volume: a limit on appearance of a galaxy in a dark matter halo A. Tikhonov and A. Klypin; Dim baryons in the cosmic web C. Impey; A census of baryons in galaxy clusters and groups A. Gonzalez, D. Zaritsky and A. Zabludo; Statistical properties of the intercluster light from SDSS image stacking S. Zibetti; QSO strong gravitational lensing and the detection of dark halos A. Maccio; Strong gravitational lensing: bright galaxies and lost dark-matter L. Koopmans; Mapping the distribution of luminous and dark matter in strong lensing galaxies I. Ferreras, P. Saha, L. Williams and S. Burles; Tidal debris posing as dark galaxies P. Duc, F. Bournaud and E. Brinks

  14. Intergroup Contact and Social Change: Implications of Negative and Positive Contact for Collective Action in Advantaged and Disadvantaged Groups.

    Science.gov (United States)

    Reimer, Nils Karl; Becker, Julia C; Benz, Angelika; Christ, Oliver; Dhont, Kristof; Klocke, Ulrich; Neji, Sybille; Rychlowska, Magdalena; Schmid, Katharina; Hewstone, Miles

    2017-01-01

    Previous research has shown that (a) positive intergroup contact with an advantaged group can discourage collective action among disadvantaged-group members and (b) positive intergroup contact can encourage advantaged-group members to take action on behalf of disadvantaged outgroups. Two studies investigated the effects of negative as well as positive intergroup contact. Study 1 ( n = 482) found that negative but not positive contact with heterosexual people was associated with sexual-minority students' engagement in collective action (via group identification and perceived discrimination). Among heterosexual students, positive and negative contacts were associated with, respectively, more and less LGB (lesbian, gay, bisexual) activism. Study 2 ( N = 1,469) found that only negative contact (via perceived discrimination) predicted LGBT (lesbian, gay, bisexual, and transgender) students' collective action intentions longitudinally while only positive contact predicted heterosexual/cisgender students' LGBT activism. Implications for the relationship between intergroup contact, collective action, and social change are discussed.

  15. Galaxy angular momentum

    International Nuclear Information System (INIS)

    Thompson, L.A.

    1974-01-01

    In order to test the theories which purport to explain the origin of galaxy angular momentum, this study presents new data for about 1000 individual galaxies in eight rich clusters. The clusters which are studied include Virgo, A 119, A 400, A 1656 (Coma), A 2147, A 2151 (Hercules), A 2197, and A 2199. Selected samples of these data are used to investigate systematic alignment effects in clusters of galaxies and to investigate the intrinsic ellipticities of E, SO, and spiral galaxies. The following new results are reported: Galaxies in the cluster A 2197 show a significant alignment effect (chi 2 probability less than 0.0002), and the preferential direction of alignment corresponds approximately to the major axis of the overall cluster elongation. None of the other seven clusters show any significant alignment trends. The spiral galaxy samples in four clusters (Virgo, A 1656, A 2151, and A 2197) were large enough to analyze the number distributions of forward and reverse winding spirals. Large and small spiral galaxies have identical ellipticity distributions. Large E and SO galaxies tend to be more spherical, and small E and SO galaxies more flattened. The intrinsic ellipticities of E, SO, and spiral galaxies are the same for galaxies in the ''field'' and for galaxies in rich clusters. Six models of galaxy formation are reviewed, and the major []mphasis is placed on how each model explains the origin of galaxy angular momentum. (Diss. Abstr. Int., B)

  16. An intermediate-mass black hole in the darf galaxy Pox 52

    Science.gov (United States)

    Barth, Aaron

    2005-01-01

    Do dwarf elliptical and dwarf spiral galaxies contain central black holes with masses below 106 solar masses? Beyond the Local Group dynamical searches for black holes in this mass range are very difficult but the detection of accretion-powered nuclear activity could be used to infer the presence of a black hole. The nearby dwarf spiral galaxy NGC 4395 hosts a faint Seyfert 1 nucleus with a likely black hole mass in the range 104-105 solar masses and for more than a decade it has been the only known example of a Seyfert 1 nucleus in a dwarf galaxy. I will present new Keck spectra of the dwarf galaxy POX 52 which demonstrate that it has a Seyfert 1 spectrum nearly identical to that of NGC 4395. Its velocity dispersion is 37 km/s suggesting a possible black hole mass of order 105 solar masses. I will discuss the prospects for systematic searches for nuclear activity in dwarf galaxies and the implications for black hole demographics.

  17. An Intermediate-Mass Black Hole in the Dwarf Galaxy Pox 52

    Science.gov (United States)

    Barth, Aaron

    Do dwarf elliptical and dwarf spiral galaxies contain central black holes with masses below 106 solar masses? Beyond the Local Group dynamical searches for black holes in this mass range are very difficult but the detection of accretion-powered nuclear activity could be used to infer the presence of a black hole. The nearby dwarf spiral galaxy NGC 4395 hosts a faint Seyfert 1 nucleus with a likely black hole mass in the range 104-105 solar masses and for more than a decade it has been the only known example of a Seyfert 1 nucleus in a dwarf galaxy. I will present new Keck spectra of the dwarf galaxy POX 52 which demonstrate that it has a Seyfert 1 spectrum nearly identical to that of NGC 4395. Its velocity dispersion is 37 km/s suggesting a possible black hole mass of order 105 solar masses. I will discuss the prospects for systematic searches for nuclear activity in dwarf galaxies and the implications for black hole demographics.

  18. Polar ring galaxies in the Galaxy Zoo

    Science.gov (United States)

    Finkelman, Ido; Funes, José G.; Brosch, Noah

    2012-05-01

    We report observations of 16 candidate polar-ring galaxies (PRGs) identified by the Galaxy Zoo project in the Sloan Digital Sky Survey (SDSS) data base. Deep images of five galaxies are available in the SDSS Stripe82 data base, while to reach similar depth we observed the remaining galaxies with the 1.8-m Vatican Advanced Technology Telescope. We derive integrated magnitudes and u-r colours for the host and ring components and show continuum-subtracted Hα+[N II] images for seven objects. We present a basic morphological and environmental analysis of the galaxies and discuss their properties in comparison with other types of early-type galaxies. Follow-up photometric and spectroscopic observations will allow a kinematic confirmation of the nature of these systems and a more detailed analysis of their stellar populations.

  19. GALAXY ROTATION AND RAPID SUPERMASSIVE BINARY COALESCENCE

    Energy Technology Data Exchange (ETDEWEB)

    Holley-Bockelmann, Kelly [Vanderbilt University, Nashville, TN (United States); Khan, Fazeel Mahmood, E-mail: k.holley@vanderbilt.edu [Institute of Space Technology (IST), Islamabad (Pakistan)

    2015-09-10

    Galaxy mergers usher the supermassive black hole (SMBH) in each galaxy to the center of the potential, where they form an SMBH binary. The binary orbit shrinks by ejecting stars via three-body scattering, but ample work has shown that in spherical galaxy models, the binary separation stalls after ejecting all the stars in its loss cone—this is the well-known final parsec problem. However, it has been shown that SMBH binaries in non-spherical galactic nuclei harden at a nearly constant rate until reaching the gravitational wave regime. Here we use a suite of direct N-body simulations to follow SMBH binary evolution in both corotating and counterrotating flattened galaxy models. For N > 500 K, we find that the evolution of the SMBH binary is convergent and is independent of the particle number. Rotation in general increases the hardening rate of SMBH binaries even more effectively than galaxy geometry alone. SMBH binary hardening rates are similar for co- and counterrotating galaxies. In the corotating case, the center of mass of the SMBH binary settles into an orbit that is in corotation resonance with the background rotating model, and the coalescence time is roughly a few 100 Myr faster than a non-rotating flattened model. We find that counterrotation drives SMBHs to coalesce on a nearly radial orbit promptly after forming a hard binary. We discuss the implications for gravitational wave astronomy, hypervelocity star production, and the effect on the structure of the host galaxy.

  20. GALAXY ROTATION AND RAPID SUPERMASSIVE BINARY COALESCENCE

    International Nuclear Information System (INIS)

    Holley-Bockelmann, Kelly; Khan, Fazeel Mahmood

    2015-01-01

    Galaxy mergers usher the supermassive black hole (SMBH) in each galaxy to the center of the potential, where they form an SMBH binary. The binary orbit shrinks by ejecting stars via three-body scattering, but ample work has shown that in spherical galaxy models, the binary separation stalls after ejecting all the stars in its loss cone—this is the well-known final parsec problem. However, it has been shown that SMBH binaries in non-spherical galactic nuclei harden at a nearly constant rate until reaching the gravitational wave regime. Here we use a suite of direct N-body simulations to follow SMBH binary evolution in both corotating and counterrotating flattened galaxy models. For N > 500 K, we find that the evolution of the SMBH binary is convergent and is independent of the particle number. Rotation in general increases the hardening rate of SMBH binaries even more effectively than galaxy geometry alone. SMBH binary hardening rates are similar for co- and counterrotating galaxies. In the corotating case, the center of mass of the SMBH binary settles into an orbit that is in corotation resonance with the background rotating model, and the coalescence time is roughly a few 100 Myr faster than a non-rotating flattened model. We find that counterrotation drives SMBHs to coalesce on a nearly radial orbit promptly after forming a hard binary. We discuss the implications for gravitational wave astronomy, hypervelocity star production, and the effect on the structure of the host galaxy

  1. Recent star formation in interacting galaxies

    International Nuclear Information System (INIS)

    Joseph, R.D.; Wright, G.S.

    1985-01-01

    The subset of galaxy-galaxy interactions which have resulted in a merger are, as a class, ultraluminous IR galaxies. Their IR luminosities span a narrow range which overlaps with the most luminous Seyfert galaxies. However, in contrast with Seyfert galaxies, the available optical, IR, and radio properties of mergers show no evidence for a compact non-thermal central source, and are easily understood in terms of a burst of star formation of extraordinary intensity and spatial extent; they are 'super starbursts'. We argue that super starbursts occur in the evolution of most mergers, and discuss the implications of super starbursts for the suggestion that mergers evolve into elliptical galaxies. Finally, we note that merger-induced shocks are likely to leave the gas from both galaxies in dense molecular form which will rapidly cool, collapse, and fragment. Thus a merger might in fact be expected to result in a burst of star formation of exceptional intensity and spatial extent, i.e. a super starburst. (author)

  2. Green valley galaxies as a transition population in different environments

    Science.gov (United States)

    Coenda, Valeria; Martínez, Héctor J.; Muriel, Hernán

    2018-02-01

    We present a comparative analysis of the properties of passive, star-forming and transition (green valley) galaxies in four discrete environments: field, groups, the outskirts and the core of X-ray clusters. We construct samples of galaxies from the Sloan Digital Sky Survey in these environments so that they are bound to have similar redshift distributions. The classification of galaxies into the three sequences is based on the UV-optical colour NUV - r. We study a number of galaxy properties: stellar mass, morphology, specific star formation rate and the history of star formation. The analysis of green valley (GV) galaxies reveals that the physical mechanisms responsible for external quenching become more efficient moving from the field to denser environments. We confirm previous findings that GV galaxies have intermediate morphologies; moreover, we find that this appears to be independent of the environment. Regarding the stellar mass of GV galaxies, we find that they tend to be more massive in the field than in denser environments. On average, GV galaxies account for ∼ 20 per cent of all galaxies in groups and X-ray clusters. We find evidence that the field environment is inefficient in transforming low-mass galaxies. GV galaxies have average star formation histories intermediate between passive and star-forming galaxies, and have a clear and consistent dependence on the environment: both, the quenching time and the amplitude of the star formation rate, decrease towards higher density environments.

  3. Alignments of galaxies within cosmic filaments from SDSS DR7

    International Nuclear Information System (INIS)

    Zhang, Youcai; Yang, Xiaohu; Wang, Huiyuan; Wang, Lei; Mo, H. J.; Van den Bosch, Frank C.

    2013-01-01

    Using a sample of galaxy groups selected from the Sloan Digital Sky Survey Data Release 7, we examine the alignment between the orientation of galaxies and their surrounding large-scale structure in the context of the cosmic web. The latter is quantified using the large-scale tidal field, reconstructed from the data using galaxy groups above a certain mass threshold. We find that the major axes of galaxies in filaments tend to be preferentially aligned with the directions of the filaments, while galaxies in sheets have their major axes preferentially aligned parallel to the plane of the sheets. The strength of this alignment signal is strongest for red, central galaxies, and in good agreement with that of dark matter halos in N-body simulations. This suggests that red, central galaxies are well aligned with their host halos, in quantitative agreement with previous studies based on the spatial distribution of satellite galaxies. There is a luminosity and mass dependence that brighter and more massive galaxies in filaments and sheets have stronger alignment signals. We also find that the orientation of galaxies is aligned with the eigenvector associated with the smallest eigenvalue of the tidal tensor. These observational results indicate that galaxy formation is affected by large-scale environments and strongly suggest that galaxies are aligned with each other over scales comparable to those of sheets and filaments in the cosmic web.

  4. Alignments of galaxies within cosmic filaments from SDSS DR7

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Youcai; Yang, Xiaohu [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Nandan Road 80, Shanghai 200030 (China); Wang, Huiyuan [Key Laboratory for Research in Galaxies and Cosmology, University of Science and Technology of China, Hefei, Anhui 230026 (China); Wang, Lei [Purple Mountain Observatory, the Partner Group of MPI für Astronomie, 2 West Beijing Road, Nanjing 210008 (China); Mo, H. J. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305 (United States); Van den Bosch, Frank C., E-mail: yczhang@shao.ac.cn, E-mail: xyang@sjtu.edu.cn [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States)

    2013-12-20

    Using a sample of galaxy groups selected from the Sloan Digital Sky Survey Data Release 7, we examine the alignment between the orientation of galaxies and their surrounding large-scale structure in the context of the cosmic web. The latter is quantified using the large-scale tidal field, reconstructed from the data using galaxy groups above a certain mass threshold. We find that the major axes of galaxies in filaments tend to be preferentially aligned with the directions of the filaments, while galaxies in sheets have their major axes preferentially aligned parallel to the plane of the sheets. The strength of this alignment signal is strongest for red, central galaxies, and in good agreement with that of dark matter halos in N-body simulations. This suggests that red, central galaxies are well aligned with their host halos, in quantitative agreement with previous studies based on the spatial distribution of satellite galaxies. There is a luminosity and mass dependence that brighter and more massive galaxies in filaments and sheets have stronger alignment signals. We also find that the orientation of galaxies is aligned with the eigenvector associated with the smallest eigenvalue of the tidal tensor. These observational results indicate that galaxy formation is affected by large-scale environments and strongly suggest that galaxies are aligned with each other over scales comparable to those of sheets and filaments in the cosmic web.

  5. Star Formation in Irregular Galaxies.

    Science.gov (United States)

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  6. Combining Galaxy-Galaxy Lensing and Galaxy Clustering

    Energy Technology Data Exchange (ETDEWEB)

    Park, Youngsoo [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Krause, Elisabeth [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Dodelson, Scott [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Jain, Bhuvnesh [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Amara, Adam [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Becker, Matt [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Bridle, Sarah [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Clampitt, Joseph [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Crocce, Martin [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Honscheid, Klaus [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Gaztanaga, Enrique [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Sanchez, Carles [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Wechsler, Risa [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

    2015-01-01

    Combining galaxy-galaxy lensing and galaxy clustering is a promising method for inferring the growth rate of large scale structure, a quantity that will shed light on the mechanism driving the acceleration of the Universe. The Dark Energy Survey (DES) is a prime candidate for such an analysis, with its measurements of both the distribution of galaxies on the sky and the tangential shears of background galaxies induced by these foreground lenses. By constructing an end-to-end analysis that combines large-scale galaxy clustering and small-scale galaxy-galaxy lensing, we also forecast the potential of a combined probes analysis on DES datasets. In particular, we develop a practical approach to a DES combined probes analysis by jointly modeling the assumptions and systematics affecting the different components of the data vector, employing a shared halo model, HOD parametrization, photometric redshift errors, and shear measurement errors. Furthermore, we study the effect of external priors on different subsets of these parameters. We conclude that DES data will provide powerful constraints on the evolution of structure growth in the universe, conservatively/ optimistically constraining the growth function to 8%/4.9% with its first-year data covering 1000 square degrees, and to 4%/2.3% with its full five-year data covering 5000 square degrees.

