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Sample records for hughes electronics galaxy

  1. Necrology: Hugh Carson Cutler

    Directory of Open Access Journals (Sweden)

    David L. Browman

    1999-05-01

    Full Text Available Hugh Carson Cutler, forner curator of Economic Botany at the Missouri Botanical Gardens, was one of the first generation paleoethnobotanists in this country. A pioneer in the field, and instrumental in getting American archaeologists to begin to employ flotation techniques for recovery of botanical remains. Cutler, the son of Manuel and Mary Cutler. was born September 8. 1912 in Milwaukee. Wisconsin. and died September 22, 1998 in Topeka, Kansas.

  2. Non-Maxwellian electron distributions in clusters of galaxies

    NARCIS (Netherlands)

    Kaastra, J.S.; Bykov, A.M.; Werner, N.

    2009-01-01

    Context. Thermal X-ray spectra of clusters of galaxies and other sources are commonly calculated assuming Maxwellian electron distributions. There are situations where this approximation is not valid, for instance near interfaces of hot and cold gas and near shocks. Aims. The presence of non-thermal

  3. The Many Worlds of Hugh Everett III

    CERN Document Server

    ,

    2011-01-01

    A review of Peter Byrne's biography of Hugh Everett III, "The Many Worlds of Hugh Everett III: Multiple Universes, Mutual Assured Destruction, and the Meltdown of a Nuclear Family", (Oxford University Press, 2010).

  4. A guide to Hughes' syndrome.

    Science.gov (United States)

    Sheehan, Tina Louise

    Hughes' syndrome, or antiphospholipid syndrome, is thought to be the cause of one in four strokes in people aged less than 40 years. It is an antiinflammatory autoimmune disorder in which the blood has a tendency to clot too quickly. It can affect any artery or vein in the body and the main symptoms are thrombosis, pregnancy loss and the presence of antibodies. If detected it can be treated effectively.

  5. Nonthermal Radiation and Acceleration of Electrons in Clusters of Galaxies

    CERN Document Server

    Petrosyan, V

    2002-01-01

    Recent observations of excess radiation at extreme ultraviolet and hard X-ray energies straddling the well known thermal soft X-ray emission have provided new tools and puzzles for investigation of the acceleration of nonthermal particles in the intercluster medium of clusters of galaxies. It is shown that these radiations can be produced by the inverse Compton upscattering of the cosmic microwave background photons by the same population of relativistic electrons that produce the well known diffuse radio radiation via the synchrotron mechanism. It is shown that the commonly discussed discrepancy between the value of the magnetic field required for the production of these radiation with that obtained from Faraday rotation measures could be resolved by more realistic models and by considerations of observational selection effects. In a brief discussion of the acceleration process it is argued that the most likely scenario is reacceleration of injected relativistic electrons involving shocks and turbulence. The...

  6. Remembrance of Hugh E. Huxley, a founder of our field.

    Science.gov (United States)

    Pollard, Thomas D; Goldman, Yale E

    2013-09-01

    Hugh E. Huxley (1924-2013) carried out structural studies by X-ray fiber diffraction and electron microscopy that established how muscle contracts. Huxley's sliding filament mechanism with an ATPase motor protein taking steps along an actin filament, established the paradigm not only for muscle contraction but also for other motile systems using actin and unconventional myosins, microtubules and dynein and microtubules and kinesin.

  7. The Blues Poetry of Langston Hughes

    Science.gov (United States)

    Waldron, Edward E.

    1971-01-01

    The author discusses the criteria of the blues as an American art form. He then shows how Langston Hughes captures the mood, the feeling, the rhythm and the impact of the blues in his poetry. (Author/LF)

  8. Interaction effects on galaxy pairs with Gemini/GMOS- I: Electron density

    CERN Document Server

    Krabbe, A C; Dors, O L; Pastoriza, M G; Winge, C; Hagele, G F; Cardaci, M V; Rodrigues, I

    2013-01-01

    We present an observational study about the impacts of the interactions in the electron density of \\ion{H}{ii} regions located in 7 systems of interacting galaxies. The data consist of long-slit spectra in the range 4400-7300 A, obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS). The electron density was determined using the ratio of emission lines [SII]6716/6731. Our results indicate that the electron density estimates obtained of HII regions from our sample of interacting galaxies are systematically higher than those derived for isolated galaxies. The mean electron density values of interacting galaxies are in the range of $N_{\\rm e}=24-532$\\,$ \\rm cm^{-3}$, while those obtained for isolated galaxies are in the range of $N_{\\rm e}=40-137\\: \\rm cm^{-3}$. Comparing the observed emission lines with predictions of photoionization models, we verified that almost all the \\ion{H}{ii} regions of the galaxies AM\\,1054A, AM\\,2058B, and AM\\,2306B, have emission lines excited by shock gas. For th...

  9. The case for electron re-acceleration at galaxy cluster shocks

    Science.gov (United States)

    van Weeren, Reinout J.; Andrade-Santos, Felipe; Dawson, William A.; Golovich, Nathan; Lal, Dharam V.; Kang, Hyesung; Ryu, Dongsu; Brìggen, Marcus; Ogrean, Georgiana A.; Forman, William R.; Jones, Christine; Placco, Vinicius M.; Santucci, Rafael M.; Wittman, David; Jee, M. James; Kraft, Ralph P.; Sobral, David; Stroe, Andra; Fogarty, Kevin

    2017-01-01

    On the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow through accretion from these large-scale filaments and by mergers with other clusters and groups. In a growing number of galaxy clusters, elongated Mpc-sized radio sources have been found1,2 . Also known as radio relics, these regions of diffuse radio emission are thought to trace relativistic electrons in the intracluster plasma accelerated by low-Mach-number shocks generated by cluster-cluster merger events 3 . A long-standing problem is how low-Mach-number shocks can accelerate electrons so efficiently to explain the observed radio relics. Here, we report the discovery of a direct connection between a radio relic and a radio galaxy in the merging galaxy cluster Abell 3411-3412 by combining radio, X-ray and optical observations. This discovery indicates that fossil relativistic electrons from active galactic nuclei are re-accelerated at cluster shocks. It also implies that radio galaxies play an important role in governing the non-thermal component of the intracluster medium in merging clusters.

  10. Langston Hughes and his poem "Harlem"

    Institute of Scientific and Technical Information of China (English)

    郝红

    2005-01-01

    @@ James Langston Hughes was born February 1,1902, in Joplin, Missouri. His parents divorced when he was a small child, and his father moved to Mexico. He was raised by his Grandmother until he was thirteen, when he moved to Lincoln,Illinois, to live with his mother and her husband, eventually settling in Cleveland, Ohio.

  11. Hugh Maaskant : architect van de vooruitgang

    NARCIS (Netherlands)

    Provoost, M.

    2003-01-01

    Hugh Maaskant (1907–1977) is best known as the architect who made the biggest mark on the post-war reconstruction of Rotterdam with such buildings as the Groothandelsgebouw, the Hilton Hotel and the Lijnbaan flats. Beginning his career in 1937 as the partner of Willem van Tijen, Maaskant embarked on

  12. Responses to Hugh Heclo's "On Thinking Institutionally"

    Science.gov (United States)

    Fennell, Robert C.; Ascough, Richard S.; Liew, Tat-siong Benny; McLain, Michael; Westfield, Nancy Lynne

    2010-01-01

    Hugh Heclo's recent book "On Thinking Institutionally" (Paradigm Publishers, 2008) analyzes changes that have taken place in the past half century in how North Americans tend to think and act in institutions. The volume is receiving particular attention as it can be applied to higher education and to religious denominations, and so deserves…

  13. Hugh Maaskant : architect van de vooruitgang

    NARCIS (Netherlands)

    Provoost, Michelle

    2003-01-01

    Hugh Maaskant (1907–1977) is best known as the architect who made the biggest mark on the post-war reconstruction of Rotterdam with such buildings as the Groothandelsgebouw, the Hilton Hotel and the Lijnbaan flats. Beginning his career in 1937 as the partner of Willem van Tijen, Maaskant embarked on

  14. Relativistic Electron Shock Drift Acceleration in Low Mach Number Galaxy Cluster Shocks

    CERN Document Server

    Matsukiyo, Shuichi; Yamazaki, Ryo; Umeda, Takayuki

    2011-01-01

    An extreme case of electron shock drift acceleration in low Mach number collisionless shocks is investigated as a plausible mechanism of initial acceleration of relativistic electrons in large-scale shocks in galaxy clusters where upstream plasma temperature is of the order of 10 keV and a degree of magnetization is not too small. One-dimensional electromagnetic full particle simulations reveal that, even though a shock is rather moderate, a part of thermal incoming electrons are accelerated and reflected through relativistic shock drift acceleration and form a local nonthermal population just upstream of the shock. The accelerated electrons can self-generate local coherent waves and further be back-scattered toward the shock by those waves. This may be a scenario for the first stage of the electron shock acceleration occurring at the large-scale shocks in galaxy clusters such as CIZA J2242.8+5301 which has well defined radio relics.

  15. Scattering of emission lines in galaxy cluster cores: measuring electron temperature

    CERN Document Server

    Khedekar, S; Sazonov, S; Sunyaev, R; Emsellem, E

    2014-01-01

    The central galaxies of some clusters can be strong emitters in the Ly$\\alpha$ and H$\\alpha$ lines. This emission may arise either from the cool/warm gas located in the cool core of the cluster or from the bright AGN within the central galaxy. The luminosities of such lines can be as high as $10^{42} - 10^{44}$ erg/s. This emission originating from the core of the cluster will get Thomson scattered by hot electrons of the intra-cluster medium (ICM) with an optical depth $\\sim$ 0.01 giving rise to very broad ($\\Delta \\lambda / \\lambda \\sim$ 15%) features in the scattered spectrum. We discuss the possibility of measuring the electron density and temperature using information on the flux and width of the highly broadened line features.

  16. An estimate of the electron density in filaments of galaxies at z~0.1

    CERN Document Server

    Fraser-McKelvie, Amelia; Lazendic, Jasmina S

    2011-01-01

    Most of the baryons in the Universe are thought to be contained within filaments of galaxies, but as yet, no single study has published the observed properties of a large sample of known filaments to determine typical physical characteristics such as temperature and electron density. This paper presents a comprehensive large-scale search conducted for X-ray emission from a population of 41 bona fide filaments of galaxies to determine their X-ray flux and electron density. The sample is generated from Pimbblet et al.'s (2004) filament catalogue, which is in turn sourced from the 2 degree Field Galaxy Redshift Survey (2dFGRS). Since the filaments are expected to be very faint and of very low density, we used stacked ROSAT All-Sky Survey data. We detect a net surface brightness from our sample of filaments of (1.6 +/- 0.1) x 10^{-14} erg cm^{-2} s^{-1} arcmin^{-1} in the 0.9-1.3 keV energy band for 1 keV plasma, which implies an electron density of n_{e} = (4.7 +/- 0.2) x 10^{-4} h_{100}^{1/2} cm^{-3}. Finally, ...

  17. On the Hughes model and numerical aspects

    KAUST Repository

    Gomes, Diogo A.

    2017-01-05

    We study a crowd model proposed by R. Hughes in [11] and we describe a numerical approach to solve it. This model comprises a Fokker-Planck equation coupled with an eikonal equation with Dirichlet or Neumann data. First, we establish a priori estimates for the solutions. Second, we study radial solutions and identify a shock formation mechanism. Third, we illustrate the existence of congestion, the breakdown of the model, and the trend to the equilibrium. Finally, we propose a new numerical method and consider two examples.

  18. Hugh Maaskant: architect van de vooruitgang

    OpenAIRE

    Provoost, M.

    2003-01-01

    Hugh Maaskant (1907–1977) is best known as the architect who made the biggest mark on the post-war reconstruction of Rotterdam with such buildings as the Groothandelsgebouw, the Hilton Hotel and the Lijnbaan flats. Beginning his career in 1937 as the partner of Willem van Tijen, Maaskant embarked on his most prolific period after establishing an independent practice in 1955. He produced the lion’s share of his work in the 1950s and ’60s, the very period architectural critics generally regard ...

  19. Donald Hugh Blocher (1928-2013).

    Science.gov (United States)

    Dowd, E Thomas

    2015-01-01

    This article memorializes Donald Hugh Blocher (1928-2013). Blocher, a giant in counseling psychology, was elected a fellow of the American Psychological Association (APA) in 1973, received a Distinguished Achievement Award from Harvard University in 1968, and served as president of APA Division 17 (Society of Counseling Psychology) in 1980. He obtained a Fulbright Lectureship at the University of Keele (United Kingdom) for 1968-1969, where he helped develop a counseling psychology program according to American standards. He also published many books, book chapters, and articles over the course of his professional career.

  20. Hugh Owen Thomas (1834-1891)

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    @@ Hugh Owen Thomas被称为英国骨科之父,他对英国乃至世界骨科作出了杰出的贡献. 早在17世纪,接骨师已经作为一个社会地位较高的职业在英国、法国兴盛起来.接骨师的技术通常是在家族内部传承而不会对外传授.

  1. Sandy ja Hugh - paar või mitte? / Hugh Grant, Sandra Bullock

    Index Scriptorium Estoniae

    Grant, Hugh, 1960-

    2003-01-01

    Romantilises komöödias "Kaks nädalat armumiseks" ("Two Weeks Notice"), režissöör Marc Lawrence, mängivad kaks kuulsat näitlejat. Staarid oma suhetest : Hugh Grant : "Sandra on geenius"; Sandra Bullock : "Oleme temaga nagu kaksikud!"

  2. Sandy ja Hugh - paar või mitte? / Hugh Grant, Sandra Bullock

    Index Scriptorium Estoniae

    Grant, Hugh, 1960-

    2003-01-01

    Romantilises komöödias "Kaks nädalat armumiseks" ("Two Weeks Notice"), režissöör Marc Lawrence, mängivad kaks kuulsat näitlejat. Staarid oma suhetest : Hugh Grant : "Sandra on geenius"; Sandra Bullock : "Oleme temaga nagu kaksikud!"

  3. Obituary: Lawrence Hugh Aller, 1913-2003

    Science.gov (United States)

    Kaler, James B.

    2003-12-01

    physics to the observations, which he ardently sought. Little pleased him more than gathering photons, except perhaps for making atomic calculations with which he could analyze spectra. His real love was gaseous nebulae, specifically planetary nebulae (which he called his ``hobby"), the graceful shells of gas surrounding dying stars that are making their transitions to becoming white dwarfs. His range of simultaneous research projects was staggering. Having been an undergraduate student at Michigan in the late 1950s, I followed him to UCLA to work on my doctorate. When I arrived, I found him engaged in stellar spectroscopy, solar research, nebular theory, nebular observations (he tossed a box of plates at me and said in effect, ``here is your thesis"), and of all things Mie scattering theory to explain the zodiacal light! A list of his discoveries and influences is impressive. A sample: Lawrence played a major role in Menzel's group, which produced the famed ``Physical Processes in Gaseous Nebulae," an 18-part series that ran in the Astrophysical Journal from 1937 to 1945 and that explained nebular spectra. He was among the first to promulgate what in the 1940s was utter heresy, that the chemical compositions of stars could differ from one another. He was the first to observe gradients in spiral galaxies, which ultimately turned out to be the result of abundance variations. David Bohm and Lawrence established the existence of Maxwellian velocity distributions in nebular plasmas. Leo Goldberg, Edith Müller, and he were instrumental in establishing the chemical composition of the Sun. His observations of planetaries were legion. Never content with current observational and analytical capabilities, he sought out the latest equipment, from image tubes through CCDs to the best computers, ever looking ahead. His work was honored in 1992, when he received the American Astronomical Society's Russell Prize. Perhaps Lawrence's greatest legacy involved his teaching and writing. At

  4. Acute Charles Bonnet Syndrome following Hughes procedure.

    Science.gov (United States)

    Wilson, Michelle E; Pointdujour-Lim, Renelle; Lally, Sara; Shields, Carol L; Rabinowitz, Michael P

    2016-10-01

    A 69-year-old male experienced monocular formed visual hallucinations after occlusion of the right eye following resection of eyelid basal cell carcinoma and reconstruction with a Hughes procedure (tarsoconjunctival flap). His symptoms included recurrent, well-defined, organized, complex, formed images of small children playing in the snow. These visual phenomena occurred only in the occluded eye, began several hours after surgery, and recurred intermittently several times daily for 4 days, lasting several minutes with each occurrence. The patient retained insight into the false nature of the images throughout the duration of his symptoms, and the hallucinations resolved spontaneously while the flap was still in place. To our knowledge, this is the first reported case of Charles Bonnet Syndrome (CBS) following a Hughes procedure in a patient with normal visual acuity in the non-occluded fellow eye. Unlike other reported cases of acute onset CBS following transient monocular occlusion, hallucinations in the occluded eye remitted prior to restoration of vision in the occluded eye. Ophthalmologists should be aware of the potential for CBS following even transient monocular occlusion and should consider warning patients about its potential to occur.

  5. Cosmic Ray Electrons, Positrons and the Synchrotron emission of the Galaxy: consistent analysis and implications

    CERN Document Server

    Di Bernardo, Giuseppe; Gaggero, Daniele; Grasso, Dario; Maccione, Luca

    2012-01-01

    A multichannel analysis of cosmic ray electron and positron spectra and of the diffuse synchrotron emission of the Galaxy is performed by using the DRAGON code. This study is aimed at probing the interstellar electron source spectrum down to E ~ 1 GeV and at constraining several propagation parameters. We find that above 4 GeV the electron source spectrum is compatible with a power-law of index -2.5. Below 4 GeV instead it must be significantly suppressed and the total lepton spectrum is dominated by secondary particles. The positron spectrum and fraction measured below a few GeV are consistently reproduced only within low reacceleration models. We also constrain the scale-height zt of the cosmic-ray distribution using three independent (and, in two cases, original) arguments, showing that values of z_t < 2 kpc are excluded. This result may have strong implications for particle dark matter searches.

  6. Suppression of Electron Thermal Conduction in the High β Intracluster Medium of Galaxy Clusters

    Science.gov (United States)

    Roberg-Clark, G. T.; Drake, J. F.; Reynolds, C. S.; Swisdak, M.

    2016-10-01

    Understanding the thermodynamic state of the hot intracluster medium (ICM) in a galaxy cluster requires knowledge of the plasma transport processes, especially thermal conduction. The basic physics of thermal conduction in plasmas with ICM-like conditions has yet to be elucidated, however. We use particle-in-cell simulations and analytic models to explore the dynamics of an ICM-like plasma (with small gyroradius, large mean free path, and strongly sub-dominant magnetic pressure) driven by the diffusive heat flux associated with thermal conduction. Linear theory reveals that whistler waves are driven unstable by electron heat flux, even when the heat flux is weak. The resonant interaction of electrons with these waves then plays a critical role in scattering electrons and suppressing the heat flux. In a 1D model where only whistler modes that are parallel to the magnetic field are captured, the only resonant electrons are moving in the opposite direction to the heat flux, and the electron heat flux suppression is small. In 2D or more, oblique whistler modes also resonate with electrons moving in the direction of the heat flux. The overlap of resonances leads to effective symmetrization of the electron distribution function and a strong suppression of heat flux. The results suggest that thermal conduction in the ICM might be strongly suppressed, possibly to negligible levels.

  7. Hugh Blairs Lectures on Rhetoric and Belles Lettres

    DEFF Research Database (Denmark)

    Schatz-Jakobsen, Claus

    1989-01-01

    Artiklen nærlæser dekonstruktivt dele af den skotske retorikprofessor Hugh Blairs Lecures on Rhetoric and Belles Lettres (1783) og påviser splittelsen mellem to vidt forskellige retorik- og liltteraturhistoriske interesser, neoklassicistiske vs. romantiske....

  8. Síndrome de Hughes-Stovin

    Directory of Open Access Journals (Sweden)

    Sonia Pankl

    2015-04-01

    Full Text Available El síndrome de Hughes-Stovin es una entidad infrecuente caracterizada por trombosis venosa profunda y aneurismas de la arteria pulmonar, siendo su etiología y patogenia desconocida. Algunos autores la consideran una variante de la enfermedad de Behcet. Su curso natural es generalmente fatal. Se presenta con tos, disnea, hemoptisis, dolor torácico y fiebre. El tratamiento es con esteroides y agentes citotóxicos hasta la cirugía. Presentamos el caso de un hombre de 41 años que consultó por disnea, hemoptisis y dolor torácico, llegándose al diagnóstico de trombosis venosa profunda de miembro inferior derecho, trombo-embolismo de pulmón y aneurismas de arterias pulmonares. Recibió tratamiento con corticoides en altas dosis y 6 pulsos de ciclofosfamida de 1 gramo durante 6 meses, con regresión completa de los aneurismas y de la sintomatología.

  9. Fast variability of tera-electron volt gamma rays from the radio galaxy M87.

    Science.gov (United States)

    Aharonian, F; Akhperjanian, A G; Bazer-Bachi, A R; Beilicke, M; Benbow, W; Berge, D; Bernlöhr, K; Boisson, C; Bolz, O; Borrel, V; Braun, I; Brown, A M; Bühler, R; Büsching, I; Carrigan, S; Chadwick, P M; Chounet, L-M; Coignet, G; Cornils, R; Costamante, L; Degrange, B; Dickinson, H J; Djannati-Ataï, A; Drury, L O'c; Dubus, G; Egberts, K; Emmanoulopoulos, D; Espigat, P; Feinstein, F; Ferrero, E; Fiasson, A; Fontaine, G; Funk, Seb; Funk, S; Füssling, M; Gallant, Y A; Giebels, B; Glicenstein, J F; Goret, P; Hadjichristidis, C; Hauser, D; Hauser, M; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hoffmann, A; Hofmann, W; Holleran, M; Hoppe, S; Horns, D; Jacholkowska, A; de Jager, O C; Kendziorra, E; Kerschhaggl, M; Khélifi, B; Komin, Nu; Konopelko, A; Kosack, K; Lamanna, G; Latham, I J; Le Gallou, R; Lemière, A; Lemoine-Goumard, M; Lenain, J-P; Lohse, T; Martin, J M; Martineau-Huynh, O; Marcowith, A; Masterson, C; Maurin, G; McComb, T J L; Moulin, E; de Naurois, M; Nedbal, D; Nolan, S J; Noutsos, A; Orford, K J; Osborne, J L; Ouchrif, M; Panter, M; Pelletier, G; Pita, S; Pühlhofer, G; Punch, M; Ranchon, S; Raubenheimer, B C; Raue, M; Rayner, S M; Reimer, A; Ripken, J; Rob, L; Rolland, L; Rosier-Lees, S; Rowell, G; Sahakian, V; Santangelo, A; Saugé, L; Schlenker, S; Schlickeiser, R; Schröder, R; Schwanke, U; Schwarzburg, S; Schwemmer, S; Shalchi, A; Sol, H; Spangler, D; Spanier, F; Steenkamp, R; Stegmann, C; Superina, G; Tam, P H; Tavernet, J-P; Terrier, R; Tluczykont, M; van Eldik, C; Vasileiadis, G; Venter, C; Vialle, J P; Vincent, P; Völk, H J; Wagner, S J; Ward, M

    2006-12-01

    The detection of fast variations of the tera-electron volt (TeV) (10(12) eV) gamma-ray flux, on time scales of days, from the nearby radio galaxy M87 is reported. These variations are about 10 times as fast as those observed in any other wave band and imply a very compact emission region with a dimension similar to the Schwarzschild radius of the central black hole. We thus can exclude several other sites and processes of the gamma-ray production. The observations confirm that TeV gamma rays are emitted by extragalactic sources other than blazars, where jets are not relativistically beamed toward the observer.

  10. INTEGRAL/SPI Observations of Electron-Positron Annihilation Radiation from our Galaxy

    Science.gov (United States)

    Teegarden, B. J.; Watanabe, K.; Knoedlseder, J.; Jean, P.; Lonjou, V.; Weidenspointner, G.; Skinner, G.; von Ballmoos, P.; Vedrenne, G.; Roques, J.-P.; Schanne, S.; Schoenfelder, V.

    2004-12-01

    The spectrometer on INTEGRAL (SPI) is a coded-aperture gamma-ray telescope with moderate angular resolution (3 deg) and superior energy resolution (2 keV at 511 keV). One of it's principal science goals is the detailed study of 511 keV electron-positron annihilation from our Galaxy. The origin of this radiation remains a mystery, however current morphological studies suggest an older stellar population. There has also been recent speculation on the possibility of the existence of light (< 100 MeV) dark matter particles whose annihilation or decay could produce the observed 511 keV emission. In this paper we summarize the current results from SPI, compare them with previous results and discuss their implication on possible models for the production of the annihilation radiation. INTEGRAL is a project of ESA. This work was supported by NASA and CNES.

  11. Metal-poor dwarf galaxies in the SIGRID galaxy sample. II. The electron temperature-abundance calibration and the parameters that affect it

    CERN Document Server

    Nicholls, David C; Sutherland, Ralph S; Jerjen, Helmut; Kewley, Lisa J; Basurah, Hassan

    2014-01-01

    In this paper, we use the Mappings photoionization code to explore the physical parameters that impact on the measurement of electron temperature and abundance in HII regions. In the previous paper we presented observations and measurements of physical properties from the spectra of seventeen HII regions in fourteen isolated dwarf irregular galaxies from the SIGRID sample. Here, we analyze these observations further, together with three additional published data sets. We explore the effects of optical thickness, electron density, ionization parameter, ionization source, and non-equilibrium effects on the relation between electron temperature and metallicity. We present a standard model that fits the observed data remarkably well at metallicities between 1/10 and 1 solar. We investigate the effects of optically thin HII regions, and show that they can have a considerable effect on the measured electron temperature, and that there is evidence that some of the observed objects are optically thin. We look at the ...

  12. A new method to probe the thermal electron content of the Galaxy through spectral analysis of background sources

    CERN Document Server

    Jones, D I; Haverkorn, M

    2016-01-01

    We present a new method for probing the thermal electron content of the Galaxy by spectral analysis of background point sources in the absorption-only limit to the radiative transfer equation. In this limit, calculating the spectral index, $\\alpha$, of these sources using a natural logarithm results in an additive factor, which we denote $\\alpha_\\mathrm{EM}$, resulting from the absorption of radiation due to the Galactic thermal electron population. We find that this effect is important at very low frequencies ($\

  13. Cosmic ray electrons, positrons and the synchrotron emission of the Galaxy: consistent analysis and implications

    Energy Technology Data Exchange (ETDEWEB)

    Bernardo, Giuseppe Di [Department of Physics, University of Gothenburg, SE 412 96 Gothenburg (Sweden); Evoli, Carmelo [II. Institut für Theoretische Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany); Gaggero, Daniele [SISSA, Via Bonomea 265, 34136 Trieste (Italy); Grasso, Dario [Dipartimento di Fisica, Università di Siena, Via Roma 56, I-56100 Siena (Italy); Maccione, Luca, E-mail: giuseppe.dibernardo@physics.gu.se, E-mail: carmelo.evoli@desy.de, E-mail: dgaggero@sissa.it, E-mail: dario.grasso@pi.infn.it, E-mail: luca.maccione@lmu.de [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, D-80805 München (Germany)

    2013-03-01

    A multichannel analysis of cosmic ray electron and positron spectra and of the diffuse synchrotron emission of the Galaxy is performed by using the DRAGON code. This study is aimed at probing the interstellar electron source spectrum down to E ∼< 1GeV and at constraining several propagation parameters. We find that above 4GeV the e{sup −} source spectrum is compatible with a power-law of index ∼ 2.5. Below 4GeV instead it must be significantly suppressed and the total lepton spectrum is dominated by secondary particles. The positron spectrum and fraction measured below a few GeV are consistently reproduced only within low reacceleration models. We also constrain the scale-height z{sub t} of the cosmic-ray distribution using three independent (and, in two cases, original) arguments, showing that values of z{sub t} ∼< 2kpc are excluded. This result may have strong implications for particle dark matter searches.

  14. Radiologic diagnosis of Fitz-Hugh-Curtis syndrome

    Institute of Scientific and Technical Information of China (English)

    WANG Cheng-lin; GUO Xue-jun; YUAN Zhi-dong; SHI Qiao; HU Xiao-hong; FANG Lin

    2009-01-01

    @@ Litz-Hugh-Curtis syndrome (FHCS) was reported by Curtis after he found a fibrous adhesion between the surface of the liver and peritoneum in patients with gonococcal pelvic inflammation during laparoscopy in 1930, and the first report by Fitz-Hugh as acute gonococcal peritonitis in the right upper quadrant abdomen was published in 1934.1,2 The so-called FHCS is believed to originate from an inflammation in the pelvis which may ascend toward the diaphragmatic surface of the liver along the right paracolic gutters to cause the inflammation of the liver caosule with right upper abdominal pain.3-7

  15. Francesca Hughes: Architecture of Error: Matter, Measure and the Misadventure of Precision

    DEFF Research Database (Denmark)

    Foote, Jonathan

    2016-01-01

    Review of "Architecture of Error: Matter, Measure and the Misadventure of Precision" by Francesca Hughes (MIT Press, 2014)......Review of "Architecture of Error: Matter, Measure and the Misadventure of Precision" by Francesca Hughes (MIT Press, 2014)...

  16. Hugh Grant's Image Restoration Discourse: An Actor Apologizes.

    Science.gov (United States)

    Benoit, William L.

    1997-01-01

    Examines the strategies used by actor Hugh Grant (in his appearances on talk shows) to help restore his reputation after he was arrested for lewd behavior with a prostitute. Uses this case as a springboard to contrast entertainment image repair with political and corporate image repair, arguing that important situational differences can be…

  17. Additional Responses to Hugh Heclo's "On Thinking Institutionally"

    Science.gov (United States)

    Lincoln, Timothy D.; Fennell, Robert C.

    2011-01-01

    Issue 13:3 of this journal (July 2010) included a "Conversation" on Hugh Heclo's recent publication "On Thinking Institutionally" (Paradigm Publishers, 2008) with a book review by Robert Fennell and responses by Richard Ascough, Tat-siong Benny Liew, Michael McLain, and Lynne Westfield. Here we publish two additional responses to this same book.…

  18. Vernon Hughes and the Quest for the Proton's Spin

    Science.gov (United States)

    Jaffe, Robert L.

    2004-12-01

    Vernon Hughes dedicated much of the latter part of his career to the question "What carries the spin of the proton?" The question remains unanswered and near the top of the list of fascinating questions in QCD. I present a perspective on the question and Vernon's pursuit of an answer.

  19. Dr. Vernon W. Hughes, 81, authority on the subatomic

    CERN Multimedia

    Lavietes, S

    2002-01-01

    "Dr. Vernon W. Hughes, a Yale physicist whose investigation of particles called muons poked holes in standard subatomic theory and provided evidence for the existence of previously undetected matter, died at Yale-New Haven Hospital last Tuesday" (1/2 page).

  20. Hugh Hefner - maailma esi-playboy / Neeme Raud

    Index Scriptorium Estoniae

    Raud, Neeme, 1969-

    2004-01-01

    Ajakirja Playboy asutajast Hugh Hefner'ist, tema elufilosoofiast ja põhimõtetest erootikaväljaande sisu kujundamisel. Ärijuhi Christie Hefner'i sõnul on rahvusvahelise multimeedia-meelelahutusfirma praeguseks eesmärgiks brändi sobitamine erinevatesse meediavormidesse. Lisa: Mis on Playboy?

  1. Differential Response: What to Make of the Existing Research? A Response to Hughes et al.

    Science.gov (United States)

    Drake, Brett

    2013-01-01

    This article is a response to "Issues in Differential Response", a review of the current evidence pertaining to differential response (DR) programs in child protective services (CPS). In my view, the Hughes, Rycus, Saunders-Adams, Hughes, and Hughes article suffers from several weaknesses. First, DR programs are critiqued as if they were…

  2. The galaxy-wide distributions of mean electron density in the HII regions of M51 and NGC 4449

    CERN Document Server

    Gutiérrez, Leonel

    2010-01-01

    Using ACS-HST images to yield continuum subtracted photometric maps in H\\alpha of the Sbc galaxy M51 and the dwarf irregular galaxy NGC 4449, we produced extensive (over 2000 regions for M51, over 200 regions for NGC4449) catalogues of parameters of their HII regions: their H\\alpha luminosities, equivalent radii and coordinates with respect to the galaxy centers. From these data we derived, for each region, its mean luminosity weighted electron density, , determined from the H\\alpha luminosity and the radius, R, of the region. Plotting these densities against the radii of the regions we find excellent fits for varying as R^{-1/2}. This relatively simple relation has not, as far as we know, been predicted from models of HII region structure, and should be useful in constraining future models. Plotting the densities against the galactocentric radii, r, of the regions we find good exponential fits, with scale lengths of close to 10 kpc for both galaxies. These values are comparable to the scale lengths of the H...

  3. SPECTROSCOPIC STUDY OF STAR-FORMING GALAXIES IN FILAMENTS AND THE FIELD AT z ∼ 0.5: EVIDENCE FOR ENVIRONMENTAL DEPENDENCE OF ELECTRON DENSITY

    Energy Technology Data Exchange (ETDEWEB)

    Darvish, Behnam; Mobasher, Bahram; Hemmati, Shoubaneh; Shivaei, Irene [University of California, Riverside, 900 University Ave, Riverside, CA 92521 (United States); Sobral, David [Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, OAL, Tapada da Ajuda, PT 1349-018 Lisboa (Portugal); Nayyeri, Hooshang, E-mail: bdarv001@ucr.edu [University of California, Irvine, Irvine, CA 92697 (United States)

    2015-12-01

    We study the physical properties of a spectroscopic sample of 28 star-forming galaxies in a large filamentary structure in the COSMOS field at z ∼ 0.53, with spectroscopic data taken with the Keck/DEIMOS spectrograph, and compare them with a control sample of 30 field galaxies. We spectroscopically confirm the presence of a large galaxy filament (∼8 Mpc), along which five confirmed X-ray groups exist. We show that within the uncertainties, the ionization parameter, equivalent width (EW), EW versus specific star-formation rate (sSFR) relation, EW versus stellar mass relation, line-of-sight velocity dispersion, dynamical mass, and stellar-to-dynamical mass ratio are similar for filament and field star-forming galaxies. However, we show that, on average, filament star-forming galaxies are more metal enriched (∼0.1–0.15 dex), possibly owing to the inflow of the already-enriched intrafilamentary gas into filament galaxies. Moreover, we show that electron densities are significantly lower (a factor of ∼17) in filament star-forming systems compared to those in the field, possibly because of a longer star-formation timescale for filament star-forming galaxies. Our results highlight the potential pre-processing role of galaxy filaments and intermediate-density environments on the evolution of galaxies, which has been highly underestimated.

  4. Langston Hughes and his poem “Harlem”

    Institute of Scientific and Technical Information of China (English)

    郝红

    2005-01-01

    James Langston Hughes was born February 1. 1902, in Joplin, Missouri. His parents divorced when he was a small child, and his father moved to Mexico. He was raised by his Grandmother until he was thirteen, when he moved to Lincoln,Illinois, to live with his mother and her husband, eventually settling in Cleveland, Ohio. It was in I,incoln, Illinois, that Hughes began writing poetry. Following graduation, he spent a year in Mexico and a year at Columbia University. During these years, he held old jobs as an assistant cook, launderer, and a busboy, and traveled to Africa and Europe working as a seaman. In November 1924, he moved to Washington,

  5. Fitz-Hugh-Curtis综合征7例

    Institute of Scientific and Technical Information of China (English)

    焦浦生

    2000-01-01

    @@ FHC综合征Fitz-Hugh-Curtis Syntrome)是继发于盆腔感染的肝包膜炎症反应性疾病.该综合征典型临床表现是右上腹痛,发热伴有盆腔炎.现将我院近年来诊治FHC综合征7例总结中下.