  7. Item Construction Using Reflective, Formative, or Rasch Measurement Models: Implications for Group Work

    Science.gov (United States)

    Peterson, Christina Hamme; Gischlar, Karen L.; Peterson, N. Andrew

    2017-01-01

    Measures that accurately capture the phenomenon are critical to research and practice in group work. The vast majority of group-related measures were developed using the reflective measurement model rooted in classical test theory (CTT). Depending on the construct definition and the measure's purpose, the reflective model may not always be the…

  8. Web-based tailored lifestyle programs: exploration of the target group's interests and implications for practice.

    NARCIS (Netherlands)

    Verheijden, M.W.; Jans, M.P.; Hildebrandt, V.H.

    2008-01-01

    An important challenge in Web-based health promotion is to increase the reach of the target audience by taking the target groups' desires into consideration. Data from 505 members of a Dutch Internet panel (representative for Dutch Internet users) were used to asses the target group's interests and

  9. Life of Pizza Pie: The Implications of Sub-Group Comparisons in Education

    Science.gov (United States)

    Thomas, Tara N.

    2013-01-01

    Current educational statistics have pitted subgroups against one another without consideration of the actual population sizes of each group. This paper is intended to provided a clearer understanding of the current usage of sub-group comparisons in American education. (Contains 4 figures.)

  10. The Distance to M54 using Infrared Photometry of RR Lyrae Variable Stars and the Implications of its Relation to the Sagittarius Dwarf Galaxy

    Science.gov (United States)

    Gupta, Arvind F.; Beaton, Rachael L.; Majewski, Steven R.; SMHASH Team

    2018-01-01

    CDM cosmological models predict that dark matter halo density profiles will have central cusps. Yet for many dwarf spheroidal galaxies (dSphs), this expectation is in contrast with observations of cored, rather than cusped, halos. This 'cusp-core problem' is apparent in the Sagittarius Dwarf Galaxy (Sgr), one of the largest satellites of the Milky Way. The globular cluster M54, one of several clusters associated with Sgr, coincides in on-sky position with the center of the main body of Sgr. While several studies find that M54 lies within the center of Sgr, other findings show that M54 is offset from the center by several kiloparsecs along our line of sight. The latter requires Sgr to have a cored dark matter distribution. In the presence of a cuspy halo, the orbit of M54 would have decayed via dynamical friction and the cluster would have fallen to the center of Sgr. A clear determination of the relation of the two bodies may help us better understand the distribution of dark matter in Sgr and other dSphs. Here we present a measurement of the distance modulus to M54 using a set of RR Lyrae variable stars in near-infrared Magellan data mid-infrared Spitzer data. The magnitudes of individual stars are measured using multi-epoch PSF photometry and light curve fitting. From precise RR Lyrae period-luminosity relations at these wavelengths, we then find the mean M54 distance modulus to be 17.126 ± 0.023 (ran) ± 0.080 (sys). Our result is consistent with a distance measurement to Sgr derived via nearly identical methods and thus also consistent with the expectation of a central cusp in the dark matter density profile of Sgr.

  11. Joint XMM-Newton and Chandra observations of the NGC 1407/1400 complex: A tail of an early-type galaxy and a tale of a nearby merging group

    Energy Technology Data Exchange (ETDEWEB)

    Su, Yuanyuan [Department of Physics and Astronomy, University of California at Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); Gu, Liyi [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo (Japan); White III, Raymond E.; Irwin, Jimmy, E-mail: yuanyuas@uci.edu [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 (United States)

    2014-05-10

    The nearby group centered on its bright central galaxy NGC 1407 has been suggested by previous kinematic studies to be an unusually dark system. It is also known for hosting a bright galaxy, NGC 1400, with a large radial velocity (1200 km s{sup –1}) with respect to the group center. Previous ROSAT X-ray observations revealed an extended region of enhanced surface brightness just eastward of NGC 1400. We investigate the NGC 1407/1400 complex with XMM-Newton and Chandra observations. We find that the temperature and metallicity of the enhanced region are different (cooler and more metal rich) than those of the surrounding group gas but are consistent with those of the interstellar medium (ISM) in NGC 1400. The relative velocity of NGC 1400 is large enough that much of its ISM could have been ram pressure stripped while plunging through the group atmosphere. We conclude that the enhanced region is likely to be hot gas stripped from the ISM of NGC 1400. We constrain the motion of NGC 1400 using the pressure jump at its associated stagnation front and the total mass profile of the NGC 1407 group. We conclude that NGC 1400 is moving within ∼30° of the line of sight with Mach number M≲3. We do not detect any obvious shock features in this complex, perhaps because of the high line-of-sight motion of NGC 1400. With an XMM-Newton pointing on the relatively relaxed eastern side of NGC 1407, we derive a hydrostatic mass for this group of ∼1 × 10{sup 13} M {sub ☉} within 100 kpc. The total mass extrapolated to the virial radius (681 kpc) is 3.8 × 10{sup 13} M {sub ☉}, which puts an upper limit of ∼300 M{sub ⊙}/L{sub B{sub ⊙}} on the mass-to-light ratio of this group. This suggests that the NGC 1407 group is not an unusually dark group.

  12. Some problems of the origin of galaxy nests

    International Nuclear Information System (INIS)

    Metlov, V.G.

    1979-01-01

    The origin of galaxy nests have been studied. The nests of galaxies consist of a few (more than two) galaxies in contact with each other and strongly distorted by mutual interaction. Their colour, geometrical and morphological characteristics are compared with ones of ordinary galaxies and groups of galaxies. Conclusions are drawn that 5% to 15% of the total number of nests may be the evolutionary products of tight groups of galaxies (with diameter 11 Msub(Sun)). About half of such objects consist of elliptical galaxies. Galaxies in sufficiently tight groups may merge in consequence of dynamical friction. The remaining (85-95%) nests origin may be possibly explained by different kinds of instabilities in certain flat galaxies, with transformation of one galaxy to the nest, or by interaction of two galaxies containing large amounts of gas and consequent intensive star formation in very large regions, or by other causes. To establish relative contribution of each possible phenomenon in nests origin, it is required to carry out further detailed investigations of these objects

  13. Communication patterns within a group of shelter dogs and implications for their welfare.

    Science.gov (United States)

    Petak, Irena

    2013-01-01

    Keeping shelter dogs in groups provides them with a more socially and physically enriched environment, but eventually it may cause them stress. Understanding dogs' communication could help shelter staff recognize and prevent undesirable communicative patterns and encourage desirable ones. Therefore, the objective of this study was to determine communication patterns in a group of dogs in a shelter. The observed dogs were engaged in different classes of dyadic and group interactions. Certain dogs were frequently initiators of dyadic interactions, and different dogs were the recipients. The predominant form of dyadic interactions was a neutral one, and aggressive behavior was rarely observed. The tendency of certain dogs to interact continuously may represent a nuisance for less social individuals. All of the dogs participated in 3 defined classes of group interactions. At the group level, the dogs frequently interact vocally or olfactorily. A major welfare problem may be very vocal dogs because their vocalizations are noisy and broadcast far-reaching signals. The frequency of some group interactions was reduced by the amount of time the dogs had in the shelter.

  14. Genetic Diversity of Globally Dispersed Lacustrine Group I Haptophytes: Implications for Quantitative Temperature Reconstructions

    Science.gov (United States)

    Richter, N.; Longo, W. M.; Amaral-Zettler, L. A.; Huang, Y.

    2017-12-01

    There are significant uncertainties surrounding the forcings that drive terrestrial temperature changes on local and regional scales. Quantitative temperature reconstructions from terrestrial sites, such as lakes, help to unravel the fundamental processes that drive changes in temperature on different temporal and spatial scales. Recent studies at Brown University show that distinct alkenones, long chain ketones produced by haptophytes, are found in many freshwater, alkaline lakes in the Northern Hemisphere, highlighting these systems as targets for quantitative continental temperature reconstructions. These freshwater alkenones are produced by the Group I haptophyte phylotype and are characterized by a distinct signature: the presence of isomeric tri-unsaturated ketones and absence of alkenoates. There are currently no cultured representatives of the "Group I" haptophytes, hence they are only known based on their rRNA gene signatures. Here we present robust evidence that Northern Hemispheric freshwater, alkaline lakes with the characteristic "Group I" alkenone signature all host the same clade of Isochrysidales haptophytes. We employed next generation DNA amplicon sequencing to target haptophyte specific hypervariable regions of the large and small-subunit ribosomal RNA gene from 13 different lakes from three continents (i.e., North America, Europe, and Asia). Combined with previously published sequences, our genetic data show that the Group I haptophyte is genetically diverse on a regional and global scale, and even within the same lake. We present two case studies from a suite of five lakes in Alaska and three in Iceland to assess the impact of various environmental factors affecting Group I diversity and alkenone production. Despite the genetic diversity in this group, the overall ketone signature is conserved. Based on global surface sediment samples and in situ Alaskan lake calibrations, alkenones produced by different operational taxonomic units of the Group

  15. Demise of faint satellites around isolated early-type galaxies

    Science.gov (United States)

    Park, Changbom; Hwang, Ho Seong; Park, Hyunbae; Lee, Jong Chul

    2018-02-01

    The hierarchical galaxy formation scenario in the Cold Dark Matter cosmology with a non-vanishing cosmological constant Λ and geometrically flat space (ΛCDM) has been very successful in explaining the large-scale distribution of galaxies. However, there have been claims that ΛCDM over-predicts the number of satellite galaxies associated with massive galaxies compared with observations—the missing satellite galaxy problem1-3. Isolated groups of galaxies hosted by passively evolving massive early-type galaxies are ideal laboratories for identifying the missing physics in the current theory4-11. Here, we report—based on a deep spectroscopic survey—that isolated massive and passive early-type galaxies without any signs of recent wet mergers or accretion episodes have almost no satellite galaxies fainter than the r-band absolute magnitude of about Mr = -14. If only early-type satellites are used, the cutoff is at the somewhat brighter magnitude of about Mr = -15. Such a cutoff has not been found in other nearby satellite galaxy systems hosted by late-type galaxies or those with merger features. Various physical properties of satellites depend strongly on the host-centric distance. Our observations indicate that the satellite galaxy luminosity function is largely determined by the interaction of satellites with the environment provided by their host.

  16. On order and chaos in the mergers of galaxies

    Science.gov (United States)

    Vandervoort, Peter O.

    2018-03-01

    This paper describes a low-dimensional model of the merger of two galaxies. The governing equations are the complete sets of moment equations of the first and second orders derived from the collisionless Boltzmann equations representing the galaxies. The moment equations reduce to an equation governing the relative motion of the galaxies, tensor virial equations, and equations governing the kinetic energy tensors. We represent the galaxies as heterogeneous ellipsoids with Gaussian stratifications of their densities, and we represent the mean stellar motions in terms of velocity fields that sustain those densities consistently with the equation of continuity. We reduce and solve the governing equations for a head-on encounter of a dwarf galaxy with a giant galaxy. That reduction includes the effect of dynamical friction on the relative motion of the galaxies. Our criterion for chaotic behaviour is sensitivity of the motion to small changes in the initial conditions. In a survey of encounters and mergers of a dwarf galaxy with a giant galaxy, chaotic behaviour arises mainly in non-linear oscillations of the dwarf galaxy. The encounter disrupts the dwarf, excites chaotic oscillations of the dwarf, or excites regular oscillations. Dynamical friction can drive a merger to completion within a Hubble time only if the dwarf is sufficiently massive. The survey of encounters and mergers is the basis for a simple model of the evolution of a `Local Group' consisting of a giant galaxy and a population of dwarf galaxies bound to the giant as satellites on radial orbits.

  17. Sedimentary petrography of the Early Proterozoic Pretoria Group, Transvaal Sequence, South Africa: implications for tectonic setting

    Science.gov (United States)

    Schreiber, U. M.; Eriksson, P. G.; van der Neut, M.; Snyman, C. P.

    1992-11-01

    Sandstone petrography, geochemistry and petrotectonic assemblages of the predominantly clastic sedimentary rocks of the Early Proterozoic Pretoria Group, Transvaal Sequence, point to relatively stable cratonic conditions at the beginning of sedimentation, interrupted by minor rifting events. Basement uplift and a second period of rifting occurred towards the end of Pretoria Group deposition, which was followed by the intrusion of mafic sill swarms and the emplacement of the Bushveld Complex in the Kaapvaal Craton at about 2050 Ma, the latter indicating increased extensional tectonism, and incipient continental rifting. An overall intracratonic lacustrine tectonic setting for the Pretoria Group is supported by periods of subaerial volcanic activity and palaeosol formation, rapid sedimentary facies changes, significant arkosic sandstones, the presence of non-glacial varves and a highly variable mudrock geochemistry.

  18. Combat-related, chronic posttraumatic stress disorder: implications for group-therapy intervention.

    Science.gov (United States)

    Makler, S; Sigal, M; Gelkopf, M; Kochba, B B; Horeb, E

    1990-07-01

    The patient with combat-related chronic Posttraumatic Stress Disorder suffers from a wide spectrum of maladaptive behaviors. This paper delineates the work that has been done with such a population in group therapy. The plan that is proposed takes into account three interrelated sets of factors: factors important for creating an effective working relation; curative factors; and particular themes. Each of these factors is analyzed in the light of the particularities of group work with such a population. Each of the points discussed is based upon the relevant literature, upon the experience of the therapist, and illustrated with examples.

  19. Sagittarius Dwarf Galaxy

    Science.gov (United States)

    Ibata, R.; Murdin, P.

    2000-11-01

    The Sagittarius DWARF GALAXY is the closest member of the Milky Way's entourage of satellite galaxies. Discovered by chance in 1994, its presence had previously been overlooked because it is largely hidden by the most crowded regions of our own Galaxy with which it is merging....

  20. Tidal interaction of galaxies

    International Nuclear Information System (INIS)

    Kozlov, N.N.; Syunyaev, R.A.; Ehneev, T.M.

    1974-01-01

    One of the hypotheses explaining the occurrence of anomalous details in interacting galaxies has been investigated. Pairs of galaxies with 'tails' oppositely directed or neighbouring galaxies with cofferdams 'bridges', as if connecting the galaxies, are called interacting galaxies. The hypothesis connects the origin of cofferdams and 'tails' of interacting galaxies with tidal effects ; the action of power gravitational forces in the intergalactic space. A source of such forces may be neighbouring stellar systems or invisible bodies, for instance, 'dead' quasars after a gravitational collapse. The effect of large masses of matter on the galaxy evolution has been investigated in the Institute of Applied Mathematics of the Academy of Sciences of the USSSR in 1971-1972 by numerical simulation of the process on a digital computer with the subsequent data transmission on a display. Different versions of a massive body flight relative to a galaxy disk are considered. Photographs of a display screen at different moments of time are presented. As a result of mathematical simulation of galaxies gravitational interactions effects are discovered which resemble real structures in photographs of galaxies. It seems to be premature to state that namely these mechanisms cause the formation of 'tails' and cofferdams between galaxies. However, even now it is clear that the gravitational interaction strongly affects the dynamics of the stellar system evolution. Further studies should ascertain a true scale of this effect and its genuine role in galaxy evolution

  1. Suites of dwarfs around Nearby giant galaxies

    International Nuclear Information System (INIS)

    Karachentsev, Igor D.; Kaisina, Elena I.; Makarov, Dmitry I.

    2014-01-01

    The Updated Nearby Galaxy Catalog (UNGC) contains the most comprehensive summary of distances, radial velocities, and luminosities for 800 galaxies located within 11 Mpc from us. The high density of observables in the UNGC makes this sample indispensable for checking results of N-body simulations of cosmic structures on a ∼1 Mpc scale. The environment of each galaxy in the UNGC was characterized by a tidal index Θ 1 , depending on the separation and mass of the galaxy's main disturber (MD). We grouped UNGC galaxies with a common MD in suites, and ranked suite members according to their Θ 1 . All suite members with positive Θ 1 are assumed to be physical companions of the MD. About 58% of the sample are members of physical groups. The distribution of suites by the number of members, n, follows a relation N(n) ∼ n –2 . The 20 most populated suites contain 468 galaxies, i.e., 59% of the UNGC sample. The fraction of MDs among the brightest galaxies is almost 100% and drops to 50% at M B = –18 m . We discuss various properties of MDs, as well as galaxies belonging to their suites. The suite abundance practically does not depend on the morphological type, linear diameter, or hydrogen mass of the MD, the tightest correlation being with the MD dynamical mass. Dwarf galaxies around MDs exhibit well-known segregation effects: the population of the outskirts has later morphological types, richer H I contents, and higher rates of star formation activity. Nevertheless, there are some intriguing cases where dwarf spheroidal galaxies occur at the far periphery of the suites, as well as some late-type dwarfs residing close to MDs. Comparing simulation results with galaxy groups, most studies assume the Local Group is fairly typical. However, we recognize that the nearby groups significantly differ from each other and there is considerable variation in their properties. The suites of companions around the Milky Way and M31, consisting of the Local Group, do not

  2. Metaphors and the Pejorative Framing of Marginalized Groups: Implications for Social Work Education

    Science.gov (United States)

    O'Brien, Gerald V.

    2009-01-01

    Although the importance of metaphors is described in the social work literature, few articles or books in the profession have considered the role of metaphors in social policy, especially in providing a negative frame within which marginalized groups can be considered. This negative framing naturally supports aversive social policies designed to…

  3. Genetic survey of a group of children with clefting: implications for genetic counseling

    NARCIS (Netherlands)

    Hofstee, Y.; Kors, N.; Hennekam, R. C.

    1993-01-01

    A cleft lip, cleft palate, or both are associated with a high frequency of other anomalies. This study gives an inventory of associated anomalies in a consecutive group of children (n = 36) with clefts, referred to a local multidisciplinary cleft team in the Netherlands. In 47.2% of cleft patients

  4. Focus Group Research on the Implications of Adopting the Unified English Braille Code

    Science.gov (United States)

    Wetzel, Robin; Knowlton, Marie

    2006-01-01

    Five focus groups explored concerns about adopting the Unified English Braille Code. The consensus was that while the proposed changes to the literary braille code would be minor, those to the mathematics braille code would be much more extensive. The participants emphasized that "any code that reduces the number of individuals who can access…

  5. Treatment fairness and group norms in times of turmoil : Implications for employee well-beini

    NARCIS (Netherlands)

    Miles, P.|info:eu-repo/dai/nl/41329238X

    2010-01-01

    Employee well-being is important for individual employees and for the organizations they work for. However, current difficult economic times cause employees to experience unfavorable conditions (e.g., uncertainty, unfair outcomes and low cohesive groups) and this thesis attempts to provide

  6. Multi-Family Groups for Multi-Stressed Families: Initial Outcomes and Future Implications

    Science.gov (United States)

    Jackson, Jerrold M.

    2015-01-01

    Purpose: To examine the influence of caregiver stress on attendance among urban families involved in a multiple family group (MFG) intervention, as well as pre/post changes in childhood behavioral difficulties, caregiver stress, caregiver depressive symptoms, caregiver coping by substance use, and caregiver motivation to change. Methods:…

  7. Aptitude for Destruction. Volume 1: Organizational Learning in Terrorist Groups and Its Implications for Combating Terrorism

    Science.gov (United States)

    2005-01-01

    jihad in Af- ghanistan. Over its history, the group has had active cells in several different coun- tries, including Indonesia, Malaysia , the...and South Armagh, London, UK: Coronet Books, LIR, 2000. Hedberg, Bo, "How Organizations Learn and Unlearn?" in Paul C. Nystrim and William H. Starbuck

  8. New Tools for Examining Undergraduate Students' STEM Stereotypes: Implications for Women and Other Underrepresented Groups

    Science.gov (United States)

    Nassar-McMillan, Sylvia C.; Wyer, Mary; Oliver-Hoyo, Maria; Schneider, Jennifer

    2011-01-01

    Although both domestic U.S. and international statistics on population demographics within science, technology, engineering, and mathematics (STEM) fields indicate overall gains and more even representation among various groups, caution must be taken to interpret these gains as suggesting blanket improvement in underrepresentation issues. When…

  9. Functional groups of fossil marattialeans: chemotaxonomic implications for Pennsylvanian tree ferns and pteridophylls

    Czech Academy of Sciences Publication Activity Database

    Pšenička, J.; Zodrow, E. L.; Mastalerz, M.; Bek, Jiří

    2005-01-01

    Roč. 61, 3-4 (2005), s. 259-280 ISSN 0166-5162 R&D Projects: GA AV ČR(CZ) IAA3013902 Institutional research plan: CEZ:AV0Z30130516 Keywords : interdisciplinary approach * functional groups * FTIR Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.397, year: 2005

  10. Modeling Group Differences in OLS and Orthogonal Regression: Implications for Differential Validity Studies

    Science.gov (United States)

    Kane, Michael T.; Mroch, Andrew A.

    2010-01-01

    In evaluating the relationship between two measures across different groups (i.e., in evaluating "differential validity") it is necessary to examine differences in correlation coefficients and in regression lines. Ordinary least squares (OLS) regression is the standard method for fitting lines to data, but its criterion for optimal fit…

  11. Evolution and function of fossoriality in the carnivora: implications for group-living

    Directory of Open Access Journals (Sweden)

    Michael James Noonan

    2015-10-01

    Full Text Available The societies of group-living carnivores that neither hunt nor interact cooperatively may arise due to ecological drivers and/or constraints. In this study we evaluate whether group-living may be intrinsically associated with fossoriality; a link that is well supported in other taxa, but hitherto under-evaluated in the Carnivora. We make two over-arching predictions: i that fossoriality will be associated with carnivoran sociality; and ii that this association will be most evident in those species making extended use of subterranean dens. From a meta-analysis of key behavioural, ecological, ontological, and trophic traits, we demonstrate that three quarters of carnivore species exhibit some reliance on underground dens. Congruence between life-history traits and metrics of fossoriality evidenced that: 1 there are phylogenetic, and morphological constraints on wholly fossorial life-histories; 2 fossoriality correlated positively with the extent of offspring altriciality, linked to the use of natal dens; 3 burrow use increased with latitude; and 4 insectivorous carnivores were more fossorial than predatory carnivores. Corroborating work in the Rodentia, fossorial traits associated strongly with carnivoran group-living tendencies, where species utilising subterranean natal dens are 2.5 times more likely to form groups than those that do not. Furthermore, using comparative analyses, we evidence support for an evolutionary relationship between diet, fossoriality and sociality. We propose that fossorial dens act as a safe haven, promoting fitness benefits, territorial inheritance and cooperative breeding. We conclude that, among smaller (<15kg den-using carnivores, and especially for omnivorous/ insectivorous species for which food resource dispersion is favorable, continued cohabitation at natal dens can promote cohabitation among adults; that is, philopatric benefits leading to (not necessarily cooperative spatial groups.

  12. 21 centimeter study of spiral galaxies in the Coma supercluster

    International Nuclear Information System (INIS)

    Gavazzi, G.

    1987-01-01

    High-sensitivity, 21 cm line observations of 130 galaxies in the Coma/A1367 Supercluster region are presented and used to study the large-scale distribution of galaxies in the direction of the Coma Supercluster and the H I content in spiral galaxies as a function of the local galaxy density. Groups of galaxies are found to form a quasi-continuous structure that connects the Local Supercluster to the Coma Supercluster. This structure is composed of real filaments only in the vicinity of the Coma Cluster. Spiral galaxies in the surveyed groups and multiple systems have H I content not dissimilar from that of isolated galaxies. Galaxies within about 1 Abell radius from the Coma Cluster contain about three times less hydrogen on average than isolated galaxies. There is a strong tendency for galaxies that are more severely H I-depleted to be redder and of earlier Hubble type. In the Coma Cluster a considerable fraction of late-type, blue galaxies have large deficiency parameters. 51 references

  13. Electricity company managers' views of environmental issues: Implications for environmental groups and government

    International Nuclear Information System (INIS)

    Fischhoff, Maya E.

    2007-01-01

    The electricity industry's environmental impacts are a matter of acute interest to many outsiders, including government and environmental groups-and they have sought to affect those impacts through regulations, public pressure, and technical assistance. These approaches reflect outsiders' intuitive theories regarding the industry's goals, practices, and capabilities. The research reported here provides a systematic insiders' view on these processes, based on in-depth interviews with 70 middle managers in two electricity companies heavily reliant on coal. It finds managers sincerely committed to environmental action, but often frustrated by confusing regulatory requirements, perceived costs, and other challenges. It identifies ways of enabling middle managers to act on their commitment, with lessons relevant for outside groups and those within companies seeking to effect change

  14. Characterization and evolutionary implications of the triad Asp-Xxx-Glu in group II phosphopantetheinyl transferases.

    Science.gov (United States)

    Wang, Yue-Yue; Li, Yu-Dong; Liu, Jian-Bo; Ran, Xin-Xin; Guo, Yuan-Yang; Ren, Ni-Ni; Chen, Xin; Jiang, Hui; Li, Yong-Quan

    2014-01-01

    Phosphopantetheinyl transferases (PPTases), which play an essential role in both primary and secondary metabolism, are magnesium binding enzymes. In this study, we characterized the magnesium binding residues of all known group II PPTases by biochemical and evolutionary analysis. Our results suggested that group II PPTases could be classified into two subgroups, two-magnesium-binding-residue-PPTases containing the triad Asp-Xxx-Glu and three-magnesium-binding-residue-PPTases containing the triad Asp-Glu-Glu. Mutations of two three-magnesium-binding-residue-PPTases and one two-magnesium-binding-residue-PPTase indicate that the first and the third residues in the triads are essential to activities; the second residues in the triads are non-essential. Although variations of the second residues in the triad Asp-Xxx-Glu exist throughout the whole phylogenetic tree, the second residues are conserved in animals, plants, algae, and most prokaryotes, respectively. Evolutionary analysis suggests that: the animal group II PPTases may originate from one common ancestor; the plant two-magnesium-binding-residue-PPTases may originate from one common ancestor; the plant three-magnesium-binding-residue-PPTases may derive from horizontal gene transfer from prokaryotes.

  15. Pregnancy hormone concentrations across ethnic groups: implications for later cancer risk.

    Science.gov (United States)

    Potischman, Nancy; Troisi, Rebecca; Thadhani, Ravi; Hoover, Robert N; Dodd, Kevin; Davis, William W; Sluss, Patrick M; Hsieh, Chung-Cheng; Ballard-Barbash, Rachel

    2005-06-01

    A variety of in utero factors have been associated with risk of adult cancers, particularly birth weight, toxemia, and gestational age. These factors are thought to reflect hormonal exposures during pregnancy. We hypothesized that the prenatal hormonal milieu may explain part of the variation in cancer rates across ethnic groups, for example, the higher incidence of breast cancer in the Caucasian compared with Hispanic women and the higher incidence of prostate and lower incidence of testicular cancers among African-Americans compared with Caucasians. We measured hormones in early pregnancy blood samples from three ethnic groups in a health care plan in Boston, MA. Mean levels of androstenedione, testosterone, estrone, and prolactin were significantly lower in Caucasian women compared with Hispanic women. Although not statistically significant, estradiol levels were lower in Caucasian compared with Hispanic or African-American women. Concentrations of androstenedione, testosterone, and progesterone were notably higher in African-American compared with Caucasian or Hispanic women. These data are consistent with hypotheses that in utero hormonal exposures may explain some of the ethnic group differences in cancer risk.

  16. Dependence of the clustering properties of galaxies on stellar velocity dispersion in the Main galaxy sample of SDSS DR10

    Science.gov (United States)

    Deng, Xin-Fa; Song, Jun; Chen, Yi-Qing; Jiang, Peng; Ding, Ying-Ping

    2014-08-01

    Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we investigate the dependence of the clustering properties of galaxies on stellar velocity dispersion by cluster analysis. It is found that in the luminous volume-limited Main galaxy sample, except at r=1.2, richer and larger systems can be more easily formed in the large stellar velocity dispersion subsample, while in the faint volume-limited Main galaxy sample, at r≥0.9, an opposite trend is observed. According to statistical analyses of the multiplicity functions, we conclude in two volume-limited Main galaxy samples: small stellar velocity dispersion galaxies preferentially form isolated galaxies, close pairs and small group, while large stellar velocity dispersion galaxies preferentially inhabit the dense groups and clusters. However, we note the difference between two volume-limited Main galaxy samples: in the faint volume-limited Main galaxy sample, at r≥0.9, the small stellar velocity dispersion subsample has a higher proportion of galaxies in superclusters ( n≥200) than the large stellar velocity dispersion subsample.

  17. KECK SPECTROSCOPY OF LYMAN-BREAK GALAXIES AND ITS IMPLICATIONS FOR THE UV-CONTINUUM AND Lyα LUMINOSITY FUNCTIONS AT z > 6

    International Nuclear Information System (INIS)

    Jiang Linhua; Egami, Eiichi; Walth, Gregory; Kashikawa, Nobunari; Matsuda, Yuichi; Shimasaku, Kazuhiro; Nagao, Tohru; Ota, Kazuaki; Ouchi, Masami

    2011-01-01

    We present Keck spectroscopic observations of z > 6 Lyman-break galaxy (LBG) candidates in the Subaru Deep Field (SDF). The candidates were selected as i'-dropout objects down to z' = 27 AB magnitudes from an ultra-deep SDF z'-band image. With the Keck spectroscopy we identified 19 LBGs with prominent Lyα emission lines at 6 ≤ z ≤ 6.4. The median value of the Lyα rest-frame equivalent widths (EWs) is ∼50 Å, with four EWs >100 Å. This well-defined spectroscopic sample spans a UV-continuum luminosity range of –21.8 ≤ M UV ≤ –19.5 (0.6 ∼ 5 L* UV ) and a Lyα luminosity range of (0.3-3) × 10 43 erg s –1 (0.3-3 L* Lyα ). We derive the UV and Lyα luminosity functions (LFs) from our sample at (z) ∼ 6.2 after we correct for sample incompleteness. We find that our measurement of the UV LF is consistent with the results of previous studies based on photometric LBG samples at 5 6.

  18. Naturally occurring arsenic in the Miocene Hawthorn Group, southwestern Florida: Potential implication for phosphate mining

    International Nuclear Information System (INIS)

    Lazareva, Olesya; Pichler, Thomas

    2007-01-01

    To understand the mineralogical association, concentration, and distribution of arsenic (As) in the Hawthorn Group, the chemical and mineralogical composition of 362 samples that were collected from 16 cores in southwestern Florida were examined in detail. In the study area, the Hawthorn Group consisted primarily of a basal carbonate unit (the Arcadia Formation) and an upper siliciclastic unit (The Peace River Formation). The Peace River Formation contains appreciable amounts of phosphate and is currently being exploited for phosphate ore. Samples were taken from cores of each formation at intervals of 7.5 m. In addition, to the interval samples, sections likely to have high As concentrations, such as zones with pyrite crystals, hydrous ferric oxides, green clays, and organic material, were collected and analyzed. Bulk As concentrations were determined by hydride generation-atomic fluorescence spectrometry (HG-AFS) after digestion with aqua regia (3:1 HCl and HNO 3 ). The elements Fe, Al, Si, Mg, Ca, S, and P were measured on the same solutions by inductively coupled plasma optical emission spectrometry (ICP-OES). The identification of discrete minerals was aided by scanning electron microscopy (SEM) and chemical compositions within the sample matrix and in individual minerals were obtained by electron-probe microanalysis (EMPA). This detailed mineralogical and geochemical study demonstrated that: (1) As in the Hawthorn Group varied from formation to formation and was mostly concentrated in trace minerals, such as pyrite; (2) average As concentrations significantly changed from 8.8 mg/kg (σ = 8.6 mg/kg) in the Peace River Formation to 3.0 mg/kg (σ = 3.7 mg/kg) in the Tampa Member of the Arcadia Formation. Arsenic concentrations for all Hawthorn samples varied from 0.1 to 69.0 mg/kg; (3) pyrite, with one exception, occurred as framboids and was unevenly distributed throughout the Hawthorn Group; (4) pyrite framboids were located inside a francolite (carbonate

  19. Chemical evolution of galaxies

    CERN Document Server

    Matteucci, Francesca

    2012-01-01

    The term “chemical evolution of galaxies” refers to the evolution of abundances of chemical species in galaxies, which is due to nuclear processes occurring in stars and to gas flows into and out of galaxies. This book deals with the chemical evolution of galaxies of all morphological types (ellipticals, spirals and irregulars) and stresses the importance of the star formation histories in determining the properties of stellar populations in different galaxies. The topic is approached in a didactical and logical manner via galaxy evolution models which are compared with observational results obtained in the last two decades: The reader is given an introduction to the concept of chemical abundances and learns about the main stellar populations in our Galaxy as well as about the classification of galaxy types and their main observables. In the core of the book, the construction and solution of chemical evolution models are discussed in detail, followed by descriptions and interpretations of observations of ...