  6. Bifurcaciones del Sistema de FitzHugh-Nagumo (FHN

    Directory of Open Access Journals (Sweden)

    Fernando Ongay Larios

    2011-01-01

    Full Text Available La familia paramétrica de los sistemas de FitzHugh-Nagumo es rica en bifurcaciones (Rocsoreanu et al., 2000. En este artículo estudiamos las bifurcaciones silla-nodo y de Hopf desde el punto de vista matemático de esta familia y se describen completamente los conjuntos de bifurcación en el espacio de parámetros.

  7. The Spin Structure of the Nucleon:. a Hughes Legacy

    Science.gov (United States)

    Cates, Gordon D.

    2004-12-01

    More than any other individual, Vernon Hughes can be pointed to as the father of the experimental investigation of nucleon spin structure. Even theoretical development in this area was spurred on by Vernon's pioneering efforts to make the control of spin degrees of freedom an experimental reality. This talk traces some of Vernon's work in this area, as well as examining, briefly and not in a complete fashion, some of the other work that can be looked upon as Vernon's legacy.

  8. Search for Extremely Metal-poor Galaxies in the Sloan Digital Sky Survey (II): high electron temperature objects

    CERN Document Server

    Almeida, J Sanchez; Morales-Luis, A B; Munoz-Tunon, C; Garcia-Benito, R; Nuza, S E; Kitaura, F S

    2016-01-01

    Extremely metal-poor (XMP) galaxies are defined to have gas-phase metallicity smaller than a tenth of the solar value (12 + log[O/H] < 7.69). They are uncommon, chemically and possibly dynamically primitive, with physical conditions characteristic of earlier phases of the Universe. We search for new XMPs in the Sloan Digital Sky Survey (SDSS) in a work that complements Paper I. This time high electron temperature objects are selected; since metals are a main coolant of the gas, metal- poor objects contain high-temperature gas. Using the algorithm k-means, we classify 788677 spectra to select 1281 galaxies having particularly intense [OIII]4363 with respect to [OIII]5007, which is a proxy for high electron temperature. The metallicity of these candidates was computed using a hybrid technique consistent with the direct method, rendering 196 XMPs. A less restrictive noise constraint provides a larger set with 332 candidates. Both lists are provided in electronic format. The selected XMP sample have mean stell...

  9. Hugh de Wardener - the Man and the Scientist.

    Science.gov (United States)

    Phillips, M E; de Wardener, S

    2016-02-01

    Hugh de Wardener died on 29th September 2013, ten days before his 98th birthday. He had a diverse upbringing and qualified in Medicine in 1939. He joined the army but was captured in 1942 and imprisoned in Singapore and Thailand until 1945. His clinical care of fellow prisoners was highly regarded. He preserved their clinical records and used them, post-war, to write two Lancet papers. One showed, for the first time, that Wernickes encephalopathy could be caused by severe malnutrition and cured by small doses of vitamin B1. His later academic interests were based on the emphasis he placed on renal physiology. This applied to the topic most associated with his name-Natriuretic Hormone. Whilst de Wardener never isolated this hormone, his early experiments, demonstrating that a third factor other than GFR and aldosterone affected renal sodium transport, were substantiated by others. Hugh had many research interests: pyelonephritis, renal histology, maintenance dialysis and metabolic/renal bone disease. In his later years he researched intensively into the role of sodium and salt in the aetiology of essential hypertension. Hugh was president of the International Society of Nephrology (1969-72) and the UK Renal Association (1975-78). He received many awards and recognitions from across the world, many of them after his (so-called) retirement. Throughout his career he never neglected the care of his patients. As Bob Schrier wrote in his obituary of de Wardener in Kidney International he was a caring physicianwhose dedication to his patients welfare was exemplary.

  10. Some Numerical Aspects on Crowd Motion - The Hughes Model

    KAUST Repository

    Gomes, Diogo A.

    2016-01-06

    Here, we study a crowd model proposed by R. Hughes in [5] and we describe a numerical approach to solve it. This model comprises a Fokker-Planck equation coupled with an Eikonal equation with Dirichlet or Neumann data. First, we establish a priori estimates for the solution. Second, we study radial solutions and identify a shock formation mechanism. Third, we illustrate the existence of congestion, the breakdown of the model, and the trend to the equilibrium. Finally, we propose a new numerical method and consider two numerical examples.

  11. Spectroscopic Study of Star-forming Galaxies in Filaments and the Field at $z\\sim$0.5: Evidence for Environmental Dependence of Electron Density

    CERN Document Server

    Darvish, Behnam; Sobral, David; Hemmati, Shoubaneh; Nayyeri, Hooshang; Shivaei, Irene

    2015-01-01

    We study the physical properties of a spectroscopic sample of 28 star-forming galaxies in a large filamentary structure in the COSMOS field at $z\\sim$0.53, with spectroscopic data taken with the Keck/DEIMOS spectrograph, and compare them with a control sample of 30 field galaxies. We spectroscopically confirm the presence of a large galaxy filament ($\\sim$ 8 Mpc), along which five confirmed X-ray groups exist. We show that within the uncertainties, the ionization parameter, equivalent width (EW), EW versus specific star-formation rate (sSFR) relation, EW versus stellar mass relation, line-of-sight velocity dispersion, dynamical mass, and stellar-to-dynamical mass ratio are similar for filament and field star-forming galaxies. However, we show that on average, filament star-forming galaxies are more metal-enriched ($\\sim$ 0.1$-$0.15 dex), possibly due to the inflow of the already enriched intrafilamentary gas into filament galaxies. Moreover, we show that electron densities are significantly lower (a factor of...

  12. Surviving To Write and Writing To Survive: The Complex Case of Langston Hughes.

    Science.gov (United States)

    Ostrom, Hans

    Studying the life of Langston Hughes in the context of how to teach freshman composition can shed light on two sometimes conflicting pedagogies, the expressivist and the social-constructionist. A discouraging period of fierce criticism, illness, depression, and financial woes coincided with Hughes' 39th birthday, which his biographer Arnold…

  13. The Progression About Fitz-Hugh-Curtis Syndrome Study%Fitz-Hugh-Curtis综合征研究进展

    Institute of Scientific and Technical Information of China (English)

    靳翠平; 尚玉敏

    2009-01-01

    Fitz-Hugh-Curtis综合征是盆腔感染合并肝周围炎,主要涉及肝包膜而无肝实质损害,在慢性盆腔炎患者中较为常见.病原菌主要是淋病奈瑟菌及衣原体,主要临床表现为右下腹痛,并可导致慢性腹痛、不孕、异位妊娠等多种并发症.可结合腹腔CT、相关实验室检验及腹腔镜检查对其进行诊断及鉴别诊断,并通过敏感抗生素及腹腔镜手术进行有效治疗.就Fitz-Hugh-Curtis综合征病因与发病机制、临床特征、并发症、诊断、治疗及相关意义进行综述.

  14. Synchrotron and inverse-Compton emission from radio galaxies with non-uniform magnetic field and electron distributions

    CERN Document Server

    Hardcastle, M J

    2013-01-01

    I investigate the effect of non-uniform magnetic fields in the extended structures of radio galaxies on the observed synchrotron and inverse-Compton emission. On the assumption of an isotropic field, with a given power spectrum and a Gaussian distribution of the Cartesian components of the magnetic field strength, I derive a simple integral that can be used numerically to calculate the synchrotron emissivity from any electron population. In the case of power-law spectra, I show that it is possible to estimate the difference between the synchrotron emissivity from a region with such a field and that from the commonly assumed arrangement where $B$ is constant everywhere, though fully tangled, and that this difference is small, though it increases if the electron energy density scales with the field. An aged electron spectrum in such a field produces a characteristic curved synchrotron spectrum which differs significantly from the classical Jaffe-Perola spectrum, and I discuss some effects that this might have o...

  15. A Powerful Friendship: Theodore von Karman and Hugh L. Dryden

    Science.gov (United States)

    Gorn, Michael

    2003-01-01

    During their long personal friendship and professional association, Theodore von Karman (1882-1963) and Hugh L. Dryden (1898-1965) exercised a pivotal if somewhat elusive influence over American aeronautics and spaceflight. Both decisive figures in organizing scientists and engineers at home and abroad, both men of undisputed eminence in their technical fields, their range of contacts in government, academia, the armed forces, industry, and professional societies spanned the globe to an extent unparalleled then as now. Moreover, because they coordinated their activities closely, their combined influence far exceeded the sum of each one s individual contributions. This paper illustrates their personal origins as well as the foundations of their friendship, how their relationship became a professional alliance, and their joint impact on the world of aeronautics and astronautics during the twentieth century.

  16. Realistic model of compact VLSI FitzHugh-Nagumo oscillators

    Science.gov (United States)

    Cosp, Jordi; Binczak, Stéphane; Madrenas, Jordi; Fernández, Daniel

    2014-02-01

    In this article, we present a compact analogue VLSI implementation of the FitzHugh-Nagumo neuron model, intended to model large-scale, biologically plausible, oscillator networks. As the model requires a series resistor and a parallel capacitor with the inductor, which is the most complex part of the design, it is possible to greatly simplify the active inductor implementation compared to other implementations of this device as typically found in filters by allowing appreciable, but well modelled, nonidealities. We model and obtain the parameters of the inductor nonideal model as an inductance in series with a parasitic resistor and a second order low-pass filter with a large cut-off frequency. Post-layout simulations for a CMOS 0.35 μm double-poly technology using the MOSFET Spice BSIM3v3 model confirm the proper behaviour of the design.

  17. Right Pleural Effusion in Fitz-Hugh-Curtis Syndrome

    Directory of Open Access Journals (Sweden)

    Tajiri,Takuma

    2006-10-01

    Full Text Available Right pleural effusion was diagnosed in a 36-year-old woman with right upper quadrant pain and fever. Enhanced pelvic computed tomography performed because of irregular genital bleeding revealed the pelvic inflammatory disease. Upon further questioning, the patient confirmed that she had recently undergone therapy for Chlamydia trachomatis infection. Therefore she was given an injection of tetracycline because we suspected Fitz-Hugh-Curtis syndrome (FHCS, a pelvic inflammatory disease characterized by perihepatitis associated with chlamydial infection. A remarkable clinical response to antibiotics was noted. The right upper quadrant pain was due to perihepatitis, and the final diagnosis was FHCS. Right pleural effusion may be caused by inflammation of the diaphragm associated with perihepatitis. Once chlamydial infection reaches the subphrenic liver, conditions in the closed space between the liver and diaphragm due to inflammatory adhesion may be conductive to chlamydial proliferation. The possibility of FHCS should be considered in patients and carefully distinguished from other abdominal diseases.

  18. Suzaku measurement of electron and magnetic energy densities in the east lobe of the giant radio galaxy DA 240

    CERN Document Server

    Isobe, Naoki; Tashiro, Makoto S

    2011-01-01

    A careful analysis of the Suzaku data of the giant radio galaxy DA 240, of which the size is 1.48 Mpc, revealed diffuse X-ray emission associated with its east lobe. The diffuse X-ray spectrum was described with a simple power-law model with a photon index of 1.92 (-0.17+0.13) (-0.06+0.04), where the first and second errors represent the statistical and systematic ones. The agreement with the synchrotron radio photon index, 1.95 +- 0.01 in 326 -- 608.5 MHz, ensures that the excess X-ray emission is attributed to the inverse Compton emission from the synchrotron-radiating electrons, boosting up the cosmic microwave background photons. From the X-ray flux density, 51.5 +-3.9 (-5.4+6.2) nJy at 1 keV derived with the photon index fixed at the radio index, in comparison with the synchrotron radio intensity of 10.30 +- 0.12 Jy at 326 MHz, the magnetic and electron energy densities was estimated as u_m = (3.0 +-0.2 +-0.4) \\times 10^(-14) ergs/cm3 and u_e = (3.4 (-0.2+0.3) (-0.4+0.5)) \\times 10^(-14) ergs/cm3 integra...

  19. The non-thermal emission of extended radio galaxy lobes with curved electron spectra

    CERN Document Server

    Duffy, Peter

    2011-01-01

    The existing theoretical framework for the energies stored in the synchrotron-emitting lobes of radio galaxies and quasars doesn't properly account for the curved spectral shape that many of them exhibit. We characterise these spectra using parameters that are straightforwardly observable in the era of high-resolution, low-frequency radio astronomy: the spectral curvature and the turnover in the frequency spectrum. This characterisation gives the Lorentz factor at the turnover in the energy distribution (we point out that this is distinctly different from the Lorentz factor corresponding to the turnover frequency in a way that depends on the amount of curvature in the spectrum) and readily gives the equipartition magnetic field strength and the total energy of the radiating plasma obviating the need for any assumed values of the cutoff frequencies to calculate these important physical quantities. This framework readily yields the form of the X-ray emission due to inverse-Compton (IC) scattering of Cosmic Micr...

  20. Hughes, Twain, Child, and Sanger: Four Who Locked Horns with the Censors

    Science.gov (United States)

    Meltzer, Milton

    1969-01-01

    A look at the lives and conflicts of four writers--Langston Hughes, Mark Twain, Lydia Maria Child, and Margaret Sanger--who faced public criticism and censorship because oftheir views on controversial issues. (RM)

  1. Investidura com a doctor honoris causa de l'Excm. Sr. Hugh Scott Fogler

    OpenAIRE

    Diversos autors

    2016-01-01

    Investidura com a doctor honoris causa del senyor Hugh Scott Fogler. Sessió acadèmica extraordinària, 15 d'abril de 2016. Elogi del candidat a càrrec del doctor Azael Fabregat Llagostera. Discurs d’investidura pronunciat pel senyor Hugh Scott Fogler. Paraules de benvinguda pronunciades pel doctor Josep Anton Ferré Vidal, Rector Magfc. de la Universitat.

  2. STS-40 Payload Specialist Millie Hughes-Fulford trains in JSC's SLS mockup

    Science.gov (United States)

    1987-01-01

    STS-40 Payload Specialist Millie Hughes-Fulford conducts Spacelab Life Sciences 1 (SLS-1) Experiment No. 198, Pulmonary Function During Weightlessness, in JSC's Life Sciences Project Division (LSPD) SLS mockup located in the Bioengineering and Test Support Facility Bldg 36. Hughes-Fulford monitors instruments and settings on Rack 8's panels. Behind her in the center aisle are the body mass measurement device (foreground) and the stowed bicycle ergometer.

  3. Pulmonary cytotoxicity of secondary metabolites of Stachybotrys chartarum (Ehrenb.) Hughes.

    Science.gov (United States)

    Pieckova, Elena; Hurbankova, Marta; Cerna, Silvia; Pivovarova, Zuzana; Kovacikova, Zuzana

    2006-01-01

    Damp dwellings represent suitable conditions for extended indoor moulds. A cellulolytic micromycete Stachybotrys chartarum (Ehrenb.) Hughes is considered to be a tertiary colonizer of surfaces in affected buildings. Known adverse health effects of S. chartarum result from its toxins--trichothecenes or atranones, as well as spirolactams. Mechanism of their potential pathological effects on the respiratory tract has not yet been sufficiently clarified. The cytotoxic effects of complex chloroform-extractable endo- (in biomass) and exometabolites (in cultivation medium) of an indoor S. chartarum isolate of an atranone chemotype, grown on a liquid medium with yeast extract and sucrose at 25 degrees C for 14 d, on lung tissue were evaluated in the 3-day experiment. For the purpose, 4 mg of toxicants were intratracheally instilled in 200 g Wistar male rats. A trichothecene mycotoxin diacetoxyscirpenol was used as the positive control. Bronchoalveolar lavage (BAL) parameters--viability and phagocytic activity of alveolar macrophages (AM), activity of lactate dehydrogenase, acid phosphatase and cathepsin D in cell-free BAL fluid (BALF), as well as in BAL cells, were measured. Acute exposure to the metabolites caused statistically significant changes, indicating lung tissue injury in the experimental animals. Decreased AM viability and increased activity of lysosomal enzyme cathepsin D in BAL cells after fungal exometabolite exposure were the most impressive. As toxic principles were found predominantly in the growth medium, toxins were more likely responsible for lung cell damage than e.g. fungal cell wall components. S. chartarum toxic metabolites can contribute to the ill health of occupants of mouldy building after inhalation of contaminated aerosol.

  4. Clinical outcome of Fitz-Hugh-Curtis syndrome mimicking acute biliary disease

    Institute of Scientific and Technical Information of China (English)

    Seong Yong Woo; Jin Il Kim; Dae Young Cheung; Se Hyun Cho; Soo-Heon Park; Joon-Yeol Han; Jae Kwang Kim

    2008-01-01

    AIM: To analyze the clinical characteristics of patients diagnosed with Fitz-Hugh-Curtis syndrome.METHODS: The clinical courses of patients that visited St. Mary's Hospital with abdominal pain from January 2005 to December 2006 and were diagnosed with Fitz-Hugh-Curtis syndrome were examined.RESULTS: Fitz-Hugh-Curtis syndrome was identified in 22 female patients of childbearing age; their mean age was 31.0 + 8.1 years. Fourteen of these cases presented with pain in the upper right abdomen alone or together with pain in the lower abdomen,and six patients presented with pain only in the lower abdomen. The first impression at the time of visit was acute cholecystitis or cholangitis in 10 patients and acute appendicitis or pelvic inflammatory disease in eight patients. Twenty-one patients were diagnosed by abdominal computer tomograghy (CT), and the results of abdominal sonography were normal for 10 of these patients. Ch/amydia trichomatis was isolated from 18 patients. Two patients underwent laparoscopic adhesiotomy and 20 patients were completely cured by antibiotic treatment.CONCLUSION: For women of childbearing age with acute pain in the upper right abdomen alone or together with pain in the lower abdomen, Fitz-HughCurtis syndrome should be considered during differential diagnosis. Moreover, in cases suspected to be Fitz-HughCurtis syndrome, abdominal c-r, rather than abdominal sonography, assists in the diagnosis.

  5. Case of Fitz-Hugh-Curtis syndrome in male without presentation of sexually transmitted disease.

    Science.gov (United States)

    Yi, Haram; Shim, Chan Sup; Kim, Gyu Won; Kim, Jung Seok; Choi, In Zoo

    2015-11-16

    Fitz-Hugh-Curtis syndrome is a type of perihepatitis that causes liver capsular infection without infecting the hepatic parenchyma or pelvis. Fitz-Hugh-Curtis syndrome is known to occur commonly in women of childbearing age who do not use oral contraceptives and have sexual partners older than 25 years of age. However, the syndrome has been reported to occur rarely in males. The clinical symptoms are right upper quadrant pain and tenderness, and pleuritic right sided chest pain. The clinical presentation is similar in male and female. We experienced a case of Fitz-Hugh-Curtis syndrome in a 60-year-old man with the chief complaint of right upper quadrant abdominal pain. Despite a previous history of gonorrhea, we have also described our experiences of improved symptoms and recovery with allopathic medicines and have thereby reported the present case with a literature review.

  6. Real time optical edge enhancement using a Hughes liquid crystal light valve

    Science.gov (United States)

    Chao, Tien-Hsin

    1989-01-01

    The discovery of an edge enhancement effect in using a Hughes CdS liquid crystal light valve (LCLV) is reported. An edge-enhanced version of the input writing image can be directly obtained by operating the LCLV at a lower bias frequency and bias voltage. Experimental conditions in which this edge enhancement effect can be optimized are described. Experimental results show that the SNR of the readout image using this technique is superior to that obtained using high-pass filtering. The repeatability of this effect is confirmed by obtaining an edge enhancement result using two different Hughes LCLVs. The applicability of this effect to improve discrimination capability in optical pattern recognition is addressed. The results show that the Hughes LCLV can be used in both continuous tone and edge-enhancing modes by simply adjusting its bias conditions.

  7. On the Hughes' model for pedestrian flow: The one-dimensional case

    KAUST Repository

    Di Francesco, Marco

    2011-02-01

    In this paper we investigate the mathematical theory of Hughes\\' model for the flow of pedestrians (cf. Hughes (2002) [17]), consisting of a non-linear conservation law for the density of pedestrians coupled with an eikonal equation for a potential modelling the common sense of the task. For such an approximated system we prove existence and uniqueness of entropy solutions (in one space dimension) in the sense of Kružkov (1970) [22], in which the boundary conditions are posed following the approach of Bardos et al. (1979) [7]. We use BV estimates on the density ρ and stability estimates on the potential Π in order to prove uniqueness. Furthermore, we analyze the evolution of characteristics for the original Hughes\\' model in one space dimension and study the behavior of simple solutions, in order to reproduce interesting phenomena related to the formation of shocks and rarefaction waves. The characteristic calculus is supported by numerical simulations. © 2010 Elsevier Inc.

  8. Real time optical edge enhancement using a Hughes liquid crystal light valve

    Science.gov (United States)

    Chao, Tien-Hsin

    1989-01-01

    The discovery of an edge enhancement effect in using a Hughes CdS liquid crystal light valve (LCLV) is reported. An edge-enhanced version of the input writing image can be directly obtained by operating the LCLV at a lower bias frequency and bias voltage. Experimental conditions in which this edge enhancement effect can be optimized are described. Experimental results show that the SNR of the readout image using this technique is superior to that obtained using high-pass filtering. The repeatability of this effect is confirmed by obtaining an edge enhancement result using two different Hughes LCLVs. The applicability of this effect to improve discrimination capability in optical pattern recognition is addressed. The results show that the Hughes LCLV can be used in both continuous tone and edge-enhancing modes by simply adjusting its bias conditions.

  9. Symposium Festschrift Hughes (Vernon W) to Celebrate his 70th birthday

    CERN Document Server

    1992-01-01

    The contents of this book are derived from a celebration of the 70th birthday of Vernon W Hughes. Professor Hughes' career has touched on several areas in modern physics ranging from precision measurements of the fundamental properties of atoms to measurements of spin structure functions of the proton via deep inelastic muon scattering at the world's highest energy fixed target machines. This observance of his 70th birthday brings together experimental and theoretical physicists who are leaders of the many fields in which he has made contributions.

  10. 77 FR 1975 - Union Pacific Railroad Company-Discontinuance of Service Exemption-in Pittsburg, Hughes, and...

    Science.gov (United States)

    2012-01-12

    ..., Hughes, and Seminole Counties, Okla. (the line). The line traverses United States Postal Service Zip... discontinue service over a portion of a line of railroad known as the Shawnee Branch Line, between milepost... in Hughes County, which makes the line 0.19 miles longer than the terminal mileposts would...

  11. Rivers and Hughes's Construction of Black Culture in White America——Textual Analysis of "The Negro Speaks of RAvers"

    Institute of Scientific and Technical Information of China (English)

    曾慧

    2009-01-01

    Langston Hughes's central purpose in writing is "to explain and illuminate the Negro condition in America". By means of textual analysis, this thesis is to discover how the images of rivers in "The Negro Speaks of Rivers" construct the black culture, to find Hughes's identity in America.

  12. IN MEMORIAM: Hugh P Kelly, 3 September 1931 - 29 June 1992

    Science.gov (United States)

    Hansen, Jørgen E.

    1993-01-01

    It is said that Racah was one of the few physicists who was able not only to read Hermann Weyl's book "The Theory of Groups and Quantum Mechanics" but also to understand enough to use it himself. Something similar applies to Hugh Kelly, who introduced the methods of Many-Body Perturbation Theory (MBPT), which was being developed by nuclear physicists like Keith Brueckner whom Hugh worked with as a post-doc, into atomic physics. Since atomic physics with its "known" forces is a perfect area in which to apply the methods of MBPT, it is clear that this would have happened sooner or later. Hugh Kelly's achievement is that it happened very early. Hugh's death this summer after a long battle with cancer is a great loss to atomic physics and to his many friends in the community. Hugh P Kelly got his PhD from the University of California at Berkeley in 1963 under the supervision of Kenneth Watson and in 1965 he was hired as assistant Professor at the University of Virginia. His appointment was to a large extent due to the support of M E Rose, also a nuclear physicist with interest in atoms as is clear from his book "Elementary Theory of Angular Momentum". Hugh remained at the University of Virginia for the rest of his life, over the years serving as Department Chairman, Faculty Dean and, during the last years, as University Provost, but throughout Hugh pursued his real passion which was Physics. It is a clear sign of his dedication that he is sole author on a large number of papers particularly of course in the early years when he alone was Atomic Theory in Charlottesville. Hugh contributed to many areas of atomic physics although early on photoionization became his favourite subject and the one where he made his main contribution: first for closed shell atoms, but later extending his techniques to open shell systems for which the normal MBPT techniques did not apply. Hugh had a good nose for finding projects that were of topical interest and many of his papers are

  13. 75 FR 24973 - United States v. Baker Hughes Inc., et al.

    Science.gov (United States)

    2010-05-06

    .... IV. Trade and Commerce A. Background 1. Overview of Drilling and Completion Process 11. Offshore... impose on each other's pricing. Post merger, Baker Hughes will likely find it profitable to raise the... transaction may present a profitable opportunity to remove one or two vessels from the Gulf, an opportunity...

  14. The Political Economy of Rhetorical Style: Hugh Blair's Response to the Civic-Commercial Dilemma

    Science.gov (United States)

    Longaker, Mark Garrett

    2008-01-01

    Recent scholarship treats Hugh Blair's "Lectures" on Rhetoric and Belles Lettres (1783) as an effort to endorse either the liberal or the civic political traditions in eighteenth-century Scotland. This essay questions this orthodoxy by reading the "Lectures", and in particular Blair's attention to considerations of rhetorical…

  15. Markov chain Monte Carlo approach to parameter estimation in the FitzHugh-Nagumo model

    DEFF Research Database (Denmark)

    Jensen, Anders Christian; Ditlevsen, Susanne; Kessler, Mathieu

    2012-01-01

    Excitability is observed in a variety of natural systems, such as neuronal dynamics, cardiovascular tissues, or climate dynamics. The stochastic FitzHugh-Nagumo model is a prominent example representing an excitable system. To validate the practical use of a model, the first step is to estimate m...

  16. Principles and Practices Fostering Inclusive Excellence: Lessons from the Howard Hughes Medical Institute's Capstone Institutions

    Science.gov (United States)

    DiBartolo, Patricia Marten; Gregg-Jolly, Leslie; Gross, Deborah; Manduca, Cathryn A.; Iverson, Ellen; Cooke, David B., III; Davis, Gregory K.; Davidson, Cameron; Hertz, Paul E.; Hibbard, Lisa; Ireland, Shubha K.; Mader, Catherine; Pai, Aditi; Raps, Shirley; Siwicki, Kathleen; Swartz, Jim E.

    2016-01-01

    Best-practices pedagogy in science, technology, engineering, and mathematics (STEM) aims for inclusive excellence that fosters student persistence. This paper describes principles of inclusivity across 11 primarily undergraduate institutions designated as Capstone Awardees in Howard Hughes Medical Institute's (HHMI) 2012 competition. The Capstones…

  17. The Political Economy of Rhetorical Style: Hugh Blair's Response to the Civic-Commercial Dilemma

    Science.gov (United States)

    Longaker, Mark Garrett

    2008-01-01

    Recent scholarship treats Hugh Blair's "Lectures" on Rhetoric and Belles Lettres (1783) as an effort to endorse either the liberal or the civic political traditions in eighteenth-century Scotland. This essay questions this orthodoxy by reading the "Lectures", and in particular Blair's attention to considerations of rhetorical style, against their…

  18. "Comments on Greenhow, Robelia, and Hughes": Expanding the New Literacies Conversation

    Science.gov (United States)

    Leu, Donald J.; O'Byrne, W. Ian; Zawilinski, Lisa; McVerry, J. Greg; Everett-Cacopardo, Heidi

    2009-01-01

    Using a popularized notion such as Web 2.0 limits research efforts by employing a binary construct, one initially prompted by commercial concerns. Instead, the authors of this article, commenting on Greenhow, Robelia, and Hughes (2009), suggest that continuous, not dichotomous, change in the technologies of literacy and learning defines the…

  19. Hugh E. Huxley: cambiando el paradigma de la contracción muscular, desde dentro. [Hugh E. Huxley: changing from inside the paradigm of muscle contraction].

    OpenAIRE

    Adolfo Araci

    2014-01-01

    Desde un punto de vista físico se puede entender la fibra muscular como un motor, es decir, un sistema capaz de transformar la energía química en energía mecánica, que se utiliza para realizar un trabajo. Por lo tanto, para entender cómo ocurre dicho proceso de transformación es necesario conocer la ultraestructura de la fibra muscular. Esta es, sin duda, la principal aportación al acervo científico del recientemente fallecido Hugh Emor Huxley (1924-2013). Huxley se graduó en Física en el Chr...

  20. Hugh E. Huxley: cambiando el paradigma de la contracción muscular, desde dentro. [Hugh E. Huxley: changing from inside the paradigm of muscle contraction].

    OpenAIRE

    Adolfo Araci

    2014-01-01

    Desde un punto de vista físico se puede entender la fibra muscular como un motor, es decir, un sistema capaz de transformar la energía química en energía mecánica, que se utiliza para realizar un trabajo. Por lo tanto, para entender cómo ocurre dicho proceso de transformación es necesario conocer la ultraestructura de la fibra muscular. Esta es, sin duda, la principal aportación al acervo científico del recientemente fallecido Hugh Emor Huxley (1924-2013). Huxley se graduó en Física en el Chr...

  1. Fitz-Hugh-Curtis syndrome: abdominal pain in women of 26 years old Síndrome de Fitz-Hugh-Curtis: dolor abdominal en mujer de 26 años

    OpenAIRE

    Liseth Rivero-Sánchez; Elsa María López-Soriano; Luisa Guarner-Aguilar

    2011-01-01

    Fitz-Hugh-Curtis syndrome is an inflammation of the liver capsule as a complication of pelvic inflammatory disease, whose most common etiologic agent is the C. trachomatis. The acute phase of the Fitz-Hugh-Curtis syndrome may present itself with pain in right upper abdomen, commonly confused with other hepatobiliary and gastrointestinal tract diseases. Definitive diagnosis is now possible with non-invasive techniques such as ultrasound, computed tomography, as well as techniques to isolate th...

  2. Numerical bifurcation analysis of two coupled FitzHugh-Nagumo oscillators

    CERN Document Server

    Hoff, Anderson; Manchein, Cesar; Albuquerque, Holokx A

    2015-01-01

    The behavior of neurons can be modeled by the FitzHugh-Nagumo oscillator model, consisting of two nonlinear differential equations, which simulates the behavior of nerve impulse conduction through the neuronal membrane. In this work, we numerically study the dynamical behavior of two coupled FitzHugh-Nagumo oscillators. We consider unidirectional and bidirectional couplings, for which Lyapunov and isoperiodic diagrams were constructed calculating the Lyapunov exponents and the number of the local maxima of a variable in one period interval of the time-series, respectively. By numerical continuation method the bifurcation curves are also obtained for both couplings. The dynamics of the networks here investigated are presented in terms of the variation between the coupling strength of the oscillators and other parameters of the system. For the network of two oscillators unidirectionally coupled, the results show the existence of Arnold tongues, self-organized sequentially in a branch of a Stern-Brocot tree and ...

  3. The fusion of the imagination and the material universe: Hugh Hood, Flying a red kite (1962

    Directory of Open Access Journals (Sweden)

    Aleksander Kustec

    1999-12-01

    Full Text Available In the first weeks of January 1957 Hugh (John Blagdon Hood moved to Hartford, Connecticut, U. S. A, where he became Professor at Saint Joseph College. At the time Hood did not know that he was going to become one of Canada's greatest stylists and contemporary short story writers. Between January 1957 and March 1962, when he was going through a final selection o short stories for his first book, Flying a Red Kite (FRK, Hugh Hood wrote thirty-eight short stories and two novels (God Rest You Merry and Hungry Generations. The numbers show that Hood was an extremely productive writer in that period. From the thirty-eight stories he chose eleven for FRK, fourteen of them were published in subsequent collections, in various journals and short story anthologies, while thirteen of them have not been published yet.

  4. The 2016 Hughes Lecture: What's new in maternal morbidity and mortality?

    Science.gov (United States)

    Arendt, K W

    2016-05-01

    Each year, the Board of Directors of the Society for Obstetric Anesthesia and Perinatology selects an individual to review a given year's published obstetric anesthesiology literature. This individual then produces a syllabus of the year's most influential publications, delivers the Ostheimer Lecture at the Society's annual meeting, the Hughes Lecture at the following year's Sol Shnider meeting, and writes corresponding review articles. This 2016 Hughes Lecture review article focuses specifically on the 2014 publications that relate to maternal morbidity and mortality. It begins by discussing the 2014 research that was published on severe maternal morbidity and maternal mortality in developed countries. This is followed by a discussion of specific coexisting diseases and specific causes of severe maternal mortality. The review ends with a discussion of worldwide maternal mortality and the 2014 publications that examined the successes and the shortfalls in the work to make childbirth safe for women throughout the entire world.

  5. Two-frequency self-oscillations in a FitzHugh-Nagumo neural network

    Science.gov (United States)

    Glyzin, S. D.; Kolesov, A. Yu.; Rozov, N. Kh.

    2017-01-01

    A new mathematical model of a one-dimensional array of FitzHugh-Nagumo neurons with resistive-inductive coupling between neighboring elements is proposed. The model relies on a chain of diffusively coupled three-dimensional systems of ordinary differential equations. It is shown that any finite number of coexisting stable invariant two-dimensional tori can be obtained in this chain by suitably increasing the number of its elements.

  6. Selected results from LLNL-Hughes RAR for West Coast Scotland Experiment 1991

    Energy Technology Data Exchange (ETDEWEB)

    Lehman, S K; Johnston, B; Twogood, R; Wieting, M; Yorkey, T; Robey, H [Lawrence Livermore National Lab., CA (United States); Whelan, D; Nagele, R [Hughes Aircraft Co., Los Angeles, CA (United States)

    1993-01-05

    The joint US -- UK 1991 West Coast Scotland Experiment (WCSEX) was held in two locations. From July 5 to 12, 1991, in Upper Loch Linnhe, and from July 18 to July 26, 1991, in the Sound of Sleat. The LLNL-Hughes team fielded a fully polarimetric X-band hill-side real aperture radar to collect internal wave wake data. We present here a sample data set of the best radar runs.

  7. Symmetric bursting behaviors in the generalized FitzHugh-Nagumo model.

    Science.gov (United States)

    Abbasian, A H; Fallah, H; Razvan, M R

    2013-08-01

    In the current paper, we have investigated the generalized FitzHugh-Nagumo model. We have shown that symmetric bursting behaviors of different types could be observed in this model with an appropriate recovery term. A modified version of this system is used to construct bursting activities. Furthermore, we have shown some numerical examples of delayed Hopf bifurcation and canard phenomenon in the symmetric bursting of super-Hopf/homoclinic type near its super-Hopf and homoclinic bifurcations, respectively.

  8. Young CAS biologist gets five-year grant from Howard Hughes Medical Institute

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    Dr. TANG Chun, an outstanding young biologist from the CAS Wuhan Institute of Physics and Mathematics (WIPM) was announced in January 2012 to have won the first International Early Career Award from Howard Hughes Medical Institute with a five-year grant totaling up to 650,000 US dollars. Dr. Tang is an expert in using novel nuclear magnetic resonance methods to study the behavior and function of proteins,

  9. 耦合的Fitz-Hugh-Nagumo模型的初边值问题

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    首先研究了具有耦合的 Fitz-Hugh-Nagumo 模型初值问题的渐近性. 其次,所对应的平衡态方程解的基本性态也将被讨论. 最后, 该模型的初边值问题古典解的最大吸引子的存在性将首次被证明.