  20. An analysis of malar fat volume in two age groups: implications for craniofacial surgery.

    Science.gov (United States)

    Corey, Christina L; Popelka, Gerald R; Barrera, Jose E; Most, Sam P

    2012-12-01

    Objective To evaluate how malar fat pad (MFP) volumes vary with age, after controlling for gender and body mass index (BMI). Study Design A prospective case-control study evaluating volume of the MFP in women of two age groups. Methods Soft tissue dimensions were measured in eight subjects using magnetic resonance imaging. A multiplanar localizing sequence, followed in sagittal and coronal orientations using a turbo spin echo sequence, was performed to define the MFP. Volumetric calculations were then performed using a 3D image analysis application (Dextroscope, Volume Interactions, Republic of Singapore) to circumscribe areas, orient dimensions, and calculate volumes of the MFP. Results These data reveal no significant difference in the mean (standard deviation) right MFP (p = 0.50), left MFP (p = 0.41), or total MFP (p = 0.45) volumes when comparing the two age groups. In addition, these data indicate that there was no correlation between age and total MFP volume (Pearson correlation coefficient 0.27). Moreover, there was no correlation between age and the ratio of total volume/BMI (Pearson correlation coefficient -0.18). Conclusions Although the sample size of this study was small, these data indicate that ptosis of midfacial fat is more important than volume loss in midfacial aging. These data would suggest repositioning as the primary modality for craniofacial reconstruction.

  1. Evolution of high mobility group nucleosome-binding proteins and its implications for vertebrate chromatin specialization.

    Science.gov (United States)

    González-Romero, Rodrigo; Eirín-López, José M; Ausió, Juan

    2015-01-01

    High mobility group (HMG)-N proteins are a family of small nonhistone proteins that bind to nucleosomes (N). Despite the amount of information available on their structure and function, there is an almost complete lack of information on the molecular evolutionary mechanisms leading to their exclusive differentiation. In the present work, we provide evidence suggesting that HMGN lineages constitute independent monophyletic groups derived from a common ancestor prior to the diversification of vertebrates. Based on observations of the functional diversification across vertebrate HMGN proteins and on the extensive silent nucleotide divergence, our results suggest that the long-term evolution of HMGNs occurs under strong purifying selection, resulting from the lineage-specific functional constraints of their different protein domains. Selection analyses on independent lineages suggest that their functional specialization was mediated by bursts of adaptive selection at specific evolutionary times, in a small subset of codons with functional relevance-most notably in HMGN1, and in the rapidly evolving HMGN5. This work provides useful information to our understanding of the specialization imparted on chromatin metabolism by HMGNs, especially on the evolutionary mechanisms underlying their functional differentiation in vertebrates. © The Author 2014. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  2. The MASSIVE Survey - V. Spatially resolved stellar angular momentum, velocity dispersion, and higher moments of the 41 most massive local early-type galaxies

    Science.gov (United States)

    Veale, Melanie; Ma, Chung-Pei; Thomas, Jens; Greene, Jenny E.; McConnell, Nicholas J.; Walsh, Jonelle; Ito, Jennifer; Blakeslee, John P.; Janish, Ryan

    2017-01-01

    We present spatially resolved two-dimensional stellar kinematics for the 41 most massive early-type galaxies (ETGs; MK ≲ -25.7 mag, stellar mass M* ≳ 1011.8 M⊙) of the volume-limited (D McDonald Observatory, covering a 107 arcsec × 107 arcsec field of view (often reaching 2 to 3 effective radii). We measure the 2D spatial distribution of each galaxy's angular momentum (λ and fast or slow rotator status), velocity dispersion (σ), and higher order non-Gaussian velocity features (Gauss-Hermite moments h3 to h6). Our sample contains a high fraction (˜80 per cent) of slow and non-rotators with λ ≲ 0.2. When combined with the lower mass ETGs in the ATLAS3D survey, we find the fraction of slow rotators to increase dramatically with galaxy mass, reaching ˜50 per cent at MK ˜ -25.5 mag and ˜90 per cent at MK ≲ -26 mag. All of our fast rotators show a clear anticorrelation between h3 and V/σ, and the slope of the anticorrelation is steeper in more round galaxies. The radial profiles of σ show a clear luminosity and environmental dependence: the 12 most luminous galaxies in our sample (MK ≲ -26 mag) are all brightest cluster/group galaxies (except NGC 4874) and all have rising or nearly flat σ profiles, whereas five of the seven `isolated' galaxies are all fainter than MK = -25.8 mag and have falling σ. All of our galaxies have positive average h4; the most luminous galaxies have average h4 ˜ 0.05, while less luminous galaxies have a range of values between 0 and 0.05. Most of our galaxies show positive radial gradients in h4, and those galaxies also tend to have rising σ profiles. We discuss the implications for the relationship among dynamical mass, σ, h4, and velocity anisotropy for these massive galaxies.

  3. Implementation of the AAPM Task Group 21 protocol by the Radiological Physics Center and its implications

    International Nuclear Information System (INIS)

    Gastorf, R.J.; Hanson, W.F.; Shalek, R.J.; Berkley, L.W.

    1984-01-01

    The Radiation Therapy Committee of the American Association of Physicists in Medicine appointed Task Group 21 to write a new protocol for the calibration of high-energy photon and electron therapy beams. This protocol updates the physical parameters used in the calculations and is intended to account for differences in ionization chamber design and some differences between phantom materials that were not considered in previous protocols. This paper discusses how the Radiological Physics Center (RPC) intends to implement the new protocol, the changes required in the RPC calibration techniques, and the magnitude of the change in the RPC calculations of absorbed dose resulting from the implementation of the new protocol. Although the change in the RPC absorbed-dose calculations will be only 0%-2% over the range of photon and electron energies of interest, some institutions using specific dosimetry systems may find their absorbed-dose calculations changing by 4% or more

  4. Iranian migrants' discourses of health and the implications for using standardized health measures with minority groups.

    Science.gov (United States)

    Momenzadeh, Sirous; Posner, Natasha

    2003-10-01

    This paper explores the concept of health implied in the SF-36 within a group of Iranians in Australia. Qualitative data were collected from a sample of 21 people--10 females and 11 males. For the first time, the NUD*IST program was used to organize and manage the data in Persian (also known as Farsi), the language spoken by Iranians. Health was defined in terms of holistic, spiritual, social, physical/emotional aspects, and absence-of-disorder dimensions. Among these, physical, absence of disorder, holistic, and spiritual aspects of health were mentioned more frequently than other themes. The findings of the study raise concerns about the extent to which the SF-36 captures the diversity of the concept of health as expressed by the sample of Iranian migrants.

  5. Galaxy Zoo: dust in spiral galaxies star

    OpenAIRE

    Masters, Karen L.; Nichol, Robert; Bamford, Steven; Mosleh, Moein; Lintott, Chris J.; Andreescu, Dan; Edmondson, Edward M.; Keel, William C.; Murray, Phil; Raddick, M. Jordan; Schawinski, Kevin; Slosar, Anze; Szalay, Alexander S.; Thomas, Daniel; Vandenberg, Jan

    2010-01-01

    We investigate the effect of dust on spiral galaxies by measuring the inclination dependence of optical colours for 24 276 well-resolved Sloan Digital Sky Survey (SDSS) galaxies visually classified via the Galaxy Zoo project. We find clear trends of reddening with inclination which imply a total extinction from face-on to edge-on of 0.7, 0.6, 0.5 and 0.4 mag for the ugri passbands (estimating 0.3 mag of extinction in z band). We split the sample into ‘bulgy’ (early-type) and ‘discy’ (late-typ...

  6. Chemical Basis for Qualitative and Quantitative Differences Between ABO Blood Groups and Subgroups: Implications for Organ Transplantation.

    Science.gov (United States)

    Jeyakanthan, M; Tao, K; Zou, L; Meloncelli, P J; Lowary, T L; Suzuki, K; Boland, D; Larsen, I; Burch, M; Shaw, N; Beddows, K; Addonizio, L; Zuckerman, W; Afzali, B; Kim, D H; Mengel, M; Shapiro, A M J; West, L J

    2015-10-01

    Blood group ABH(O) carbohydrate antigens are carried by precursor structures denoted type I-IV chains, creating unique antigen epitopes that may differ in expression between circulating erythrocytes and vascular endothelial cells. Characterization of such differences is invaluable in many clinical settings including transplantation. Monoclonal antibodies were generated and epitope specificities were characterized against chemically synthesized type I-IV ABH and related glycans. Antigen expression was detected on endomyocardial biopsies (n = 50) and spleen (n = 11) by immunohistochemical staining and on erythrocytes by flow cytometry. On vascular endothelial cells of heart and spleen, only type II-based ABH antigens were expressed; type III/IV structures were not detected. Type II-based ABH were expressed on erythrocytes of all blood groups. Group A1 and A2 erythrocytes additionally expressed type III/IV precursors, whereas group B and O erythrocytes did not. Intensity of A/B antigen expression differed among group A1 , A2 , A1 B, A2 B and B erythrocytes. On group A2 erythrocytes, type III H structures were largely un-glycosylated with the terminal "A" sugar α-GalNAc. Together, these studies define qualitative and quantitative differences in ABH antigen expression between erythrocytes and vascular tissues. These expression profiles have important implications that must be considered in clinical settings of ABO-incompatible transplantation when interpreting anti-ABO antibodies measured by hemagglutination assays with reagent erythrocytes. © Copyright 2015 The American Society of Transplantation and the American Society of Transplant Surgeons.

  7. Prenatal and neonatal Group B Streptococcus screening and serotyping in Lebanon: incidence and implications.

    Science.gov (United States)

    Seoud, Muheiddine; Nassar, Anwar H; Zalloua, Pierre; Boghossian, Nansi; Ezeddine, Jihad; Fakhoury, Hassan; Abboud, Joseph; Melki, Imad; Araj, George; Nacouzi, Ghinwa; Sanyoura, May; Yunis, Khalid

    2010-03-01

    The study aimed at determining the prevalence, risk factors, perinatal transmission, and serotypes of Group B Streptococcus (GBS) among pregnant women and their newborns in Beirut, Lebanon. This was a cross-sectional study of all pregnant women admitted from February to September 2006 to three major hospitals. Overall, 137 of 775 (17.7%) mothers and 50 of 682 newborns (7.3%) tested positive for GBS. Maternal colonization was not associated with maternal age, household income, gravidity, intrapartum fever, preterm labor, or premature rupture of membrane. Transmission rate was 40/120 (30%). Serotype 5 (24.1%) was the most common followed by serotype 1a (15.0%), 3 (14.4%), 2 (11.8%) and 1b (7.5%). Pregnant women in Lebanon appear to have a relatively high prevalence of GBS colonization with no identifiable risk factors for its acquisition. These results could provide basis for the institution of a national policy for universal maternal GBS screening to reduce neonatal morbidity and mortality.

  8. Invasive Group A Streptococcal Infection and Vaccine Implications, Auckland, New Zealand

    Science.gov (United States)

    Safar, Atheer; Stewart, Joanna; Trenholme, Adrian; Drinkovic, Dragana; Peat, Briar; Taylor, Susan; Read, Kerry; Roberts, Sally; Voss, Lesley

    2011-01-01

    We aimed to assess the effect of invasive group A streptococcal (GAS) infection and the potential effects of a multivalent GAS vaccine in New Zealand. During January 2005–December 2006, we conducted prospective population-based laboratory surveillance of Auckland residents admitted to all public hospitals with isolation of GAS from normally sterile sites. Using emm typing, we identified 225 persons with confirmed invasive GAS infection (median 53 years of age; range 0–97 years). Overall incidence was 8.1 cases per 100,00 persons per year (20.4/100,000/year for Maori and Pacific Islanders; 24.4/100,000/year for persons >65 years of age; 33/100,000/year for infants Auckland’s lowest socioeconomic quintile. Twenty-two persons died, for an overall case-fatality rate of 10% (63% for toxic shock syndrome). Seventy-four percent of patients who died had an underlying condition. To the population in our study, the proposed 26-valent vaccine would provide limited benefit. PMID:21749758

  9. Implications of Antibiotic Resistance in the Management of Helicobacter pylori Infection: Canadian Helicobacter Study Group

    Directory of Open Access Journals (Sweden)

    RH Hunt

    2000-01-01

    Full Text Available Eradication of Helicobacter pylori from the gastric and duodenal mucosa is an important clinical goal in the treatment of infected patients with peptic ulcer disease and other H pylori-associated conditions. Although several oral drug combination regimens are associated with eradication rates of approximately 85% in controlled trials, the success rate in patients infected with a resistant strain of H pylori is closer to 75%. Resistance to metronidazole and clarithromycin, which are common components of combination treatment regimens, is of greatest concern. Reported rates of H pylori resistance to various antibiotics vary considerably. In Canada, the data documenting H pylori susceptibility are limited but suggest that resistance to these antibiotics varies geographically and within specific treatment groups. Although susceptibility testing is not a prerequisite for initial treatment of individual patients infected with H pylori, formal efforts to identify and monitor both the causes and prevalence of antibiotic resistance across Canada are a much needed step in the ongoing management of this important infection. Recommended treatment regimens may be useful, even for treating apparently resistant H pylori strains. However, it is important to understand the mechanisms of the development of resistant strains to manage patients with treatment failure better.

  10. High Expression of High-Mobility Group Box 1 in Menstrual Blood: Implications for Endometriosis.

    Science.gov (United States)

    Shimizu, Keiko; Kamada, Yasuhiko; Sakamoto, Ai; Matsuda, Miwa; Nakatsuka, Mikiya; Hiramatsu, Yuji

    2017-11-01

    Endometriosis is a benign gynecologic disease characterized by the presence of ectopic endometrium and associated with inflammation and immune abnormalities. However, the molecular basis for endometriosis is not well understood. To address this issue, the present study examined the expression of high-mobility group box (HMGB) 1 in menstrual blood to investigate its role in the ectopic growth of human endometriotic stromal cells (ESCs). A total of 139 patients were enrolled in this study; 84 had endometriosis and 55 were nonendometriotic gynecological patients (control). The HMGB1 levels in various fluids were measured by enzyme-linked immunosorbent assay. Expression of receptor for advanced glycation end products (RAGE) in eutopic and ectopic endometrium was assessed by immunohistochemistry, and RAGE and vascular endothelial growth factor ( VEGF) messenger RNA expression in HMGB1- and lipopolysaccharide (LPS)-treated ESCs was evaluated by real-time polymerase chain reaction. The HMGB1 concentration was higher in menstrual blood than in serum or peritoneal fluid ( P endometriosis following retrograde menstruation when complexed with other factors such as LPS by inducing inflammation and angiogenesis.

  11. An automatic taxonomy of galaxy morphology using unsupervised machine learning

    Science.gov (United States)

    Hocking, Alex; Geach, James E.; Sun, Yi; Davey, Neil

    2018-01-01

    We present an unsupervised machine learning technique that automatically segments and labels galaxies in astronomical imaging surveys using only pixel data. Distinct from previous unsupervised machine learning approaches used in astronomy we use no pre-selection or pre-filtering of target galaxy type to identify galaxies that are similar. We demonstrate the technique on the Hubble Space Telescope (HST) Frontier Fields. By training the algorithm using galaxies from one field (Abell 2744) and applying the result to another (MACS 0416.1-2403), we show how the algorithm can cleanly separate early and late type galaxies without any form of pre-directed training for what an 'early' or 'late' type galaxy is. We then apply the technique to the HST Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) fields, creating a catalogue of approximately 60 000 classifications. We show how the automatic classification groups galaxies of similar morphological (and photometric) type and make the classifications public via a catalogue, a visual catalogue and galaxy similarity search. We compare the CANDELS machine-based classifications to human-classifications from the Galaxy Zoo: CANDELS project. Although there is not a direct mapping between Galaxy Zoo and our hierarchical labelling, we demonstrate a good level of concordance between human and machine classifications. Finally, we show how the technique can be used to identify rarer objects and present lensed galaxy candidates from the CANDELS imaging.