  10. The Hughes Court and Radical Dissent: The Case of Dirk De Jonge and Angelo Herndon

    OpenAIRE

    Tushnet, Mark V.

    2012-01-01

    Scattered Supreme Court decisions in the early twentieth century dealt with the Constitution’s protection of freedom of speech. Radical dissent over United States participation in World War I and the nation’s intervention against the Bolshevik revolution in Russia led the Court to its first sustained engagement with free speech cases. By the time Chief Justice Hughes took the center chair, the national government largely had abandoned its pursuit of radical dissenters, some of whom played la...

  11. Percutaneous transhepatic venous embolization of pulmonary artery aneurysm in Hughes-Stovin syndrome

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Kyung Ah; Kim, Man Deuk; Oh, Do Yun; Park, Pil Won [Bundang CHA General Hospital, Pochon CHA University, Seongnam (Korea, Republic of)

    2007-08-15

    Hughes-Stovin syndrome is an extremely rare entity. We present a case of a 42-year-old man, who developed deep vein and inferior vena cava (IVC) thrombosis, repeated internal bleeding and pulmonary artery aneurysms (PAAs). The patient presented with massive hemoptysis and with PAAs of a 2.5 cm maximum diameter. We describe the successful percutaneous transhepatic venous embolization of the PAAs due to occluded common vascular pathways to the pulmonary artery.

  12. A política de Hugh Dalton e o Bloqueio Económico (1940-1942)

    OpenAIRE

    Mariana Castro

    2015-01-01

    The World War II was a scenery of conflict and protagonists. Hugh Dalton was Minister of Economics of War between 1940 and 1942 in England. Highlighted by the measure in economic blockade the belligerents and neutral countries, proposing the control of smuggling through the prohibition of exports and imports with the German enemy, in other words ‘dry internally and externally “to weaken. This essay focuses on Hugh Dalton policy, leaving few clues and suggestions for further study ...

  13. 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......-the-art cosmological simulation, Illustris, follow a tight relation between star formation rate and stellar mass. This relation agrees well with the observed relation at a redshift of z = 0 and z = 4, but at intermediate redshifts of z ' 2 the normalisation is lower than in real observations. This is highlighted...

  14. Spectrophotometric Study of Galaxies with UV Excess

    Science.gov (United States)

    Kazarian, M. A.; Karapetian, E. L.

    2004-01-01

    Results from a spectrophotometric study of 21 galaxies with UV excess are presented. The half widths (FWHM) and equivalent widths of observed spectrum lines of these galaxies, as well as the relative intensities of the emission lines observed in the spectrum of the galaxy Kaz243, are determined. It is conjectured that the latter galaxy has the properties of an Sy2 type galaxy. The electron densities and masses of the gaseous components are found for 15 galaxies, along with the masses of 8 galaxies for which the ratio M/L has been calculated. It is shown that the spectral structures of these galaxies do not depend on whether they are members of physical systems or are isolated.

  15. Galaxy Disks

    NARCIS (Netherlands)

    van der Kruit, P. C.; Freeman, K. C.

    The disks of disk galaxies contain a substantial fraction of their baryonic matter and angular momentum, and much of the evolutionary activity in these galaxies, such as the formation of stars, spiral arms, bars and rings, and the various forms of secular evolution, takes place in their disks. The

  16. Galaxy formation

    CERN Document Server

    Silk, Joseph; Dvorkin, Irina

    2015-01-01

    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.

  17. Galaxy Formation

    DEFF Research Database (Denmark)

    Sparre, Martin

    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......-the-art cosmological simulation, Illustris, follow a tight relation between star formation rate and stellar mass. This relation agrees well with the observed relation at a redshift of z = 0 and z = 4, but at intermediate redshifts of z ' 2 the normalisation is lower than in real observations. This is highlighted...... of GRB host galaxies is affected by the fact that GRBs appear mainly to happen in low-metallicity galaxies. Solving this problem will make it possible to derive the total cosmic star formation rate more reliably from number counts of GRBs....

  18. A "Queen of Hearts" trial of organ markets: why Scheper-Hughes's objections to markets in human organs fail.

    Science.gov (United States)

    Taylor, J S

    2007-04-01

    Nancy Scheper-Hughes is one of the most prominent critics of markets in human organs. Unfortunately, Scheper-Hughes rejects the view that markets should be used to solve the current (and chronic) shortage of transplant organs without engaging with the arguments in favour of them. Scheper-Hughes's rejection of such markets is of especial concern, given her influence over their future, for she holds, among other positions, the status of an adviser to the World Health Organization (Geneva) on issues related to global transplantation. Given her influence, it is important that Scheper-Hughes's moral condemnation of markets in human organs be subject to critical assessment. Such critical assessment, however, has not generally been forthcoming. A careful examination of Scheper-Hughes's anti-market stance shows that it is based on serious mischaracterisations of both the pro-market position and the medical and economic realities that underlie it. In this paper, the author will expose and correct these mischaracterisations and, in so doing, show that her objections to markets in human organs are unfounded.

  19. HARP model rotor test at the DNW. [Hughes Advanced Rotor Program

    Science.gov (United States)

    Dawson, Seth; Jordan, David; Smith, Charles; Ekins, James; Silverthorn, Lou

    1989-01-01

    Data from a test of a dynamically scaled model of the Hughes Advanced Rotor Program (HARP) bearingless model main rotor and 369K tail rotor are reported. The history of the HARP program and its goals are reviewed, and the main and tail rotor models are described. The test facilities and instrumentation are described, and wind tunnel test data are presented on hover, forward flight performance, and blade-vortex interaction. Performance data, acoustic data, and dynamic data from near field/far field and shear layer studies are presented.

  20. The spike timing precision of FitzHugh-Nagumo neuron network coupled by gap junctions

    Institute of Scientific and Technical Information of China (English)

    Zhang Su-Hua; Zhan Yong; Yu Hui; An Hai-Long; Zhao Tong-Jun

    2006-01-01

    It has been proved recently that the spike timing can play an important role in information transmission, so in this paper we develop a network with N-unit FitzHugh-Nagumo neurons coupled by gap junctions and discuss the dependence of the spike timing precision on synaptic coupling strength, the noise intensity and the size of the neuron ensemble. The calculated results show that the spike timing precision decreases as the noise intensity increases; and the ensemble spike timing precision increases with coupling strength increasing. The electric synapse coupling has a more important effect on the spike timing precision than the chemical synapse coupling.

  1. Markov chain Monte Carlo approach to parameter estimation in the FitzHugh-Nagumo model.

    Science.gov (United States)

    Jensen, Anders Chr; Ditlevsen, Susanne; Kessler, Mathieu; Papaspiliopoulos, Omiros

    2012-10-01

    Excitability is observed in a variety of natural systems, such as neuronal dynamics, cardiovascular tissues, or climate dynamics. The stochastic FitzHugh-Nagumo model is a prominent example representing an excitable system. To validate the practical use of a model, the first step is to estimate model parameters from experimental data. This is not an easy task because of the inherent nonlinearity necessary to produce the excitable dynamics, and because the two coordinates of the model are moving on different time scales. Here we propose a Bayesian framework for parameter estimation, which can handle multidimensional nonlinear diffusions with large time scale separation. The estimation method is illustrated on simulated data.

  2. Synchronization in heterogeneous FitzHugh-Nagumo networks with hierarchical architecture

    Science.gov (United States)

    Plotnikov, S. A.; Lehnert, J.; Fradkov, A. L.; Schöll, E.

    2016-07-01

    We study synchronization in heterogeneous FitzHugh-Nagumo networks. It is well known that heterogeneities in the nodes hinder synchronization when becoming too large. Here we develop a controller to counteract the impact of these heterogeneities. We first analyze the stability of the equilibrium point in a ring network of heterogeneous nodes. We then derive a sufficient condition for synchronization in the absence of control. Based on these results we derive the controller providing synchronization for parameter values where synchronization without control is absent. We demonstrate our results in networks with different topologies. Particular attention is given to hierarchical (fractal) topologies, which are relevant for the architecture of the brain.

  3. Hub-enhanced noise-sustained synchronization of an externally forced FitzHugh-Nagumo ring

    Science.gov (United States)

    Sánchez, Alejandro D.; Izús, Gonzalo G.; dell'Erba, Matías G.; Deza, Roberto R.

    2017-02-01

    A ring of FitzHugh-Nagumo units with antiphase coupling between their activator fields and submitted to a adiabatic harmonic subthreshold signal, is in turn globally coupled in electrical mode with the activator field of a hub. Noise sustained synchronization of neural activity with the signal is numerically observed, and theoretically characterized. The different dynamical regimes are elucidated using the concept of nonequilibrium potential, and the hub is found to promote network synchronization. The minimum noise intensities triggering the activation and synchronization processes are estimated in the framework of a three-neuron model.

  4. Synchronization and associative memory of FitzHugh-Nagumo neuronal networks with randomly distributed time delays

    Energy Technology Data Exchange (ETDEWEB)

    Peng, J H; Wu, Y J [School of Information Science and Engineering, East China University of Science and Technology, Shanghai 200237 (China); Yu, H J [Department of Mechanics, Shanghai Jiao Tong University, Shanghai 200240 (China)], E-mail: jhpeng@ecust.edu.cn

    2008-02-15

    Synchronization and associative memory in a neural network composed of the widely discussed FitzHugh-Nagumo neurons is investigated in this paper. Based on the reality of the microscopic biological structure in the neural system, the couplings among those neurons are accompanied with randomly distributed time delays which models the times needed for pulses propagating on the axons from the presynaptic neurons to the postsynaptic neurons. The memory is represented in the spatiotemporal firing pattern of the neurons, and the memory retrieval is accomplished with the fluctuations of the noise in the system.

  5. Evidence that the maximum electron energy in hotspots of FR II galaxies is not determined by synchrotron cooling

    CERN Document Server

    Araudo, Anabella T; Crilly, Aidan; Blundell, Katherine M

    2016-01-01

    It has been suggested that relativistic shocks in extragalactic sources may accelerate the highest energy cosmic rays. The maximum energy to which cosmic rays can be accelerated depends on the structure of magnetic turbulence near the shock but recent theoretical advances indicate that relativistic shocks are probably unable to accelerate particles to energies much larger than a PeV. We study the hotspots of powerful radiogalaxies, where electrons accelerated at the termination shock emit synchrotron radiation. The turnover of the synchrotron spectrum is typically observed between infrared and optical frequencies, indicating that the maximum energy of non-thermal electrons accelerated at the shock is < TeV for a canonical magnetic field of ~100 micro Gauss. Based on theoretical considerations we show that this maximum energy cannot be constrained by synchrotron losses as usually assumed, unless the jet density is unreasonably large and most of the jet upstream energy goes to non-thermal particles. We test ...

  6. QUALITATIVE INTERPRETATION OF GALAXY SPECTRA

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez Almeida, J.; Morales-Luis, A. B. [Instituto de Astrofisica de Canarias, E-38205 La Laguna, Tenerife (Spain); Terlevich, R.; Terlevich, E. [Instituto Nacional de Astrofisica, Optica y Electronica, Tonantzintla, Puebla (Mexico); Cid Fernandes, R., E-mail: jos@iac.es, E-mail: abml@iac.es, E-mail: rjt@ast.cam.ac.uk, E-mail: eterlevi@inaoep.mx, E-mail: cid@astro.ufsc.br [Departamento de Fisica-CFM, Universidade Federal de Santa Catarina, P.O. Box 476, 88040-900 Florianopolis, SC (Brazil)

    2012-09-10

    We describe a simple step-by-step guide to qualitative interpretation of galaxy spectra. Rather than an alternative to existing automated tools, it is put forward as an instrument for quick-look analysis and for gaining physical insight when interpreting the outputs provided by automated tools. Though the recipe is for general application, it was developed for understanding the nature of the Automatic Spectroscopic K-means-based (ASK) template spectra. They resulted from the classification of all the galaxy spectra in the Sloan Digital Sky Survey data release 7, thus being a comprehensive representation of the galaxy spectra in the local universe. Using the recipe, we give a description of the properties of the gas and the stars that characterize the ASK classes, from those corresponding to passively evolving galaxies, to H II galaxies undergoing a galaxy-wide starburst. The qualitative analysis is found to be in excellent agreement with quantitative analyses of the same spectra. We compare the mean ages of the stellar populations with those inferred using the code STARLIGHT. We also examine the estimated gas-phase metallicity with the metallicities obtained using electron-temperature-based methods. A number of byproducts follow from the analysis. There is a tight correlation between the age of the stellar population and the metallicity of the gas, which is stronger than the correlations between galaxy mass and stellar age, and galaxy mass and gas metallicity. The galaxy spectra are known to follow a one-dimensional sequence, and we identify the luminosity-weighted mean stellar age as the affine parameter that describes the sequence. All ASK classes happen to have a significant fraction of old stars, although spectrum-wise they are outshined by the youngest populations. Old stars are metal-rich or metal-poor depending on whether they reside in passive galaxies or in star-forming galaxies.

  7. 空间离散Fitz-Hugh-Nagumo方程和双稳反应扩散方程组的渐近行为%Asymptotic Behavioui of Spatial Discretized Fitz-Hugh-Nagumo Equations and Bistable Reaction Diffusion Equations

    Institute of Scientific and Technical Information of China (English)

    黄建华; 路钢

    2000-01-01

    In this paper, we discuss the asymptotic behaviour of spatial disretization of Fitz-Hugh-Nagumo equations and bistable reaction diffusion equations with Neumamn boundary conditions, and the invariant regions, absorbing sets and global attractors are obtained and the estimation of Hausdorff dimension is given.%本文利用扰动方法,研究了Fitz-Hugh-Nagumo方程和双稳反应扩散方程在Neuman边值条件下空间离散后的渐近行为,证明了两个格微分方程组的不变区域、吸引集和整体吸引子的存在性,并给出了离散Fitz-Hugh-Nagumo方程的整体吸引子的Hausdorff维数估计.

  8. Les galaxies

    Science.gov (United States)

    Combes, Francoise

    2016-08-01

    Considerable progress has been made on galaxy formation and evolution in recent years, and new issues. The old Hubble classification according to the tuning fork of spirals, lenticulars and ellipticals, is still useful but has given place to the red sequence, the blue cloud and the green valley, showing a real bimodality of types between star forming galaxies (blue) and quenched ones (red). Large surveys have shown that stellar mass and environment density are the two main factors of the evolution from blue to red sequences. Evolution is followed directly with redshift through a look-back time of more than 12 billion years. The most distant galaxy at z=11. has already a stellar mass of a billion suns. In an apparent anti-hierarchical scenario, the most massive galaxies form stars early on, while essentially dwarf galaxies are actively star-formers now. This downsizing feature also applies to the growth of super-massive black holes at the heart of each bulgy galaxy. The feedback from active nuclei is essential to explain the distribution of mass in galaxies, and in particular to explain why the fraction of baryonic matter is so low, lower by more than a factor 5 than the baryonic fraction of the Universe. New instruments just entering in operation, like MUSE and ALMA, provide a new and rich data flow, which is developed in this series of articles.

  9. Montage of a Queering Deferred: Memory, Ownership, and Archival Silencing in the Rhetorical Biography of Langston Hughes.

    Science.gov (United States)

    Summers, Ian

    2016-01-01

    This article explores the intersection of archival privilege and heteronormative bias in the queering of Langston Hughes. Although it has been a common belief in LGBTQ communities that Hughes was gay, the battle over how his sexuality is defined in various biographical texts involves broader issues of dominant representations of sexuality and who gets to speak for those no longer able to speak for themselves. As such, the article examines the texts Looking for Langston and The Life of Langston Hughes as well as the discourses that surrounded both. Through this case study, it is apparent that there are still numerous cultural challenges posed to historical queering and that scholars must take an inventive approach to overcome them.

  10. Berta and Adelaide: the policy of consolidation of the royal power of Hugh of Arles

    Directory of Open Access Journals (Sweden)

    Giacomo Vignodelli

    2012-10-01

    Full Text Available Both twins dowers made up by Hugh of Provence, king of Italic Kingdom, for his betrothal with Berta and that of his son Lothair with Adelaide, have to be understood within the policy of strengthening the royal power led by the king in the Thirties of the Tenth century: the dowers are in fact the crown of that policy. The double dower constitution supplies the king of Italy the opportunity to reserve for himself (and for the new formed young royal couple a strong control of the center of the Po valley around Pavia and dismantles (for the benefit of the royal domain ducal bases of power in Tuscia. The analysis of the work of Hugh allows us to understand its policy towards the aristocracy and the mechanisms for the promotion of new families (Aleramici, Obertenghi, Canossa. The original documents of dower were kept in the monastery of St. Salvatore of Pavia, founded by Adelaide; this locations isn’t due to the goods endowment of the monastery but to their importance as instrument of political legitimacy of the new Ottonian royal family.

  11. Frequency Effect of Harmonic Noise on the FitzHugh-Nagumo Neuron Model

    Institute of Scientific and Technical Information of China (English)

    宋艳丽

    2011-01-01

    Using harmonic noise,the frequency effect of noise on the FitzHugh-Nagumo neuron model is investigated.The results show that the neuron has a resonance characteristic and responds strongly to the noise with a certain frequency at fixed power.Driven by the noise with this frequency,the train is most regular and the coefficient of variation R has a minimum.The imperfect synchronization takes place,which,however,is optimal only for noise with an appropriate frequency.It is shown that there exists coherence resonance related to frequency.%Using harmonic noise, the frequency effect of noise on the FitzHugh-Nagumo neuron model is investigated. The results show that the neuron has a resonance characteristic and responds strongly to the noise with a certain frequency at fixed power. Driven by the noise with this frequency, the train is most regular and the coefficient of variation R has a minimum. The imperfect synchronization takes place, which, however, is optimal only for noise with an appropriate frequency. It is shown that there exists coherence resonance related to frequency.

  12. 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.

  13. SÍNDROME DE FITZ-HUGH-CURTIS COMO HALLAZGO DURANTE CIRUGÍA GINECOLÓGICA

    OpenAIRE

    Ricci A,Paolo; Solà D,Vicente; Pardo S,Jack

    2009-01-01

    El síndrome de Fitz-Hugh-Curtis es una perihepatitis producida por una peritonitis secundaria al ascenso de bacterias, como resultado de una enfermedad inflamatoria pélvica. En la etapa crónica se pueden observar adherencias entre la pared abdominal y la superficie hepática, caracterizadas por la semejanza a "cuerdas de violín". Esta imagen es considerada criterio diagnóstico. Se presenta un caso de hallazgo de síndrome de Fitz-Hugh-Curtis, pesquisado durante la inspección rutinaria de la cav...

  14. SÍNDROME DE FITZ-HUGH-CURTIS COMO HALLAZGO DURANTE CIRUGÍA GINECOLÓGICA

    OpenAIRE

    Ricci A,Paolo; Solà D,Vicente; Pardo S,Jack

    2009-01-01

    El síndrome de Fitz-Hugh-Curtis es una perihepatitis producida por una peritonitis secundaria al ascenso de bacterias, como resultado de una enfermedad inflamatoria pélvica. En la etapa crónica se pueden observar adherencias entre la pared abdominal y la superficie hepática, caracterizadas por la semejanza a "cuerdas de violín". Esta imagen es considerada criterio diagnóstico. Se presenta un caso de hallazgo de síndrome de Fitz-Hugh-Curtis, pesquisado durante la inspección rutinaria de la cav...

  15. Fitz-Hugh-Curtis syndrome: abdominal pain in women of 26 years old Síndrome de Fitz-Hugh-Curtis: dolor abdominal en mujer de 26 años

    Directory of Open Access Journals (Sweden)

    Liseth Rivero-Sánchez

    2011-10-01

    Full Text Available Fitz-Hugh-Curtis syndrome is an inflammation of the liver capsule as a complication of pelvic inflammatory disease, whose most common etiologic agent is the C. trachomatis. The acute phase of the Fitz-Hugh-Curtis syndrome may present itself with pain in right upper abdomen, commonly confused with other hepatobiliary and gastrointestinal tract diseases. Definitive diagnosis is now possible with non-invasive techniques such as ultrasound, computed tomography, as well as techniques to isolate the responsible germ, available in most centers.El síndrome de Fitz-Hugh-Curtis es una inflamación de la cápsula hepática, como complicación de una enfermedad inflamatoria pélvica, cuyo agente etiológico más frecuente es la C. trachomatis. La fase aguda del síndrome de Fitz-Hugh-Curtis puede presentarse con dolor en cuadrante superior derecho del abdomen, confundiéndose comúnmente con otras enfermedades hepatobiliares y del tracto gastrointestinal. El diagnóstico definitivo es posible hoy en día por técnicas no invasivas como ecografía, tomografía computarizada, además de técnicas para el aislamiento del germen responsable disponibles en la mayoría de los centros.

  16. University receives $1.4 million science education award from Howard Hughes Medical Institute to support innovate undergraduate science education

    OpenAIRE

    Owczarski, Mark

    2010-01-01

    Virginia Tech was among 50 top research universities nationwide to receive a Precollege and Undergraduate Science Education Program award from the Howard Hughes Medical Institute (HHMI) that will be used to encourage university faculty to develop new ways to teach and inspire undergraduate students about science and research.

  17. Pretext, Context, Subtext: Textual Power in the Writing of Langston Hughes, Richard Wright, and Martin Luther King, Jr.

    Science.gov (United States)

    Bogumil, Mary L.; Molino, Michael R.

    1990-01-01

    Studies verbal pretexts, social subtexts, and interpretive contexts of works by Langston Hughes, Richard Wright, and Martin Luther King, Jr. Notes that cultural repression is propagated (and dispelled) in part through the power of language. Notes that these texts are relevant for teaching textual power in hopes of affecting social change. (RS)

  18. First LOFAR results on galaxy clusters

    NARCIS (Netherlands)

    Ferrari, C.; van Bemmel, I.; Bonafede, A.; Bîrzan, L.; Brüggen, M.; Brunetti, G.; Cassano, R.; Conway, J.; De Gasperin, F.; Heald, G.; Jackson, N.; Macario, G.; McKean, J.; Offringa, A. R.; Orrù, E.; Pizzo, R.; Rafferty, D. A.; Röttgering, H. J. A.; Shulevski, A.; Tasse, C.; van der Tol, S.; van Weeren, R. J.; Wise, M.; van Zwieten, J.E.; Boissier, S.; de Laverny, P.; Nardetto, N.; Samadi, R.; Valls-Gabaud, D.; Wozniak, H.; Boissier, S.; de Laverny, P.; Nardetto, N.; Samadi, R.; Valls-Gabaud, D.; Wozniak, H.

    2012-01-01

    Deep radio observations of galaxy clusters have revealed the existence of diffuse radio sources related to the presence of relativistic electrons and weak magnetic fields in the intracluster volume. The role played by this non-thermal intracluster component on the thermodynamical evolution of galaxy

  19. Theoretical analysis and control results for the FitzHugh-Nagumo equation

    Directory of Open Access Journals (Sweden)

    Marko Antonio Rojas-Medar

    2008-12-01

    Full Text Available In this paper we are concerned with some theoretical questions for the FitzHugh-Nagumo equation. First, we recall the system, we briefly explain the meaning of the variables and we present a simple proof of the existence and uniqueness of strong solution. We also consider an optimal control problem for this system. In this context, the goal is to determine how can we act on the system in order to get good properties. We prove the existence of optimal state-control pairs and, as an application of the Dubovitski-Milyoutin formalism, we deduce the corresponding optimality system. We also connect the optimal control problem with a controllability question and we construct a sequence of controls that produce solutions that converge strongly to desired states. This provides a strategy to make the system behave as desired. Finally, we present some open questions related to the control of this equation.

  20. The synchronization of FitzHugh-Nagumo neuron network coupled by gap junction

    Institute of Scientific and Technical Information of China (English)

    Zhan Yong; Zhang Su-Hua; Zhao Tong-Jun; An Hai-Long; Zhang Zhen-Dong; Han Ying-Rong; Liu Hui; Zhang Yu-Hong

    2008-01-01

    It is well known that the strong coupling can synchronize a network of nonlinear oscillators. Synchronization provides the basis of the remarkable computational performance of the brain. In this paper the FitzHugh-Nagumo neuron network is constructed. The dependence of the synchronization on the coupling strength, the noise intensity and the size of the neuron network has been discussed. The results indicate that the coupling among neurons works to improve the synchronization, and noise increases the neuron random dynamics and the local fluctuations; the larger the size of network, the worse the synchronization. The dependence of the synchronization on the strength of the electric synapse coupling and chemical synapse coupling has also been discussed, which proves that electric synapse coupling can enhance the synchronization of the neuron network largely.

  1. A correspondence between the models of Hodgkin-Huxley and FitzHugh-Nagumo revisited

    Science.gov (United States)

    Postnikov, Eugene B.; Titkova, Olga V.

    2016-11-01

    We present the discussion on the possibility to scale the classical dimensionless FitzHugh-Nagumo model of neuronal self-sustained oscillations to the range of variables corresponding to the results, which are provided by the biophysically relevant reduced two-dimensional Hodgkin-Huxley equations (the Rinzel model). It is shown that there exists a relatively simple choice of affine transformation, which results in time-dependent solutions, which reproduce with a high accuracy the time course of the recovery variable and the sharp onsets (intervals of fast motions on a phase trajectories) of the voltage spikes. As for the latter, the reasons for unavoidable difference are discussed as well as a necessity of taking into account applied current values during such a scaling procedure.

  2. Stochastic bifurcation in FitzHugh Nagumo ensembles subjected to additive and/or multiplicative noises

    Science.gov (United States)

    Hasegawa, Hideo

    2008-02-01

    We have studied the dynamical properties of finite N-unit FitzHugh-Nagumo (FN) ensembles subjected to additive and/or multiplicative noises, reformulating the augmented moment method (AMM) with the Fokker-Planck equation (FPE) method [H. Hasegawa, J. Phys. Soc. Japan 75 (2006) 033001]. In the AMM, original 2N-dimensional stochastic equations are transformed to eight-dimensional deterministic ones, and the dynamics is described in terms of averages and fluctuations of local and global variables. The stochastic bifurcation is discussed by a linear stability analysis of the deterministic AMM equations. The bifurcation transition diagram of multiplicative noise is rather different from that of additive noise: the former has the wider oscillating region than the latter. The synchronization in globally-coupled FN ensembles is also investigated. Results of the AMM are in good agreement with those of direct simulations (DSs).

  3. Phase Propagations in a Coupled Oscillator-Excitor System of FitzHugh-Nagumo Models

    Institute of Scientific and Technical Information of China (English)

    ZHOU Lu-Qun; OUYANG Qi

    2006-01-01

    @@ A one-dimensional array of 2N + 1 automata with FitzHugh-Nagumo dynamics, in which one is set to be oscillatory and the others are excitable, is investigated with bi-directional interactions. We find that 1 : 1 rhythm propagation in the array depends on the appropriate couple strength and the excitability of the system. On the two sides of the 1: 1 rhythm area in parameter space, two different kinds of dynamical behaviour of the pacemaker, i.e. phase-locking phenomena and canard-like phenomena, are shown. The latter is found in company with chaotic pattern and period doubling bifurcation. When the coupling strength is larger than a critical value,the whole system ends to a steady state.

  4. Fitz-Hugh-Curtis syndrome lacking typical characteristics of pelvic inflammatory disease.

    Science.gov (United States)

    Mitaka, Hayato; Kitazono, Hidetaka; Deshpande, Gautam A; Hiraoka, Eiji

    2016-06-22

    A 23-year-old Japanese woman, previously a commercial sex worker, presented with a 2-day history of right upper quadrant (RUQ) abdominal pain, worse on deep inspiration. She had noticed increased vaginal discharge 2 months earlier and had developed dull, lower abdominal pain 3 weeks prior to presentation. Although pelvic examination and transvaginal ultrasonography revealed neither a tubal nor ovarian pathology, abdominal CT scan with contrast demonstrated early enhancement of the hepatic capsule, a finding pathognomonic for Fitz-Hugh-Curtis syndrome (FHCS). Cervical discharge PCR assay confirmed Chlamydia trachomatis infection. This case highlights that normal gynaecological evaluation may be insufficient to rule out FHCS, for which physicians should have a high index of suspicion when seeing any woman of reproductive age with RUQ pain. 2016 BMJ Publishing Group Ltd.

  5. Identification of the FitzHugh-Nagumo Model Dynamics via Deterministic Learning

    Science.gov (United States)

    Dong, Xunde; Wang, Cong

    In this paper, a new method is proposed for the identification of the FitzHugh-Nagumo (FHN) model dynamics via deterministic learning. The FHN model is a classic and simple model for studying spiral waves in excitable media, such as the cardiac tissue, biological neural networks. Firstly, the FHN model described by partial differential equations (PDEs) is transformed into a set of ordinary differential equations (ODEs) by using finite difference method. Secondly, the dynamics of the ODEs is identified using the deterministic learning theory. It is shown that, for the spiral waves generated by the FHN model, the dynamics underlying the recurrent trajectory corresponding to any spatial point can be accurately identified by using the proposed approach. Numerical experiments are included to demonstrate the effectiveness of the proposed method.

  6. The African-American grandmother in autobiographical works by Frederick Douglass, Langston Hughes, and Maya Angelou.

    Science.gov (United States)

    Hill-Lubin, M A

    1991-01-01

    Using the autobiographies of Frederick Douglass, Langston Hughes, and Maya Angelou, this article demonstrates that the portrait of the African-American grandmother is one of action, involvement, hope, and dignity. In examining the works, we observe her functioning in three areas: as the preserver and most tenacious survivor of the African extended family; second, as repository and distributor of the family history, wisdom, and black lore; this role places her at the foundation of the Black, oral and written, literary and creative traditions; and third, as the retainer and transmitter of values and ideals that support and enhance her humanity, her family, and her community. This function emphasizes her spirituality. It is suggested that the grandmother, having played an important role in the growth, development, and artistic flowering of the autobiographer, can become a model and source of empowerment for future generations.

  7. Hugh E. Huxley: cambiando el paradigma de la contracción muscular, desde dentro. [Hugh E. Huxley: changing from inside the paradigm of muscle contraction].

    Directory of Open Access Journals (Sweden)

    Adolfo Araci

    2014-04-01

    Full Text Available Desde un punto de vista físico se puede entender la fibra muscular como un motor, es decir, un sistema capaz de transformar la energía química en energía mecánica, que se utiliza para realizar un trabajo. Por lo tanto, para entender cómo ocurre dicho proceso de transformación es necesario conocer la ultraestructura de la fibra muscular. Esta es, sin duda, la principal aportación al acervo científico del recientemente fallecido Hugh Emor Huxley (1924-2013. Huxley se graduó en Física en el Christ’s College de Cambdrige, tras ver interrumpidos temporalmente sus estudios por su dedicación como operario de radar de la Royal Air Force entre 1943 y 1947, durante la Segunda Guerra Mundial (Pollard y Goldman, 2013; Spudich, 2013. Tras su graduación se incorporó como el primer estudiante de doctorado a una unidad de nueva creación del Medical Research Council, el “Laboratorio de Biología Molecular”, dirigida por Max Perutz y John Kendrew, siendo este último el director de sus tesis doctoral, que fue defendida en 1952 (Spudich, 2013. El uso de la técnicas de difracción de rayos X, que permitían el estudio en niveles de resolución inalcanzables con las técnicas microscópicas del momento, y su aplicación a la descripción de la ultraestructura muscular, fueron el objeto de su tesis doctoral, para el desarrollo de la cual diseñó y construyó sus propios instrumentos. El esclarecimiento de los aspectos estructurales implicados en la contracción muscular se convirtió desde entonces en la pregunta central de su biografía científica.

  8. The SAMI Galaxy Survey: first 1000 galaxies

    CERN Document Server

    Allen, J T

    2014-01-01

    The Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey is an ongoing project to obtain integral field spectroscopic observations of ~3400 galaxies by mid-2016. Including the pilot survey, a total of ~1000 galaxies have been observed to date, making the SAMI Galaxy Survey the largest of its kind in existence. This unique dataset allows a wide range of investigations into different aspects of galaxy evolution. The first public data from the SAMI Galaxy Survey, consisting of 107 galaxies drawn from the full sample, has now been released. By giving early access to SAMI data for the entire research community, we aim to stimulate research across a broad range of topics in galaxy evolution. As the sample continues to grow, the survey will open up a new and unique parameter space for galaxy evolution studies.

  9. The Long-Time Behavior of Legendre Spectral Approximation to Fitz-Hugh-Nagumo Equation%Fitz-Hugh-Nagumo方程Legendre谱逼近的长时间性态

    Institute of Scientific and Technical Information of China (English)

    张伟斌

    2005-01-01

    利用Legendre谱方法对Fitz-Hugh-Nagumo方程在空间方向半离散,得到了其近似解的误差估计,并且证明了近似整体吸引子的存在性和上半连续性,从而为研究该方程的长时间行为提供了一个有效的算法.

  10. Galaxy Evolution

    Science.gov (United States)

    Matteucci, F.

    We review both the observational and theoretical constraints on the evolution of the abundances of heavy elements in gas and stars in galaxies of different morphological type. The main aim of this work is to document the progress made in our understanding of the physical processes regulating the chemical evolution of galaxies during the last sixteen years since the appearance, in this same journal (volume 5, page 287), of the well know review of Beatrice Tinsley, to whom I dedicate this paper. Finally, this article is addressed particularly to readers who do not actively work on galactic chemical evolution and who might use it as a cook book where the main ingredients are discussed and useful recipes can be found.

  11. Galaxy formation.

    Science.gov (United States)

    Peebles, P J

    1998-01-01

    It is argued that within the standard Big Bang cosmological model the bulk of the mass of the luminous parts of the large galaxies likely had been assembled by redshift z approximately 10. Galaxy assembly this early would be difficult to fit in the widely discussed adiabatic cold dark matter model for structure formation, but it could agree with an isocurvature version in which the cold dark matter is the remnant of a massive scalar field frozen (or squeezed) from quantum fluctuations during inflation. The squeezed field fluctuations would be Gaussian with zero mean, and the distribution of the field mass therefore would be the square of a random Gaussian process. This offers a possibly interesting new direction for the numerical exploration of models for cosmic structure formation.

  12. Galaxy Disks

    CERN Document Server

    van der Kruit, P C

    2011-01-01

    The formation and evolution of galactic disks is particularly important for understanding how galaxies form and evolve, and the cause of the variety in which they appear to us. Ongoing large surveys, made possible by new instrumentation at wavelengths from the ultraviolet (GALEX), via optical (HST and large groundbased telescopes) and infrared (Spitzer) to the radio are providing much new information about disk galaxies over a wide range of redshift. Although progress has been made, the dynamics and structure of stellar disks, including their truncations, are still not well understood. We do now have plausible estimates of disk mass-to-light ratios, and estimates of Toomre's $Q$ parameter show that they are just locally stable. Disks are mostly very flat and sometimes very thin, and have a range in surface brightness from canonical disks with a central surface brightness of about 21.5 $B$-mag arcsec$^{-2}$ down to very low surface brightnesses. It appears that galaxy disks are not maximal, except possibly in ...

  13. "Galaxy," Defined

    CERN Document Server

    Willman, Beth

    2012-01-01

    A growing number of low luminosity and low surface brightness astronomical objects challenge traditional notions of both galaxies and star clusters. To address this challenge, we propose a definition of galaxy that does not depend on a cold dark matter model of the universe: A galaxy is a gravitationally bound collection of stars whose properties cannot be explained by a combination of baryons and Newton's laws of gravity. We use this definition to critically examine the classification of ultra-faint dwarfs, globular clusters, ultra-compact dwarfs, and tidal dwarfs. While kinematic studies provide an effective diagnostic of the definition in many regimes, they can be less useful for compact or very faint systems. To explore the utility of using the [Fe/H] spread as a diagnostic, we use published spectroscopic [Fe/H] measurements of 16 Milky Way dwarfs and 24 globular clusters to uniformly calculate their [Fe/H] spreads and associated uncertainties. Our principal results are: (i) no known, old star cluster wit...

  14. Dwarf spheroidal galaxies keystones of galaxy evolution

    CERN Document Server

    Gallagher, S C; Gallagher, S; Wyse, 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.

  15. Delcam立足中国再创辉煌--访Delcam公司总经理Hugh Humphreys

    Institute of Scientific and Technical Information of China (English)

    王崇民; 朱旭

    2004-01-01

    @@ 进入2004年以来,Delcam(中国)公司表现得非常活跃,在进行一系列人事调整之后,西安办事处正式挂牌,紧接着又将北京迪勒克斯科技发展有限公司纳入旗下,使其成为Delcam(中国)华北地区增值经销商,在签约仪式上,记者见到了专程从英国前来祝贺的Delcam PLC集团公司总经理HughHumphreys先生,开朗、风趣的HughHumphreys先生非常愉快地接受了本刊记者的采访.

  16. 2002 Report to Congress: Evaluating the Consensus Best Practices Developed through the Howard Hughes Medical Institute’s Collaborative Hazardous Waste Management Demonstration Project

    Science.gov (United States)

    This report discusses a collaborative project initiated by the Howard Hughes Medical Institute (HHMI) to establish and evaluate a performance-based approach to management of hazardous wastes in the laboratories of academic research institutions.

  17. New type of chimera structures in a ring of bistable FitzHugh-Nagumo oscillators with nonlocal interaction

    Science.gov (United States)

    Shepelev, I. A.; Vadivasova, T. E.; Bukh, A. V.; Strelkova, G. I.; Anishchenko, V. S.

    2017-04-01

    We study the spatiotemporal dynamics of a ring of nonlocally coupled FitzHugh-Nagumo oscillators in the bistable regime. A new type of chimera patterns has been found in the noise-free network and when isolated elements do not oscillate. The region of existence of these structures has been explored when the coupling range and the coupling strength between the network elements are varied.

  18. Lian-Sheng Ma, Editor-in-Chief of WJG, warmly meets Professor Hugh J Freeman from the University of British Columbia

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Lian-Sheng Ma, Editor-in-Chief of World Journal of Gastroenterology (WJG), warmly met Professor Hugh J Freeman from the University of British Columbia at Peninsula Hotel in Beijing on August 28, 2007. Professor Hugh J Freeman gave much helpful advice toward the further development of WJG. He will serve as series editor for a new column called OBSERVER which will start in WJG in 2008.

  19. The Dynamics of Radio Galaxies and Double–Double Radio Galaxies

    Indian Academy of Sciences (India)

    C. Konar; M. Jamrozy; M. J. Hardcastle; J. H. Croston; S. Nandi; D. J. Saikia; J. Machalski

    2011-12-01

    Relativistic and magnetized plasma ejected by radio loud AGNs through jets form the diffuse lobes of radio galaxies. The radiating particles (electron/electron–positron) in lobes emit in radio via the synchrotron process and X-ray via inverse-Compton scattering of cosmic microwave background photons. The thermal environment around radio galaxies emits X-rays via the thermal bremsstrahlung process. By combining information from these processes we can measure physical conditions in and around the radio lobes and thus study the dynamics of radio galaxies, including double–double radio galaxies.

  20. Dynamical System Approach for Edge Detection Using Coupled FitzHugh-Nagumo Neurons.

    Science.gov (United States)

    Li, Shaobai; Dasmahapatra, Srinandan; Maharatna, Koushik

    2015-12-01

    The prospect of emulating the impressive computational capabilities of biological systems has led to considerable interest in the design of analog circuits that are potentially implementable in very large scale integration CMOS technology and are guided by biologically motivated models. For example, simple image processing tasks, such as the detection of edges in binary and grayscale images, have been performed by networks of FitzHugh-Nagumo-type neurons using the reaction-diffusion models. However, in these studies, the one-to-one mapping of image pixels to component neurons makes the size of the network a critical factor in any such implementation. In this paper, we develop a simplified version of the employed reaction-diffusion model in three steps. In the first step, we perform a detailed study to locate this threshold using continuous Lyapunov exponents from dynamical system theory. Furthermore, we render the diffusion in the system to be anisotropic, with the degree of anisotropy being set by the gradients of grayscale values in each image. The final step involves a simplification of the model that is achieved by eliminating the terms that couple the membrane potentials of adjacent neurons. We apply our technique to detect edges in data sets of artificially generated and real images, and we demonstrate that the performance is as good if not better than that of the previous methods without increasing the size of the network.

  1. The relaxation time of processes in a FitzHugh-Nagumo neural system with time delay

    Energy Technology Data Exchange (ETDEWEB)

    Gong Ailing; Zeng Chunhua [Faculty of Science, Kunming University of Science and Technology, Kunming 650093 (China); Wang Hua, E-mail: zchh2009@126.com [Province Engineering Research Center of Industrial Energy Conservation and New Technology, Kunming University of Science and Technology, Kunming, Yunnan 650093 (China)

    2011-08-01

    In this paper, we study the relaxation time (RT) of the steady-state correlation function in a FitzHugh-Nagumo neural system under the presence of multiplicative and additive white noises and time delay. The noise correlation parameter {lambda} can produce a critical behavior in the RT as functions of the multiplicative noise intensity D, the additive noise intensity Q and the time delay {tau}. That is, the RT decreases as the noise intensities D and Q increase, and increases as the time delay {tau} increases below the critical value of {lambda}. However, above the critical value, the RT first increases, reaches a maximum, and then decreases as D, Q and {tau} increase, i.e. a noise intensity D or Q and a time delay {tau} exist, at which the time scales of the relaxation process are at their largest. In addition, the additive noise intensity Q can also produce a critical behavior in the RT as a function of {lambda}. The noise correlation parameter {lambda} first increases the RT of processes, then decreases it below the critical value of Q. Above the critical value, {lambda} increases it.

  2. Robust Synchronization of Delayed Chaotic FitzHugh-Nagumo Neurons under External Electrical Stimulation

    Directory of Open Access Journals (Sweden)

    Muhammad Rehan

    2012-01-01

    Full Text Available Synchronization of chaotic neurons under external electrical stimulation (EES is studied in order to understand information processing in the brain and to improve the methodologies employed in the treatment of cognitive diseases. This paper investigates the dynamics of uncertain coupled chaotic delayed FitzHugh-Nagumo (FHN neurons under EES for incorporated parametric variations. A global nonlinear control law for synchronization of delayed neurons with known parameters is developed. Based on local and global Lipschitz conditions, knowledge of the bounds on the neuronal states, the Lyapunov-Krasovskii functional, and the L2 gain reduction, a less conservative local robust nonlinear control law is formulated to address the problem of robust asymptotic synchronization of delayed FHN neurons under parametric uncertainties. The proposed local control law guarantees both robust stability and robust performance and provides the L2 bound for uncertainty rejection in the synchronization error dynamics. Separate conditions for single-input and multiple-input control schemes for synchronization of a wide class of FHN systems are provided. The results of the proposed techniques are verified through numerical simulations.

  3. THE ONE-DIMENSIONAL HUGHES MODEL FOR PEDESTRIAN FLOW: RIEMANN-TYPE SOLUTIONS

    Institute of Scientific and Technical Information of China (English)

    Debora Amadori; M. Di Francesco

    2012-01-01

    This paper deals with a coupled system consisting of a scalar conservation law and an eikonal equation,called the Hughes model.Introduced in [24],this model attempts to describe the motion of pedestrians in a densely crowded region,in which they are seen as a 'thinking' (continuum) fluid.The main mathematical difficulty is the discontinuous gradient of the solution to the eikonal equation appearing in the flux of the conservation law.On a one dimensional interval with zero Dirichlet conditions (the two edges of the interval are interpreted as 'targets'),the model can be decoupled in a way to consider two classical conservation laws on two sub-domains separated by a turning point at which the pedestrians change their direction.We shall consider solutions with a possible jump discontinuity around the turning point.For simplicity,we shall assume they are locally constant on both sides of the discontinuity.We provide a detailed description of the localin-time behavior of the solution in terms of a 'global' qualitative property of the pedestrian density (that we call 'relative evacuation rate'),which can be interpreted as the attitude of the pedestrians to direct towards the left or the right target.We complement our result with explicitly computable examples.

  4. Noise-sustained synchronization between electrically coupled FitzHugh-Nagumo networks

    Science.gov (United States)

    Cascallares, Guadalupe; Sánchez, Alejandro D.; dell'Erba, Matías G.; Izús, Gonzalo G.

    2015-09-01

    We investigate the capability of electrical synapses to transmit the noise-sustained network activity from one network to another. The particular setup we consider is two identical rings with excitable FitzHugh-Nagumo cell dynamics and nearest-neighbor antiphase intra-ring coupling, electrically coupled between corresponding nodes. The whole system is submitted to independent local additive Gaussian white noises with common intensity η, but only one ring is externally forced by a global adiabatic subthreshold harmonic signal. We then seek conditions for a particular noise level to promote synchronized stable firing patterns. By running numerical integrations with increasing η, we observe the excitation activity to become spatiotemporally self-organized, until η is so strong that spoils sync between networks for a given value of the electric coupling strength. By means of a four-cell model and calculating the stationary probability distribution, we obtain a (signal-dependent) non-equilibrium potential landscape which explains qualitatively the observed regimes, and whose barrier heights give a good estimate of the optimal noise intensity for the sync between networks.

  5. Subthreshold and suprathreshold vibrational resonance in the FitzHugh-Nagumo neuron model

    Science.gov (United States)

    Zhu, Jinjie; Kong, Chen; Liu, Xianbin

    2016-09-01

    We study the subthreshold and suprathreshold vibrational resonance in the FitzHugh-Nagumo neuron model. For the subthreshold situation, two cases where the stationary states are equilibrium point and limit cycle are considered, where different natures of vibrational resonance are observed via theoretical and numerical methods. Especially when the frequency of the high-frequency driving force is near the so-called canard-resonance frequency, the firing rate can be significantly enhanced at the presence of noise. For the suprathreshold situation, we show that the local maxima of the response amplitude are located at the transition boundaries of different phase-locking patterns. The minimal required forcing amplitudes of high-frequency signal of the firing onset are just multiples of the spiking frequency. Furthermore, phase portraits and time series show that the presence of the global maxima of the response results from not only the suprathreshold but also the subthreshold phase-locking modes. In spite of the distinct characteristics for two stationary states on subthreshold oscillation, the suprathreshold vibrational resonance showed no qualitative difference between the two cases.

  6. Adaptable Analytical Vistas Illumine a Touchstone: Langston Hughes as Minor Author/Poet

    Directory of Open Access Journals (Sweden)

    Mzenga A. Wanyama

    2013-12-01

    Full Text Available The authentic association of spontaneity, as a spur or basis for artistic expression, with the vaunted notion of autonomy in literary creationis nowhere more clearly established than in the work of theorists Gilles Deleuze and Felix Guattari as they, inter-alia, explicate the unique literary repertoire bestowed upon the world by Franz Kafka. In their acclaimed works: Kafka: Toward a Minor Literature and Anti-Oedipus: Capitalism and Schizophrenia,they offered to literary theory the fascinating and analytically productive constructs of deterritorialization and anti-Oedipus in the context of a compelling portraiture of the ways in which various institutionalized relationships subtly prescribe and reinforce inequity in society’s power mechanics that tendentiously impact, among other realities, the nature and quality of literary products. They offered, in the process, a refreshing definition of minor literature that unequivocally restores to literature its distinctive place and role in the amalgamated adjudications of society’s intergroup dissensions. In this regard, the present paper subscribes to the idea that spontaneity equaled the intrinsic and immutable desire of the gifted literary mind of African-American author/poet Langston Hughes to reach expressivity in accordance, strictly, with his unalloyed literary vision and thus made autonomy the inevitable upshot of his inspiration and practice.

  7. Galaxies Collide to Create Hot, Huge Galaxy

    Science.gov (United States)

    2009-01-01

    This image of a pair of colliding galaxies called NGC 6240 shows them in a rare, short-lived phase of their evolution just before they merge into a single, larger galaxy. The prolonged, violent collision has drastically altered the appearance of both galaxies and created huge amounts of heat turning NGC 6240 into an 'infrared luminous' active galaxy. A rich variety of active galaxies, with different shapes, luminosities and radiation profiles exist. These galaxies may be related astronomers have suspected that they may represent an evolutionary sequence. By catching different galaxies in different stages of merging, a story emerges as one type of active galaxy changes into another. NGC 6240 provides an important 'missing link' in this process. This image was created from combined data from the infrared array camera of NASA's Spitzer Space Telescope at 3.6 and 8.0 microns (red) and visible light from NASA's Hubble Space Telescope (green and blue).

  8. The Galaxy End Sequence

    Science.gov (United States)

    Eales, Stephen; de Vis, Pieter; Smith, Matthew W. L.; Appah, Kiran; Ciesla, Laure; Duffield, Chris; Schofield, Simon

    2017-03-01

    A common assumption is that galaxies fall in two distinct regions of a plot of specific star formation rate (SSFR) versus galaxy stellar mass: a star-forming galaxy main sequence (GMS) and a separate region of 'passive' or 'red and dead galaxies'. Starting from a volume-limited sample of nearby galaxies designed to contain most of the stellar mass in this volume, and thus representing the end-point of ≃12 billion years of galaxy evolution, we investigate the distribution of galaxies in this diagram today. We show that galaxies follow a strongly curved extended GMS with a steep negative slope at high galaxy stellar masses. There is a gradual change in the morphologies of the galaxies along this distribution, but there is no clear break between early-type and late-type galaxies. Examining the other evidence that there are two distinct populations, we argue that the 'red sequence' is the result of the colours of galaxies changing very little below a critical value of the SSFR, rather than implying a distinct population of galaxies. Herschel observations, which show at least half of early-type galaxies contain a cool interstellar medium, also imply continuity between early-type and late-type galaxies. This picture of a unitary population of galaxies requires more gradual evolutionary processes than the rapid quenching process needed to explain two distinct populations. We challenge theorists to predict quantitatively the properties of this 'Galaxy End Sequence'.

  9. Galaxy Zoo: Mergers - Dynamical models of interacting galaxies

    Science.gov (United States)

    Holincheck, Anthony J.; Wallin, John F.; Borne, Kirk; Fortson, Lucy; Lintott, Chris; Smith, Arfon M.; Bamford, Steven; Keel, William C.; Parrish, Michael

    2016-06-01

    The dynamical history of most merging galaxies is not well understood. Correlations between galaxy interaction and star formation have been found in previous studies, but require the context of the physical history of merging systems for full insight into the processes that lead to enhanced star formation. We present the results of simulations that reconstruct the orbit trajectories and disturbed morphologies of pairs of interacting galaxies. With the use of a restricted three-body simulation code and the help of citizen scientists, we sample 105 points in parameter space for each system. We demonstrate a successful recreation of the morphologies of 62 pairs of interacting galaxies through the review of more than 3 million simulations. We examine the level of convergence and uniqueness of the dynamical properties of each system. These simulations represent the largest collection of models of interacting galaxies to date, providing a valuable resource for the investigation of mergers. This paper presents the simulation parameters generated by the project. They are now publicly available in electronic format at http://data.galaxyzoo.org/mergers.html. Though our best-fitting model parameters are not an exact match to previously published models, our method for determining uncertainty measurements will aid future comparisons between models. The dynamical clocks from our models agree with previous results of the time since the onset of star formation from starburst models in interacting systems and suggest that tidally induced star formation is triggered very soon after closest approach.

  10. A Direct Comparison of HI and Lyα Morphologies in Two LARS Galaxies

    Science.gov (United States)

    Fitzgibbon, Kathleen; Cannon, John M.; Freeland, Emily; Hayes, Matthew; Östlin, Göran; LARS Team

    2016-01-01

    The Lyman-Alpha Reference Sample (LARS) and its extension (eLARS) represent an exhaustive campaign to reverse-engineer galaxies. The main goal is to understand how Lyα is transported within galaxies: what fraction of it escapes, and what physical properties affect Lyα morphology and radiative transport (e.g. dust and gas content, metallicity, kinematics, properties of the stellar population). Neutral hydrogen emission, which can be used to determine a galaxy's structure and kinematics, was observed using the B and C configurations of the Very Large Array in two galaxies from the sample: LARS02 and LARS09. Images of the HI mass surface density and of the intensity weighted HI velocity field were created at angular scales of ~8 arcseconds. Extended HI gas is detected at high significance up to ˜30 kpc from the optical body of LARS02. LARS09 has a severely disturbed optical morphology; our new HI observations reveal that LARS09 is interacting with the nearby field galaxy SDSS J082353.65+280622.2. In combination with direct imaging of the Lyα morphology from the Hubble Space Telescope, this program has produced the first direct comparison of Lyα and HI morphologies. These observations demonstrate concept for a significant observational campaign that will produce similar comparisons in the remaining 40 LARS+eLARS galaxies.KF was partially supported by a Science Education Award from the Howard Hughes Medical Institute (HHMI) to Macalester College.

  11. OBITUARY: Eur.Ing. Professor David Dew-Hughes in memoriam

    Science.gov (United States)

    Campbell, Archie; Dew-Hughes, Denise; Donaldson, Gordon; Palmer, Richard

    2007-06-01

    We regret to announce the death of David Dew-Hughes, the second Honorary Editor of Superconductor Science and Technology, in Autumn 2006. He was born in Manchester, the eldest of three children, attended Manchester Grammar School and took his first degree in metallurgy at Birmingham, before undertaking a Doctorate of Engineering at Yale University. After initial work for IBM on semiconductors, he returned to England as a lecturer in metallurgy at Cambridge University. There he devoted his career to superconductivity long before it became fashionable, starting a group on the properties of what we now know as type II materials, with his students Jan Evetts, Archie Campbell and Anant Narlikar. Between them they paved the way to our understanding of the magnetic vortex properties of these materials, and thus to the development of modern practical materials for superconducting magnets. Eur.Ing. Professor David Dew-Hughes 1932-2006 In 1965 he became a founding Senior Lecturer in physics at Lancaster University, moving to Brookhaven National Laboratory in 1974. His final academic post was in engineering science at Oxford University where he also held a University College Tutorial Fellowship. As long ago as 1971 David wrote an authoritative review for Reports on Progress in Physics on 'The metallurgical enhancement of type II superconductors'. Following the discovery of high-Tc superconductivity, IOP Publishing launched Superconductor Science and Technology in 1988 and he was a founder member of its Editorial Board. When Jan Evetts retired as Honorary Editor in 1992, David was the natural choice as his successor. He served a five year term and remained on the Board as Deputy Editor until the end of 2000. To mark the 10th anniversary of high-temperature superconductivity in 1997, David edited a special issue of Superconductor Science and Technology in which past and present members of the Editorial Board contributed reviews of their specialities. He noted that at that time

  12. CT Diagnosis of Fitz-Hugh and Curtis Syndrome: Value of the Arterial Phase Scan

    Energy Technology Data Exchange (ETDEWEB)

    Joo, Seung Ho; Kim, Myeong Jin; Lim, Joon Seok; Kim, Joo Hee; Kim, Ki Whang [Yonsei University College of Medicine, Seoul (Korea, Republic of)

    2007-02-15

    We wanted to evaluate the role of the arterial phase (AP) together with the portal venous phase (PP) scans in the diagnosis of Fitz-Hugh-Curtis syndrome (FHCS) with using computed tomography (CT). Twenty-five patients with FHCS and 25 women presenting with non-specifically diagnosed acute abdominal pain and who underwent biphasic CT examinations were evaluated. The AP scan included the upper abdomen, and the PP scan included the whole abdomen. Two radiologists blindly and retrospectively reviewed the PP scans first and then they reviewed the AP plus PP scans. The diagnostic accuracy of FHCS on each image set was compared for each reader by analyzing the area under the receiver operating characteristic curve (Az). Weighted kappa (wk) statistics were used to measure the interobserver agreement for the presence of CT signs of the pelvic inflammatory disease (PID) on the PP images and FHCS as the diagnosis based on the increased perihepatic enhancement on both sets of images. The individual diagnostic accuracy of FHCS was higher on the biphasic images (Az = 0.905 and 0.942 for reader 1 and 2, respectively) than on the PP images alone (Az = 0.806 and 0.706, respectively). The interobserver agreement for the presence of PID on the PP images was moderate (wk = 0.530). The interobserver agreement for FHCS as the diagnosis was moderate on only the PP images (wk = 0.413), but it was substantial on the biphasic images (wk 0.719). Inclusion of the AP scan is helpful to depict the increased perihepatic enhancement, and it improves the diagnostic accuracy of FHCS on CT.

  13. Optical spectrophotometry of Wolf-Rayet galaxies

    Science.gov (United States)

    Vacca, William D.; Conti, Peter S.

    1992-01-01

    We have obtained long-slit optical spectra of 10 Wolf-Rayet galaxies and four other starburst galaxies. Using the nebular emission lines we have determined the electron temperatures, electron densities, extinctions, oxygen abundances, mass of ionized hydrogen, and numbers of ionizing photons due to hot stars in these galaxies. The various forbidden line ratios clearly indicate a stellar origin for the emission-line spectrum. From the flux of the broad He II 4686 A emission feature we have estimated the number of Wolf-Rayet stars present. We have accounted for the contribution of these stars to the total ionizing flux and have calculated the ratio of the number of these stars to the number of O stars. Wolf-Rayet galaxies are among the youngest examples of the starburst phenomenon, which we observed at a propitious moment.

  14. How Hugh Hampton Young's treatment of President Woodrow Wilson's urinary retention and urosepsis affected the resolution of World War I.

    Science.gov (United States)

    Fogg, Ryan; Kutikov, Alexander; Uzzo, Robert G; Canter, Daniel

    2011-09-01

    President Woodrow Wilson was never able to gain ratification of the Treaty of Versailles, the peace accord to end World War I. Before he could convince the American people of the importance of ratification, Wilson suffered a stroke followed by life threatening urinary sepsis due to urinary retention, and was treated by the father of modern urology, Hugh Hampton Young. The effects of these health problems are examined in the context of their implications on international affairs. Biographical sources and primary documentation of Wilson's physicians were reviewed to determine the effect of Wilson's stroke on his voiding habits. Hugh Hampton Young's evaluation and decision making is examined in depth. In the fall of 1919 President Wilson was recovering from a stroke. Shortly after the stroke his preexisting voiding dysfunction progressed to urinary retention from which urinary sepsis developed. Hugh Hampton Young advised on Wilson's case and counseled patience over surgery. The President began voiding spontaneously and recovered from sepsis. The illness left him severely weakened and unable to mount an aggressive campaign to persuade the U.S. Senate of the importance of ratifying the Treaty of Versailles. His personal physician, Admiral Cary T. Grayson, stated that the President was mentally never the same after the sepsis. Wilson's voiding dysfunction contributed to his inability to win approval for the Treaty of Versailles and the League of Nations. As a result, the United States returned to a policy of isolationism and Europe plunged into 2 decades of upheaval, leading to World War II. Copyright © 2011 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

  15. 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)

  16. The ingenious Mr Hughes: Combining forced, flat, and reverse perspective all in one art piece to pit objects against surfaces

    Science.gov (United States)

    Papathomas, Thomas V; Baker, Nicholas; Yeshua, Arielle S; Zhuang, Xiaohua; Ng, Andrew

    2012-01-01

    The artist Patrick Hughes has ingeniously painted rows of stacked Brillo boxes in Forced into Reverse Perspective. The geometry is in reverse perspective, predicting only one type of illusory motion for each planar surface for moving viewers. He “broke” these surfaces into objects by painting the boxes in three types of perspective (planar, forced, and reverse). Our experiments confirmed that he succeeded in eliciting different types of illusory motion, including “differential motion” between boxes for most viewers. In some sense, this illustrates the superiority of secondary (painted) over primary (physical) cues. PMID:23145280

  17. The Ingenious Mr Hughes: Combining Forced, Fat, and Reverse Perspective All in One Art Piece to Pit Objects against Surfaces

    Directory of Open Access Journals (Sweden)

    Thomas V Papathomas

    2012-04-01

    Full Text Available The artist Patrick Hughes has ingeniously painted rows of stacked Brillo boxes in Forced into Reverse Perspective. The geometry is in reverse perspective, predicting only one type of illusory motion for each planar surface for moving viewers. He “broke” these surfaces into objects by painting the boxes in three types of perspective (planar, forced, and reverse. Our experiments confirmed that he succeeded in eliciting different types of illusory motion, including “differential motion” between boxes for most viewers. In some sense, this illustrates the superiority of secondary (painted over primary (physical cues.

  18. 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.

  19. Maurice Hugh Frederick Wilkins CBE: 15 December 1916 - 5 October 2004.

    Science.gov (United States)

    Arnott, Struther; Kibble, T W B; Shallice, Tim

    2006-01-01

    Maurice Hugh Frederick Wilkins was the 'Third man of the double helix; according to the publishers who were allowed to foist this title on his late-written autobiography. Certainly it is for his role in the discover of the duplex secondary structure of DNA that he will be remembered. It might be argued that he was the first man, rather than the third, for it was his successful revival of X-ray diffraction studies of DNA and his earliest result in 1950, a pattern of a well-oriented and polycrystalline DNA of unprecedented quality, that allowed him to conclude almost immediately that the basic framework of the genetical material was simple and symmetrical, and that the symmetrical structure took the form of a helix. This same pattern, displayed at a conference in Naples six months later, was the major inspiration for the involvement of J. D. Watson (ForMemRS 1981) in modelling DNA structure in collaboration with F. H. C. Crick (FRS 1959). Crick was a personal friend of Maurice's and was more involved with studies of proteins until the progress of Maurice's research programme and Watson's enthusiastic presence in Cambridge convinced him to put nucleic acids first. The carefully crafted citation for the 1960 Lasker Award, which these three men shared in 1960, put Maurice's name first and accurately referred to '...the painstaking x-ray diffraction studies of Wilkins that provided a most important clue that was pursued in a ingenious fashion and to a logical conclusion by Crick and Watson...'. Maurice's diffraction studies of DNA were not only the alpha but also the omega of the double helix because it left to him to remedy a major flaw in the original (1953) Watson-Crick conjecture. Maurice Wilkin's early acceptance of DNA as the genetic material and his recognition that it had structures that could and should be tackled by X-ray diffraction analyses, not necessarily under his exclusive control, was important in ensuring that the essence of DNA's structure was

  20. Mode stability analysis in the beam-wave interaction process for a three-gap Hughes-type coupled cavity chain

    Institute of Scientific and Technical Information of China (English)

    Luo Ji-Run; Cui Jian; Zhu Min; Guo Wei

    2013-01-01

    Based on space-charge wave theory,the formulae of the beam-wave coupling coefficient and the beam-loaded conductance are given for the beam-wave interaction in an N-gap Hughes-type coupled cavity chain.The ratio of the nonbeam-loaded quality factor of the coupled cavity chain to the beam quality factor is used to determine the stability of the beam-wave interaction.As an example,the stabilities of the beam-wave interaction in a three-gap Hughes-type coupled cavity chain are discussed with the formulae and the CST code for the operations of the 2π,π,and π/2 modes,respectively.The results show that stable operation of the 2π,π,and π/2 modes may all be realized in an extended-interaction klystron with the three-gap Hughes-type coupled cavity chain.

  1. Galaxy International Mall Unveiled

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    An agreement between Galaxy International Mall (hereinafter referred to as Galaxy) and its three main partners was signed on January 12, 2011, in the city of Tianjin. The partners are Lotte Department

  2. The Void Galaxy Survey

    CERN Document Server

    van de Weygaert, R; Platen, E; Beygu, B; van Gorkom, J H; van der Hulst, J M; Aragon-Calvo, M A; Peebles, P J E; Jarrett, T; Rhee, G; Kovac, K; Yip, C -W

    2011-01-01

    The Void Galaxy Survey (VGS) is a multi-wavelength program to study $\\sim$60 void galaxies. Each has been selected from the deepest interior regions of identified voids in the SDSS redshift survey on the basis of a unique geometric technique, with no a prior selection of intrinsic properties of the void galaxies. The project intends to study in detail the gas content, star formation history and stellar content, as well as kinematics and dynamics of void galaxies and their companions in a broad sample of void environments. It involves the HI imaging of the gas distribution in each of the VGS galaxies. Amongst its most tantalizing findings is the possible evidence for cold gas accretion in some of the most interesting objects, amongst which are a polar ring galaxy and a filamentary configuration of void galaxies. Here we shortly describe the scope of the VGS and the results of the full analysis of the pilot sample of 15 void galaxies.

  3. The Galaxy End Sequence

    CERN Document Server

    Eales, Stephen; Smith, Matthew; Appah, Kiran; Ciesla, Laure; Duffield, Chris; Schofield, Simon

    2016-01-01

    A common assumption is that galaxies fall in two distinct regions on a plot of specific star-formation rate (SSFR) versus galaxy stellar mass: a star-forming Galaxy Main Sequence (GMS) and a separate region of `passive' or `red and dead galaxies'. Starting from a volume-limited sample of nearby galaxies designed to contain most of the stellar mass in this volume, and thus being a fair representation of the Universe at the end of 12 billion years of galaxy evolution, we investigate the distribution of galaxies in this diagram today. We show that galaxies follow a strongly curved extended GMS with a steep negative slope at high galaxy stellar masses. There is a gradual change in the morphologies of the galaxies along this distribution, but there is no clear break between early-type and late-type galaxies. Examining the other evidence that there are two distinct populations, we argue that the `red sequence' is the result of the colours of galaxies changing very little below a critical value of the SSFR, rather t...

  4. Satellite galaxies in nearby groups of galaxies

    CERN Document Server

    Vennik, J

    2015-01-01

    We analyse distribution, kinematics and star-formation (SF) properties of satellite galaxies in three different samples of nearby groups. We find that studied groups are generally well approximated by low-concentration NFW model, show a variety of LOS velocity dispersion profiles and signs of SF quenching in outskirts of dwarf satellite galaxies.

  5. Fitz-Hugh-Curtis综合征在输卵管妊娠和不孕中的发生率及其意义%EXPLORATION ON INCIDENCE OF FITZ-HUGH-CURTIS SYNDROME IN TUBAL PREGNANCY AND TUBAL INFERTILITY

    Institute of Scientific and Technical Information of China (English)

    左绪磊

    2003-01-01

    目的:了解Fitz-Hugh-Curtis综合征在输卵管妊娠和输卵管不孕中的发生率,探讨它们在输卵管妊娠和输卵管不孕发生中的作用.方法:在腹腔镜检查和治疗妇科疾病时,确诊Fitz-Hugh-Curtis综合征遗留的典型病理改变和输卵管周围炎性病变.肿瘤、多囊卵巢综合征、子宫肌瘤等非输卵管炎性疾病患者作为对照组.结果:在109例输卵管妊娠患者中,发现慢性肝周围炎15例(13.8%),升结肠-腹壁粘连10例(9.2%),单纯输卵管周围炎性粘连24例(20.2%).而在112例对照组患者中,发现慢性肝周围炎患者2例(1.8%),升结肠-腹壁粘连患者2例(1.8%),输卵管周围炎性粘连患者2例(1.8%).与对照组相比,输卵管妊娠中肝周围炎发生率明显高于对照组(P<0.01),升结肠-腹壁粘连发生率也高于对照组(P<0.05).在20例经腹腔镜检查诊断为输卵管不孕的患者中,发现肝周围炎5例(25%),未发现升结肠-腹壁粘连.与对照组相比,输卵管性不孕患者中肝周围炎发生率明显高于对照组,差别有极显著意义P<0.001).结论:Fitz-Hugh-Curtis综合征在输卵管妊娠和不孕患者中的发生率与国外接近.肝周围炎、升结肠-腹壁粘连从侧面反映了盆腔炎性疾病在输卵管妊娠和输卵管不孕中起着重要作用.

  6. Morphology of galaxies

    CERN Document Server

    Wadadekar, Yogesh

    2012-01-01

    The study of the morphology of galaxies is important in order to understand the formation and evolution of galaxies and their sub-components as a function of luminosity, environment, and star-formation and galaxy assembly over cosmic time. Disentangling the many variables that affect galaxy evolution and morphology, requires large galaxy samples and automated ways to measure morphology. The advent of large digital sky surveys, with unprecedented depth and resolution, coupled with sophisticated quantitative methods for morphology measurement are providing new insights in this fast evolving field of astronomical research.

  7. How Do Galaxies Grow?

    Science.gov (United States)

    2008-08-01

    Astronomers have caught multiple massive galaxies in the act of merging about 4 billion years ago. This discovery, made possible by combining the power of the best ground- and space-based telescopes, uniquely supports the favoured theory of how galaxies form. ESO PR Photo 24/08 ESO PR Photo 24/08 Merging Galaxies in Groups How do galaxies form? The most widely accepted answer to this fundamental question is the model of 'hierarchical formation', a step-wise process in which small galaxies merge to build larger ones. One can think of the galaxies forming in a similar way to how streams merge to form rivers, and how these rivers, in turn, merge to form an even larger river. This theoretical model predicts that massive galaxies grow through many merging events in their lifetime. But when did their cosmological growth spurts finish? When did the most massive galaxies get most of their mass? To answer these questions, astronomers study massive galaxies in clusters, the cosmological equivalent of cities filled with galaxies. "Whether the brightest galaxies in clusters grew substantially in the last few billion years is intensely debated. Our observations show that in this time, these galaxies have increased their mass by 50%," says Kim-Vy Tran from the University of Zürich, Switzerland, who led the research. The astronomers made use of a large ensemble of telescopes and instruments, including ESO's Very Large Telescope (VLT) and the Hubble Space Telescope, to study in great detail galaxies located 4 billion light-years away. These galaxies lie in an extraordinary system made of four galaxy groups that will assemble into a cluster. In particular, the team took images with VIMOS and spectra with FORS2, both instruments on the VLT. From these and other observations, the astronomers could identify a total of 198 galaxies belonging to these four groups. The brightest galaxies in each group contain between 100 and 1000 billion of stars, a property that makes them comparable

  8. Magnetic fields in spiral galaxies

    Science.gov (United States)

    Krause, Marita

    2015-03-01

    The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At λ6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).

  9. Using Galaxy Winds to Constrain Galaxy Evolution

    Science.gov (United States)

    Churchill, Christopher W.; Klypin, A.; Ceverino, D.; Kacprzak, G.; Klimek, E.