  12. KECK SPECTROSCOPY OF LYMAN-BREAK GALAXIES AND ITS IMPLICATIONS FOR THE UV-CONTINUUM AND Ly{alpha} LUMINOSITY FUNCTIONS AT z > 6

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Linhua; Egami, Eiichi; Walth, Gregory [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Kashikawa, Nobunari [Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Matsuda, Yuichi [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Shimasaku, Kazuhiro [Department of Astronomy, University of Tokyo, Hongo, Tokyo 113-0033 (Japan); Nagao, Tohru [Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho, Matsuyama 790-8577 (Japan); Ota, Kazuaki [Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Ouchi, Masami [Institute for Cosmic Ray Research, University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa City, Chiba 77-8582 (Japan)

    2011-12-10

    We present Keck spectroscopic observations of z > 6 Lyman-break galaxy (LBG) candidates in the Subaru Deep Field (SDF). The candidates were selected as i'-dropout objects down to z' = 27 AB magnitudes from an ultra-deep SDF z'-band image. With the Keck spectroscopy we identified 19 LBGs with prominent Ly{alpha} emission lines at 6 {<=} z {<=} 6.4. The median value of the Ly{alpha} rest-frame equivalent widths (EWs) is {approx}50 A, with four EWs >100 A. This well-defined spectroscopic sample spans a UV-continuum luminosity range of -21.8 {<=} M{sub UV} {<=} -19.5 (0.6 {approx} 5 L*{sub UV}) and a Ly{alpha} luminosity range of (0.3-3) Multiplication-Sign 10{sup 43} erg s{sup -1} (0.3-3 L*{sub Ly{alpha}}). We derive the UV and Ly{alpha} luminosity functions (LFs) from our sample at (z) {approx} 6.2 after we correct for sample incompleteness. We find that our measurement of the UV LF is consistent with the results of previous studies based on photometric LBG samples at 5 < z < 7. Our Ly{alpha} LF is also generally in agreement with the results of Ly{alpha}-emitter surveys at z {approx} 5.7 and 6.6. This study shows that deep spectroscopic observations of LBGs can provide unique constraints on both the UV and Ly{alpha} LFs at z > 6.

  13. Eudialyte-group minerals from the Monte de Trigo alkaline suite, Brazil: composition and petrological implications

    Directory of Open Access Journals (Sweden)

    Gaston Eduardo Enrich Rojas

    Full Text Available ABSTRACT: The Monte de Trigo alkaline suite is a SiO2-undersaturated syenite-gabbroid association from the Serra do Mar alkaline province. Eudialyte-group minerals (EGMs occur in one nepheline microsyenite dyke, associated with aegirine-augite, wöhlerite, låvenite, magnetite, zircon, titanite, britholite, and pyrochlore. Major compositional variations include Si (25.09- 25.57 apfu , Nb (0.31- 0.76 apfu , Fe (1.40-2.13 apfu , and Mn (1.36- 2.08 apfu . The EGMs also contain relatively high contents of Ca (6.13- 7.10 apfu , moderate enrichment of rare earth elements (0.38-0.67 apfu , and a relatively low Na content (11.02-12.28 apfu , which can be correlated with their transitional agpaitic assemblage. EGM compositions indicate a complex solid solution that includes eudialyte, kentbrooksite, feklichevite, zirsilite-(Ce, georgbarsanovite, and manganoeudialyte components. EGM trace element analyses show low Sr and Ba contents and a negative Eu/Eu* anomaly, which are interpreted as characteristic of the parental magma due to the previous fractionation of plagioclase and/or alkali feldspar. The EGMs from the dyke border have higher contents of Fe, Sr (2,161-2,699 ppm, Mg (1,179-3,582 ppm, and Zn (732- 852 ppm than those at the dyke center. These differences are related to the incorporation of xenoliths and xenocrysts of melatheralitic host rock into the nepheline-syenitic magma followed by crystal-melt diffusive exchange.

  14. Antibiotic resistance of canine Staphylococcus intermedius group (SIG)--practical implications.

    Science.gov (United States)

    Chrobak, D; Kizerwetter-Swida, M; Rzewuska, M; Binek, M

    2011-01-01

    A total of 221 SIG strains were isolated from clinical samples of canine origin submitted to the Diagnostic Laboratory of the Division of Bacteriology and Molecular Biology at the Warsaw University of Life Sciences in Warsaw during the period 2006-2010. The aim of the study was to investigate the frequency of prevalence of methicillin-resistant SIG strains and to determine the MIC values of cephalotin, amoxicillin/clavulanic acid, ciprofloxacin, clindamycin, gentamicin, chloramphenicol, mupirocin for a collection of randomly selected 79 strains belonging to Staphylococcus intermedius group (SIG), including 23 mecA-positive and 56 mecA-negative strains. All isolates were identified as belonging to SIG based on their phenotypic properties and PCR amplification of S. intermedius-specific fragment of the 16S rRNA gene. The mecA gene was detected in 26 (12%) of 221 SIG strains. All tested mecA-negative SIG strains were susceptible to amoxicillin/clavulanic acid and cephalotin. One of the 56 mecA-negative SIG strains was resistant to ciprofloxacin, six (11%) to gentamicin. It was found that sixteen (29%) of 56 mecA-negative SIG strains were resistant to clindamycin. Most of the mecA-positive SIG strains were resistant to ciprofloxacin (96%), clindamycin (96%), and gentamicin (96%). Only one MRSIG strain was resistant to chloramphenicol. All examined mecA-positive SIG strains were found to be susceptible to mupirocin. Our results imply that staphylococcal multidrug resistance has become more prevalent, which could lead to difficulties in effective treatment. With some resistant strains the only therapeutic possibility are antimicrobial agents important in human medicine. New regulations for veterinary medicine concerning appropriate therapy of infections caused by multidrug-resistat staphylococci are needed.

  15. Modelling the IRAS colors of galaxies

    International Nuclear Information System (INIS)

    Helou, G.

    1987-01-01

    A physical interpretation is proposed for the color-color diagram of galaxies which are powered only by star formation. The colors of each galaxy result from the combination of two components: cirrus-like emission from the neutral disk, and warmer emission from regions directly involved in on-going star formation. This approach to modelling the emission is based on dust properties, but independent evidence for it is found in the relation between the color sequence and the luminosity sequence. Implications of data and interpretations are discussed and possible tests mentioned for the model

  16. Chaperonin of Group I: Oligomeric Spectrum and Biochemical and Biological Implications

    Directory of Open Access Journals (Sweden)

    Silvia Vilasi

    2018-01-01

    Full Text Available Chaperonins play various physiological roles and can also be pathogenic. Elucidation of their structure, e.g., oligomeric status and post-translational modifications (PTM, is necessary to understand their functions and mechanisms of action in health and disease. Group I chaperonins form tetradecamers with two stacked heptameric rings. The tetradecamer is considered the typical functional complex for folding of client polypeptides. However, other forms such as the monomer and oligomers with smaller number of subunits than the classical tetradecamer, also occur in cells. The properties and functions of the monomer and oligomers, and their roles in chaperonin-associated diseases are still incompletely understood. Chaperonin I in eukaryotes occurs in various locations, not just the mitochondrion, which is its canonical place of residence and function. Eukaryotic Chaperonin I, namely Hsp60 (designated HSP60 or HSPD1 in humans has, indeed, been found in the cytosol; the plasma-cell membrane; on the outer surface of cells; in the intercellular space; in biological liquids such as lymph, blood, and cerebrospinal fluid; and in secretions, for instance saliva and urine. Hsp60 has also been found in cell-derived vesicles such as exosomes. The functions of Hsp60 in all these non-canonical locales are still poorly characterized and one of the questions not yet answered is in what form, i.e., monomer or oligomer, is the chaperonin present in these non-canonical locations. In view of the steady increase in interest on chaperonopathies over the last several years, we have studied human HSP60 to determine its role in various diseases, its locations in cells and tissues and migrations in the body, and its post-translational modifications that might have an impact on its location and function. We also carried out experiments to characterize the oligomeric status of extramitochondrial of HSP60 in solution. Here, we provide an overview of our results, focusing on

  17. The structure of nearby clusters of galaxies Hierarchical clustering and an application to the Leo region

    CERN Document Server

    Materne, J

    1978-01-01

    A new method of classifying groups of galaxies, called hierarchical clustering, is presented as a tool for the investigation of nearby groups of galaxies. The method is free from model assumptions about the groups. The scaling of the different coordinates is necessary, and the level from which one accepts the groups as real has to be determined. Hierarchical clustering is applied to an unbiased sample of galaxies in the Leo region. Five distinct groups result which have reasonable physical properties, such as low crossing times and conservative mass-to-light ratios, and which follow a radial velocity- luminosity relation. Only 4 out of 39 galaxies were adopted as field galaxies. (27 refs).

  18. Star Formation Histories of Dwarf Irregular Galaxies

    Science.gov (United States)

    Skillman, Evan

    1995-07-01

    We propose to obtain deep WFPC2 `BVI' color-magnitude diagrams {CMDs} for the dwarf irregular {dI} Local Group galaxies GR 8, Leo A, Pegasus, and Sextans A. In addition to resolved stars, we will use star clusters, and especially any globulars, to probe the history of intense star formation. These data will allow us to map the Pop I and Pop II stellar components, and thereby construct the first detailed star formation histories for non-interacting dI galaxies. Our results will bear on a variety of astrophysical problems, including the evolution of small galaxies, distances in the Local Group, age-metallicity distributions in small galaxies, ages of dIs, and the physics of star formation. The four target galaxies are typical dI systems in terms of luminosity, gas content, and H II region abundance, and represent a range in current star forming activity. They are sufficiently near to allow us to reach to stars at M_V = 0, have 0.1 of the luminosity of the SMC and 0.25 of its oxygen abundance. Unlike the SMC, these dIs are not near giant galaxies. This project will allow the extension of our knowledge of stellar populations in star forming galaxies from the spirals in the Local Group down to its smallest members. We plan to take maximum advantage of the unique data which this project will provide. Our investigator team brings extensive and varied experience in studies of dwarf galaxies, stellar populations, imaging photometry, and stellar evolution to this project.

  19. Diversity among galaxy clusters

    International Nuclear Information System (INIS)

    Struble, M.F.; Rood, H.J.

    1988-01-01

    The classification of galaxy clusters is discussed. Consideration is given to the classification scheme of Abell (1950's), Zwicky (1950's), Morgan, Matthews, and Schmidt (1964), and Morgan-Bautz (1970). Galaxies can be classified based on morphology, chemical composition, spatial distribution, and motion. The correlation between a galaxy's environment and morphology is examined. The classification scheme of Rood-Sastry (1971), which is based on clusters's morphology and galaxy population, is described. The six types of clusters they define include: (1) a cD-cluster dominated by a single large galaxy, (2) a cluster dominated by a binary, (3) a core-halo cluster, (4) a cluster dominated by several bright galaxies, (5) a cluster appearing flattened, and (6) an irregularly shaped cluster. Attention is also given to the evolution of cluster structures, which is related to initial density and cluster motion

  20. Galaxy formation and evolution

    CERN Document Server

    Mo, Houjun; White, Simon

    2010-01-01

    The rapidly expanding field of galaxy formation lies at the interface between astronomy, particle physics, and cosmology. Covering diverse topics from these disciplines, all of which are needed to understand how galaxies form and evolve, this book is ideal for researchers entering the field. Individual chapters explore the evolution of the Universe as a whole and its particle and radiation content; linear and nonlinear growth of cosmic structure; processes affecting the gaseous and dark matter components of galaxies and their stellar populations; the formation of spiral and elliptical galaxies; central supermassive black holes and the activity associated with them; galaxy interactions; and the intergalactic medium. Emphasizing both observational and theoretical aspects, this book provides a coherent introduction for astronomers, cosmologists, and astroparticle physicists to the broad range of science underlying the formation and evolution of galaxies.

  1. The Properties of Faint Field Galaxies

    Science.gov (United States)

    Driver, Simon. P.

    1994-12-01

    One of the current drawbacks of Charge Coupled Devices (CCDs) is their restrictive fields of view. The Hitchhiker CCD camera overcomes this limitation by operating in parallel with existing instrumentation and is able to cover a large area as well as large volumes. Hitchhiker is mounted on the 4.2m William Herschel Telescope and has been operating for two years. The first use of the Hitchhiker data set has been to study the general properties of faint galaxies. The observed trend of how the differential numbers of galaxies vary with magnitude agrees extremely well with those of other groups and covers, for the first time, all four major optical bandpasses. This multi-band capability has also allowed the study of how the colors of galaxies change with magnitude and how the correlation of galaxies on the sky varies between the optical bandpasses. A dwarf dominated model has been developed to explain these observations and challenges our knowledge of the space-density of dwarf galaxies. The model demonstrates that a simple upward turn in the luminosity distribution of galaxies, similar to that observed in clusters, would remain undetected by the field surveys yet can explain many of the observations without recourse to non-passive galaxy evolution. The conclusion is that the field luminosity distribution is not constrained at faint absolute magnitudes. A combination of a high density of dwarf galaxies and mild evolution could explain all the observations. Continuing work with HST and the Medium Deep Survey Team now reveals the morphological mix of galaxies down to mI ~ 24.0. The results confirm that ellipticals and early-type spirals are well fitted by standard no-evolution models whilst the late-type spirals can only be fitted by strong evolution and/or a significant turn-up in the local field LF.

  2. Wide-field kinematic structure of early-type galaxy halos

    Science.gov (United States)

    Arnold, Jacob Antony

    2013-12-01

    The stellar halos of nearby galaxies bare the signatures of the mass-assembly processes that have driven galaxy evolution over the last ˜10 Gyr. Finding and interpreting these relict clues in galaxies within and beyond the local group offers one of the most promising avenues for understanding how galaxies accumulate their stars over time. To tackle this problem we have performed a systematic study of the wide-field kinematic structure of nearby (Dspectroscopy out to several effective radii (˜3 R e). The 22 galaxies presented here span a range of environments (field, group, and cluster), intrinsic luminosities (-22.4 infrared Calcium II triplet. For each spectrum, we parameterize the line-of-sight velocity distribution (LOSVD) as a truncated Gauss-Hermite series convolved with an optimally weighted combination of stellar templates. These kinematic measurements (V, sigma, h3, and h4) are combined with literature values to construct spatially resolved maps of large-scale kinematic structure. A variety of kinematic behaviors are observed beyond ~1 Re, potentially reflecting the stochastic and chaotic assembly of stellar bulges and halos in early-type galaxies. Next, we describe a global analysis (out to 5 Re) of kinematics and metallicity in the nearest S0 galaxy, NGC 3115, along with implications for its assembly history. The data include high-quality wide-field imaging and multi-slit spectra of the field stars and globular clusters (GCs). Within two effective radii, the bulge (as traced by the stars and metal-rich GCs) is flattened and rotates rapidly. At larger radii, the rotation declines dramatically, while the characteristic GC metallicities also decrease with radius. We argue that this pattern is not naturally explained by a binary major merger, but instead by a two-phase assembly process where the inner regions have formed in an early violent, dissipative phase, followed by the protracted growth of the outer parts via minor mergers. To test this hypothesis

  3. The origin of galaxies

    International Nuclear Information System (INIS)

    Carr, B.J.

    1982-01-01

    The existence of galaxies implies that the early Universe must have contained initial density fluctuations. Overdense regions would then expand more slowly than the background and eventually - providing the fluctuations were not damped out first - they would stop expanding altogether and collapse to form bound objects. To understand how galaxies form we therefore need to know: how the initial density fluctuations arise, under what circumstances they evolve into bound objects, and how the bound objects develop the observed characteristics of galaxies. (author)

  4. Galaxy correlations and cosmology

    International Nuclear Information System (INIS)

    Fall, S.M.

    1979-01-01

    Correlations in the distribution of galaxies provide some important clues about the structure and evolution of the Universe on scales larger than individual galaxies. In recent years much effort has been devoted to estimating and interpreting galaxy correlations. This is a review of these efforts. It is meant to provide both an introductory overview of the subject and a critical assessment of some recent developments

  5. Neighbours of our galaxy

    International Nuclear Information System (INIS)

    Wielebinski, R.

    1982-01-01

    Large telescope and radio-astronomy bring remote regions of the universe into view. Radio waves are emitted by all celestial objects. Precise examination of our own galaxy, the Milky Way, is useful for investigating more remote objects. Some of the remote galaxies are noteworthy, because they emit up to 1,000 times more radio waves than their neighbours. Centaurus A is an example of such an active galaxy. (orig.)