    2010-01-01

    Analysis of mock quasar spectra of metal absorption lines in the proximity of formed galaxies in cosmological simulation is a highly promising for understanding the role of galaxies in IGM physics, or IGM physics in the role of galaxy formation in context of the cosmic web. Such analysis using neutral hydrogen in the cosmic web has literally revolutionized our understanding of the Lyman alpha forest. We are undertaking a wholesale approach to use powerful Lambda-CDM simulations to interpret absorption line data from redshift 1-3 starbursting galaxies e.g. Lyman break galaxies, etc) The data with which direct quantitative comparison is made are from the DEEP survey (Weiner et al.) and the collective work of Steidel et al. and collaborators. The simulations are performed using the Eulerian Gasdynamics plus N-body Adaptive Refinement Tree (ART) code, which has gas cell resolutions of 20-50 pc. Physical processes implemented in the code include realistic radiative cooling, star formation, metal enrichment and thermal feedback due to type II and type Ia supernovae. We quantitatively compare the spatial and kinematic distribution of HI, MgII, CIV, and OVI of absorption lines over a range of impact parameters for various simulated galaxies as a function of redshift, and discuss key insights for interpreting the underlying temperature, density, and ionization structure of the halo/cosmic-web interface, and the influence of galaxies on its chemical enrichment.

  10. Positive Intervention for Serious Behavior Problems: Best Practices in Implementing the Hughes Bill (A.B. 2586) and the Positive Behavioral Intervention Regulations.

    Science.gov (United States)

    Wright, Diana Browning; Gurman, Harvey B.

    This manual provides guidelines to educators attempting to comply with California's Hughes Bill, which is intended to ensure the rights of special education students to have positive behavioral intervention plans designed to bring lasting behavioral changes without interventions that cause pain or trauma. An introductory chapter summarizes the…

  11. Influence of spatially modified tissue on atrial fibrillation patterns: Insight from solutions of the FitzHugh-Nagumo equations

    CERN Document Server

    Lenk, Claudia; Maass, Philipp

    2010-01-01

    We study the interplay between traveling action potentials and spatial inhomogeneities in the FitzHugh-Nagumo model to investigate possible mechanisms for the occurrence of fibrillatory states in the atria of the heart. Different dynamical patterns such as ectopic foci, localized and meandering spiral waves are found depending on the characteristics of the inhomogeneities. Their appearance in dependence of the size and strength of the inhomogeneities is quantified by phase diagrams. Furthermore it is shown that regularly paced waves in a region R, that is connected by a small bridge connection to another region L with perturbing waves emanating from an additional pacemaker, can be strongly disturbed, so that a fibrillatory state emerges in region R after a transient time interval. This finding supports conjectures that fibrillatory states in the right atrium can be induced by self-excitatory pacemakers in the left atrium.

  12. Frédéric Sylvanise. Langston Hughes, poète jazz, poète blues

    Directory of Open Access Journals (Sweden)

    Hélène CHRISTOL

    2011-03-01

    Full Text Available La Renaissance de Harlem a été redécouverte en France au début du XXIe siècle, grâce à l’organisation de manifestations publiques et universitaires ainsi que la publication de nombreuses études qui « revisitent » la période et les œuvres de ses écrivains et de ses artistes.  L’ouvrage de Frédéric Sylvanise, Langston Hughes, poète jazz, poète blues, publié par les éditions de l’ENS en 2009, apporte sa pierre à cet édifice critique puisqu’il se penche sur certains recueils de poésie de cet écri...

  13. Stability Switches and Hopf Bifurcation in a Coupled FitzHugh-Nagumo Neural System with Multiple Delays

    Directory of Open Access Journals (Sweden)

    Shengwei Yao

    2014-01-01

    Full Text Available A FitzHugh-Nagumo (FHN neural system with multiple delays has been proposed. The number of equilibrium point is analyzed. It implies that the neural system exhibits a unique equilibrium and three ones for the different values of coupling weight by employing the saddle-node bifurcation of nontrivial equilibrium point and transcritical bifurcation of trivial one. Further, the stability of equilibrium point is studied by analyzing the corresponding characteristic equation. Some stability criteria involving the multiple delays and coupling weight are obtained. The results show that the neural system exhibits the delay-independence and delay-dependence stability. Increasing delay induces the stability switching between resting state and periodic activity in some parameter regions of coupling weight. Finally, numerical simulations are taken to support the theoretical results.

  14. A data base for galaxy evolution modeling

    NARCIS (Netherlands)

    Leitherer, C; Alloin, D; FritzVonAlvensleben, U; Gallagher, JS; Huchra, JP; Matteucci, F; OConnell, RW; Beckman, JE; Bertelli, GP; Bica, E; Boisson, C; Bonatto, C; Bothun, GD; Bressan, A; Brodie, JP; Bruzual, G; Burstein, D; Buser, R; Caldwell, N; Casuso, E; Cervino, M; Charlot, S; Chavez, M; Chiosi, C; Christian, CA; Cuisinier, F; Dallier, R; deKoter, A; Delisle, S; Diaz, AI; Dopita, MA; Dorman, B; Fagotto, F; Fanelli, MN; Fioc, M; GarciaVargas, ML; Girardi, L; Goldader, JD; Hardy, E; Heckman, TM; Iglesias, J; Jablonka, P; Joly, M; Jones, L; Kurth, O; Lancon, A; Lejeune, T; Loxen, J; Maeder, A; Malagnini, ML; Marigo, P; MasHesse, JM; Meynet, G; Moller, CS; Molla, ML; Morossi, C; Nasi, E; Nichols, JS; Odegaard, KJR; Parker, JWM; Pastoriza, MG; Peletier, R; Robert, C; RoccaVolmerange, B; Schaerer, D; Schmidt, A; Schmitt, HR; Schommer, RA; Schmutz, W; Silva, L; Stasinska, G; Sutherland, RS; Tantalo, R; Traat, P; Vallenari, A; Vazdekis, A; Walborn, NR; Worthey, G

    1996-01-01

    This paper represents a collective effort to provide an extensive electronic data base useful for the interpretation of the spectra and evolution of galaxies. A broad variety of empirical and theoretical data is discussed here, and the data are made fully available in the AAS CD-ROM Series, Vol. 7.

  15. Galaxy Formation Theory

    CERN Document Server

    Benson, Andrew J

    2010-01-01

    We review the current theory of how galaxies form within the cosmological framework provided by the cold dark matter paradigm for structure formation. Beginning with the pre-galactic evolution of baryonic material we describe the analytical and numerical understanding of how baryons condense into galaxies, what determines the structure of those galaxies and how internal and external processes (including star formation, merging, active galactic nuclei etc.) determine their gross properties and evolution. Throughout, we highlight successes and failings of current galaxy formation theory. We include a review of computational implementations of galaxy formation theory and assess their ability to provide reliable modeling of this complex phenomenon. We finish with a discussion of several "hot topics" in contemporary galaxy formation theory and assess future directions for this field.

  16. Amazing Andromeda Galaxy

    Science.gov (United States)

    2006-01-01

    The many 'personalities' of our great galactic neighbor, the Andromeda galaxy, are exposed in this new composite image from NASA's Galaxy Evolution Explorer and the Spitzer Space Telescope. The wide, ultraviolet eyes of Galaxy Evolution Explorer reveal Andromeda's 'fiery' nature -- hotter regions brimming with young and old stars. In contrast, Spitzer's super-sensitive infrared eyes show Andromeda's relatively 'cool' side, which includes embryonic stars hidden in their dusty cocoons. Galaxy Evolution Explorer detected young, hot, high-mass stars, which are represented in blue, while populations of relatively older stars are shown as green dots. The bright yellow spot at the galaxy's center depicts a particularly dense population of old stars. Swaths of red in the galaxy's disk indicate areas where Spitzer found cool, dusty regions where stars are forming. These stars are still shrouded by the cosmic clouds of dust and gas that collapsed to form them. Together, Galaxy Evolution Explorer and Spitzer complete the picture of Andromeda's swirling spiral arms. Hints of pinkish purple depict regions where the galaxy's populations of hot, high-mass stars and cooler, dust-enshrouded stars co-exist. Located 2.5 million light-years away, the Andromeda is our largest nearby galactic neighbor. The galaxy's entire disk spans about 260,000 light-years, which means that a light beam would take 260,000 years to travel from one end of the galaxy to the other. By comparison, our Milky Way galaxy's disk is about 100,000 light-years across. This image is a false color composite comprised of data from Galaxy Evolution Explorer's far-ultraviolet detector (blue), near-ultraviolet detector (green), and Spitzer's multiband imaging photometer at 24 microns (red).

  17. The Stuff Between Galaxies

    Institute of Scientific and Technical Information of China (English)

    1995-01-01

    The space between stars in our galaxy,astronomers know, is sprinkled with a diffuse mixture of gas and dust.But what about the immense starless reaches separating galaxies? In the 1960s astronomers discovered isolated, galaxy-size clouds of hydrogen out there.Now an observation made by the repaired Hubble Space Telescope has revealed that intergalactic space is also permeated by a thin fog of ionized helium.

  18. On Galaxies and Homology

    OpenAIRE

    Novak, Gregory S.; Jonsson, Patrik; Primack, Joel R.; Cox, Thomas J.; Dekel, Avishai

    2012-01-01

    The definition of homology for single-component galaxies is clear, but for multi-component (luminous and dark matter) galaxies there is some ambiguity. We attempt to clarify the situation by carefully separating the different concepts of homology that have been used to date. We argue that the most useful definition is that a set of galaxies is homologous if they are the same in all respects up to a set of three dimensional scaling constants which may differ from one galaxy to the next. Noting...

  19. The effects of assembly bias on cosmological inference from galaxy-galaxy lensing and galaxy clusters

    CERN Document Server

    McEwen, Joseph E

    2016-01-01

    The combination of galaxy-galaxy lensing (GGL) and galaxy clustering is a promising route to measuring the amplitude of matter clustering and testing modified gravity theories of cosmic acceleration. Halo occupation distribution (HOD) modeling can extend the approach down to nonlinear scales, but galaxy assembly bias could introduce systematic errors by causing the HOD to vary with large scale environment at fixed halo mass. We investigate this problem using the mock galaxy catalogs created by Hearin & Watson (2013, HW13), which exhibit significant assembly bias because galaxy luminosity is tied to halo peak circular velocity and galaxy colour is tied to halo formation time. The preferential placement of galaxies (especially red galaxies) in older halos affects the cutoff of the mean occupation function $\\langle N_\\text{cen}(M_\\text{min}) \\rangle$ for central galaxies, with halos in overdense regions more likely to host galaxies. The effect of assembly bias on the satellite galaxy HOD is minimal. We intro...

  20. Local Analogs for High-redshift Galaxies: Resembling the Physical Conditions of the Interstellar Medium in High-redshift Galaxies

    CERN Document Server

    Bian, Fuyan; Dopita, Michael; Juneau, Stephanie

    2016-01-01

    We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [OIII]/H$\\beta$ versus [NII]/H$\\alpha$ nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums and compact galaxy sizes. In particular, the ionization parameters and electron densities in these analogs are comparable to those in $z\\simeq2-3$ galaxies, but higher than those in normal SDSS galaxies by $\\simeq$0.6~dex and $\\simeq$0.9~dex, respectively. The mass-metallicity relation (MZR) in these local analogs shows $-0.2$~dex offset from that in SDSS star-forming galaxies at the low mass end, which is consistent with the MZR of the $z\\sim2-3$ galaxies. We compare the lo...

  1. A epistemologia de Hugh Lacey em diálogo com a Economia Feminista: neutralidade, objetividade e pluralismo Hugh Lacey's epistemology dialogs with feminist economy: neutrality, objectivity and pluralism

    Directory of Open Access Journals (Sweden)

    Brena Paula Magno Fernandez

    2008-08-01

    Full Text Available A Economia Feminista é um dos mais recentes programas de pesquisa em ciência econômica. Desde a publicação de Beyond Economic Man, organizado por Marianne Ferber e Julie Nelson,¹ ele vem se desenvolvendo com crescente força, sobretudo nos Estados Unidos. Entretanto, a pesquisa feminista, em geral, e a economia feminista, em particular, são freqüentemente consideradas como menos objetivas do que as pesquisas tradicionais, e isso porque estas últimas seriam livres de valores, enquanto as primeiras não. Após traçar algumas definições centrais da Economia Feminista, propomos, a partir do modelo crítico de Hugh Lacey,² que: i almejar a objetividade não significa defender uma metodologia isenta de influências valorativas, ii a neutralidade é (e deve ser defensável para o conjunto da prática científica e, finalmente, iii a defesa da pluralidade de abordagens científicas é o meio através do qual a neutralidade da ciência como uma prática social pode ser salvaguardada.Feminist Economics is one of the most recent research programs in economic science. Since the publication of Beyond Economic Man, edited by Ferber and Nelson (1993, it has been developed with increasing strength, especially in the United States. However, feminist researches in general and feminist economics in particular are often perceived to be less objective than conventional research, on the grounds that the latter would be value-neutral and the former would not. After drawing up some central definitions of Feminist Economics, we follow Hugh Lacey's critical model (1998, 1999 and propose that: i to aim for objectivity does not mean to defend a methodology that is free from axiological influences, ii neutrality is (and ought to be defensible for scientific practice as a whole, and finally, iii the defense of a plurality of scientific approaches is the way through which the neutrality of science as a social practice can be safeguarded.

  2. Dwarf-Galaxy Cosmology

    CERN Document Server

    Schulte-Ladbeck, Regina; Brinks, Elias; Kravtsov, Andrey

    2010-01-01

    Dwarf galaxies provide opportunities for drawing inferences about the processes in the early universe by observing our "cosmological backyard"-the Local Group and its vicinity. This special issue of the open-access journal Advances in Astronomy is a snapshot of the current state of the art of dwarf-galaxy cosmology.

  3. 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.)

  4. 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...

  5. 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.)

  6. The galaxy ancestor problem

    CERN Document Server

    Disney, Mike

    2011-01-01

    HST finds galaxies whose Tolman dimming should exceed 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 this 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 neighborhood easily today. Conversely the ancestors of the Milky Way and its obvious neighbors will have completely sunk below the sky at z>1.2 although their diffuse light could account for the missing Reionization flux. This Succeeding Prominent Dynasties Hypothesis (SPDH) fits the existing observations both naturally and well,including the bizarre distributions of galaxy surface brightnesses found in deep fields, the angular size ~ inverse (1+z) law,'Downsizing' which turn...

  7. Interacting Galaxies with MOND

    CERN Document Server

    Tiret, O

    2007-01-01

    We compare N-body simulations performed in MOND with analogs in Newtonian gravity with dark matter (DM). We have developed a code which solves the Poisson equation in both gravity models. It is a grid solver using adaptive mesh refinement techniques, allowing us to study isolated galaxies as well as interacting galaxies. Galaxies in MOND are found to form bars faster and stronger than in the DM model. In Newton dynamics, it is difficult to reproduce the observed high frequency of strong bars, while MOND appears to fit better the observations. Galaxy interactions and mergers, such as the Antennae, are also simulated with Newton and MOND dynamics. In the latter, dynamical friction is much weaker, and merging time-scales are longer. The formation of tidal dwarf galaxies in tidal tails are also compared in MOND and Newton+DM models.

  8. Faint Blue Galaxies

    CERN Document Server

    Ellis, Richard S

    1997-01-01

    The physical properties of the faint blue galaxy population are reviewed in the context of observational progress made via deep spectroscopic surveys and Hubble Space Telescope imaging of field galaxies at various limits, and theoretical models for the integrated star formation history of the Universe. Notwithstanding uncertainties in the properties of the local population of galaxies, convincing evidence has emerged from several independent studies for a rapid decline in the volume-averaged star formation rate of field galaxies since a redshift z~1. Together with the small angular sizes and modest mean redshift of the faintest detectable sources, these results can be understood in hierarchical models where the bulk of the star formation occurred at redshifts between z~1-2. The physical processes responsible for the subsequent demise of the faint blue galaxy population remains unclear. Considerable progress will be possible when the evolutionary trends can be monitored in the context of independent physical p...

  9. Galaxy Distribution in Clusters of Galaxies

    Science.gov (United States)

    Okamoto, T.; Yachi, S.; Habe, A.

    beta-discrepancy have been pointed out from comparison of optical and X-ray observations of clusters of galaxies. To examine physical reason of beta-discrepancy, we use N-body simulation which contains two components, dark particles and galaxies which are identified by using adaptive-linking friend of friend technique at a certain red-shift. The gas component is not included here, since the gas distribution follows the dark matter distribution in dark halos (Jubio F. Navarro, Carlos S. Frenk and Simon D. M. White 1995). We find that the galaxy distribution follows the dark matter distribution, therefore beta-discrepancy does not exist, and this result is consistent with the interpretation of the beta-discrepancy by Bahcall and Lubin (1994), which was based on recent observation.

  10. First LOFAR results on galaxy clusters

    CERN Document Server

    Ferrari, C; Bonafede, A; Bîrzan, L; Brüggen, M; Brunetti, G; Cassano, R; Conway, J; De Gasperin, F; Heald, G; Jackson, N; Macario, G; McKean, J; Offringa, A R; Orrù, E; Pizzo, R; Rafferty, D A; Röttgering, H J A; Shulevski, A; Tasse, C; van der Tol, S; van Weeren, R J; Wise, M; van Zwieten, J E

    2012-01-01

    Deep radio observations of galaxy clusters have revealed the existence of diffuse radio sources related to the presence of relativistic electrons and weak magnetic fields in the intracluster volume. The role played by this non-thermal intracluster component on the thermodynamical evolution of galaxy clusters is debated, with important implications for cosmological and astrophysical studies of the largest gravitationally bound structures of the Universe. The low surface brightness and steep spectra of diffuse cluster radio sources make them more easily detectable at low-frequencies. LOFAR is the first instrument able to detect diffuse radio emission in hundreds of massive galaxy clusters up to their formation epoch. We present the first observations of clusters imaged by LOFAR and the huge perspectives opened by this instrument for non-thermal cluster studies.

  11. Vibrational and Stochastic Resonance in the FitzHugh-Nagumo Neural Model with Multiplicative and Additive Noise

    Institute of Scientific and Technical Information of China (English)

    HE Zheng-You; ZHOU Yu-Rong

    2011-01-01

    The vibrational resonance and stochastic resonance phenomena in the FitzHugh-Nagumo (FHN) neural model,driven by a high-frequency (HF) signal and a low-frequency (LF) signal and by coupled multiplicative and additive noises,is investigated.For the case that the frequency of the HF signal is much higher than that of the LF signal,under the adiabatic approximation condition,the expression of the signal-to-noise ratio (SNR) with respect to the LF signal is obtained.It is shown that the SNR is a non-monotonous function of the amplitude and frequency of the HF signal In addition,the SNR varies non-monotonically with the increasing intensities of the multiplicative and additive noise as well as with the increasing system parameters of the FHN model The influence of the coupling strength between the multiplicative and additive noises on the SNR is discussed.Stochastic resonance (SR) describes the phenomenon where an appropriate amount of noise is of constructive use in the sense that a weak signal becomes amplified upon harvesting the ambient noise in nonlinear systems.[1] Since its first discovery in the early eighties,SR has been observed in a great variety of systems pertaining to different disciplines such as physics,chemistry,engineering,biology and biomedical sciences.[1-4] The phenomenon vibrational resonance (VR) was named by Landa and McClintock.[5]%The vibrational resonance and stochastic resonance phenomena in the FitzHugh-Nagumo (FHN) neural model, driven by a high-frequency (HF) signal and a low-frequency (LF) signal and by coupled multiplicative and additive noises, is investigated. For the case that the frequency of the HF signal is much higher than that of the LF signal, under the adiabatic approximation condition, the expression of the signal-to-noise ratio (SNR) with respect to the LF signal is obtained. It is shown that the SNR is a non-monotonous function of the amplitude and frequency of the HF signal. In addition, the SNR varies non

  12. 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

  13. The Cosmic Dance of Distant Galaxies

    Science.gov (United States)

    2006-03-01

    plane of a large number of optical fibres. This is done in such a way that each of them guides the light from one particular celestial object towards the spectrograph that records the spectra of all these objects simultaneously. The size of the available field-of-view is no less than about 25 arcmin across, i.e. almost as large as the full moon. The individual fibres are moved and positioned "on the objects" in the field by means of the OzPoz positioner. See also ESO PR 13/02. [3]: The results will be published in a series of three papers in the leading research journal, Astronomy and Astrophysics (click on the title to access the papers): "3D spectroscopy with VLT/GIRAFFE - I: The true Tully-Fisher relationship at z~ 0.6" (Flores H., Hammer F., Puech M. et al.); "3D spectroscopy with VLT/GIRAFFE - II: Are Luminous Compact Galaxies merger remnants?" (Puech M., Hammer F., Flores H. et al.); and "3D spectroscopy with VLT/GIRAFFE - III: Mapping electron densities in distant galaxies" (Puech M., Flores H., Hammer F. & Lehnert M.D.).

  14. WeirdestGalaxies: Outlier Detection Algorithm on Galaxy Spectra

    Science.gov (United States)

    Baron, Dalya; Poznanski, Dovi

    2017-05-01

    WeirdestGalaxies finds the weirdest galaxies in the Sloan Digital Sky Survey (SDSS) by using a basic outlier detection algorithm. It uses an unsupervised Random Forest (RF) algorithm to assign a similarity measure (or distance) between every pair of galaxy spectra in the SDSS. It then uses the distance matrix to find the galaxies that have the largest distance, on average, from the rest of the galaxies in the sample, and defined them as outliers.

  15. Active galaxies in a complete sample of isolated galaxies

    OpenAIRE

    Sabater, J.; Leon, S.; Verdes-Montenegro, L.; Bergond, G.; Carpio, J.; Combes, F.; Espada, D.; Garc??a, E.; Huchtmeier, W.; Lisenfeld, Ute; Santander-Vela, J. D.; Sulentic, J.; Verley, S.

    2006-01-01

    Galaxy evolution depends strongly on the environment, in particular, galaxy-galaxy interaction can induce nuclear activity by removing angular momentum from the gas so feeding the central black hole. Hence a higher rate of nuclear activity is expected in interacting galaxies. Different studies of this topic lead to contradictory results. Some works conclude that galaxies hosting an active galactic nuclei (AGN) have a higher rate of companions than non active ones. On the other hand other stud...

  16. Negative Resistance Circuit for Damping an Array of Coupled FitzHugh-Nagumo Oscillators

    DEFF Research Database (Denmark)

    Tamaševičius, Arūnas; Adomaitienė, Elena; Bumelienė, Skaidra;

    2015-01-01

    An analog circuit, based on a negative impedance converter and a capacitor, for damping oscillations in an array of mean-field coupled neuronal FitzHugh–Nagumo (FHN) type oscillators is described. The circuit is essentially a two-terminal feedback controller. When coupled to an array of the FHN o...... oscillators, it stabilizes their unstable steady states. Both, numerical simulations and hardware experiments with the analog electronic circuits have been performed. The results for an array, composed of three mean-field coupled FHN oscillators, are presented....

  17. Negative Resistance Circuit for Damping an Array of Coupled FitzHugh-Nagumo Oscillators

    DEFF Research Database (Denmark)

    Tamaševičius, Arūnas; Adomaitienė, Elena; Bumelienė, Skaidra

    2015-01-01

    An analog circuit, based on a negative impedance converter and a capacitor, for damping oscillations in an array of mean-field coupled neuronal FitzHugh–Nagumo (FHN) type oscillators is described. The circuit is essentially a two-terminal feedback controller. When coupled to an array of the FHN...... oscillators, it stabilizes their unstable steady states. Both, numerical simulations and hardware experiments with the analog electronic circuits have been performed. The results for an array, composed of three mean-field coupled FHN oscillators, are presented....

  18. Isolamento e caracterização de Pseudomonas maltophilia (Hugh & Ryschenkow, 1960 de material clínico humano, na cidade do Rio de Janeiro Isolating and characterization of Pseudomonas maltophilia (Hugh & Ryschenkow, 1960 from human clinical specimens, in Rio de Janeiro, Guanabara, Brazil

    Directory of Open Access Journals (Sweden)

    Altair A. Zebral

    1973-01-01

    Full Text Available Os autores estudaram as propriedades morfo-bioquímicas e a sensibilidade às substâncias antimicrobianas, de uma nova e rara espécie de Pseudomonas, a Pseudomonas maltophilia (Hugh & Ryschenkow, 1960, isolada de secração vaginal. Como características marcantes, dentre mais de 65 testadas, as amostras estudadas mostraram ser: oxidase negativa e lisina descarboxilase positiva; produziram desoxiribonuclease e um pigmento escuro que se difunde no meio; atacaram oxidativamente a maltose tanto em meio complexo nitrogenado como em meio de Hugh & Leifson e hidrolisaram a esculina. As amostras foram sensíveis ao cloranfenicol, gentamicina, kanamicina, colistin e gabromicina.The authors have studied the morpho-biochemical properties and the sensibility at antimicrobial drugs, of specie of Pseudomonas, the Pseudomonas maltophilia, (Hugh & Ryschenkow, 1960, isolated from vaginal secretion. Since important characteristics among more of sixty-five tested, the strains studied show to be: oxidase negative and lysine decarboxylase positive; to present deoxyrononuclease activity and produced a diffusible brown pigment: acid was produced by oxidation of maltose as much in nitrogenous complex medium as in Hugh & Leifson medium and they hydrolise the esculin. the strains was sensible, for the colistin chloranfenicol, gabromycin, gentamycin and nalidix acid.

  19. A Cluster and a Sea of Galaxies

    Science.gov (United States)

    2010-05-01

    of galaxies, and was integrated with an additional 1361 clusters in 1989. Abell put together this impressive collection by visual inspection of photographic plates of the sky, seeking those areas where more galaxies than average were found at approximately the same distance from us. [2] Ten percent of a galaxy cluster's mass consists of a very hot mixture of protons and electrons (a plasma), with temperatures as high as ten million degrees or more, which makes it visible to X-ray telescopes. [3] Astronomers refer to these slight distortions as weak gravitational lensing, as opposed to strong gravitational lensing, characterised by more spectacular phenomena such as giant arcs, rings and multiple images. [4] A weak lensing study of the galaxy cluster Abell 315 has been published in a paper that appeared in Astronomy & Astrophysics in 2009 ("Weak lensing observations of potentially X-ray underluminous galaxy clusters", by J. Dietrich et al.). [5] The blue, green or red tracks indicate that each asteroid has been detected through one of the three filters, respectively. Each track is composed of several, smaller sub-tracks, reflecting the sequence of several exposures performed in each of the filters; from the length of these sub-tracks, the distance to the asteroid can be calculated. More information ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world

  20. Fitz-Hugh-Curtis综合征的腹腔镜诊断及病原菌研究

    Institute of Scientific and Technical Information of China (English)

    姜海燕; 于宏艳; 殷丽华; 姚常晖

    2006-01-01

    Fitz-Hugh-Curtis综合征(FHCS)是盆腔炎合并肝周围炎,诊断需依据直视下观察肝表面和盆腔脏器的炎症表现,和(或)直接从肝表面、盆腔脏器表面检出病原菌,因此受条件限制有许多困难。我们充分利用腹腔镜的探查功能使本病的诊断变得容易。以往报道FHCS病原菌为淋球菌,随着沙眼衣原体感染的急剧增加,本病的报道亦日见增多,由此对其病原菌也提出了质疑。所以本研究拟用腹腔镜协助诊断FHCS及其病原菌,以指导临床诊断与治疗。

  1. Synchronization of coupled different chaotic FitzHugh-Nagumo neurons with unknown parameters under communication-direction-dependent coupling.

    Science.gov (United States)

    Iqbal, Muhammad; Rehan, Muhammad; Khaliq, Abdul; Saeed-ur-Rehman; Hong, Keum-Shik

    2014-01-01

    This paper investigates the chaotic behavior and synchronization of two different coupled chaotic FitzHugh-Nagumo (FHN) neurons with unknown parameters under external electrical stimulation (EES). The coupled FHN neurons of different parameters admit unidirectional and bidirectional gap junctions in the medium between them. Dynamical properties, such as the increase in synchronization error as a consequence of the deviation of neuronal parameters for unlike neurons, the effect of difference in coupling strengths caused by the unidirectional gap junctions, and the impact of large time-delay due to separation of neurons, are studied in exploring the behavior of the coupled system. A novel integral-based nonlinear adaptive control scheme, to cope with the infeasibility of the recovery variable, for synchronization of two coupled delayed chaotic FHN neurons of different and unknown parameters under uncertain EES is derived. Further, to guarantee robust synchronization of different neurons against disturbances, the proposed control methodology is modified to achieve the uniformly ultimately bounded synchronization. The parametric estimation errors can be reduced by selecting suitable control parameters. The effectiveness of the proposed control scheme is illustrated via numerical simulations.

  2. Synchronization of Coupled Different Chaotic FitzHugh-Nagumo Neurons with Unknown Parameters under Communication-Direction-Dependent Coupling

    Directory of Open Access Journals (Sweden)

    Muhammad Iqbal

    2014-01-01

    Full Text Available This paper investigates the chaotic behavior and synchronization of two different coupled chaotic FitzHugh-Nagumo (FHN neurons with unknown parameters under external electrical stimulation (EES. The coupled FHN neurons of different parameters admit unidirectional and bidirectional gap junctions in the medium between them. Dynamical properties, such as the increase in synchronization error as a consequence of the deviation of neuronal parameters for unlike neurons, the effect of difference in coupling strengths caused by the unidirectional gap junctions, and the impact of large time-delay due to separation of neurons, are studied in exploring the behavior of the coupled system. A novel integral-based nonlinear adaptive control scheme, to cope with the infeasibility of the recovery variable, for synchronization of two coupled delayed chaotic FHN neurons of different and unknown parameters under uncertain EES is derived. Further, to guarantee robust synchronization of different neurons against disturbances, the proposed control methodology is modified to achieve the uniformly ultimately bounded synchronization. The parametric estimation errors can be reduced by selecting suitable control parameters. The effectiveness of the proposed control scheme is illustrated via numerical simulations.

  3. Effect of spatially correlated noise on stochastic synchronization in globally coupled FitzHugh-Nagumo neuron systems

    Directory of Open Access Journals (Sweden)

    Yange Shao

    2014-01-01

    Full Text Available The phenomenon of stochastic synchronization in globally coupled FitzHugh-Nagumo (FHN neuron system subjected to spatially correlated Gaussian noise is investigated based on dynamical mean-field approximation (DMA and direct simulation (DS. Results from DMA are in good quantitative or qualitative agreement with those from DS for weak noise intensity and larger system size. Whether the consisting single FHN neuron is staying at the resting state, subthreshold oscillatory regime, or the spiking state, our investigation shows that the synchronization ratio of the globally coupled system becomes higher as the noise correlation coefficient increases, and thus we conclude that spatial correlation has an active effect on stochastic synchronization, and the neurons can achieve complete synchronization in the sense of statistics when the noise correlation coefficient tends to one. Our investigation also discloses that the noise spatial correlation plays the same beneficial role as the global coupling strength in enhancing stochastic synchronization in the ensemble. The result might be useful in understanding the information coding mechanism in neural systems.

  4. Pulse propagation and failure in the discrete FitzHugh-Nagumo model subject to high-frequency stimulation.

    Science.gov (United States)

    Ratas, Irmantas; Pyragas, Kestutis

    2012-10-01

    We investigate the effect of a homogeneous high-frequency stimulation (HFS) on a one-dimensional chain of coupled excitable elements governed by the FitzHugh-Nagumo equations. We eliminate the high-frequency term by the method of averaging and show that the averaged dynamics depends on the parameter A=a/ω equal to the ratio of the amplitude a to the frequency ω of the stimulating signal, so that for large frequencies an appreciable effect from the HFS is attained only at sufficiently large amplitudes. The averaged equations are analyzed by an asymptotic theory based on the different time scales of the recovery and excitable variables. As a result, we obtain the main characteristics of a propagating pulse as functions of the parameter A and derive an analytical criterion for the propagation failure. We show that depending on the parameter A, the HFS can either enhance or suppress pulse propagation and reveal the mechanism underlying these effects. The theoretical results are confirmed by numerical simulations of the original system with and without noise.

  5. 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

  6. Galaxy 'Hunting' Made Easy

    Science.gov (United States)

    2007-09-01

    Galaxies found under the Glare of Cosmic Flashlights Astronomers using ESO's Very Large Telescope have discovered in a single pass about a dozen otherwise invisible galaxies halfway across the Universe. The discovery, based on a technique that exploits a first-class instrument, represents a major breakthrough in the field of galaxy 'hunting'. ESO PR Photo 40a/07 ESO PR Photo 40a/07 Newly Found Galaxies (SINFONI/VLT) The team of astronomers led by Nicolas Bouché have used quasars to find these galaxies. Quasars are very distant objects of extreme brilliance, which are used as cosmic beacons that reveal galaxies lying between the quasar and us. The galaxy's presence is revealed by a 'dip' in the spectrum of the quasar - caused by the absorption of light at a specific wavelength. The team used huge catalogues of quasars, the so-called SDSS and 2QZ catalogues, to select quasars with dips. The next step was then to observe the patches of the sky around these quasars in search for the foreground galaxies from the time the Universe was about 6 billion years old, almost half of its current age. "The difficulty in actually spotting and seeing these galaxies stems from the fact that the glare of the quasar is too strong compared to the dim light of the galaxy," says Bouché. This is where observations taken with SINFONI on ESO's VLT made the difference. SINFONI is an infrared 'integral field spectrometer' that simultaneously delivers very sharp images and highly resolved colour information (spectra) of an object on the sky. ESO PR Photo 32e/07 ESO PR Photo 40b/07 Chasing 'Hidden' Galaxies (Artist's Impression) With this special technique, which untangles the light of the galaxy from the quasar light, the team detected 14 galaxies out of the 20 pre-selected quasar patches of sky, a hefty 70% success rate. "This high detection rate alone is a very exciting result," says Bouché. "But, these are not just ordinary galaxies: they are most notable ones, actively forming a lot of

  7. Accretion by the Galaxy

    Directory of Open Access Journals (Sweden)

    Binney J.

    2012-02-01

    Full Text Available Cosmology requires at least half of the baryons in the Universe to be in the intergalactic medium, much of which is believed to form hot coronae around galaxies. Star-forming galaxies must be accreting from their coronae. Hi observations of external galaxies show that they have Hi halos associated with star formation. These halos are naturally modelled as ensembles of clouds driven up by supernova bubbles. These models can fit the data successfully only if clouds exchange mass and momentum with the corona. As a cloud orbits, it is ablated and forms a turbulent wake where cold high-metallicity gas mixes with hot coronal gas causing the prompt cooling of the latter. As a consequence the total mass of Hi increases. This model has recently been used to model the Leiden-Argentina-Bonn survey of Galactic Hi. The values of the model’s parameters that are required to model NGC 891, NGC 2403 and our Galaxy show a remarkable degree of consistency, despite the very different natures of the two external galaxies and the dramatic difference in the nature of the data for our Galaxy and the external galaxies. The parameter values are also consistent with hydrodynamical simulations of the ablation of individual clouds. The model predicts that a galaxy that loses its cool-gas disc for instance through a major merger cannot reform it from its corona; it can return to steady star formation only if it can capture a large body of cool gas, for example by accreting a gas-rich dwarf. Thus the model explains how major mergers can make galaxies “red and dead.”

  8. 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 matt

  9. Evolution of galaxy habitability

    OpenAIRE

    Gobat, R.; Hong, S. E.

    2016-01-01

    We combine a semi-analytic model of galaxy evolution with constraints on circumstellar habitable zones and the distribution of terrestrial planets to probe the suitability of galaxies of different mass and type to host habitable planets, and how it evolves with time. We find that the fraction of stars with terrestrial planets in their habitable zone (known as habitability) depends only weakly on galaxy mass, with a maximum around 4e10 Msun. We estimate that 0.7% of all stars in Milky Way type...

  10. Executing SADI services in Galaxy.

    Science.gov (United States)

    Aranguren, Mikel Egaña; González, Alejandro Rodríguez; Wilkinson, Mark D

    2014-01-01

    In recent years Galaxy has become a popular workflow management system in bioinformatics, due to its ease of installation, use and extension. The availability of Semantic Web-oriented tools in Galaxy, however, is limited. This is also the case for Semantic Web Services such as those provided by the SADI project, i.e. services that consume and produce RDF. Here we present SADI-Galaxy, a tool generator that deploys selected SADI Services as typical Galaxy tools. SADI-Galaxy is a Galaxy tool generator: through SADI-Galaxy, any SADI-compliant service becomes a Galaxy tool that can participate in other out-standing features of Galaxy such as data storage, history, workflow creation, and publication. Galaxy can also be used to execute and combine SADI services as it does with other Galaxy tools. Finally, we have semi-automated the packing and unpacking of data into RDF such that other Galaxy tools can easily be combined with SADI services, plugging the rich SADI Semantic Web Service environment into the popular Galaxy ecosystem. SADI-Galaxy bridges the gap between Galaxy, an easy to use but "static" workflow system with a wide user-base, and SADI, a sophisticated, semantic, discovery-based framework for Web Services, thus benefiting both user communities.

  11. 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

  12. Galaxies and Cladistics

    CERN Document Server

    Fraix-Burnet, Didier

    2009-01-01

    The Hubble tuning fork diagram, based on morphology and established in the 1930s, has always been the preferred scheme for classification of galaxies. However, the current large amount of multiwavelength data, most often spectra, for objects up to very high distances, asks for more sophisticated statistical approaches. Interpreting formation and evolution of galaxies as a ?transmission with modification' process, we have shown that the concepts and tools of phylogenetic systematics can be heuristically transposed to the case of galaxies. This approach, which we call ?astrocladistics', has successfully been applied on several samples. Many difficulties still remain, some of them being specific to the nature of both galaxies and their diversification processes, some others being classical in cladistics, like the pertinence of the descriptors in conveying any useful evolutionary information.

  13. Collision Induced Galaxy Formation

    CERN Document Server

    Balland, C; Schäffer, R

    1997-01-01

    We present a semi-analytical model in which galaxy collisions and strong tidal interactions, both in the field and during the collapse phase of groups and clusters help determine galaxy morphology. From a semi-analytical analysis based on simulation results of tidal collisions (Aguilar & White 1985), we propose simple rules for energy exchanges during collisions that allow to discriminate between different Hubble types: efficient collisions result in the disruption of disks and substantial star formation, leading to the formation of elliptical galaxies; inefficient collisions allow a large gas reservoir to survive and form disks. Assuming that galaxy formation proceeds in a Omega_0=1 Cold Dark Matter universe, the model both reproduces a number of observations and makes predictions, among which are the redshifts of formation of the different Hubble types in the field. When the model is normalized to the present day abundance of X-ray clusters, the amount of energy exchange needed to produce elliptical gal...

  14. Galaxies and chaos

    CERN Document Server

    Voglis, Nikos

    2003-01-01

    Galaxies and Chaos examines the application of tools developed for Nonlinear Dynamical Systems to Galactic Dynamics and Galaxy Formation, as well as to related issues in Celestial Mechanics. The contributions collected in this volume have emerged from selected presentations at a workshop on this topic and key chapters have been suitably expanded in order to be accessible to nonspecialist researchers and postgraduate students wishing to enter this exciting field of research.

  15. SUPERLUMINOUS SPIRAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Ogle, Patrick M.; Lanz, Lauranne; Nader, Cyril; Helou, George, E-mail: ogle@ipac.caltech.edu [IPAC, California Institute of Technology, Mail Code 220-6, Pasadena, CA 91125 (United States)

    2016-02-01

    We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity L{sub r} = 8–14L* (4.3–7.5 × 10{sup 44} erg s{sup −1}). These super spiral galaxies are also giant and massive, with diameter D = 57–134 kpc and stellar mass M{sub stars} = 0.3–3.4 × 10{sup 11}M{sub ⊙}. We find 53 super spirals out of a complete sample of 1616 SDSS galaxies with redshift z < 0.3 and L{sub r} > 8L*. The closest example is found at z = 0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and Wide-field Infrared Survey Explorer colors are consistent with normal star-forming spirals on the blue sequence. However, the extreme masses and rapid SFRs of 5–65 M{sub ⊙} yr{sup −1} place super spirals in a sparsely populated region of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a diverse range of environments, from isolation to cluster centers. We find four super spiral galaxy systems that are late-stage major mergers—a possible clue to their formation. We suggest that super spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become massive lenticular galaxies after they are cut off from their gas supply and their disks fade.

  16. The Integral Sign Galaxy

    Science.gov (United States)

    Noll, Keith

    2007-07-01

    We will observe the unusual warped disk galaxy known as the Integral Sign Galaxy, UGC 3697, with a small two-position WFPC2 mosaic. Observations will be obtained in three broad band filters and the resulting image will be released on the 19th anniversary of the launch of the Hubble Space Telescope on ~April 24, 2009. Multidrizzled mosaics will be made available through the archive.

  17. Galaxy Formation and Evolution

    Science.gov (United States)

    Nagamine, Kentaro; Reddy, Naveen; Daddi, Emanuele; Sargent, Mark T.

    2016-07-01

    In this chapter, we discuss the current status of observational and computational studies on galaxy formation and evolution. In particular, a joint analysis of star-formation rates (SFRs), stellar masses, and metallicities of galaxies throughout cosmic time can shed light on the processes by which galaxies build up their stellar mass and enrich the environment with heavy elements. Comparison of such observations and the results of numerical simulations can give us insights on the physical importance of various feedback effects by supernovae and active galactic nuclei. In Sect. 1, we first discuss the primary methods used to deduce the SFRs, stellar masses, and (primarily) gas-phase metallicities in high-redshift galaxies. Then, we show how these quantities are related to each other and evolve with time. In Sect. 2, we further examine the distribution of SFRs in galaxies following the `Main Sequence' paradigm. We show how the so-called `starbursts' display higher specific SFRs and SF efficiencies by an order of magnitude. We use this to devise a simple description of the evolution of the star-forming galaxy population since z ˜3 that can successfully reproduce some of the observed statistics in the infrared (IR) wavelength. We also discuss the properties of molecular gas. In Sect. 3, we highlight some of the recent studies of high-redshift galaxy formation using cosmological hydrodynamic simulations. We discuss the physical properties of simulated galaxies such as luminosity function and escape fraction of ionizing photons, which are important statistics for reionization of the Universe. In particular the escape fraction of ionizing photons has large uncertainties, and studying gamma-ray bursts (which is the main topic of this conference) can also set observational constraints on this uncertain physical parameter as well as cosmic star formation rate density.

  18. Magnetic fields in ring galaxies

    CERN Document Server

    Moss, D; Silchenko, O; Sokoloff, D; Horellou, C; Beck, R

    2016-01-01

    Many galaxies contain magnetic fields supported by galactic dynamo action. However, nothing definitive is known about magnetic fields in ring galaxies. Here we investigate large-scale magnetic fields in a previously unexplored context, namely ring galaxies, and concentrate our efforts on the structures that appear most promising for galactic dynamo action, i.e. outer star-forming rings in visually unbarred galaxies. We use tested methods for modelling $\\alpha-\\Omega$ galactic dynamos, taking into account the available observational information concerning ionized interstellar matter in ring galaxies. Our main result is that dynamo drivers in ring galaxies are strong enough to excite large-scale magnetic fields in the ring galaxies studied. The variety of dynamo driven magnetic configurations in ring galaxies obtained in our modelling is much richer than that found in classical spiral galaxies. In particular, various long-lived transients are possible. An especially interesting case is that of NGC 4513 where th...

  19. Superluminous Spiral Galaxies

    CERN Document Server

    Ogle, Patrick M; Nader, Cyril; Helou, George

    2015-01-01

    We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity L_r=8-14L* (4.3-7.5E44 erg/s). These super spiral galaxies are also giant and massive, with diameter D=57-134 kpc and stellar mass M_stars=0.3-3.4E11 M_sun. We find 53 super spirals out of a complete sample of 1,616 SDSS galaxies with redshift z8L*. The closest example is found at z=0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the extreme masses and rapid SFRs of 5-65 M_sun/yr place super spirals in a sparsely populated region of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a diverse range of environments, from isolation to cluster centers. We find four super spiral galaxy systems that are late-stage major mergers--a possible clue to their formation. We su...

  20. Coma cluster of galaxies

    Science.gov (United States)

    1999-01-01

    Atlas Image mosaic, covering 34' x 34' on the sky, of the Coma cluster, aka Abell 1656. This is a particularly rich cluster of individual galaxies (over 1000 members), most prominently the two giant ellipticals, NGC 4874 (right) and NGC 4889 (left). The remaining members are mostly smaller ellipticals, but spiral galaxies are also evident in the 2MASS image. The cluster is seen toward the constellation Coma Berenices, but is actually at a distance of about 100 Mpc (330 million light years, or a redshift of 0.023) from us. At this distance, the cluster is in what is known as the 'Hubble flow,' or the overall expansion of the Universe. As such, astronomers can measure the Hubble Constant, or the universal expansion rate, based on the distance to this cluster. Large, rich clusters, such as Coma, allow astronomers to measure the 'missing mass,' i.e., the matter in the cluster that we cannot see, since it gravitationally influences the motions of the member galaxies within the cluster. The near-infrared maps the overall luminous mass content of the member galaxies, since the light at these wavelengths is dominated by the more numerous older stellar populations. Galaxies, as seen by 2MASS, look fairly smooth and homogeneous, as can be seen from the Hubble 'tuning fork' diagram of near-infrared galaxy morphology. Image mosaic by S. Van Dyk (IPAC).

  1. Searches For Primeval Galaxies

    CERN Document Server

    Collins, C A

    1998-01-01

    A primeval galaxy represents the earliest stages of a galaxy's life and as such provides clues to the early history of the Universe and the evolution of stars and galaxies. Over the last 20 years astronomers have been engaged in the quest to detect the faint signals from these objects, believed to lie at a distance comparable with the size of the Universe. A wide variety of observational techniques have been employed in this search, with astronomers eagerly awaiting each new generation of astronomical telescope or detector in the hope of finally solving the mystery to the origin of galaxies -- or at least placing new and interesting constraints. Until recently, primeval galaxies have eluded detection in these searches, however experiments over the last couple of years which use either 10m-class optical telescopes or state-of-the-art submillimetre array detectors, may hold the clue to the origin of structure as they have finally uncovered what appears to be a widespread population of young galaxies.

  2. Dissection of a Galaxy

    Science.gov (United States)

    2004-01-01

    Sometimes, the best way to understand how something works is to take it apart. The same is true for galaxies like NGC 300, which NASA's Spitzer Space Telescope has divided into its various parts. NGC 300 is a face-on spiral galaxy located 7.5 million light-years away in the southern constellation Sculptor. This false-color image taken by the infrared array camera on Spitzer readily distinguishes the main star component of the galaxy (blue) from its dusty spiral arms (red). The star distribution peaks strongly in the central bulge where older stars congregate, and tapers off along the arms where younger stars reside. Thanks to Spitzer's unique ability to sense the heat or infrared emission from dust, astronomers can now clearly trace the embedded dust structures within NGC 300's arms. When viewed at visible wavelengths, the galaxy's dust appears as dark lanes, largely overwhelmed by bright starlight. With Spitzer, the dust - in particular organic compounds called polycyclic aromatic hydrocarbons - can be seen in vivid detail (red). These organic molecules are produced, along with heavy elements, by the stellar nurseries that pepper the arms. The findings provide a better understanding of spiral galaxy mechanics and, in the future, will help decipher more distant galaxies, whose individual components cannot be resolved. This image was taken on Nov. 21, 2003 and is composed of photographs obtained at four wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red).

  3. Triple Scoop from Galaxy Hunter

    Science.gov (United States)

    2006-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 1Figure 2Figure 3 Silver Dollar Galaxy: NGC 253 (figure 1) Located 10 million light-years away in the southern constellation Sculptor, the Silver Dollar galaxy, or NGC 253, is one of the brightest spiral galaxies in the night sky. In this edge-on view from NASA's Galaxy Evolution Explorer, the wisps of blue represent relatively dustless areas of the galaxy that are actively forming stars. Areas of the galaxy with a soft golden glow indicate regions where the far-ultraviolet is heavily obscured by dust particles. Gravitational Dance: NGC 1512 and NGC 1510 (figure 2) In this image, the wide ultraviolet eyes of NASA's Galaxy Evolution Explorer show spiral galaxy NGC 1512 sitting slightly northwest of elliptical galaxy NGC 1510. The two galaxies are currently separated by a mere 68,000 light-years, leading many astronomers to suspect that a close encounter is currently in progress. The overlapping of two tightly wound spiral arm segments makes up the light blue inner ring of NGC 1512. Meanwhile, the galaxy's outer spiral arm is being distorted by strong gravitational interactions with NGC 1510. Galaxy Trio: NGC 5566, NGC 5560, and NGC 5569 (figure 3) NASA's Galaxy Evolution Explorer shows a triplet of galaxies in the Virgo cluster: NGC 5560 (top galaxy), NGC 5566 (middle galaxy), and NGC 5569 (bottom galaxy). The inner ring in NGC 5566 is formed by two nearly overlapping bright arms, which themselves spring from the ends of a central bar. The bar is not visible in ultraviolet because it consists of older stars or low mass stars that do not emit energy at ultraviolet wavelengths. The outer disk of NGC 5566 appears warped, and the disk of NGC 5560 is clearly disturbed. Unlike its galactic neighbors, the disk of NGC 5569 does not appear to have been distorted by any passing galaxies.

  4. Matching Supernovae to Galaxies

    Science.gov (United States)

    Kohler, Susanna

    2016-12-01

    One of the major challenges for modern supernova surveys is identifying the galaxy that hosted each explosion. Is there an accurate and efficient way to do this that avoids investing significant human resources?Why Identify Hosts?One problem in host galaxy identification. Here, the supernova lies between two galaxies but though the centroid of the galaxy on the right is closer in angular separation, this may be a distant background galaxy that is not actually near the supernova. [Gupta et al. 2016]Supernovae are a critical tool for making cosmological predictions that help us to understand our universe. But supernova cosmology relies on accurately identifying the properties of the supernovae including their redshifts. Since spectroscopic followup of supernova detections often isnt possible, we rely on observations of the supernova host galaxies to obtain redshifts.But how do we identify which galaxy hosted a supernova? This seems like a simple problem, but there are many complicating factors a seemingly nearby galaxy could be a distant background galaxy, for instance, or a supernovas host could be too faint to spot.The authors algorithm takes into account confusion, a measure of how likely the supernova is to be mismatched. In these illustrations of low (left) and high (right) confusion, the supernova is represented by a blue star, and the green circles represent possible host galaxies. [Gupta et al. 2016]Turning to AutomationBefore the era of large supernovae surveys, searching for host galaxies was done primarily by visual inspection. But current projects like the Dark Energy Surveys Supernova Program is finding supernovae by the thousands, and the upcoming Large Synoptic Survey Telescope will likely discover hundreds of thousands. Visual inspection will not be possible in the face of this volume of data so an accurate and efficient automated method is clearly needed!To this end, a team of scientists led by Ravi Gupta (Argonne National Laboratory) has recently

  5. GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Storm, Emma M.; Jeltema, Tesla E.; Profumo, Stefano [Department of Physics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)

    2012-08-20

    Star formation in galaxies is observed to be associated with gamma-ray emission, presumably from non-thermal processes connected to the acceleration of cosmic-ray nuclei and electrons. The detection of gamma rays from starburst galaxies by the Fermi Large Area Telescope (LAT) has allowed the determination of a functional relationship between star formation rate and gamma-ray luminosity. Since star formation is known to scale with total infrared (8-1000 {mu}m) and radio (1.4 GHz) luminosity, the observed infrared and radio emission from a star-forming galaxy can be used to quantitatively infer the galaxy's gamma-ray luminosity. Similarly, star-forming galaxies within galaxy clusters allow us to derive lower limits on the gamma-ray emission from clusters, which have not yet been conclusively detected in gamma rays. In this study, we apply the functional relationships between gamma-ray luminosity and radio and IR luminosities of galaxies derived by the Fermi Collaboration to a sample of the best candidate galaxy clusters for detection in gamma rays in order to place lower limits on the gamma-ray emission associated with star formation in galaxy clusters. We find that several clusters have predicted gamma-ray emission from star formation that are within an order of magnitude of the upper limits derived in Ackermann et al. based on non-detection by Fermi-LAT. Given the current gamma-ray limits, star formation likely plays a significant role in the gamma-ray emission in some clusters, especially those with cool cores. We predict that both Fermi-LAT over the course of its lifetime and the future Cerenkov Telescope Array will be able to detect gamma-ray emission from star-forming galaxies in clusters.

  6. Hypolipidemic and Antioxidant Effects of Malus toringoides (Rehd.) Hughes Leaves in High-Fat-Diet-Induced Hyperlipidemic Rats.

    Science.gov (United States)

    Huang, Shan; Liu, Haifeng; Meng, Ning; Li, Bin; Wang, Jule

    2017-03-01

    Malus toringoides (Rehd.) Hughes (MT) leaves are traditionally used as a medicine for treating or preventing cardiovascular disease in Tibet. In addition to the effect of this medicinal plant on thrombosis, we tested its effect on dyslipidemia in a hypolipidemic rat model. A total of 60 healthy Sprague-Dawley rats were randomly divided into six groups, as follows: normal control, model control, simvastatin groups, and MT low-, medium-, and high-dose groups. The normal controls were fed with a normal diet, whereas all other groups were fed with a high-fat diet. After 6 weeks, the high-fat diet had induced hyperlipidemia in the rats, which were then orally administered with different doses of MT leaf extract (50, 100, and 200 mg/kg) for an additional 6 weeks. Serum levels of total cholesterol (TC), triglycerides (TG), low- and high-density lipoprotein cholesterol (LDL-c and HDL-c, respectively), as well as the antioxidant capacity of glutathione peroxidase (GSHP-x), superoxide dismutase (SOD), and malondialdehyde (MDA) were measured at the end of the study. MT significantly reduced serum TC, TG, and LDL-c and increased the HDL-c content in MT-treated rats compared with the model group. These changes were dose dependent. MT treatment also significantly elevated the activity of SOD and GSHP-x, and decreased the serum levels of MDA compared with untreated hyperlipidemic rats, thereby increasing serum antioxidant capacity. In addition, MT reduced liver steatosis in hyperlipidemic rats. Overall, MT exerts considerable hypolipidemic and antioxidant properties.

  7. Mean-field description and propagation of chaos in networks of Hodgkin-Huxley and FitzHugh-Nagumo neurons.

    Science.gov (United States)

    Baladron, Javier; Fasoli, Diego; Faugeras, Olivier; Touboul, Jonathan

    2012-05-31

    We derive the mean-field equations arising as the limit of a network of interacting spiking neurons, as the number of neurons goes to infinity. The neurons belong to a fixed number of populations and are represented either by the Hodgkin-Huxley model or by one of its simplified version, the FitzHugh-Nagumo model. The synapses between neurons are either electrical or chemical. The network is assumed to be fully connected. The maximum conductances vary randomly. Under the condition that all neurons' initial conditions are drawn independently from the same law that depends only on the population they belong to, we prove that a propagation of chaos phenomenon takes place, namely that in the mean-field limit, any finite number of neurons become independent and, within each population, have the same probability distribution. This probability distribution is a solution of a set of implicit equations, either nonlinear stochastic differential equations resembling the McKean-Vlasov equations or non-local partial differential equations resembling the McKean-Vlasov-Fokker-Planck equations. We prove the well-posedness of the McKean-Vlasov equations, i.e. the existence and uniqueness of a solution. We also show the results of some numerical experiments that indicate that the mean-field equations are a good representation of the mean activity of a finite size network, even for modest sizes. These experiments also indicate that the McKean-Vlasov-Fokker-Planck equations may be a good way to understand the mean-field dynamics through, e.g. a bifurcation analysis.Mathematics Subject Classification (2000): 60F99, 60B10, 92B20, 82C32, 82C80, 35Q80.

  8. The SAMI Galaxy Survey: Shocks and Outflows in a normal star-forming galaxy

    CERN Document Server

    Ho, I-Ting; Dopita, Michael A; Medling, Anne M; Allen, J T; Bland-Hawthorn, Joss; Bloom, Jessica V; Bryant, Julia J; Croom, Scott M; Fogarty, L M R; Goodwin, Michael; Green, Andy W; Konstantopoulos, Iraklis S; Lawrence, Jon S; Owers, Matt S; Richards, Samuel; Sharp, Rob

    2014-01-01

    We demonstrate the feasibility and potential of using large integral field spectroscopic surveys to investigate the prevalence of galactic-scale outflows in the local Universe. Using integral field data from SAMI and the Wide Field Spectrograph, we study the nature of an isolated disk galaxy, SDSS J090005.05+000446.7 (z = 0.05386). In the integral field datasets, the galaxy presents skewed line profiles changing with position in the galaxy. The skewed line profiles are caused by different kinematic components overlapping in the line-of-sight direction. We perform spectral decomposition to separate the line profiles in each spatial pixel as combinations of (1) a narrow kinematic component consistent with HII regions, (2) a broad kinematic component consistent with shock excitation, and (3) an intermediate component consistent with shock excitation and photoionisation mixing. The three kinematic components have distinctly different velocity fields, velocity dispersions, line ratios, and electron densities. We m...

  9. How environment drives galaxy evolution: lessons learnt from satellite galaxies

    CERN Document Server

    Pasquali, A

    2015-01-01

    It is by now well established that galaxy evolution is driven by intrinsic and environmental processes, both contributing to shape the observed properties of galaxies. A number of early studies, both observational and theoretical, have shown that the star formation activity of galaxies depends on their environmental local density and also on galaxy hierarchy, i.e. centrals vs. satellites. In fact, contrary to their central (most massive) galaxy of a group/cluster, satellite galaxies are stripped of their gas and stars, and have their star formation quenched by their environment. Large galaxy surveys like SDSS now permit us to investigate in detail environment-driven transformation processes by comparing centrals and satellites. In this paper I summarize what we have so far learnt about environmental effects by analysing the observed properties of local central and satellite galaxies in SDSS, as a function of their stellar mass and the dark matter mass of their host group/cluster.

  10. Oxygen Abundance Measurements of SHIELD Galaxies

    CERN Document Server

    Haurberg, Nathalie C; Cannon, John M; Marshall, Melissa V

    2015-01-01

    We have derived oxygen abundances for 8 galaxies from the Survey of HI in Extremely Low-mass Dwarfs (SHIELD). The SHIELD survey is an ongoing study of very low-mass galaxies, with M$_{\\rm HI}$ between 10$^{6.5}$ and 10$^{7.5}$ M$_{\\odot}$, that were detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. H$\\alpha$ images from the WIYN 3.5m telescope show that these 8 SHIELD galaxies each possess one or two active star-forming regions which were targeted with long-slit spectral observations using the Mayall 4m telescope at KPNO. We obtained a direct measurement of the electron temperature by detection of the weak [O III] $\\lambda$4363 line in 2 of the HII regions. Oxygen abundances for the other HII regions were estimated using a strong-line method. When the SHIELD galaxies are plotted on a B-band luminosity-metallicity diagram they appear to suggest a slightly shallower slope to the relationship than normally seen. However, that offset is systematically reduced when the near-infrared luminosity is used ins...

  11. Galaxies et trous noirs supermassifs

    Science.gov (United States)

    Collin-Zahn, Suzy

    2016-08-01

    A few percents of galaxies are classified as « active ». An active galaxy is a galaxy whose nucleus emits more energy than the whole galaxy in the form of electromagnetic radiation, relativistic particles, or mechanical energy. It is activated by a supermassive black hole fueled by matter falling on it, whose characteristics (Eddington luminosity, spin) are recalled. The class includes quasars and Seyfert galaxies. All massive "non active" galaxies contain a supermassive black hole, but there is not enough matter in its environment so as the nucleus becomes luminous. Different items are considered in the paper : how supermassive black holes are fueled, the accretion disc, the jets and the winds, the unified model of active galaxies, how are determined the masses of supermassive black holes, and what is the relation between the evolution of galaxies and supermassive black holes.

  12. Tidal alignment of galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Blazek, Jonathan; Vlah, Zvonimir; Seljak, Uroš

    2015-08-01

    We develop an analytic model for galaxy intrinsic alignments (IA) based on the theory of tidal alignment. We calculate all relevant nonlinear corrections at one-loop order, including effects from nonlinear density evolution, galaxy biasing, and source density weighting. Contributions from density weighting are found to be particularly important and lead to bias dependence of the IA amplitude, even on large scales. This effect may be responsible for much of the luminosity dependence in IA observations. The increase in IA amplitude for more highly biased galaxies reflects their locations in regions with large tidal fields. We also consider the impact of smoothing the tidal field on halo scales. We compare the performance of this consistent nonlinear model in describing the observed alignment of luminous red galaxies with the linear model as well as the frequently used "nonlinear alignment model," finding a significant improvement on small and intermediate scales. We also show that the cross-correlation between density and IA (the "GI" term) can be effectively separated into source alignment and source clustering, and we accurately model the observed alignment down to the one-halo regime using the tidal field from the fully nonlinear halo-matter cross correlation. Inside the one-halo regime, the average alignment of galaxies with density tracers no longer follows the tidal alignment prediction, likely reflecting nonlinear processes that must be considered when modeling IA on these scales. Finally, we discuss tidal alignment in the context of cosmic shear measurements.

  13. Hyperluminous Infrared Galaxies

    CERN Document Server

    Rowan-Robinson, M

    1999-01-01

    (39) galaxies are now known, from follow-up of faint IRAS sources and from submm observations of high redshift AGN, with far infrared luminosities > 10^{13} Lo. 13 of these, which have been found in 60 or 850 mu surveys, form an important unbiased sub-sample. 12 have been found by comparison of 60 mu surveys with quasar or radio-galaxy catalogues, or from infrared surveys with colour selection biased towards AGN, while a further 14 have been found through submm observations of known high redshift AGN. In this paper I argue, on the basis of detailed modelling of the spectral energy distributions of hyperluminous galaxies with accurate radiative transfer models, and from evidence of high gas-mass in several cases, that the bulk of the emission from these galaxies at rest-frame wavelengths >= 50 mu is due to star formation. Even after correction for the effects of lensing, hyperluminous galaxies with emission peaking at rest-frame wavelengths >= 50 mu are therefore undergoing star-formation at rates > 1000 Mo/yr...

  14. Lopsided Spiral Galaxies

    CERN Document Server

    Jog, Chanda J

    2008-01-01

    The light distribution in the disks of many galaxies is non-axisymmetric or `lopsided' with a spatial extent much larger along one half of a galaxy than the other, as in M101. Recent near-IR observations show that lopsidedness is common. The stellar disks in nearly 30 % of galaxies have significant lopsidedness, greater than 10 % measured as the Fourier amplitude of the m=1 component normalized to the average value. This asymmetry is traced particularly well by the atomic hydrogen gas distribution lying in the outer parts. The lopsidedness also occurs in the nuclear regions, where the nucleus is offset with respect to the outer isophotes. The galaxies in a group environment show higher lopsidedness. The origin of lopsidedness could be due to the disk response to a tidally distorted halo, or via gas accretion. The lopsidedness has a large 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 fueling, merging of binary black...

  15. The Effects of the Ionizing Radiation Background on Galaxy Evolution

    CERN Document Server

    Hambrick, D Clay; Naab, Thorsten; Johansson, Peter H

    2009-01-01

    We find that the amount and nature of the assumed ionizing background can strongly affect galaxy formation and evolution. Galaxy evolution simulations typically incorporate an ultraviolet background which falls off rapidly above z=3; e.g., that of Haardt & Madau (1996). However, this decline may be too steep to fit the WMAP constraints on electron scattering optical depth or observations of intermediate redshift (z ~ 2-4) Ly-alpha forest transmission. As an alternative, we present simulations of the cosmological formation of individual galaxies with UV backgrounds that decline more slowly at high redshift: both a simple intensity rescaling and the background recently derived by Faucher-Giguere (2009), which softens the spectrum at higher redshifts. We also test an approximation of the X-ray background with a similar z-dependence. We find for the test galaxies that an increase in either the intensity or hardness of ionizing radiation generically pushes star formation towards lower redshifts: although overa...

  16. Galaxy Zoo Supernovae

    CERN Document Server

    Smith, A M; Sullivan, M; Lintott, C J; Nugent, P E; Botyanszki, J; Kasliwal, M; Quimby, R; Bamford, S P; Fortson, L F; Schawinski, K; Hook, I; Blake, S; Podsiadlowski, P; Joensson, J; Gal-Yam, A; Arcavi, I; Howell, D A; Bloom, J S; Jacobsen, J; Kulkarni, S R; Law, N M; Ofek, E O; Walters, R

    2010-01-01

    This paper presents the first results from a new citizen science project: Galaxy Zoo Supernovae. This proof of concept project uses members of the public to identify supernova candidates from the latest generation of wide-field imaging transient surveys. We describe the Galaxy Zoo Supernovae operations and scoring model, and demonstrate the effectiveness of this novel method using imaging data and transients from the Palomar Transient Factory (PTF). We examine the results collected over the period April-July 2010, during which nearly 14,000 supernova candidates from PTF were classified by more than 2,500 individuals within a few hours of data collection. We compare the transients selected by the citizen scientists to those identified by experienced PTF scanners, and find the agreement to be remarkable - Galaxy Zoo Supernovae performs comparably to the PTF scanners, and identified as transients 93% of the ~130 spectroscopically confirmed SNe that PTF located during the trial period (with no false positive iden...

  17. PEARS Emission Line Galaxies

    Science.gov (United States)

    Pirzkal, Nor; Rothberg, Barry; Ly, Chun; Rhoads, James E.; Malhotra, Sangeeta; Grogin, Norman A.; Dahlen, Tomas; Meurer, Gerhardt R.; Walsh, Jeremy; Hathi, Nimish P.; Cohen, Seth; Belini, Andrea; Holwerda, Benne W.; Straughn, Amber; Mechtley, Matthew

    2012-01-01

    We present a full analysis of the Probing Evolution And Reionization Spectroscopically (PEARS) slitless grism spectroscopic data obtained vl'ith the Advanced Camera for Surveys on HST. PEARS covers fields within both the Great Observatories Origins Deep Survey (GOODS) North and South fields, making it ideal as a random surveY of galaxies, as well as the availability of a wide variety of ancillary observations to support the spectroscopic results. Using the PEARS data we are able to identify star forming galaxies within the redshift volume 0 = 10(exp 9) Solar M decreases by an order of magnitude at z<=0.5 relative to the number at 0.5 < z < 0.9 in support of the argument for galaxy downsizing.

  18. Magnetic fields in galaxies

    CERN Document Server

    Beck, Rainer

    2013-01-01

    Most of the visible matter in the Universe is ionized, so that cosmic magnetic fields are quite easy to generate and due to the lack of magnetic monopoles hard to destroy. Magnetic fields have been measured in or around practically all celestial objects, either by in-situ measurements of spacecrafts or by the electromagnetic radiation of embedded cosmic rays, gas or dust. The Earth, the Sun, solar planets, stars, pulsars, the Milky Way, nearby galaxies, more distant (radio) galaxies, quasars and even intergalactic space in clusters of galaxies have significant magnetic fields, and even larger volumes of the Universe may be permeated by "dark" magnetic fields. Information on cosmic magnetic fields has increased enormously as the result of the rapid development of observational methods, especially in radio astronomy. In the Milky Way, a wealth of magnetic phenomena was discovered, which are only partly related to objects visible in other spectral ranges. The large-scale structure of the Milky Way's magnetic fie...

  19. Slowly cooking galaxies

    CERN Document Server

    Legrand, F

    1999-01-01

    Recent spectroscopic observations of IZw~18 have revealed homogeneous abundance throughout the galaxy and several observations of other starburst galaxies have shown no significant gradient or discontinuity in the abundance distributions within the HII regions. I thus concur with Tenorio-Tagle (1996) and Devost et al. (1997) that these observed abundance homogeneities cannot be produced by the material ejected from the stars formed in the current burst and result from a previous star formation episode. Metals ejected in the current burst of star formation remain most probably hidden in a hot phase and are undetectable using optical spectroscopy. Combining various observational facts, for instance the faint star formation rate observed in low surface brightness galaxies (van Zee et al., 1997), I propose that a low and continuous star formation rate occurring during quiescent phases between bursts is a non negligible source of new elements in the interstellar medium. Using a spectrophotometric and chemical evol...

  20. Transnational Relations Between The BBC And The WDR (1960-1969: The Central Roles Of Hugh Greene And Klaus Von Bismarck

    Directory of Open Access Journals (Sweden)

    Christian Potschka

    2012-11-01

    Full Text Available This paper addresses the relationship between the BBC Director-General Hugh Carleton Greene and the director of the West German Broadcasting Corporation (WDR Klaus von Bismarck between 1960 and 1969. The thrust of the article is to point out the great potential of evaluating interpersonal relationships and their contribution to European perspectives on television history. The research is situated within transnational television historiography and it argues that the relationship between the two key personalities is manifested in multiple interdependencies, exchanges, visits and correspondences that exemplify the long-term British impact on the German broadcasting system as well as the bilateral cordial relations between the BBC and the WDR.

  1. Galaxy Zoo Supernovae

    Science.gov (United States)

    Smith, A. M.; Lynn, S.; Sullivan, M.; Lintott, C. J.; Nugent, P. E.; Botyanszki, J.; Kasliwal, M.; Quimby, R.; Bamford, S. P.; Fortson, L. F.; Schawinski, K.; Hook, I.; Blake, S.; Podsiadlowski, P.; Jönsson, J.; Gal-Yam, A.; Arcavi, I.; Howell, D. A.; Bloom, J. S.; Jacobsen, J.; Kulkarni, S. R.; Law, N. M.; Ofek, E. O.; Walters, R.

    2011-04-01

    This paper presents the first results from a new citizen science project: Galaxy Zoo Supernovae. This proof-of-concept project uses members of the public to identify supernova candidates from the latest generation of wide-field imaging transient surveys. We describe the Galaxy Zoo Supernovae operations and scoring model, and demonstrate the effectiveness of this novel method using imaging data and transients from the Palomar Transient Factory (PTF). We examine the results collected over the period 2010 April-July, during which nearly 14 000 supernova candidates from the PTF were classified by more than 2500 individuals within a few hours of data collection. We compare the transients selected by the citizen scientists to those identified by experienced PTF scanners and find the agreement to be remarkable - Galaxy Zoo Supernovae performs comparably to the PTF scanners and identified as transients 93 per cent of the ˜130 spectroscopically confirmed supernovae (SNe) that the PTF located during the trial period (with no false positive identifications). Further analysis shows that only a small fraction of the lowest signal-to-noise ratio detections (r > 19.5) are given low scores: Galaxy Zoo Supernovae correctly identifies all SNe with ≥8σ detections in the PTF imaging data. The Galaxy Zoo Supernovae project has direct applicability to future transient searches, such as the Large Synoptic Survey Telescope, by both rapidly identifying candidate transient events and via the training and improvement of existing machine classifier algorithms. This publication has been made possible by the participation of more than 10 000 volunteers in the Galaxy Zoo Supernovae project ().