  6. IMPROVED MOCK GALAXY CATALOGS FOR THE DEEP2 GALAXY REDSHIFT SURVEY FROM SUBHALO ABUNDANCE AND ENVIRONMENT MATCHING

    Energy Technology Data Exchange (ETDEWEB)

    Gerke, Brian F.; Wechsler, Risa H.; Behroozi, Peter S. [Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, M/S 29, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Cooper, Michael C. [Center for Galaxy Evolution, Department of Physics and Astronomy, University of California-Irvine, Irvine, CA 92697 (United States); Yan, Renbin [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Coil, Alison L., E-mail: bgerke@slac.stanford.edu [Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Dr., MC 0424, La Jolla, CA 92093 (United States)

    2013-09-15

    We develop empirical methods for modeling the galaxy population and populating cosmological N-body simulations with mock galaxies according to the observed properties of galaxies in survey data. We use these techniques to produce a new set of mock catalogs for the DEEP2 Galaxy Redshift Survey based on the output of the high-resolution Bolshoi simulation, as well as two other simulations with different cosmological parameters, all of which we release for public use. The mock-catalog creation technique uses subhalo abundance matching to assign galaxy luminosities to simulated dark-matter halos. It then adds color information to the resulting mock galaxies in a manner that depends on the local galaxy density, in order to reproduce the measured color-environment relation in the data. In the course of constructing the catalogs, we test various models for including scatter in the relation between halo mass and galaxy luminosity, within the abundance-matching framework. We find that there is no constant-scatter model that can simultaneously reproduce both the luminosity function and the autocorrelation function of DEEP2. This result has implications for galaxy-formation theory, and it restricts the range of contexts in which the mock catalogs can be usefully applied. Nevertheless, careful comparisons show that our new mock catalogs accurately reproduce a wide range of the other properties of the DEEP2 catalog, suggesting that they can be used to gain a detailed understanding of various selection effects in DEEP2.

  7. IMPROVED MOCK GALAXY CATALOGS FOR THE DEEP2 GALAXY REDSHIFT SURVEY FROM SUBHALO ABUNDANCE AND ENVIRONMENT MATCHING

    International Nuclear Information System (INIS)

    Gerke, Brian F.; Wechsler, Risa H.; Behroozi, Peter S.; Cooper, Michael C.; Yan, Renbin; Coil, Alison L.

    2013-01-01

    We develop empirical methods for modeling the galaxy population and populating cosmological N-body simulations with mock galaxies according to the observed properties of galaxies in survey data. We use these techniques to produce a new set of mock catalogs for the DEEP2 Galaxy Redshift Survey based on the output of the high-resolution Bolshoi simulation, as well as two other simulations with different cosmological parameters, all of which we release for public use. The mock-catalog creation technique uses subhalo abundance matching to assign galaxy luminosities to simulated dark-matter halos. It then adds color information to the resulting mock galaxies in a manner that depends on the local galaxy density, in order to reproduce the measured color-environment relation in the data. In the course of constructing the catalogs, we test various models for including scatter in the relation between halo mass and galaxy luminosity, within the abundance-matching framework. We find that there is no constant-scatter model that can simultaneously reproduce both the luminosity function and the autocorrelation function of DEEP2. This result has implications for galaxy-formation theory, and it restricts the range of contexts in which the mock catalogs can be usefully applied. Nevertheless, careful comparisons show that our new mock catalogs accurately reproduce a wide range of the other properties of the DEEP2 catalog, suggesting that they can be used to gain a detailed understanding of various selection effects in DEEP2

  8. Gas-rich dwarfs and accretion phenomena in early-type galaxies

    Science.gov (United States)

    Silk, J.; Norman, C.

    1979-01-01

    An analysis is presented of the combined effects of cloud accretion and galactic winds and coronae. An accretion model is developed wherein gas-rich dwarf galaxies are accreted into galactic halos, which provides an adequate source of H I to account for observations of neutral gas in early-type galaxies. Accretion is found to fuel the wind, thereby regulating the accretion flow and yielding a time-dependent model for star formation, enrichment, and nuclear activity. The permissible parameter range for intergalactic gas clouds and galaxy groups is discussed, along with the frequency of gas-rich dwarfs and their large ratios of gas mass to luminosity. Also considered is the occurrence of gas stripping and the consequent formation of dwarf spheroidal systems that remain in the halo, and gas clouds that dissipate and suffer further infall. A cosmological implication of the model is that, because the characteristic time scale of a gas-rich dwarf galaxy to be accreted and lose its gas is comparable to a Hubble time, there may have been a far more extensive primordial distribution of such systems at earlier epochs.

  9. The correlation functions for the clustering of galaxies and Abell clusters

    International Nuclear Information System (INIS)

    Jones, B.J.T.; Jones, J.E.; Copenhagen Univ.

    1985-01-01

    The difference in amplitudes between the galaxy-galaxy correlation function and the correlation function between Abell clusters is a consequence of two facts. Firstly, most Abell clusters with z<0.08 lie in a relatively small volume of the sampled space, and secondly, the fraction of galaxies lying in Abell clusters differs considerably inside and outside of this volume. (The Abell clusters are confined to a smaller volume of space than are the galaxies.) We discuss the implications of this interpretation of the clustering correlation functions and present a simple model showing how such a situation may arise quite naturally in standard theories for galaxy formation. (orig.)

  10. Galaxy Zoo: dust in spiral galaxies

    Science.gov (United States)

    Masters, Karen L.; Nichol, Robert; Bamford, Steven; Mosleh, Moein; Lintott, Chris J.; Andreescu, Dan; Edmondson, Edward M.; Keel, William C.; Murray, Phil; Raddick, M. Jordan; Schawinski, Kevin; Slosar, Anže; Szalay, Alexander S.; Thomas, Daniel; Vandenberg, Jan

    2010-05-01

    We investigate the effect of dust on spiral galaxies by measuring the inclination dependence of optical colours for 24276 well-resolved Sloan Digital Sky Survey (SDSS) galaxies visually classified via the Galaxy Zoo project. We find clear trends of reddening with inclination which imply a total extinction from face-on to edge-on of 0.7, 0.6, 0.5 and 0.4mag for the ugri passbands (estimating 0.3mag of extinction in z band). We split the sample into `bulgy' (early-type) and `discy' (late-type) spirals using the SDSS fracdeV (or fDeV) parameter and show that the average face-on colour of `bulgy' spirals is redder than the average edge-on colour of `discy' spirals. This shows that the observed optical colour of a spiral galaxy is determined almost equally by the spiral type (via the bulge-disc ratio and stellar populations), and reddening due to dust. We find that both luminosity and spiral type affect the total amount of extinction, with discy spirals at Mr ~ -21.5mag having the most reddening - more than twice as much as both the lowest luminosity and most massive, bulge-dominated spirals. An increase in dust content is well known for more luminous galaxies, but the decrease of the trend for the most luminous has not been observed before and may be related to their lower levels of recent star formation. We compare our results with the latest dust attenuation models of Tuffs et al. We find that the model reproduces the observed trends reasonably well but overpredicts the amount of u-band attenuation in edge-on galaxies. This could be an inadequacy in the Milky Way extinction law (when applied to external galaxies), but more likely indicates the need for a wider range of dust-star geometries. We end by discussing the effects of dust on large galaxy surveys and emphasize that these effects will become important as we push to higher precision measurements of galaxy properties and their clustering. This publication has been made possible by the participation of more than

  11. Multiple mechanisms quench passive spiral galaxies

    Science.gov (United States)

    Fraser-McKelvie, Amelia; Brown, Michael J. I.; Pimbblet, Kevin; Dolley, Tim; Bonne, Nicolas J.

    2018-02-01

    We examine the properties of a sample of 35 nearby passive spiral galaxies in order to determine their dominant quenching mechanism(s). All five low-mass (M⋆ environments. We postulate that cluster-scale gas stripping and heating mechanisms operating only in rich clusters are required to quench low-mass passive spirals, and ram-pressure stripping and strangulation are obvious candidates. For higher mass passive spirals, while trends are present, the story is less clear. The passive spiral bar fraction is high: 74 ± 15 per cent, compared with 36 ± 5 per cent for a mass, redshift and T-type matched comparison sample of star-forming spiral galaxies. The high mass passive spirals occur mostly, but not exclusively, in groups, and can be central or satellite galaxies. The passive spiral group fraction of 74 ± 15 per cent is similar to that of the comparison sample of star-forming galaxies at 61 ± 7 per cent. We find evidence for both quenching via internal structure and environment in our passive spiral sample, though some galaxies have evidence of neither. From this, we conclude no one mechanism is responsible for quenching star formation in passive spiral galaxies - rather, a mixture of mechanisms is required to produce the passive spiral distribution we see today.

  12. LOW CO LUMINOSITIES IN DWARF GALAXIES

    International Nuclear Information System (INIS)

    Schruba, Andreas; Walter, Fabian; Sandstrom, Karin; Leroy, Adam K.; Bigiel, Frank; Brinks, Elias; De Blok, W. J. G.; Kramer, Carsten; Rosolowsky, Erik; Schuster, Karl; Usero, Antonio; Weiss, Axel; Wiesemeyer, Helmut

    2012-01-01

    We present maps of 12 COJ = 2-1 emission covering the entire star-forming disks of 16 nearby dwarf galaxies observed by the IRAM HERACLES survey. The data have 13'' angular resolution, ∼250 pc at our average distance of D = 4 Mpc, and sample the galaxies by 10-1000 resolution elements. We apply stacking techniques to perform the first sensitive search for CO emission in dwarf galaxies outside the Local Group ranging from individual lines of sight, stacking over IR-bright regions of embedded star formation, and stacking over the entire galaxy. We detect five galaxies in CO with total CO luminosities of L CO2-1 = (3-28) × 10 6 K km s –1 pc 2 . The other 11 galaxies remain undetected in CO even in the stacked images and have L CO2-1 ∼ 6 K km s –1 pc 2 . We combine our sample of dwarf galaxies with a large sample of spiral galaxies from the literature to study scaling relations of L CO with M B and metallicity. We find that dwarf galaxies with metallicities of Z ≈ 1/2-1/10 Z ☉ have L CO of 2-4 orders of magnitude smaller than massive spiral galaxies and that their L CO per unit L B is 1-2 orders of magnitude smaller. A comparison with tracers of star formation (FUV and 24 μm) shows that L CO per unit star formation rate (SFR) is 1-2 orders of magnitude smaller in dwarf galaxies. One possible interpretation is that dwarf galaxies form stars much more efficiently: we argue that the low L CO /SFR ratio is due to the fact that the CO-to-H 2 conversion factor, α CO , changes significantly in low-metallicity environments. Assuming that a constant H 2 depletion time of τ dep = 1.8 Gyr holds in dwarf galaxies (as found for a large sample of nearby spirals) implies α CO values for dwarf galaxies with Z ≈ 1/2-1/10 Z ☉ that are more than one order of magnitude higher than those found in solar metallicity spiral galaxies. Such a significant increase of α CO at low metallicity is consistent with previous studies, in particular those of Local Group dwarf

  13. Induced star formation and colors of binary and interacting galaxies

    International Nuclear Information System (INIS)

    Smirnov, M.A.; Komberg, B.V.; Moskovskij Gosudarstvennyj Univ.

    1980-01-01

    The colours of 208 galaxies in pairs and groups are compared (on colour-colour diagram) with those of single galaxies of the same morphological type. Different colours of galaxies in pairs and groups can be explained if one assumes that in some of them the star formation is slowed down, while in others it is speeded up. The latter is the most conspicuous in E, SO, and Ir2 galaxies when they are accompanied by brighter spirals. The relation of abundance rate to the rate of star formation in galaxies and to the activity level of their nuclei is discussed. This relation is particularly conspicuous in the galaxies of early morphological types (E, SO, Sa) and in systems of the type Ir2 where the relative abundance of gas is significantly above the normal. It is noted that such galaxies as well as galaxies with UV excess, Seyfertlike objects, emission-line galaxies and quasars - avoid regions occupied with rich clusters and frequently occur in pairs and small groups

  14. Galaxies Gather at Great Distances

    Science.gov (United States)

    2006-01-01

    [figure removed for brevity, see original site] Distant Galaxy Cluster Infrared Survey Poster [figure removed for brevity, see original site] [figure removed for brevity, see original site] Bird's Eye View Mosaic Bird's Eye View Mosaic with Clusters [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] 9.1 Billion Light-Years 8.7 Billion Light-Years 8.6 Billion Light-Years Astronomers have discovered nearly 300 galaxy clusters and groups, including almost 100 located 8 to 10 billion light-years away, using the space-based Spitzer Space Telescope and the ground-based Mayall 4-meter telescope at Kitt Peak National Observatory in Tucson, Ariz. The new sample represents a six-fold increase in the number of known galaxy clusters and groups at such extreme distances, and will allow astronomers to systematically study massive galaxies two-thirds of the way back to the Big Bang. A mosaic portraying a bird's eye view of the field in which the distant clusters were found is shown at upper left. It spans a region of sky 40 times larger than that covered by the full moon as seen from Earth. Thousands of individual images from Spitzer's infrared array camera instrument were stitched together to create this mosaic. The distant clusters are marked with orange dots. Close-up images of three of the distant galaxy clusters are shown in the adjoining panels. The clusters appear as a concentration of red dots near the center of each image. These images reveal the galaxies as they were over 8 billion years ago, since that's how long their light took to reach Earth and Spitzer's infrared eyes. These pictures are false-color composites, combining ground-based optical images captured by the Mosaic-I camera on the Mayall 4-meter telescope at Kitt Peak, with infrared pictures taken by Spitzer's infrared array camera. Blue and green represent visible light at wavelengths of 0.4 microns and 0.8 microns

  15. Dark energy in systems of galaxies

    Science.gov (United States)

    Chernin, A. D.

    2013-11-01

    The precise observational data of the Hubble Space Telescope have been used to study nearby galaxy systems. The main result is the detection of dark energy in groups, clusters, and flows of galaxies on a spatial scale of about 1-10 Mpc. The local density of dark energy in these systems, which is determined by various methods, is close to the global value or even coincides with it. A theoretical model of the nearby Universe has been constructed, which describes the Local Group of galaxies with the flow of dwarf galaxies receding from this system. The key physical parameter of the group-flow system is zero gravity radius, which is the distance at which the gravity of dark matter is compensated by dark-energy antigravity. The model predicts the existence of local regions of space where Einstein antigravity is stronger than Newton gravity. Six such regions have been revealed in the data of the Hubble space telescope. The nearest of these regions is at a distance of 1-3 Mpc from the center of the Milky Way. Antigravity in this region is several times stronger than gravity. Quasiregular flows of receding galaxies, which are accelerated by the dark-energy antigravity, exist in these regions. The model of the nearby Universe at the scale of groups of galaxies (˜1 Mpc) can be extended to the scale of clusters (˜10 Mpc). The systems of galaxies with accelerated receding flows constitute a new and probably widespread class of metagalactic populations. Strong dynamic effects of local dark energy constitute the main characteristic feature of these systems.

  16. Galaxy Zoo: A Catalog of Overlapping Galaxy Pairs for Dust Studies

    Science.gov (United States)

    Keel, William C.; Manning, Anna M.; Holwerda, Benne W.; Mezzoprete, Massimo; Lintott, Chris J.; Schawinski, Kevin; Gay, Pamela; Masters, Karen L.

    2013-01-01

    Analysis of galaxies with overlapping images offers a direct way to probe the distribution of dust extinction and its effects on the background light. We present a catalog of 1990 such galaxy pairs selected from the Sloan Digital Sky Survey (SDSS) by volunteers of the Galaxy Zoo project. We highlight subsamples which are particularly useful for retrieving such properties of the dust distribution as UV extinction, the extent perpendicular to the disk plane, and extinction in the inner parts of disks. The sample spans wide ranges of morphology and surface brightness, opening up the possibility of using this technique to address systematic changes in dust extinction or distribution with galaxy type. This sample will form the basis for forthcoming work on the ranges of dust distributions in local disk galaxies, both for their astrophysical implications and as the low-redshift part of a study of the evolution of dust properties. Separate lists and figures show deep overlaps, where the inner regions of the foreground galaxy are backlit, and the relatively small number of previously-known overlapping pairs outside the SDSS DR7 sky coverage.

  17. The formation of galaxies

    International Nuclear Information System (INIS)

    Gunn, J.E.