  2. Ring Around a Galaxy

    Science.gov (United States)

    1999-01-01

    Space Telescope Science Institute astronomers are giving the public chances to decide where to aim NASA's Hubble Space Telescope. Guided by 8,000 Internet voters, Hubble has already been used to take a close-up, multi-color picture of the most popular object from a list of candidates, the extraordinary 'polar-ring' galaxy NGC 4650A. Located about 130 million light-years away, NGC 4650A is one of only 100 known polar-ring galaxies. Their unusual disk-ring structure is not yet understood fully. One possibility is that polar rings are the remnants of colossal collisions between two galaxies sometime in the distant past, probably at least 1 billion years ago. What is left of one galaxy has become the rotating inner disk of old red stars in the center. Meanwhile, another smaller galaxy which ventured too close was probably severely damaged or destroyed. The bright bluish clumps, which are especially prominent in the outer parts of the ring, are regions containing luminous young stars, examples of stellar rebirth from the remnants of an ancient galactic disaster. The polar ring appears to be highly distorted. No regular spiral pattern stands out in the main part of the ring, and the presence of young stars below the main ring on one side and above on the other shows that the ring is warped and does not lie in one plane. Determining the typical ages of the stars in the polar ring is an initial goal of our Polar Ring Science Team that can provide a clue to the evolution of this unusual galaxy. The HST exposures were acquired by the Hubble Heritage Team, consisting of Keith Noll, Howard Bond, Carol Christian, Jayanne English, Lisa Frattare, Forrest Hamilton, Anne Kinney and Zolt Levay, and guest collaborators Jay Gallagher (University of Wisconsin-Madison), Lynn Matthews (National Radio Astronomy Observatory-Charlottesville), and Linda Sparke (University of Wisconsin-Madison).

  3. Galaxies & the universe

    CERN Document Server

    Homer, Charlene

    2007-01-01

    Get the big picture about Galaxies and our Universe. From the smallest particles of matter to the biggest star system, our universe is made up of all things that exist in space. Our resource takes you through the Milky Way Galaxy, Black Holes and Gravity, then on to Nebulae, Sources of Light and the Speed of Light, and finally to Quasars, the most distant objects in the universe. Written using simplified language and vocabulary, our resource presents science concepts in a way that makes them accessible to students and easier to understand. Comprised of reading passages, student activities for

  4. Galaxy alignments: An overview

    CERN Document Server

    Joachimi, Benjamin; Kitching, Thomas D; Leonard, Adrienne; Mandelbaum, Rachel; Schäfer, Björn Malte; Sifón, Cristóbal; Hoekstra, Henk; Kiessling, Alina; Kirk, Donnacha; Rassat, Anais

    2015-01-01

    The alignments between galaxies, their underlying matter structures, and the cosmic web constitute vital ingredients for a comprehensive understanding of gravity, the nature of matter, and structure formation in the Universe. We provide an overview on the state of the art in the study of these alignment processes and their observational signatures, aimed at a non-specialist audience. The development of the field over the past one hundred years is briefly reviewed. We also discuss the impact of galaxy alignments on measurements of weak gravitational lensing, and discuss avenues for making theoretical and observational progress over the coming decade.

  5. Galaxy S II

    CERN Document Server

    Gralla, Preston

    2011-01-01

    Unlock the potential of Samsung's outstanding smartphone with this jargon-free guide from technology guru Preston Gralla. You'll quickly learn how to shoot high-res photos and HD video, keep your schedule, stay in touch, and enjoy your favorite media. Every page is packed with illustrations and valuable advice to help you get the most from the smartest phone in town. The important stuff you need to know: Get dialed in. Learn your way around the Galaxy S II's calling and texting features.Go online. Browse the Web, manage email, and download apps with Galaxy S II's 3G/4G network (or create you

  6. Physical Coupling of Kazarian Galaxies with Surrounding Galaxies

    Science.gov (United States)

    Kazarian, M. A.; Martirosian, J. R.

    2003-04-01

    Results from a statistical study of Kazarian galaxies and the objects surrounding them are presented. It is shown that: (1) the sample of Kazarian galaxies up to 16m.0 is complete. (2) Roughly 35.7% of the Kazarian galaxies are members of clusters, 14.0% of groups, and 13.6% of binary systems, while 36.7% are single galaxies. (3) Of the 580 Kazarian galaxies, roughly 61.2% are infrared, 8.8% radio, and 2.8% x-ray sources. (4) The relative numbers of Kazarian galaxies for complete samples of I, R, and X in the different groups are systematically higher than the corresponding numbers for samples of all Kazarian galaxies.

  7. The high redshift galaxy population in hierarchical galaxy formation models

    CERN Document Server

    Kitzbichler, M G; Kitzbichler, Manfred G.; White, Simon D. M.

    2006-01-01

    We compare observations of the high redshift galaxy population to the predictions of the galaxy formation model of Croton et al. (2006). This model, implemented on the Millennium Simulation of the concordance LCDM cosmogony, introduces "radio mode" feedback from the central galaxies of groups and clusters in order to obtain quantitative agreement with the luminosity, colour, morphology and clustering properties of the low redshift galaxy population. Here we compare the predictions of this same model to the observed counts and redshift distributions of faint galaxies, as well as to their inferred luminosity and mass functions out to redshift 5. With the exception of the mass functions, all these properties are sensitive to modelling of dust obscuration. A simple but plausible treatment gives moderately good agreement with most of the data, although the predicted abundance of relatively massive (~M*) galaxies appears systematically high at high redshift, suggesting that such galaxies assemble earlier in this mo...

  8. Galaxy-galaxy Lensing: Dissipationless Simulations Versus the Halo Model

    CERN Document Server

    Mandelbaum, R; Seljak, U; Kravtsov, A V; Wechsler, R H; Mandelbaum, Rachel; Tasitsiomi, Argyro; Seljak, Uros; Kravtsov, Andrey V.; Wechsler, Risa H.

    2004-01-01

    Galaxy-galaxy lensing is a powerful probe of the relation between galaxies and dark matter halos, but its theoretical interpretation requires a careful modeling of various contributions, such as the contribution from central and satellite galaxies. For this purpose, a phenomenological approach based on the halo model has been developed, allowing for fast exploration of the parameter space of models. In this paper, we investigate the ability of the halo model to extract information from the g-g weak lensing signal by comparing it to high-resolution dissipationless simulations that resolve subhalos. We find that the halo model reliably determines parameters such as the host halo mass of central galaxies, the fraction of galaxies that are satellites, and their radial distribution inside larger halos. If there is a significant scatter present in the central galaxy host halo mass distribution, then the mean and median mass of that distribution can differ significantly from one another, and the halo model mass dete...

  9. Galaxy bachelors, couples, spouses: Star formation in interacting galaxies

    Science.gov (United States)

    Sun, Jing; Barger, Kathleen; Richstein, Hannah; SDSS-IV/MaNGA

    2017-01-01

    We investigate the star formation activity in three galaxy systems in different stages of interaction to determine how the environment of galaxies affects their star forming ability and potential. These systems include an isolated galaxy, a pair of interacting galaxies, and a pair of merging galaxies. All of the target galaxies in these systems have similar stellar masses and similar radii and are at similar redshifts. We trace the star formation activity over the past 1-2 Gyr using spatially and kinematically resolved H-alpha emission, H-alpha equivalent width, and 4000-Angstrom break maps. This work is based on data from the fourth-generation Sloan Digital Sky Survey (SDSS-IV)/Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), and is part of the Project No.0285 in SDSS-IV.

  10. Hughes Associates Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Olson, Brad [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2013-05-22

    This report focuses on the more limiting gasket material (neoprene and viton). The use of polymer based gasketing material has led the DOE to question whether the ducts will be able to maintain structural integrity during a fire.

  11. Centaurus A - The nearest active galaxy

    Science.gov (United States)

    Burns, J. O.; Price, R. M.

    1983-11-01

    Observed features of the active galaxy Centaurus A are described, and attention is given to the physical processes responsible for the two detected radio lobes. Data have been taken in visible, X ray, and radio wavelengths. Most of the radiation emitted has originated from the loss of energy by electrons through thermal processes in the interstellar gas, synchrotron radiation, and by randomly polarized atomic emission. Cen A displays features of both elliptical and spiral galaxies, with a dust lane in the middle of the ellipse holding hot, newly formed blue stars. Spectroscopic studies of the emission lines of hot gas in Cen A indicate that the source of excited gas is in the center of the galaxy. The radio region has a 2,700,000 light year extent, with a plasma jet directed from the center into the north radio lobe. X ray maps of Cen A suggest a black hole with a mass of a billion suns is the source of the jet. Electrons in the beam could be accelerated by shock waves, turbulence, or collisions with protons.

  12. Galaxy And Mass Assembly (GAMA) Blended Spectra Catalog: Strong Galaxy-Galaxy Lens and Occulting Galaxy Pair Candidates

    CERN Document Server

    Holwerda, B W; Alpaslan, M; Bauer, A; Bland-Hawthorn, J; Brough, S; Brown, M J I; Cluver, M E; Conselice, C; Driver, S P; Hopkins, A M; Jones, D H; Lopez-Sanchez, A R; Loveday, J; Meyer, M J; Moffett, A

    2015-01-01

    We present the catalogue of blended galaxy spectra from the Galaxy And Mass Assembly (GAMA) survey. These are cases where light from two galaxies are significantly detected in a single GAMA fibre. Galaxy pairs identified from their blended spectrum fall into two principal classes: they are either strong lenses, a passive galaxy lensing an emission-line galaxy; or occulting galaxies, serendipitous overlaps of two galaxies, of any type. Blended spectra can thus be used to reliably identify strong lenses for follow-up observations (high resolution imaging) and occulting pairs, especially those that are a late-type partly obscuring an early-type galaxy which are of interest for the study of dust content of spiral and irregular galaxies. The GAMA survey setup and its autoz automated redshift determination were used to identify candidate blended galaxy spectra from the cross-correlation peaks. We identify 280 blended spectra with a minimum velocity separation of 600 km/s, of which 104 are lens pair candidates, 71 e...

  13. Featured Image: Identifying Weird Galaxies

    Science.gov (United States)

    Kohler, Susanna

    2017-08-01

    Hoags Object, an example of a ring galaxy. [NASA/Hubble Heritage Team/Ray A. Lucas (STScI/AURA)]The above image (click for the full view) shows PanSTARRSobservationsof some of the 185 galaxies identified in a recent study as ring galaxies bizarre and rare irregular galaxies that exhibit stars and gas in a ring around a central nucleus. Ring galaxies could be formed in a number of ways; one theory is that some might form in a galaxy collision when a smaller galaxy punches through the center of a larger one, triggering star formation around the center. In a recent study, Ian Timmis and Lior Shamir of Lawrence Technological University in Michigan explore ways that we may be able to identify ring galaxies in the overwhelming number of images expected from large upcoming surveys. They develop a computer analysis method that automatically finds ring galaxy candidates based on their visual appearance, and they test their approach on the 3 million galaxy images from the first PanSTARRS data release. To see more of the remarkable galaxies the authors found and to learn more about their identification method, check out the paper below.CitationIan Timmis and Lior Shamir 2017 ApJS 231 2. doi:10.3847/1538-4365/aa78a3

  14. The Smallest AGN Host Galaxies

    CERN Document Server

    Greene, J E; Ho, L C

    2005-01-01

    We describe our efforts to study dwarf galaxies with active nuclei, whose black holes, with masses < 10^6 M_sun, provide the best current observational constraints on the mass distribution of primordial seed black holes. Although these low-mass galaxies do not necessarily contain classical bulges, Barth, Greene, & Ho (2005) show that their stellar velocity dispersions and black hole masses obey the same relation as more massive systems. In order to characterize the properties of the dwarf hosts without the glare of the active nucleus, we have compiled a complementary sample of narrow-line active galaxies with low-mass hosts. The host galaxy properties, both their structures and stellar populations, are consistent with the general properties of low-mass, blue galaxies from Sloan. The black holes in these galaxies are probably radiating close to their Eddington limits, suggesting we may have found Type 2 analogues of narrow-line Seyfert 1 galaxies.

  15. Formation of polar ring galaxies

    CERN Document Server

    Bournaud, F

    2003-01-01

    Polar ring galaxies are peculiar systems in which a gas rich, nearly polar ring surrounds an early-type or elliptical host galaxy. Two formation scenarios for these objects have been proposed: they are thought to form either in major galaxy mergers or by tidal accretion of the polar material from a gas rich donor galaxy. Both scenarios are studied through N-body simulations including gas dynamics and star formation. Constraints on physical parameters are drawn out, in order to determine which scenario is the most likely to occur. Polar ring galaxies from each scenario are compared with observations and we discuss whether the accretion scenario and the merging scenario account for observational properties of polar ring galaxies. The conclusion of this study is that the accretion scenario is both the most likely and the most supported by observations. Even if the merging scenario is rather robust, most polar ring galaxies are shown to be the result of tidal gas accretion events.

  16. Constraints on decaying dark matter from Fermi observations of nearby galaxies and clusters

    Energy Technology Data Exchange (ETDEWEB)

    Dugger, Leanna; Profumo, Stefano [Department of Astronomy and Department of Physics, University of California Berkeley, 601 Campbell Hall, Berkeley, CA (United States); Jeltema, Tesla E., E-mail: greentee01@gmail.com, E-mail: tesla@ucolick.org, E-mail: profumo@scipp.ucsc.edu [UCO/Lick Observatories, 1156 High St., Santa Cruz, CA 95064 (United States)

    2010-12-01

    We analyze the impact of Fermi gamma-ray observations (primarily non-detections) of selected nearby galaxies, including dwarf spheroidals, and of clusters of galaxies on decaying dark matter models. We show that the fact that galaxy clusters do not shine in gamma rays puts the most stringent limits available to-date on the lifetime of dark matter particles for a wide range of particle masses and decay final states. In particular, our results put strong constraints on the possibility of ascribing to decaying dark matter both the increasing positron fraction reported by PAMELA and the high-energy feature in the electron-positron spectrum measured by Fermi. Observations of nearby dwarf galaxies and of the Andromeda Galaxy (M31) do not provide as strong limits as those from galaxy clusters, while still improving on previous constraints in some cases.

  17. Constraints on Decaying Dark Matter from Fermi Observations of Nearby Galaxies and Clusters

    CERN Document Server

    Dugger, Leanna; Profumo, Stefano

    2010-01-01

    We analyze the impact of Fermi gamma-ray observations (primarily non-detections) of selected nearby galaxies, including dwarf spheroidals, and of clusters of galaxies on decaying dark matter models. We show that the fact that galaxy clusters do not shine in gamma rays puts the most stringent limits available to-date on the lifetime of dark matter particles for a wide range of particle masses and decay final states. In particular, our results rule out the possibility of ascribing to decaying dark matter both the increasing positron fraction reported by PAMELA and the high-energy feature in the electron-positron spectrum measured by Fermi. Observations of nearby dwarf galaxies and of the Andromeda Galaxy (M31) do not provide as strong constraints as those from galaxy clusters, while still improving on previous limits in some cases.

  18. Featured Image: Interacting Galaxies

    Science.gov (United States)

    Kohler, Susanna

    2017-06-01

    This beautiful image shows two galaxies, IC 2163 and NGC 2207, as they undergo a grazing collision 114 million light-years away. The image is composite, constructed from Hubble (blue), Spitzer (green), and ALMA (red) data. In a recent study, Debra Elmegreen (Vassar College) and collaborators used this ALMA data to trace the individual molecular clouds in the two interacting galaxies, identifying a total of over 200 clouds that each contain a mass of over a million solar masses. These clouds represent roughly half the molecular gas in the two galaxies total. Elmegreen and collaborators track the properties of these clouds and their relation to star-forming regions observed with Hubble. For more information about their observations, check out the paper linked below.A closer look at the ALMA observations for these galaxies, with the different emission regions labeled. Most of the molecular gas emission comes from the eyelids of IC 2163, and the nuclear ring and Feature i in NGC 2207. [Elmegreen et al. 2017]CitationDebra Meloy Elmegreen et al 2017 ApJ 841 43. doi:10.3847/1538-4357/aa6ba5

  19. Cosmography with Galaxy Clusters

    CERN Document Server

    Soares-Santos, M; La Barbera, F; Lopes, P A A; Annis, J

    2008-01-01

    In the present work we focus on future experiments using cluster abundance observations to constraint the Dark Energy equation of state parameter, w. To obtain tight constraints from this kind of experiment, a reliable sample of galaxy clusters must be obtained from deep and wide-field images. We therefore present the computational environment (2DPHOT) that allow us to build the galaxy catalog from the images and the Voronoi Tessellation cluster finding algorithm that we use to identify the galaxy clusters on those catalogs. To test our pipeline with data similar in quality to what will be gathered by future wide field surveys, we process images from the Deep fields obtained as part of the LEGACY Survey (four fields of one square degree each, in five bands, with depth up to r'=25). We test our cluster finder by determining the completeness and purity of the finder when applied to mock galaxy catalogs made for the Dark Energy Survey cluster finder comparison project by Risa Wechsler and Michael Busha. This pro...

  20. The Hooked Galaxy

    Science.gov (United States)

    2006-06-01

    Life is not easy, even for galaxies. Some indeed get so close to their neighbours that they get rather distorted. But such encounters between galaxies have another effect: they spawn new generations of stars, some of which explode. ESO's VLT has obtained a unique vista of a pair of entangled galaxies, in which a star exploded. Because of the importance of exploding stars, and particularly of supernovae of Type Ia [1], for cosmological studies (e.g. relating to claims of an accelerated cosmic expansion and the existence of a new, unknown, constituent of the universe - the so called 'Dark Energy'), they are a preferred target of study for astronomers. Thus, on several occasions, they pointed ESO's Very Large Telescope (VLT) towards a region of the sky that portrays a trio of amazing galaxies. MCG-01-39-003 (bottom right) is a peculiar spiral galaxy, with a telephone number name, that presents a hook at one side, most probably due to the interaction with its neighbour, the spiral galaxy NGC 5917 (upper right). In fact, further enhancement of the image reveals that matter is pulled off MCG-01-39-003 by NGC 5917. Both these galaxies are located at similar distances, about 87 million light-years away, towards the constellation of Libra (The Balance). ESO PR Photo 22/06 ESO PR Photo 22/06 The Hooked Galaxy and its Companion NGC 5917 (also known as Arp 254 and MCG-01-39-002) is about 750 times fainter than can be seen by the unaided eye and is about 40,000 light-years across. It was discovered in 1835 by William Herschel, who strangely enough, seems to have missed its hooked companion, only 2.5 times fainter. As seen at the bottom left of this exceptional VLT image, a still fainter and nameless, but intricately beautiful, barred spiral galaxy looks from a distance the entangled pair, while many 'island universes' perform a cosmic dance in the background. But this is not the reason why astronomers look at this region. Last year, a star exploded in the vicinity of the hook

  1. Outskirts of galaxies

    CERN Document Server

    Lee, Janice; Paz, Armando

    2017-01-01

    This book consists of invited reviews written by world-renowned experts on the subject of the outskirts of galaxies, an upcoming field which has been understudied so far. These regions are faint and hard to observe, yet hide a tremendous amount of information on the origin and early evolution of galaxies. They thus allow astronomers to address some of the most topical problems, such as gaseous and satellite accretion, radial migration, and merging. The book is published in conjunction with the celebration of the end of the four-year DAGAL project, an EU-funded initial training network, and with a major international conference on the topic held in March 2016 in Toledo. It thus reflects not only the views of the experts, but also the scientific discussions and progress achieved during the project and the meeting. The reviews in the book describe the most modern observations of the outer regions of our own Galaxy, and of galaxies in the local and high-redshift Universe. They tackle disks, haloes, streams, and a...

  2. Slowly cooking galaxies

    Science.gov (United States)

    Legrand, François

    2000-07-01

    Recent spectroscopic observations of IZw 18 have revealed homogeneous abundance throughout the galaxy and several observations of other starburst galaxies have shown no significant gradient or discontinuity in the abundance distributions within the H II regions. I thus concur with Tenorio-Tagle G., 1996, AJ 111, 1641 and Devost D., Roy J.R., Drissen L., 1997, ApJ 482, 765, that these observed abundance homogeneities cannot be produced by the material ejected from the stars formed in the current burst and result from a previous star-formation episode. Metals ejected in the current burst of star formation remain most probably hidden in a hot phase and are undetectable using optical spectroscopy. Combining various observational facts, for instance, the faint star-formation rate observed in low surface brightness galaxies, Van Zee L., Haynes M.P., Salzer J.J., Broeils A.H., 1997c, AJ 113, 1618. I propose that a low and continuous star-formation rate, occurring during quiescent phases between bursts, is a non negligible source of new elements in the interstellar medium. Using a spectrophotometric and chemical evolution model for galaxies, I investigated the star formation history IZw 18. I demonstrate that the continuous star formation scenario reproduces all the observed parameters of IZw 18. I discuss the consequences of such a quiet star-formation regime.

  3. The Faintest Galaxies

    NARCIS (Netherlands)

    Salvadori, Stefania; Ferrara, Andrea; Whalen, D; Bromm,; Yoshida, N

    2010-01-01

    We investigate the nature of ultra faint dwarf spheroidal galaxies (UF dSphs) in a general cosmological context, simultaneously accounting for various ``classical'' dSphs and Milky Way (MW) properties, including their metallicity distribution function (MDF). Our model successfully reproduces both

  4. Explosions during galaxy formation

    Directory of Open Access Journals (Sweden)

    Hugo Martel

    2001-01-01

    Full Text Available As an idealized model of the e ects of energy release by supernovae during galaxy formation, we consider an explosion at the center of a halo which forms at the intersection of laments in the plane of a cosmological pancake by gravitational instability during pancake collapse. Such halos resemble the virialized objects found in N{body simulations in a CDM universe and, therefore, serve as a convenient, scale{free test{bed model for galaxy formation. ASPH=P3M simulations reveal that such explosions are anisotropic. The energy and metals are channeled into the low density regions, away from the pancake plane. The pancake remains essentially undisturbed, even if the explosion is strong enough to blow away all the gas lo- cated inside the halo at the onset of the explosion and reheat the IGM surrounding the pancake. Infall quickly replenishes this ejected gas and gradually restores the gas fraction as the halo mass continues to grow. Estimates of the collapse epoch and SN energy{release for galaxies of di erent mass in the CDM model can re- late these results to scale{dependent questions of blow{out and blow{away and their implication for early IGM heating and metal enrichment and the creation of dark{matter{dominated dwarf galaxies.

  5. Galaxy Disks are Submaximal

    NARCIS (Netherlands)

    Bershady, Matthew A.; Martinsson, Thomas P. K.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A.

    2011-01-01

    We measure the contribution of galaxy disks to the overall gravitational potential of 30 nearly face-on intermediate-to-late-type spirals from the DiskMass Survey. The central vertical velocity dispersion of the disk stars (sigma(disk)(z,R=0)) is related to the maximum rotation speed (V-max) as sigm

  6. Radio Identifications of Markarian Galaxies and the Correlation between Radio and Far-Infrared Properties

    Institute of Scientific and Technical Information of China (English)

    Shao-Guang Luo; Xue-Bing Wu

    2005-01-01

    By checking DSS optical images and NVSS radio images, 782 Markarian galaxies were identified to be NVSS radio sources. A comparison of the radio luminosity at 1.4 GHz and the far-infrared (FIR) luminosity for 468 "normal"galaxies shows a tight correlation. Most of the Seyfert galaxies and quasars follow the radio-FIR relation deduced from the "normal" galaxy sample, but with a somewhat larger scatter. A total 167 Markarian galaxies, comprising 100 "normal"galaxies, 66 Seyfert galaxies and one quasar, have either excess radio emission or much lower FIR spectral index α(25μm, 60μm). These galaxies may be classified as "AGN-powered". For "normal" galaxies, the average q value (defined as the log ratio between FIR and radio luminosities) is 2.3. There seems a trend for q to slightly decrease with increasing radio luminosity. This may imply that the ongoing active star formation in galaxies with higher radio luminosities is more efficient in heating the cosmic-ray electrons.

  7. Discovering Teenage Galaxies

    Science.gov (United States)

    2007-11-01

    Staring for the equivalent of every night for two weeks at the same little patch of sky with ESO's Very Large Telescope, an international team of astronomers has found the extremely faint light from teenage galaxies billions of light years away. These galaxies, which the research team believes are the building blocks of normal galaxies like our Milky Way, had eluded detection for three decades, despite intensive searches. ESO PR Photo 52/07 ESO PR Photo 52/07 A 92-hour long spectrum Two-dimensional spectrum obtained in 92 hours of exposure time, showing the line emitter candidates. The quasar absorption lines are visible close to the centre of the image. The team, led by Martin Haehnelt of the University of Cambridge, UK, Michael Rauch and George Becker of the Observatories of the Carnegie Institution, USA, and Andy Bunker of the Anglo-Australian Observatory, reports their results in the 1 March 2008 issue of the Astrophysical Journal. "This is the first time that the sky has been searched to this depth and the unrivalled sensitivity of the picture taken with the VLT was key to succeeding," says Haehnelt. Experts have long speculated that galaxies like ours were created by the amalgamation of proto-galaxies early in the history of the Universe, but the light from these fragments was so faint that astronomers had struggled to prove they were there at all. Astronomers thought that the teenage galaxies must be out there because they were blocking part of the light from objects even further away in space. "Previous attempts have usually been frustrated by the difficulty of detecting extremely faint objects: the amount of time required even with an 8-metre class telescope like the VLT considerably exceeds typical observing time awards. We have thus exploited the periods of less good weather with the FORS2 spectrograph at the VLT, taking advantage of the service observing mode," says Becker. In service mode, ESO staff astronomers at Paranal are responsible for carrying

  8. Green valley galaxies

    Directory of Open Access Journals (Sweden)

    Salim S.

    2014-01-01

    Full Text Available The “green valley” is a wide region separating the blue and the red peaks in the ultraviolet-optical color magnitude diagram, first revealed using GALEX UV photometry. The term was coined by Christopher Martin (Caltech, in 2005. Green valley highlights the discriminating power of UV to very low relative levels of ongoing star formation, to which the optical colors, including u−r, are insensitive. It corresponds to massive galaxies below the star-forming, “main” sequence, and therefore represents a critical tool for the study of the quenching of star formation and its possible resurgence in otherwise quiescent galaxies. This article reviews the results pertaining to (predominantly disk morphology, structure, environment, dust content and gas properties of green valley galaxies in the local universe. Their relationship to AGN is also discussed. Attention is given to biases emerging from defining the “green valley” using optical colors. We review various evolutionary scenarios and we present evidence for a new one, the quasi-static view of the green valley, in which the majority (but not all of galaxies currently in the green valley were only partially quenched in the distant past and now participate in a slow cosmic decline of star formation, which also drives down the activity on the main sequence, presumably as a result of the dwindling accretion/cooling onto galaxy disks. This emerging synthetic picture is based on the findings from Fang et al. (2012, Salim et al. (2012 and Martin et al. (2007, as well as other results.

  9. Cosmological parameter constraints from galaxy-galaxy lensing and galaxy clustering with the SDSS DR7

    CERN Document Server

    Mandelbaum, Rachel; Baldauf, Tobias; Seljak, Uros; Hirata, Christopher M; Nakajima, Reiko; Reyes, Reinabelle; Smith, Robert E

    2012-01-01

    Recent studies have shown that the cross-correlation coefficient between galaxies and dark matter is very close to unity on scales outside a few virial radii of galaxy halos, independent of the details of how galaxies populate dark matter halos. This finding makes it possible to determine the dark matter clustering from measurements of galaxy-galaxy weak lensing and galaxy clustering. We present new cosmological parameter constraints based on large-scale measurements of spectroscopic galaxy samples from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). We generalise the approach of Baldauf et al. (2010) to remove small scale information (below 2 and 4 Mpc/h for lensing and clustering measurements, respectively), where the cross-correlation coefficient differs from unity. We derive constraints for three galaxy samples covering 7131 sq. deg., containing 69150, 62150, and 35088 galaxies with mean redshifts of 0.11, 0.28, and 0.40. We clearly detect scale-dependent galaxy bias for the more luminous galaxy...

  10. Detection of Gamma Rays from a Starburst Galaxy

    Science.gov (United States)

    Acero, F.; Aharonian, F.; Akhperjanian, A. G.; Anton, G.; Barres de Almeida, U.; Bazer-Bachi, A. R.; Becherini, Y.; Behera, B.; Bernlöhr, K.; Bochow, A.; Boisson, C.; Bolmont, J.; Borrel, V.; Brucker, J.; Brun, F.; Brun, P.; Bühler, R.; Bulik, T.; Büsching, I.; Boutelier, T.; Chadwick, P. M.; Charbonnier, A.; Chaves, R. C. G.; Cheesebrough, A.; Chounet, L.-M.; Clapson, A. C.; Coignet, G.; Dalton, M.; Daniel, M. K.; Davids, I. D.; Degrange, B.; Deil, C.; Dickinson, H. J.; Djannati-Ataï, A.; Domainko, W.; Drury, L. O.'C.; Dubois, F.; Dubus, G.; Dyks, J.; Dyrda, M.; Egberts, K.; Emmanoulopoulos, D.; Espigat, P.; Farnier, C.; Fegan, S.; Feinstein, F.; Fiasson, A.; Förster, A.; Fontaine, G.; Füßling, M.; Gabici, S.; Gallant, Y. A.; Gérard, L.; Gerbig, D.; Giebels, B.; Glicenstein, J. F.; Glück, B.; Goret, P.; Göring, D.; Hauser, D.; Hauser, M.; Heinz, S.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hoffmann, A.; Hofmann, W.; Hofverberg, P.; Hoppe, S.; Horns, D.; Jacholkowska, A.; de Jager, O. C.; Jahn, C.; Jung, I.; Katarzyński, K.; Katz, U.; Kaufmann, S.; Kerschhaggl, M.; Khangulyan, D.; Khélifi, B.; Keogh, D.; Klochkov, D.; Kluźniak, W.; Kneiske, T.; Komin, Nu.; Kosack, K.; Kossakowski, R.; Lamanna, G.; Lenain, J.-P.; Lohse, T.; Marandon, V.; Martineau-Huynh, O.; Marcowith, A.; Masbou, J.; Maurin, D.; McComb, T. J. L.; Medina, M. C.; Méhault, J.; Moderski, R.; Moulin, E.; Naumann-Godo, M.; de Naurois, M.; Nedbal, D.; Nekrassov, D.; Nicholas, B.; Niemiec, J.; Nolan, S. J.; Ohm, S.; Olive, J.-F.; Wilhelmi, E. de Oña; Orford, K. J.; Ostrowski, M.; Panter, M.; Arribas, M. Paz; Pedaletti, G.; Pelletier, G.; Petrucci, P.-O.; Pita, S.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raubenheimer, B. C.; Raue, M.; Rayner, S. M.; Reimer, O.; Renaud, M.; Rieger, F.; Ripken, J.; Rob, L.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Ruppel, J.; Sahakian, V.; Santangelo, A.; Schlickeiser, R.; Schöck, F. M.; Schwanke, U.; Schwarzburg, S.; Schwemmer, S.; Shalchi, A.; Sikora, M.; Skilton, J. L.; Sol, H.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Superina, G.; Szostek, A.; Tam, P. H.; Tavernet, J.-P.; Terrier, R.; Tibolla, O.; Tluczykont, M.; van Eldik, C.; Vasileiadis, G.; Venter, C.; Venter, L.; Vialle, J. P.; Vincent, P.; Vivier, M.; Völk, H. J.; Volpe, F.; Wagner, S. J.; Ward, M.; Zdziarski, A. A.; Zech, A.

    2009-11-01

    Starburst galaxies exhibit in their central regions a highly increased rate of supernovae, the remnants of which are thought to accelerate energetic cosmic rays up to energies of ~1015 electron volts. We report the detection of gamma rays—tracers of such cosmic rays—from the starburst galaxy NGC 253 using the High Energy Stereoscopic System (H.E.S.S.) array of imaging atmospheric Cherenkov telescopes. The gamma-ray flux above 220 billion electron volts is F = (5.5 ± 1.0stat ± 2.8sys) × 10-13 cm-2 s-1, implying a cosmic-ray density about three orders of magnitude larger than that in the center of the Milky Way. The fraction of cosmic-ray energy channeled into gamma rays in this starburst environment is five times as large as that in our Galaxy.

  11. Detection of gamma rays from a starburst galaxy.

    Science.gov (United States)

    Acero, F; Aharonian, F; Akhperjanian, A G; Anton, G; Barres de Almeida, U; Bazer-Bachi, A R; Becherini, Y; Behera, B; Bernlöhr, K; Bochow, A; Boisson, C; Bolmont, J; Borrel, V; Brucker, J; Brun, F; Brun, P; Bühler, R; Bulik, T; Büsching, I; Boutelier, T; Chadwick, P M; Charbonnier, A; Chaves, R C G; Cheesebrough, A; Chounet, L-M; Clapson, A C; Coignet, G; Dalton, M; Daniel, M K; Davids, I D; Degrange, B; Deil, C; Dickinson, H J; Djannati-Ataï, A; Domainko, W; Drury, L O'C; Dubois, F; Dubus, G; Dyks, J; Dyrda, M; Egberts, K; Emmanoulopoulos, D; Espigat, P; Farnier, C; Fegan, S; Feinstein, F; Fiasson, A; Förster, A; Fontaine, G; Füssling, M; Gabici, S; Gallant, Y A; Gérard, L; Gerbig, D; Giebels, B; Glicenstein, J F; Glück, B; Goret, P; Göring, D; Hauser, D; Hauser, M; Heinz, S; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hoffmann, A; Hofmann, W; Hofverberg, P; Hoppe, S; Horns, D; Jacholkowska, A; de Jager, O C; Jahn, C; Jung, I; Katarzyński, K; Katz, U; Kaufmann, S; Kerschhaggl, M; Khangulyan, D; Khélifi, B; Keogh, D; Klochkov, D; Kluźniak, W; Kneiske, T; Komin, Nu; Kosack, K; Kossakowski, R; Lamanna, G; Lenain, J-P; Lohse, T; Marandon, V; Martineau-Huynh, O; Marcowith, A; Masbou, J; Maurin, D; McComb, T J L; Medina, M C; Méhault, J; Moderski, R; Moulin, E; Naumann-Godo, M; de Naurois, M; Nedbal, D; Nekrassov, D; Nicholas, B; Niemiec, J; Nolan, S J; Ohm, S; Olive, J-F; de Oña Wilhelmi, E; Orford, K J; Ostrowski, M; Panter, M; Paz Arribas, M; Pedaletti, G; Pelletier, G; Petrucci, P-O; Pita, S; Pühlhofer, G; Punch, M; Quirrenbach, A; Raubenheimer, B C; Raue, M; Rayner, S M; Reimer, O; Renaud, M; Rieger, F; Ripken, J; Rob, L; Rosier-Lees, S; Rowell, G; Rudak, B; Rulten, C B; Ruppel, J; Sahakian, V; Santangelo, A; Schlickeiser, R; Schöck, F M; Schwanke, U; Schwarzburg, S; Schwemmer, S; Shalchi, A; Sikora, M; Skilton, J L; Sol, H; Stawarz, Ł; Steenkamp, R; Stegmann, C; Stinzing, F; Superina, G; Szostek, A; Tam, P H; Tavernet, J-P; Terrier, R; Tibolla, O; Tluczykont, M; van Eldik, C; Vasileiadis, G; Venter, C; Venter, L; Vialle, J P; Vincent, P; Vivier, M; Völk, H J; Volpe, F; Wagner, S J; Ward, M; Zdziarski, A A; Zech, A

    2009-11-20

    Starburst galaxies exhibit in their central regions a highly increased rate of supernovae, the remnants of which are thought to accelerate energetic cosmic rays up to energies of approximately 10(15) electron volts. We report the detection of gamma rays--tracers of such cosmic rays--from the starburst galaxy NGC 253 using the High Energy Stereoscopic System (H.E.S.S.) array of imaging atmospheric Cherenkov telescopes. The gamma-ray flux above 220 billion electron volts is F = (5.5 +/- 1.0(stat) +/- 2.8(sys)) x 10(-13) cm(-2) s(-1), implying a cosmic-ray density about three orders of magnitude larger than that in the center of the Milky Way. The fraction of cosmic-ray energy channeled into gamma rays in this starburst environment is five times as large as that in our Galaxy.