    1983-01-01

    The presently fashionable ideas for galaxy formation are reviewed briefly, and it is concluded that the standard isothermal heirarchy fits the available data best. A simple infall picture is presented which explains many of the observed properties of disk galaxies. (orig.)

  18. The galaxy builders

    Science.gov (United States)

    Cho, Adrian

    2018-06-01

    Philip Hopkins, a theoretical astrophysicist at the California Institute of Technology in Pasadena, likes to prank his colleagues. An expert in simulating the formation of galaxies, Hopkins sometimes begins his talks by projecting images of his creations next to photos of real galaxies and defying his audience to tell them apart. "We can even trick astronomers," Hopkins says. For decades, scientists have tried to simulate how the trillions of galaxies in the observable universe arose from clouds of gas after the big bang. But only in the past few years have the simulations begun to reproduce both the details of individual galaxies and their distribution of masses and shapes. As the fake universes improve, their role is also changing. Previously, information flowed one way: from the astronomers studying real galaxies to the modelers trying to simulate them. Now, insight is flowing the other way, too, with the models helping guide astronomers and astrophysicists. The models suggest that the earliest galaxies were oddly pickle-shaped, that wafer-thin spiral galaxies are surprisingly rugged in the face of collisions, and, perhaps most important, that galaxies must form stars far more slowly than astrophysicists expected. Progress is coming so fast, says Tiziana Di Matteo, a numerical cosmologist at Carnegie Mellon University in Pittsburgh, Pennsylvania, that "the whole thing has reached this little golden age."

  19. The Evolution of Galaxies

    Czech Academy of Sciences Publication Activity Database

    Palouš, Jan

    2007-01-01

    Roč. 17, - (2007), s. 34-40 ISSN 1220-5168. [Heliospere and galaxy. Sinaia, 03.05.2007-05.05.2007] R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : ISM structure * stars formation * evolution of galaxies Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  20. Dwarf Elliptical Galaxies

    Science.gov (United States)

    Caldwell, N.; Murdin, P.

    2000-11-01

    DWARF SPHEROIDAL GALAXIES were first identified by Shapley, who had noticed two very diffuse collections of stars on Harvard patrol plates. Although these systems had about as many stars as a GLOBULAR CLUSTER, they were of much lower density, and hence much larger radius, and thus were considered distinct galaxies. These two, named Fornax and Sculptor after the constellations in which they ap...

  1. Hubble's Menagerie of Galaxies

    Indian Academy of Sciences (India)

    Srimath

    astronom ers have even w ondered ifH ubble's galaxy typ es form an evolutionary sequence: does one type of galaxy evolve into another? 1. T he D iscovery of G alaxies. A stronom ers began to ponder these issues only after they discovered w hat ...

  2. Our galaxy is exploding

    International Nuclear Information System (INIS)

    Closets, Francois de.

    1977-01-01

    Improvements made in radioastronomy, and infrared, X and γ emission studies of the Galaxy have allowed to study the galactic nucleus, which is characterized by an intense activity. The most recent hypotheses made to explain this activity and replace it in the general context of the evolution of the galaxies are presented [fr

  3. Our aging galaxy

    International Nuclear Information System (INIS)

    Lyngaa, G.

    1980-01-01

    The origin and evolution of the galaxies is described, according to the presently prevailing theories. The various types of galaxy and their structures are described, and also the formation of stars from the gas clouds. The spiral structure and the evolution of the disc are discussed. Finally the future development on the time scale of thousands of millions of years is briefly discussed. (JIW)

  4. The Seyfert galaxy population

    International Nuclear Information System (INIS)

    Meurs, E.

    1982-01-01

    A large sample of Seyfert galaxies, many of which are Markarian galaxies, has been observed with the WSRT in lambda 21 cm continuum radiation. The results are presented, and the number of radio detected Seyferts has now increased considerably. A number of accurate optical positions are given that were needed to identify radio sources with the Seyfert galaxies observed. Optical and radio luminosity functions of Seyfert galaxies are derived. The results are compared with such functions for other categories of objects that may be related to these galaxies. The discussions focus on the possible connections between normal galaxies, Seyferts, and optically selected quasars. Three investigations are reported on individual objects that are related to Seyfert galaxies. WSRT observations of four bright, optically selected quasars are presented. The identification of an X-ray discovered BL Lacertae object is discussed. Its radio emission is on a much lower level than for other BL Lacs. Perhaps it is a radio-quiet object in this class, suggesting a comparable difference in radio emission for BL Lacs as is known for quasars. Photo-electric photometry for the Seyfert galaxy NGC 1566 is reported. Besides a monitoring programme, multi-aperture photometry is described. (Auth.)

  5. Visibility of galaxies

    International Nuclear Information System (INIS)

    Disney, M.J.

    1976-01-01

    It is stated that counts of galaxies could be seriously biased by selection effects, largely influenced by the brightness of the night sky. To illustrate this suppose the Earth were situated near the center of a giant elliptical galaxy. The mean surface brightness of the sky would then appear some 8 to 9 mag. brighter than is observed from our position in the Galaxy. Extragalactic space would then appear to be empty void; spiral and irregular galaxies would be invisible, and all that could be easily detected would be the core regions of galaxy ellipticals very similar to our own. Much of the Universe would be blinded by the surface brightness of the parent galaxy. This blinding, however, is a relative matter and the question arises as to what extent we are blinded by the spiral galaxy in which we exist. Strong indirect evidence exists that our knowledge of galaxies is heavily biased by the sky background, and the true population of extragalactic space may be very different from that seen. Other relevant work is also discussed, and further investigational work is indicated. (U.K.)

  6. Dwarf Elliptical Galaxies in the M81 Group: The Structure and Stellar Populations of BK5N and F8D1

    OpenAIRE

    Caldwell, Nelson; Armandroff, Taft E.; Da Costa, G. S.; Seitzer, Patrick

    1997-01-01

    We have obtained HST WFPC2 images through the F555W and F814W filters of two M81 group dE's: BK5N and a new system, designated F8D1. The resulting color-magnitude diagrams show the upper two magnitudes of the red giant branch. Surface brightness and total magnitude measurements indicate that BK5N and F8D1 have similar central surface brightness (24.5 and 25.4 mag/arcsec^2 in V, respectively), but F8D1's larger length scale results in it being 3 magnitudes more luminous than BK5N. BK5N lies on...

  7. Three-dimensional morphological segregation in rich clusters of galaxies

    International Nuclear Information System (INIS)

    Salvador-Sole, E.; Sanroma, M.; Jordana, J.J.R.

    1989-01-01

    The implications of the observed correlation between morphological fractions and projected number density of galaxies in rich clusters are analyzed. It is found that this correlation is the result of a well-defined intrinsic correlation that depends on cluster concentration, whether the observed correlation is strictly universal or not. This dependence is in overall agreement with that expected from the action of mechanisms of environment-induced morphological evolution of galaxies. 30 references

  8. Holes in the distribution of rich clusters of galaxies

    International Nuclear Information System (INIS)

    Burns, J.O.

    1988-01-01

    The properties of voids in the distribution of Abell clusters of galaxies are described. Cluster voids, such as that in Bootes, serve as markers of large candidate voids of galaxies. The advantages and disadvantages of using rich clusters as tracers of large-scale structures are reviewed. One new 40/h Mpc diameter void of galaxies and clusters in Pisces-Cetus is described in detail. It is found that numerical simulations of models with Gaussian initial conditions do not reproduce the void or filament structures observed within the Abell cluster catalog. The implications of this discrepancy for future observations and models are discussed. 26 references

  9. Distant Galaxy Clusters Hosting Extreme Central Galaxies

    Science.gov (United States)

    McDonald, Michael

    2014-09-01

    The recently-discovered Phoenix cluster harbors the most star-forming central cluster galaxy of any cluster in the known Universe, by nearly a factor of 10. This extreme system appears to be fulfilling early cooling flow predictions, although the lack of similar systems makes any interpretation difficult. In an attempt to find other "Phoenix-like" clusters, we have cross-correlated archival all-sky surveys (in which Phoenix was detected) and isolated 4 similarly-extreme systems which are also coincident in position and redshift with an overdensity of red galaxies. We propose here to obtain Chandra observations of these extreme, Phoenix-like systems, in order to confirm them as relaxed, rapidly-cooling galaxy clusters.

  10. Starbursts and IRAS galaxies

    International Nuclear Information System (INIS)

    Belfort, P.

    1987-01-01

    Several observational hints suggest that most of the IRAS galaxies are undergoing bursts of star formation. A simple photometric model of starburst galaxy was developed in order to check whether starburst events are really able to account for the far-infrared and optical properties of all the IRAS galaxies with HII region-like spectra. FIR activities up to a few hundred are actually easily reached with rather small bursts in red host-galaxies, and L IR /L B , EW(Hα) and U-B) versus (B-V) diagrams can be used to estimate burst strength and extinction. But more observations are required to conclude about the most extreme cases. Four typical infrared-selected IRAS galaxies are presented and their burst strength and extinction estimated

  11. MULTIPLE GALAXY COLLISIONS

    Science.gov (United States)

    2002-01-01

    Here is a sampling of 15 ultraluminous infrared galaxies viewed by NASA's Hubble Space Telescope. Hubble's sharp vision reveals more complexity within these galaxies, which astronomers are interpreting as evidence of a multiple-galaxy pileup. These images, taken by the Wide Field and Planetary Camera 2, are part of a three-year study of 123 galaxies within 3 billion light-years of Earth. The study was conducted in 1996, 1997, and 1999. False colors were assigned to these photos to enhance fine details within these coalescing galaxies. Credits: NASA, Kirk Borne (Raytheon and NASA Goddard Space Flight Center, Greenbelt, Md.), Luis Colina (Instituto de Fisica de Cantabria, Spain), and Howard Bushouse and Ray Lucas (Space Telescope Science Institute, Baltimore, Md.)

  12. Gas accretion onto galaxies

    CERN Document Server

    Davé, Romeel

    2017-01-01

    This edited volume presents the current state of gas accretion studies from both observational and theoretical perspectives, and charts our progress towards answering the fundamental yet elusive question of how galaxies get their gas. Understanding how galaxies form and evolve has been a central focus in astronomy for over a century. These studies have accelerated in the new millennium, driven by two key advances: the establishment of a firm concordance cosmological model that provides the backbone on which galaxies form and grow, and the recognition that galaxies grow not in isolation but within a “cosmic ecosystem” that includes the vast reservoir of gas filling intergalactic space. This latter aspect in which galaxies continually exchange matter with the intergalactic medium via inflows and outflows has been dubbed the “baryon cycle”. The topic of this book is directly related to the baryon cycle, in particular its least well constrained aspect, namely gas accretion. Accretion is a rare area of ast...

  13. Spectral evolution of galaxies

    International Nuclear Information System (INIS)

    Rocca-Volmerange, B.

    1989-01-01

    A recent striking event in Observational Cosmology is the discovery of a large population of galaxies at extreme cosmological distances (extended from spectral redshifts ≅ 1 to ≥ 3) corresponding to a lookback time of 80% of the Universe's age. However when galaxies are observed at such remote epochs, their appearances are affected by at least two simultaneous effects which are respectively a cosmological effect and the intrinsic evolution of their stellar populations which appear younger than in our nearby galaxies. The fundamental problem is first to disentangle the respective contributions of these two effects to apparent magnitudes and colors of distant galaxies. Other effects which are likely to modify the appearance of galaxies are amplification by gravitational lensing and interaction with environment will also be considered. (author)

  14. Age and geochemistry of the Charlestown Group, Ireland: Implications for the Grampian orogeny, its mineral potential and the Ordovician timescale

    Science.gov (United States)

    Herrington, Richard J.; Hollis, Steven P.; Cooper, Mark R.; Stobbs, Iain; Tapster, Simon; Rushton, Adrian; McConnell, Brian; Jeffries, Teresa

    2018-03-01

    Accurately reconstructing the growth of continental margins during episodes of ocean closure has important implications for understanding the formation, preservation and location of mineral deposits in ancient orogens. The Charlestown Group of county Mayo, Ireland, forms an important yet understudied link in the Caledonian-Appalachian orogenic belt located between the well documented sectors of western Ireland and Northern Ireland. We have reassessed its role in the Ordovician Grampian orogeny, based on new fieldwork, high-resolution airborne geophysics, graptolite biostratigraphy, U-Pb zircon dating, whole rock geochemistry, and an examination of historic drillcore from across the volcanic inlier. The Charlestown Group can be divided into three formations: Horan, Carracastle, and Tawnyinah. The Horan Formation comprises a mixed sequence of tholeiitic to calc-alkaline basalt, crystal tuff and sedimentary rocks (e.g. black shale, chert), forming within an evolving peri-Laurentian affinity island arc. The presence of graptolites Pseudisograptus of the manubriatus group and the discovery of Exigraptus uniformis and Skiagraptus gnomonicus favour a latest Dapingian (i.e. Yapeenian Ya 2/late Arenig) age for the Horan Formation (equivalent to c. 471.2-470.5 Ma according to the timescale of Sadler et al., 2009). Together with three new U-Pb zircon ages of 471.95-470.82 Ma from enclosing felsic tuffs and volcanic breccias, this fauna provides an important new constraint for calibrating the Middle Ordovician timescale. Overlying deposits of the Carracastle and Tawnyinah formations are dominated by LILE- and LREE-enriched calc-alkaline andesitic tuffs and flows, coarse volcanic breccias and quartz-feldspar porphyritic intrusive rocks, overlain by more silicic tuffs and volcanic breccias with rare occurrences of sedimentary rocks. The relatively young age for the Charlestown Group in the Grampian orogeny, coupled with high Th/Yb and zircon inheritance (c. 2.7 Ga) in intrusive

  15. The galaxy ancestor problem

    Science.gov (United States)

    Disney, M. J.; Lang, R. H.

    2012-11-01

    The Hubble Space Telescope (HST) findsgalaxies whose Tolman dimming exceeds 10 mag. Could evolution alone explain these as our ancestor galaxies or could they be representatives of quite a different dynasty whose descendants are no longer prominent today? We explore the latter hypothesis and argue that surface brightness selection effects naturally bring into focus quite different dynasties from different redshifts. Thus, the HST z = 7 galaxies could be examples of galaxies whose descendants are both too small and too choked with dust to be recognizable in our neighbourhood easily today. Conversely, the ancestors of the Milky Way and its obvious neighbours would have completely sunk below the sky at z > 1.2, unless they were more luminous in the past, although their diffused light could account for the missing re-ionization flux. This Succeeding Prominent Dynasties Hypothesis (SPDH) fits the existing observations both naturally and well even without evolution, including the bizarre distributions of galaxy surface brightness found in deep fields, the angular size ˜(1 + z)-1 law, 'downsizing' which turns out to be an 'illusion' in the sense that it does not imply evolution, 'infant mortality', that is, the discrepancy between stars born and stars seen, the existence of 'red nuggets', and finally the recently discovered and unexpected excess of quasar absorption line damped Lyα systems at high redshift. If galaxies were not significantly brighter in the past and the SPDH were true, then a large proportion of galaxies could remain sunk from sight, possibly at all redshifts, and these sunken galaxies could supply the missing re-ionization flux. We show that fishing these sunken galaxies out of the sky by their optical emissions alone is practically impossible, even when they are nearby. More ingenious methods are needed to detect them. It follows that disentangling galaxy evolution through studying ever higher redshift galaxies may be a forlorn hope because one could

  16. Study of GRBs Hosts Galaxies Vicinity Properties

    Science.gov (United States)

    Bernal, S.; Vasquez, N.; Hoyle, F.

    2017-07-01

    The study of GRBs host galaxies and its vicinity could provide constrains on the progenitor and an opportunity to use these violent explosions to characterize the nature of the highredshift universe. Studies of GRB host galaxies reveal a population of starforming galaxies with great diversity, spanning a wide range of masses, star formation rate, and redshifts. In order to study the galactic ambient of GRBs we used the S. Savaglio catalog from 2015 where 245 GRBs are listed with RA-Dec position and z. We choose 22 GRBs Hosts galaxies from Savaglio catalog and SDSS DR12, with z range 0population characteristics. We calculate the volumetric density populatation of glalaxies around the GRB Hosts within a volume of an sphere whit radius of 10 h-1 Mpc and find a low density compared with a typical group of galaxies. In order to know the galaxies stellar formation state, in regions where GRBs are formed, we made an analysis of color index using SDSS data of μ [λ 3543], r[λ 6231] and calculate the indexes μ-r. We find a value μ-r=2.63, it means that the galactic ambient of GRBs Host regions are statistically redder than void and wall regions on a indirect way (Voids:μ-r=2.043; Walls:μ-r=2.162). Futhermore, we used a inverse concentration index analysis, ICI=R50/R90 and find that galaxies in GRBs Hosts vicinity are also of slightly early type than void and wall galaxies. With this work we provide characteristics on the regions for future works related with highredsift universe that using the GRBs.

  17. JELLYFISH GALAXY CANDIDATES AT LOW REDSHIFT

    Energy Technology Data Exchange (ETDEWEB)

    Poggianti, B. M.; Fasano, G.; Omizzolo, A.; Gullieuszik, M.; Bettoni, D.; Paccagnella, A. [INAF-Astronomical Observatory of Padova (Italy); Moretti, A.; D’Onofrio, M. [Physics and Astronomy Department, University of Padova (Italy); Jaffé, Y. L. [Department of Astronomy, Universidad de Concepción, Concepción (Chile); Vulcani, B. [Kavli Institute for the Physics and Mathematics of the universe (WPI), The University of Tokyo Institutes for Advanced Study (UTIAS), the University of Tokyo, Kashiwa, 277-8582 (Japan); Fritz, J. [Centro de Radioastronomía y Astrofísica, CRyA, UNAM, Michoacán (Mexico); Couch, W. [Australian Astronomical Observatory, North Ryde, NSW 1670 (Australia)

    2016-03-15

    Galaxies that are being stripped of their gas can sometimes be recognized from their optical appearance. Extreme examples of stripped galaxies are the so-called “jellyfish galaxies” that exhibit tentacles of debris material with a characteristic jellyfish morphology. We have conducted the first systematic search for galaxies that are being stripped of their gas at low-z (z = 0.04−0.07) in different environments, selecting galaxies with varying degrees of morphological evidence for stripping. We have visually inspected B- and V-band images and identified 344 candidates in 71 galaxy clusters of the OMEGAWINGS+WINGS sample and 75 candidates in groups and lower mass structures in the PM2GC sample. We present the atlas of stripping candidates and a first analysis of their environment and their basic properties, such as morphologies, star formation rates and galaxy stellar masses. Candidates are found in all clusters and at all clustercentric radii, and their number does not correlate with the cluster velocity dispersion σ or X-ray luminosity L{sub X}. Interestingly, convincing cases of candidates are also found in groups and lower mass halos (10{sup 11}−10{sup 14}M{sub ⊙}), although the physical mechanism at work needs to be securely identified. All the candidates are disky, have stellar masses ranging from log M/M{sub ⊙} < 9 to > 11.5 and the majority of them form stars at a rate that is on average a factor of 2 higher (2.5σ) compared to non-stripped galaxies of similar mass. The few post-starburst and passive candidates have weak stripping evidence. We conclude that disturbed morphologies suggestive of stripping phenomena are ubiquitous in clusters and could be present even in groups and low mass halos. Further studies will reveal the physics of the gas stripping and clarify the mechanisms at work.

  18. Spin orientation for nearby galaxies

    International Nuclear Information System (INIS)

    Karachentsev, I.D.

    1989-01-01

    The spatial orientations and the absolute values of angular momentum are determined for galaxies in the Local Group and the M 81/IC 342 group. For this purpose, the data on both velocity field and the dust knots configuration have been used. The spin direction has been established unambiguously for 21 objects; however, for the remaining 14 dwarf members the spin orientations are presented by pairs of alternative directions. The distribution of the spin vectors on the sky does not slow pronounced sings of anisotropy

  19. THE M bh-σ DIAGRAM AND THE OFFSET NATURE OF BARRED ACTIVE GALAXIES

    International Nuclear Information System (INIS)

    Graham, Alister W.; Li Ihui

    2009-01-01

    From a sample of 50 predominantly inactive galaxies with direct supermassive black hole mass measurements, it has recently been established that barred galaxies tend to reside rightward of the M bh -σ relation defined by nonbarred galaxies. Either black holes in barred galaxies tend to be anemic or the central velocity dispersions in these galaxies have a tendency to be elevated by the presence of the bar. The latter option is in accord with studies connecting larger velocity dispersions in galaxies with old bars, while the former scenario is at odds with the observation that barred galaxies do not deviate from the M bh -luminosity relation. Using a sample of 88 galaxies with active galactic nuclei, whose supermassive black hole masses have been estimated from their associated emission lines, we reveal for the first time that they also display this same general behavior in the M bh -σ diagram depending on the presence of a bar or not. A new symmetrical and nonsymmetrical 'barless' M bh -σ relation is derived using 82 nonbarred galaxies. The barred galaxies are shown to reside on or up to ∼1 dex below this relation. This may explain why narrow-line Seyfert 1 galaxies appear offset from the 'barless' M bh -σ relation, and has far-reaching implications given that over half of the disk galaxy population are barred.

  20. Are spiral galaxies heavy smokers?

    International Nuclear Information System (INIS)

    Davies, J.; Disney, M.; Phillipps, S

    1990-01-01

    The dustiness of spiral galaxies is discussed. Starburst galaxies and the shortage of truly bright spiral galaxies is cited as evidence that spiral galaxies are far dustier than has been thought. The possibility is considered that the dust may be hiding missing mass

  1. THE SLOAN GREAT WALL. MORPHOLOGY AND GALAXY CONTENT

    International Nuclear Information System (INIS)

    Einasto, M.; Liivamaegi, L. J.; Tempel, E.; Saar, E.; Tago, E.; Einasto, P.; Enkvist, I.; Einasto, J.; MartInez, V. J.; Heinaemaeki, P.; Nurmi, P.

    2011-01-01

    We present the results of a study of the morphology and galaxy content of the Sloan Great Wall (SGW), the richest galaxy system in the nearby universe. We use the luminosity density field to determine superclusters in the SGW, and the fourth Minkowski functional V 3 and the morphological signature (the K 1 -K 2 shapefinder curve) to show the different morphologies of the SGW, from a single filament to a multibranching, clumpy planar system. We show that the richest supercluster in the SGW, SCl 126, and especially its core, resembles a very rich filament, while another rich supercluster in the SGW, SCl 111, resembles a 'multispider'-an assembly of high-density regions connected by chains of galaxies. We study the substructure of individual galaxy populations determined by their color in these superclusters using Minkowski functionals and find that in the high-density core of the SGW the clumpiness of red and blue galaxies is similar, but in the outskirts of superclusters the distribution of red galaxies is clumpier than that of blue galaxies. At intermediate densities, the systems of blue galaxies have tunnels through them. We assess the statistical significance of our results using the halo model and smoothed bootstrap. We study the galaxy content and the properties of groups of galaxies in the two richest superclusters of the SGW, paying special attention to bright red galaxies (BRGs) and the first ranked (the most luminous) galaxies in SGW groups. The BRGs are the nearby luminous red galaxies; they are mostly bright and red and typically reside in groups (several groups host five or more BRGs). About one-third of the BRGs are spirals. The scatter of colors of elliptical BRGs is smaller than that of spiral BRGs. About half of the BRGs and of first ranked galaxies in groups have large peculiar velocities. Groups with elliptical BRGs as their first ranked galaxies populate superclusters more uniformly than the groups that have a spiral BRG as their first ranked

  2. Anomalous evolution of the dwarf galaxy HIPASS J1321-31

    NARCIS (Netherlands)

    Pritzl, BJ; Knezek, PM; Gallagher, JS; Grossi, M; Disney, MJ; Minchin, RF; Freeman, KC; Tolstoy, E; Saha, A

    2003-01-01

    We present Hubble Space Telescope/WFPC2 observations of the dwarf galaxy HIPASS J1321-31. This unusual galaxy lies in the direction of the Centaurus A group of galaxies and has a color-magnitude diagram with a distinctive red plume of luminous stars. This feature could arise from (1) a red giant

  3. A History of H i Stripping in Virgo: A Phase-space View of VIVA Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Hyein; Chung, Aeree; Smith, Rory [Department of Astronomy, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722 (Korea, Republic of); Jaffé, Yara L., E-mail: hiyoon@galaxy.yonsei.ac.kr, E-mail: achung@yonsei.ac.kr [European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago (Chile)

    2017-04-01

    We investigate the orbital histories of Virgo galaxies at various stages of H i gas stripping. In particular, we compare the location of galaxies with different H i morphology in phase space. This method is a great tool for tracing the gas stripping histories of galaxies as they fall into the cluster. Most galaxies at the early stage of H i stripping are found in the first infall region of Virgo, while galaxies undergoing active H i stripping mostly appear to be falling in or moving out near the cluster core for the first time. Galaxies with severely stripped, yet symmetric, H i disks are found in one of two locations. Some are deep inside the cluster, but others are found in the cluster outskirts with low orbital velocities. We suggest that the latter group of galaxies belong to a “backsplash” population. These present the clearest candidates for backsplashed galaxies observationally identified to date. We further investigate the distribution of a large sample of H i-detected galaxies toward Virgo in phase space, confirming that most galaxies are stripped of their gas as they settle into the gravitational potential of the cluster. In addition, we discuss the impact of tidal interactions between galaxies and group preprocessing on the H i properties of the cluster galaxies, and link the associated star formation evolution to the stripping sequence of cluster galaxies.

  4. Rebuilding Spiral Galaxies

    Science.gov (United States)

    2005-01-01

    Major Observing Programme Leads to New Theory of Galaxy Formation Summary Most present-day large galaxies are spirals, presenting a disc surrounding a central bulge. Famous examples are our own Milky Way or the Andromeda Galaxy. When and how did these spiral galaxies form? Why do a great majority of them present a massive central bulge? An international team of astronomers [1] presents new convincing answers to these fundamental questions. For this, they rely on an extensive dataset of observations of galaxies taken with several space- and ground-based telescopes. In particular, they used over a two-year period, several instruments on ESO's Very Large Telescope. Among others, their observations reveal that roughly half of the present-day stars were formed in the period between 8,000 million and 4,000 million years ago, mostly in episodic burst of intense star formation occurring in Luminous Infrared Galaxies. From this and other evidence, the astronomers devised an innovative scenario, dubbed the "spiral rebuilding". They claim that most present-day spiral galaxies are the results of one or several merger events. If confirmed, this new scenario could revolutionise the way astronomers think galaxies formed. PR Photo 02a/05: Luminosity - Oxygen Abundance Relation for Galaxies (VLT) PR Photo 02b/05: The Spiral Rebuilding Scenario A fleet of instruments How and when did galaxies form? How and when did stars form in these island universes? These questions are still posing a considerable challenge to present-day astronomers. Front-line observational results obtained with a fleet of ground- and space-based telescopes by an international team of astronomers [1] provide new insights into these fundamental issues. For this, they embarked on an ambitious long-term study at various wavelengths of 195 galaxies with a redshift [2] greater than 0.4, i.e. located more than 4000 million light-years away. These galaxies were studied using ESO's Very Large Telescope, as well as the

  5. Comparing Dark Energy Survey and HST –CLASH observations of the galaxy cluster RXC J2248.7-4431: implications for stellar mass versus dark matter

    Energy Technology Data Exchange (ETDEWEB)

    Palmese, A.; Lahav, O.; Banerji, M.; Gruen, D.; Jouvel, S.; Melchior, P.; Aleksić, J.; Annis, J.; Diehl, H. T.; Hartley, W. G.; Jeltema, T.; Romer, A. K.; Rozo, E.; Rykoff, E. S.; Seitz, S.; Suchyta, E.; Zhang, Y.; Abbott, T. M. C.; Abdalla, F. B.; Allam, S.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Crocce, M.; Cunha, C. E.; D' Andrea, C. B.; da Costa, L. N.; Desai, S.; Dietrich, J. P.; Doel, P.; Estrada, J.; Evrard, A. E.; Flaugher, B.; Frieman, J.; Gerdes, D. W.; Goldstein, D. A.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Li, T. S.; Lima, M.; Maia, M. A. G.; Marshall, J. L.; Miller, C. J.; Miquel, R.; Nord, B.; Ogando, R.; Plazas, A. A.; Roodman, A.; Sanchez, E.; Scarpine, V.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Tucker, D.; Vikram, V.

    2016-08-20

    We derive the stellar mass fraction in the galaxy cluster RXC J2248.7-4431 observed with the Dark Energy Survey (DES) during the Science Verification period. We compare the stellar mass results from DES (five filters) with those from the Hubble Space Telescope Cluster Lensing And Supernova Survey (CLASH; 17 filters). When the cluster spectroscopic redshift is assumed, we show that stellar masses from DES can be estimated within 25 per cent of CLASH values. We compute the stellar mass contribution coming from red and blue galaxies, and study the relation between stellar mass and the underlying dark matter using weak lensing studies with DES and CLASH. An analysis of the radial profiles of the DES total and stellar mass yields a stellar-to-total fraction of f(star) = (6.8 +/- 1.7) x 10(-3) within a radius of r(200c) similar or equal to 2 Mpc. Our analysis also includes a comparison of photometric redshifts and star/galaxy separation efficiency for both data sets. We conclude that space-based small field imaging can be used to calibrate the galaxy properties in DES for the much wider field of view. The technique developed to derive the stellar mass fraction in galaxy clusters can be applied to the similar to 100 000 clusters that will be observed within this survey and yield important information about galaxy evolution.

  6. Dwarf galaxies : Important clues to galaxy formation

    NARCIS (Netherlands)

    Tolstoy, E

    2003-01-01

    The smallest dwarf galaxies are the most straight forward objects in which to study star formation processes on a galactic scale. They are typically single cell star forming entities, and as small potentials in orbit around a much larger one they are unlikely to accrete much (if any) extraneous

  7. Analysis of the star formation histories of galaxies in different environments: from low to high density

    Science.gov (United States)

    Ortega-Minakata, René A.

    2015-11-01

    formation histories of galaxies in our catalogue were found to be strongly dependent on their morphology, and consequently on their emission-line activity. Star-forming galaxies are late types that have the youngest populations; Sy2-dominated galaxies show a mixture of young and old populations, while LINER-likes have older populations; and passive, early-type galaxies have the oldest populations and have no current star formation. This is consistent with the idea that the processes that fix or change the morphology of galaxies are more internal and modulated by their mass, and are tightly related to how much gas is available to stimulate or stop star formation or AGN activity. In contrast, the star formation histories of galaxies were found to be only weakly dependent on their environmental density, with isolated galaxies showing somewhat younger populations than galaxies in high-density environments. This is consistent with the weak morphology-density relation found for the general population of galaxies, and supports the idea that morphology and formation history are tightly related and, while the processes that change the morphology are more common in the cluster environment, the environmental density itself does not directly affect much the formation history of galaxies. The stellar mass of galaxies seems to modulate their activity and morphology: massive galaxies formed more rapidly in the past, efficiently converting their gas into stars, leaving little or no gas to form stars or fuel AGN activity later on, thus making them low-intensity active galaxies or passive galaxies. The formation of these massive galaxies would then only depend on the local density of protogalaxies, so a high merger rate in environments similar to compact groups of galaxies in the past would result in an early-type galaxy, effectively explaining the relation between mass, activity, morphology, stellar mean age and velocity dispersion of galaxies. The catalogue presented here is useful and

  8. Dynamics and configurations of galaxy triplets

    International Nuclear Information System (INIS)

    Anosova, J.P.; Orlov, V.V.; Chernin, A.D.; Ivanov, A.V.; Kiseleva, L.G.

    1990-01-01

    The purpose is to infer the probable dynamical states of galaxy triplets by the observed data on their configurations. Two methods are proposed for describing the distributions of the triplet configuration parameters characterizing a tendency to alignment and hierarchy: (1) obtaining a representative sample of configurations and determining its statistical parameters (moments and percentages); and (2) dividing the region of possible configurations of triple systems (Agekian and Anosova, 1967) into a set of segments and finding the probabilities for the configurations to find themselves in each of them. Both these methods allow representation of the data by numerical simulations as well as observations. The effect of projection was studied. It rather overestimates the alignment and hierarchy of the triple systems. Among the parameters of interest there are found some parameters that are least sensitive to projection effects. The samples consist of simulated galaxy triplets (with hidden mass) as well as of 46 probably physical triple galaxies (Karachentseva et al., 1979). The observed triples as well as numerical models show a tendency to alignment. The triple galaxies do not show any tendency to hierarchy (formation of the temporary binarie