  12. X-Ray Emission from Star-Forming Galaxies - Signatures of Cosmic Rays and Magnetic Fields

    CERN Document Server

    Schober, Jennifer; Klessen, Ralf S

    2014-01-01

    The evolution of magnetic fields in galaxies is still an open problem in astrophysics. In nearby galaxies the far-infrared-radio correlation indicates the coupling between magnetic fields and star formation. The correlation arises from the synchrotron emission of cosmic ray electrons traveling through the interstellar magnetic fields. However, with an increase of the interstellar radiation field (ISRF), inverse Compton scattering becomes the dominant energy loss mechanism of cosmic ray electrons with a typical emission frequency in the X-ray regime. The ISRF depends on the one hand on the star formation rate and becomes stronger in starburst galaxies, and on the other hand increases with redshift due to the evolution of the cosmic microwave background. With a model for the star formation rate of galaxies, the ISRF, and the cosmic ray spectrum, we can calculate the expected X-ray luminosity resulting from the inverse Compton emission. Except for galaxies with an active galactic nucleus the main additional cont...

  13. Isolated Galaxies and Isolated Satellite Systems

    CERN Document Server

    Ann, H B; Choi, Yun-Young

    2009-01-01

    We search for isolated galaxies using a volume-limited sample of galaxies with 0.02r_{vir,nei} and \\rho <\\bar{\\rho} well segregates the CIG galaxies. We confirm the morphology conformity between the host and their satellites, which suggests importance of hydrodynamic interaction among galaxies within their virial radii in galaxy evolution.

  14. A pseudo-spectrum analysis of galaxy-galaxy lensing

    Science.gov (United States)

    Hikage, Chiaki; Oguri, Masamune

    2016-10-01

    We present the application of the pseudo-spectrum method to galaxy-galaxy lensing. We derive explicit expressions for the pseudo-spectrum analysis of the galaxy-shear cross-spectrum, which is the Fourier space counterpart of the stacked galaxy-galaxy lensing profile. The pseudo-spectrum method corrects observational issues such as the survey geometry, masks of bright stars and their spikes, and inhomogeneous noise, which distort the spectrum and also mix the E-mode and the B-mode signals. Using ray-tracing simulations in N-body simulations including realistic masks, we confirm that the pseudo-spectrum method successfully recovers the input galaxy-shear cross-spectrum. We also show that the galaxy-shear cross-spectrum has an excess covariance relative to the Gaussian covariance at small scales (k ≳ 1h Mpc-1) where the shot noise is dominated in the Gaussian approximation. We find that the excess is consistent with the expectation from the halo sample variance (HSV), which originates from the matter fluctuations at scales larger than the survey area. We apply the pseudo-spectrum method to the observational data of Canada-France-Hawaii Telescope Lensing survey shear catalogue and three different spectroscopic samples of Sloan Digital Sky Survey Luminous Red Galaxy, and Baryon Oscillation Spectroscopic Survey CMASS and LOWZ galaxies. The galaxy-shear cross-spectra are significantly detected at the level of 7-10σ using the analytic covariance with the HSV contribution included. We also confirm that the observed spectra are consistent with the halo model predictions with the halo occupation distribution parameters estimated from previous work. This work demonstrates the viability of galaxy-galaxy lensing analysis in the Fourier space.

  15. Reionization and Galaxy Formation in Warm Dark Matter Cosmologies

    NARCIS (Netherlands)

    Dayal, Pratika; Choudhury, Tirthankar Roy; Bromm, Volker; Pacucci, F.

    2017-01-01

    We compare model results from a semi-analytic (merger-tree based) framework for high-redshift (z ' 5 − 20) galaxy formation against reionization indicators, including the Planck electron scattering optical depth (τes) and the ionizing photon emissivity ( ˙nion), to shed light on the reionization his

  16. Reionization and Galaxy Formation in Warm Dark Matter Cosmologies

    NARCIS (Netherlands)

    Dayal, Pratika; Choudhury, Tirthankar Roy; Bromm, Volker; Pacucci, F.

    2017-01-01

    We compare model results from a semi-analytic (merger-tree based) framework for high-redshift (z ' 5 − 20) galaxy formation against reionization indicators, including the Planck electron scattering optical depth (τes) and the ionizing photon emissivity ( ˙nion), to shed light on the reionization

  17. Recent galaxy mergers and residual star formation of red sequence galaxies in galaxy clusters

    CERN Document Server

    Sheen, Yun-Kyeong; Ree, Chang H; Jaffé, Yara; Demarco, Ricardo; Treister, Ezequiel

    2016-01-01

    This study explored the GALEX ultraviolet (UV) properties of optical red sequence galaxies in 4 rich Abell clusters at z \\leq 0.1. In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV - r' colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV - r' \\leq 5), and that number was doubled (~ 72%) when using a generous criterion (NUV - r' \\leq 5.4). The trend was the same when we restricted the sample to galaxies within 0.5xR_{200}. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R_{200}. We performed a Dressler-Shectman test to check whether the RSF galaxies had any correlation with the sub-structures in ...

  18. Galaxy bias from galaxy-galaxy lensing in the DES Science Verification Data

    CERN Document Server

    Prat, J; Miquel, R; Kwan, J; Blazek, J; Bonnett, C; Amara, A; Bridle, S L; Clampitt, J; Crocce, M; Fosalba, P; Gaztanaga, E; Giannantonio, T; Hartley, W G; Jarvis, M; MacCrann, N; Percival, W J; Ross, A J; Sheldon, E; Zuntz, J; Abbott, T M C; Abdalla, F B; Annis, J; Benoit-Lévy, A; Bertin, E; Brooks, D; Burke, D L; Rosell, A Carnero; Kind, M Carrasco; Carretero, J; Castander, F J; da Costa, L N; DePoy, D L; Desai, S; Diehl, H T; Doel, P; Eifler, T F; Evrard, A E; Neto, A Fausti; Flaugher, B; Frieman, J; Gerdes, D W; Gruen, D; Gruendl, R A; Gutierrez, G; Honscheid, K; James, D J; Kuehn, K; Kuropatkin, N; Lahav, O; Lima, M; Marshall, J L; Melchior, P; Menanteau, F; Nord, B; Plazas, A A; Reil, K; Romer, A K; Roodman, A; Sanchez, E; Scarpine, V; Schubnell, M; Sevilla-Noarbe, I; Smith, R C; Soares-Santos, M; Sobreira, F; Suchyta, E; Swanson, M E C; Tarle, G; Thomas, D; Walker, A R

    2016-01-01

    We present a measurement of galaxy-galaxy lensing around a magnitude-limited ($i_{AB} < 22.5$) sample of galaxies selected from the Dark Energy Survey Science Verification (DES-SV) data. We split these lenses into three photometric-redshift bins from 0.2 to 0.8, and determine the product of the galaxy bias $b$ and cross-correlation coefficient between the galaxy and dark matter overdensity fields $r$ in each bin, using scales above 4 Mpc/$h$ comoving, where we find the linear bias model to be valid given our current uncertainties. We compare our galaxy bias results from galaxy-galaxy lensing with those obtained from galaxy clustering (Crocce et al. 2016) and CMB lensing (Giannantonio et al. 2016) for the same sample of galaxies, and find our measurements to be in good agreement with those in Crocce et al. (2016), while, in the lowest redshift bin ($z\\sim0.3$), they show some tension with the findings in Giannantonio et al. (2016). Our results are found to be rather insensitive to a large range of systemati...

  19. Galaxy Morphology - Halo Gas Connections

    CERN Document Server

    Kacprzak, G G; Steidel, C C; Kacprzak, Glenn G.; Churchill, Christopher W.; Steidel, Charles C.

    2005-01-01

    We studied a sample of 38 intermediate redshift MgII absorption-selected galaxies using (1) Keck/HIRES and VLT/UVES quasar spectra to measure the halo gas kinematics from MgII absorption profiles and (2) HST/WFPC-2 images to study the absorbing galaxy morphologies. We have searched for correlations between quantified gas absorption properties, and host galaxy impact parameters, inclinations, position angles, and quantified morphological parameters. We report a 3.2-sigma correlation between asymmetric perturbations in the host galaxy morphology and the MgII absorption equivalent width. We suggest that this correlation may indicate a connection between past merging and/or interaction events in MgII absorption-selected galaxies and the velocity dispersion and quantity of gas surrounding these galaxies.

  20. Black holes and galaxy formation

    CERN Document Server

    Propst, Raphael J

    2010-01-01

    Galaxies are the basic unit of cosmology. The study of galaxy formation is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning. The physics of galaxy formation is complicated because it deals with the dynamics of stars, thermodynamics of gas and energy production of stars. A black hole is a massive object whose gravitational field is so intense that it prevents any form of matter or radiation to escape. It is hypothesized that the most massive galaxies in the universe- "elliptical galaxies"- grow simultaneously with the supermassive black holes at their centers, giving us much stronger evidence that black holes control galaxy formation. This book reviews new evidence in the field.

  1. Galaxies appear simpler than expected

    CERN Document Server

    Disney, M J; Garcia-Appadoo, D A; West, A A; Dalcanton, J J; Cortese, L

    2008-01-01

    Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment, and feedback from supernova explosions and supermassive black holes. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular-momentum, baryon-fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free of optical selection effects, shows five independent correlations among six independent observables, despite having a wide range of properties. This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our dataset. Such a de...

  2. Supernova Feedback Keeps Galaxies Simple

    CERN Document Server

    Chakraborti, Sayan

    2011-01-01

    Galaxies evolve continuously under the influence of self-gravity, rotation, accretion, mergers and feedback. The currently favored cold dark matter cosmological framework, suggests a hierarchical process of galaxy formation, wherein the present properties of galaxies are decided by their individual histories of being assembled from smaller pieces. However, recent studies have uncovered surprising correlations among the properties of galaxies, to the extent of forming a one-parameter set lying on a single fundamental line. It has been argued in the literature that such simplicity is hard to explain within the paradigm of hierarchical galaxy mergers. One of the puzzling results, is the simple linear correlation between the neutral hydrogen mass and the surface area, implying that widely different galaxies share very similar neutral hydrogen surface densities. In this work we show that self-regulated star formation, driven by the competition between gravitational instabilities and mechanical feedback from supern...

  3. The Shocked POststarburst Galaxy Survey

    Science.gov (United States)

    Alatalo, Katherine A.; SPOGS Team

    2017-01-01

    Modern day galaxies are found to be in a bimodal distribution, both in terms of their morphologies, and in terms of their colors, and these properties are inter-related. In color space, there is a genuine dearth of intermediate colored galaxies, which has been taken to mean that the transition a galaxy undergoes to transform must be rapid. Given that this transformation is largely one-way (at z=0), identifying all initial conditions that catalyze it becomes essential. The Shocked POststarburst Galaxy Survey (http://www.spogs.org) is able to pinpoint transitioning galaxies at an earlier stage of transition than other traditional searches, possibly opening a new door to identifying new pathways over which galaxies transform from blue spirals to red ellipticals.

  4. Genesis of spiral galaxies

    CERN Document Server

    Kiselev, Valery V

    2013-01-01

    Enigmatic spiral structure of many galaxies and its huge orbital momentum originated due to the capture of lightweight bare black hole by gravity of heavy primordial gas cloud at large impact parameter. The rotating of black hole caused the formation of accretion disc from the cloud and the transfer of orbital momentum to the disc, while during the fall to the center of mass, the spiral trace of black hole in the disc did create the spiral front line of sound waves in the gas, that further evolved into the stellar spiral arms. This mechanism opens the way to study features of spiral galaxy formation, say, an influence and a significance of dark matter in this process.

  5. Molecules in galaxies

    CERN Document Server

    Omont, Alain

    2007-01-01

    The main achievements, current developments and prospects of molecular studies in external galaxies are reviewed. They are put in the context of the results of several decades of studies of molecules in local interstellar medium, their chemistry and their importance for star formation. CO observations have revealed the gross structure of molecular gas in galaxies. Together with other molecules, they are among the best tracers of star formation at galactic scales. Our knowledge about molecular abundances in various local galactic environments is progressing. They trace physical conditions and metallicity, and they are closely related to dust processes and large aromatic molecules. Major recent developments include mega-masers, and molecules in Active Galactic Nuclei; millimetre emission of molecules at very high redshift; and infrared H2 emission as tracer of warm molecular gas, shocks and photodissociation regions. The advent of sensitive giant interferometers from the centimetre to sub-millimetre range, espe...

  6. The Anatomy of Galaxies

    Science.gov (United States)

    D'Onofrio, Mauro; Rampazzo, Roberto; Zaggia, Simone; Longair, Malcolm S.; Ferrarese, Laura; Marziani, Paola; Sulentic, Jack W.; van der Kruit, Pieter C.; Laurikainen, Eija; Elmegreen, Debra M.; Combes, Françoise; Bertin, Giuseppe; Fabbiano, Giuseppina; Giovanelli, Riccardo; Calzetti, Daniela; Moss, David L.; Matteucci, Francesca; Djorgovski, Stanislav George; Fraix-Burnet, Didier; Graham, Alister W. McK.; Tully, Brent R.

    Just after WWII Astronomy started to live its "Golden Age", not differently to many other sciences and human activities, especially in the west side countries. The improved resolution of telescopes and the appearance of new efficient light detectors (e.g. CCDs in the middle eighty) greatly impacted the extragalactic researches. The first morphological analysis of galaxies were rapidly substituted by "anatomic" studies of their structural components, star and gas content, and in general by detailed investigations of their properties. As for the human anatomy, where the final goal was that of understanding the functionality of the organs that are essential for the life of the body, galaxies were dissected to discover their basic structural components and ultimately the mystery of their existence.

  7. Galaxy mapping the cosmos

    CERN Document Server

    Geach, James

    2014-01-01

    Each night, we are able to gaze up at the night sky and look at the thousands of stars that stretch to the end of our individual horizons. But the stars we see are only those that make up our own Milky Way galaxy-but one of hundreds of billions in the whole of the universe, each separated  by inconceivably huge tracts of empty space. In this book, astronomer James Geach tells the rich stories of both the evolution of galaxies and our ability to observe them, offering a fascinating history of how we've come to realize humanity's tiny place in the vast universe.             Taking us on a compel

  8. Quantitative analysis of spirality in elliptical galaxies

    CERN Document Server

    Dojcsak, Levente

    2013-01-01

    We use an automated galaxy morphology analysis method to quantitatively measure the spirality of galaxies classified manually as elliptical. The data set used for the analysis consists of 60,518 galaxy images with redshift obtained by the Sloan Digital Sky Survey (SDSS) and classified manually by Galaxy Zoo, as well as the RC3 and NA10 catalogues. We measure the spirality of the galaxies by using the Ganalyzer method, which transforms the galaxy image to its radial intensity plot to detect galaxy spirality that is in many cases difficult to notice by manual observation of the raw galaxy image. Experimental results using manually classified elliptical and S0 galaxies with redshift <0.3 suggest that galaxies classified manually as elliptical and S0 exhibit a nonzero signal for the spirality. These results suggest that the human eye observing the raw galaxy image might not always be the most effective way of detecting spirality and curves in the arms of galaxies.

  9. Structures in Galaxy Clusters

    CERN Document Server

    Escalera, E; Girardi, M; Giuricin, G; Mardirossian, F; Mazure, A; Mezzetti, M

    1993-01-01

    The analysis of the presence of substructures in 16 well-sampled clusters of galaxies suggests a stimulating hypothesis: Clusters could be classified as unimodal or bimodal, on the basis of to the sub-clump distribution in the {\\em 3-D} space of positions and velocities. The dynamic study of these clusters shows that their fundamental characteristics, in particular the virial masses, are not severely biased by the presence of subclustering if the system considered is bound.

  10. Nuclear spirals in galaxies

    OpenAIRE

    Maciejewski, Witold

    2006-01-01

    Recent high-resolution observations indicate that nuclear spirals are often present in the innermost few hundred parsecs of disc galaxies. My models show that nuclear spirals form naturally as a gas response to non-axisymmetry in the gravitational potential. Some nuclear spirals take the form of spiral shocks, resulting in streaming motions in the gas, and in inflow comparable to the accretion rates needed to power local Active Galactic Nuclei. Recently streaming motions of amplitude expected...

  11. Searching for metal-deficient emission-line galaxy candidates: the final sample of the SDSS DR12 galaxies

    Science.gov (United States)

    Guseva, N. G.; Izotov, Y. I.; Fricke, K. J.; Henkel, C.

    2017-03-01

    We present a spectroscopic study of metal-deficient dwarf galaxy candidates, selected from the SDSS DR12. The oxygen abundances were derived using the direct method in galaxies with the electron temperature-sensitive emission line [O iii]λ4363 Å measured with an accuracy better than 30%. The oxygen abundances for the remaining galaxies with larger uncertainties of the [O iii]λ4363 Å line fluxes were calculated using a strong-line semi-empirical method by Izotov and Thuan. The resulting sample consists of 287 low-metallicity candidates with oxygen abundances below 12 + log O/H = 7.65 including 23 extremely metal-deficient (XMD) candidates with 12 + log O/H ≤ 7.35. Ten out of sixteen XMDs known so far (or 60%) have been discovered by our team using the direct method. Three XMDs were found in the present study. We study relations between global parameters of low-metallicity galaxies, including absolute optical magnitudes, Hβ luminosities (or equivalently star formation rates), stellar masses, mid-infrared colours, and oxygen abundances. Low-metallicity and XMD galaxies strongly deviate to lower metallicities in L-Z, L(Hβ)-Z and M∗-Z diagrams than in relations obtained for large samples of low-redshift, star-forming galaxies with non-restricted metallicities. These less chemically evolved galaxies with stellar masses ≈106-108M⊙, Hβ luminosities ≈1038-1041 erg s-1, SFR ≈ 0.01-1.0 M⊙ yr-1, and sSFR 50 Gyr-1 have physical conditions which may be characteristic of high-redshift low-mass star-forming galaxies which are still awaiting discovery.

  12. Dark-ages reionization and galaxy formation simulation - III. Modelling galaxy formation and the epoch of reionization

    Science.gov (United States)

    Mutch, Simon J.; Geil, Paul M.; Poole, Gregory B.; Angel, Paul W.; Duffy, Alan R.; Mesinger, Andrei; Wyithe, J. Stuart B.

    2016-10-01

    We introduce MERAXES, a new, purpose-built semi-analytic galaxy formation model designed for studying galaxy growth during reionization. MERAXES is the first model of its type to include a temporally and spatially coupled treatment of reionization and is built upon a custom (100 Mpc)3 N-body simulation with high temporal and mass resolution, allowing us to resolve the galaxy and star formation physics relevant to early galaxy formation. Our fiducial model with supernova feedback reproduces the observed optical depth to electron scattering and evolution of the galaxy stellar mass function between z = 5 and 7, predicting that a broad range of halo masses contribute to reionization. Using a constant escape fraction and global recombination rate, our model is unable to simultaneously match the observed ionizing emissivity at z ≲ 6. However, the use of an evolving escape fraction of 0.05-0.1 at z ˜ 6, increasing towards higher redshift, is able to satisfy these three constraints. We also demonstrate that photoionization suppression of low-mass galaxy formation during reionization has only a small effect on the ionization history of the intergalactic medium. This lack of `self-regulation' arises due to the already efficient quenching of star formation by supernova feedback. It is only in models with gas supply-limited star formation that reionization feedback is effective at regulating galaxy growth. We similarly find that reionization has only a small effect on the stellar mass function, with no observationally detectable imprint at M* > 107.5 M⊙. However, patchy reionization has significant effects on individual galaxy masses, with variations of factors of 2-3 at z = 5 that correlate with environment.

  13. The Laniakea supercluster of galaxies

    OpenAIRE

    Tully, R. Brent; Courtois, Helene; Hoffman, Yehuda; Pomarède, Daniel

    2014-01-01

    Galaxies congregate in clusters and along filaments, and are missing from large regions referred to as voids. These structures are seen in maps derived from spectroscopic surveys that reveal networks of structure that are interconnected with no clear boundaries. Extended regions with a high concentration of galaxies are called 'superclusters', although this term is not precise. There is, however, another way to analyse the structure. If the distance to each galaxy from Earth is directly measu...

  14. The Automatic Galaxy Collision Software

    CERN Document Server

    Smith, Beverly J; Pfeiffer, Phillip; Perkins, Sam; Barkanic, Jason; Fritts, Steve; Southerland, Derek; Manchikalapudi, Dinikar; Baker, Matt; Luckey, John; Franklin, Coral; Moffett, Amanda; Struck, Curtis

    2009-01-01

    The key to understanding the physical processes that occur during galaxy interactions is dynamical modeling, and especially the detailed matching of numerical models to specific systems. To make modeling interacting galaxies more efficient, we have constructed the `Automatic Galaxy Collision' (AGC) code, which requires less human intervention in finding good matches to data. We present some preliminary results from this code for the well-studied system Arp 284 (NGC 7714/5), and address questions of uniqueness of solutions.

  15. Very high redshift radio galaxies

    Energy Technology Data Exchange (ETDEWEB)

    van Breugel, W.J.M., LLNL

    1997-12-01

    High redshift radio galaxies (HzRGs) provide unique targets for the study of the formation and evolution of massive galaxies and galaxy clusters at very high redshifts. We discuss how efficient HzRG samples ae selected, the evidence for strong morphological evolution at near-infracd wavelengths, and for jet-induced star formation in the z = 3 800 HzRG 4C41 17

  16. Star Formation in MUSCEL Galaxies

    Science.gov (United States)

    Young, Jason; Kuzio de Naray, Rachel; Wang, Sharon Xuesong

    2017-01-01

    We present preliminary star-formation histories for a subset of the low surface brightness (LSB) galaxies in the MUSCEL (MUltiwavelength observations of the Structure, Chemistry, and Evolution of LSB galaxies) program. These histories are fitted against ground-based IFU spectra in tandem with space-based UV and IR photometry. MUSCEL aims to use these histories along with kinematic analyses to determine the physical processes that have caused the evolution of LSB galaxies to diverge from their high surface brightness counterparts.

  17. Nonthermal Activity and Particle Acceleration in Clusters of Galaxies

    CERN Document Server

    Petrosyan, V

    2004-01-01

    Evidence for nonthermal activity in clusters of galaxies is well established from radio observations of synchrotron emission by relativistic electrons, and new windows (in EUV and Hard X-ray ranges) have provided more powerful tools for its investigation. The hard X-ray observations, notably from Coma, are summarized and results of a new RXTE observations of a high redshift cluster are presented. It is shown that the most likely emission mechanisms for these radiations is the inverse Compton scattering of the cosmic microwave background photons by the same electrons responsible for the radio radiation. Various scenarios for acceleration of the electrons are considered and it is shown that the most likely model is episodic acceleration by shocks or turbulence, presumably induced by merger activity, of high energy electrons injected into the intercluster medium by galaxies or active galactic nuclei.

  18. Investigating Dwarf Spiral Galaxies

    Science.gov (United States)

    Weerasooriya, Sachithra; Dunn, Jacqueline M.

    2017-01-01

    Several studies have proposed that dwarf elliptical / spheroidal galaxies form through the transformation of dwarf irregular galaxies. Early and late type dwarfs resemble each other in terms of their observed colors and light distributions (each can often be represented by exponential disks), providing reason to propose an evolutionary link between the two types. The existence of dwarf spirals has been largely debated. However, more and more recent studies are using the designation of dwarf spiral to describe their targets of interest. This project seeks to explore where dwarf spirals fit into the above mentioned evolutionary sequence, if at all. Optical colors will be compared between a sample of dwarf irregular, dwarf elliptical, and dwarf spiral galaxies. The dwarf irregular and dwarf elliptical samples have previously been found to overlap in both optical color and surface brightness profile shape when limiting the samples to their fainter members. A preliminary comparison including the dwarf spiral sample will be presented here, along with a comparison of available ultraviolet and near-infrared data. Initial results indicate a potential evolutionary link that merits further investigation.

  19. The Densest Galaxy

    CERN Document Server

    Strader, Jay; Forbes, Duncan; Fabbiano, Giuseppina; Romanowsky, Aaron; Brodie, Jean; Conroy, Charlie; Caldwell, Nelson; Pota, Vincenzo; Usher, Christopher; Arnold, Jacob

    2013-01-01

    We report the discovery of a remarkable ultra-compact dwarf galaxy around the massive Virgo elliptical galaxy NGC 4649 (M60), which we term M60-UCD1. With a dynamical mass of 2.0 x 10^8 M_sun but a half-light radius of only ~ 24 pc, M60-UCD1 is more massive than any ultra-compact dwarfs of comparable size, and is arguably the densest galaxy known in the local universe. It has a two-component structure well-fit by a sum of Sersic functions, with an elliptical, compact (r_h=14 pc; n ~ 3.3) inner component and a round, exponential, extended (r_h=49 pc) outer component. Chandra data reveal a variable central X-ray source with L_X ~ 10^38 erg/s that could be an active galactic nucleus associated with a massive black hole or a low-mass X-ray binary. Analysis of optical spectroscopy shows the object to be old (~> 10 Gyr) and of solar metallicity, with elevated [Mg/Fe] and strongly enhanced [N/Fe] that indicates light element self-enrichment; such self-enrichment may be generically present in dense stellar systems. T...

  20. Wide HI profile galaxies

    CERN Document Server

    Brosch, Noah; Zitrin, Adi

    2011-01-01

    We investigate the nature of objects in a complete sample of 28 galaxies selected from the first sky area fully covered by ALFALFA, being well-detected and having HI profiles wider than 550 km/s. The selection does not use brightness, morphology, or any other property derived from optical or other spectral bands. We investigate the degree of isolation, the morphology, and other properties gathered or derived from open data bases and show that some objects have wide HI profiles probably because they are disturbed or are interacting, or might be confused in the ALFALFA beam. We identify a sub-sample of 14 galaxies lacking immediate interacting neighbours and showing regular, symmetric, two-horned HI profiles that we propose as candidate high-mass disk systems (CHMDs). We measure the net-Halpha emission from the CHMDs and combine this with public multispectral data to model the global star formation (SF) properties of each galaxy. The Halpha observations show SFRs not higher than a few solar masses per year. Sim...

  1. Gaseous Galaxy Halos

    CERN Document Server

    Putman, M E; Joung, M R

    2012-01-01

    Galactic halo gas traces inflowing star formation fuel and feedback from a galaxy's disk and is therefore crucial to our understanding of galaxy evolution. In this review, we summarize the multi-wavelength observational properties and origin models of Galactic and low redshift spiral galaxy halo gas. Galactic halos contain multiphase gas flows that are dominated in mass by the ionized component and extend to large radii. The densest, coldest halo gas observed in neutral hydrogen (HI) is generally closest to the disk ( 10^5.5 K) and cold mode in simulations, with the compressed material close to the disk the coldest and densest, in agreement with observations. There is evidence in halo gas observations for radiative and mechanical feedback mechanisms, including escaping photons from the disk, supernova-driven winds, and a galactic fountain. Satellite accretion also leaves behind abundant halo gas. This satellite gas interacts with the existing halo medium, and much of this gas will become part of the diffuse h...

  2. ARCHANGEL: Galaxy Photometry System

    Science.gov (United States)

    Schombert, James

    2011-07-01

    ARCHANGEL is a Unix-based package for the surface photometry of galaxies. While oriented for large angular size systems (i.e. many pixels), its tools can be applied to any imaging data of any size. The package core contains routines to perform the following critical galaxy photometry functions: sky determinationframe cleaningellipse fittingprofile fittingtotal and isophotal magnitudes The goal of the package is to provide an automated, assembly-line type of reduction system for galaxy photometry of space-based or ground-based imaging data. The procedures outlined in the documentation are flux independent, thus, these routines can be used for non-optical data as well as typical imaging datasets. ARCHANGEL has been tested on several current OS's (RedHat Linux, Ubuntu Linux, Solaris, Mac OS X). A tarball for installation is available at the download page. The main routines are Python and FORTRAN based, therefore, a current installation of Python and a FORTRAN compiler are required. The ARCHANGEL package also contains Python hooks to the PGPLOT package, an XML processor and network tools which automatically link to data archives (i.e. NED, HST, 2MASS, etc) to download images in a non-interactive manner.

  3. Bondi accretion in early-type galaxies

    CERN Document Server

    Korol, V; Pellegrini, S

    2016-01-01

    Accretion onto central massive black holes in galaxies is often modelled with the Bondi solution. In this paper we study a generalization of the classical Bondi accretion theory, considering the additional effects of the gravitational potential of the host galaxy, and of electron scattering in the optically thin limit. We provide a general analysis of the bias in the estimates of the Bondi radius and mass accretion rate, when adopting as fiducial values for the density and temperature at infinity the values of these quantities measured at finite distance from the central black hole. We also give general formulae to compute the correction terms of the critical accretion parameter in relevant asymptotic regimes. A full analytical discussion is presented in the case of an Hernquist galaxy, when the problem reduces to the discussion of a cubic equation, therefore allowing for more than one critical point in the accretion structure. The results are useful for observational works (especially in the case of low-lumi...

  4. A multifrequency view of starburst galaxies

    CERN Document Server

    Becker, J K; Schoeneberg, S

    2011-01-01

    During the past few years, first observations of starburst galaxies at >GeV energies could be made with the Fermi Gamma-ray Space Telescope (GeV range) and Imaging Air Cherenkov Telescopes (TeV range). The two nearest starbursts, M82 and NGC253 were detected, and most recently, the detection of two starburst-Seyfert composites (NGC1068 and NGC4945) were reported. The emission for the two starbursts is best explained by hadronic interactions, and thus providing a first, unique opportunity to study the role of cosmic rays in galaxies. In this paper, the role of cosmic rays for the non-thermal component of galaxies is reviewed by discussing the entire non-thermal frequency range from radio emission to TeV energies. In particular, the interpretation of radio emission arising from electron synchrotron radiation is predicted to be correlated to TeV emission coming from interactions of accelerated hadrons. This is observed for the few objects known at TeV energies, but the correlation needs to be established with si...

  5. Stellar Populations of Shell Galaxies

    CERN Document Server

    Carlsten, S; Zenteno, A

    2016-01-01

    We present a study of the inner (out to $\\sim$1 R$_{\\mathrm{eff}}$) stellar populations of 9 shell galaxies. We derive stellar population parameters from long slit spectra by both analyzing the Lick indices of the galaxies and by fitting Single Stellar Population model spectra to the full galaxy spectra. The results from the two methods agree reasonably well. Many of the shell galaxies in our sample appear to have lower central $\\mathrm{Mg}_{2}$ index values than non-shell galaxies of the same central velocity dispersion, which is likely due to a past interaction event. Our shell galaxy sample shows a relation between central metallicity and velocity dispersion that is consistent with previous samples of non-shell galaxies. Analyzing the metallicity gradients in our sample, we find an average metallicity gradient of -0.16$\\pm$0.10 dex per decade in radius. We compare this with formation models to constrain the merging history of shell galaxies. We argue that our galaxies likely have undergone major mergers in...

  6. Satellite Luminosities in Galaxy Groups

    OpenAIRE

    Skibba, Ramin A.; Sheth, Ravi K.; Martino, Matthew C.

    2007-01-01

    Halo model interpretations of the luminosity dependence of galaxy clustering assume that there is a central galaxy in every sufficiently massive halo, and that this central galaxy is very different from all the others in the halo. The halo model decomposition makes the remarkable prediction that the mean luminosity of the non-central galaxies in a halo should be almost independent of halo mass: the predicted increase is about 20% while the halo mass increases by a factor of more than 20. In c...

  7. Executing SADI services in Galaxy

    OpenAIRE

    Egaña Aranguren, Mikel; Rodríguez González, Alejandro; Mark D. Wilkinson

    2014-01-01

    Background: In recent years Galaxy has become a popular workflow management system in bioinformatics, due to its ease of installation, use and extension. The availability of Semantic Web-oriented tools in Galaxy, however, is limited. This is also the case for Semantic Web Services such as those provided by the SADI project, i.e. services that consume and produce RDF. Here we present SADI-Galaxy, a tool generator that deploys selected SADI Services as typical Galaxy tools. Results: SADI-Ga...

  8. AGN feedback in galaxy formation

    CERN Document Server

    Antonuccio-Delogu, Vincenzo

    2010-01-01

    During the past decade, convincing evidence has been accumulated concerning the effect of active galactic nuclei (AGN) activity on the internal and external environment of their host galaxies. Featuring contributions from well-respected researchers in the field, and bringing together work by specialists in both galaxy formation and AGN, this volume addresses a number of key questions about AGN feedback in the context of galaxy formation. The topics covered include downsizing and star-formation time scales in massive elliptical galaxies, the connection between the epochs of supermassive black h

  9. Ginga observations of Seyfert galaxies

    Science.gov (United States)

    Awaki, H.; Koyama, K.

    1993-01-01

    We observed twenty-eight Seyfert 2 galaxies with the Japanese X-ray satellite, Ginga, and found Seyfert 2 galaxies, in general, have the X-ray spectral characteristics of obscured Seyfert 1 nuclei. This results agrees with the predictions from the Unified Seyfert model proposed by Antonucci and Miller. However, among the observed Seyfert 2 galaxies, there are a few galaxies with no evidence of an obscuration, contrary to the general predictions of the unified model. We note that type 2 active galactic nuclei (AGN) will contribute to the Cosmic Diffuse X-ray Background, if the unified Seyfert model can be extended to the far distant AGN such as quasars.

  10. Galaxies a very short introduction

    CERN Document Server

    Gribbin, John

    2008-01-01

    Galaxies: A Very Short Introduction explores the building blocks of the Universe. Standing like islands in space, each is made up of many hundreds of millions of stars in which the chemical elements are made, around which planets form, and where on at least one of those planets intelligent life has emerged. Our own galaxy, the Milky Way, is just one of several hundred million other galaxies. Yet it was only in the 1920s that we realised that there is more to the Universe. Since then, many exciting discoveries have been made about our own galaxy and about those beyond.

  11. Lopsidedness in dwarf irregular galaxies

    CERN Document Server

    Heller, A B; Almoznino, E; Van Zee, L; Salzer, J J; Heller, Ana B.; Brosch, Noah; Almoznino, Elchanan; Zee, Liese van; Salzer, John J.

    2000-01-01

    We quantify the amplitude of the lopsidedness, the azimuthal angular asymmetry index, and the concentration of star forming regions, as represented by the distribution of the H$\\alpha$ emission, in a sample of 78 late-type irregular galaxies. We bin the observed galaxies in two groups representing blue compact galaxies (BCDs) and low surface brightness dwarf galaxies (LSBs). The light distribution is analysed with a novel algorithm, which allows detection of details in the light distribution pattern. We find that while the asymmetry of the underlying continuum light, representing the older stellar generations, is relatively small, the H$\\alpha$ emission is very asymmetric and is correlated in position angle with the continuum light. We test a model of random star formation over the extent of a galaxy by simulating HII regions in artificial dwarf galaxies. The implication is that random star formation over the full extent of a galaxy may be generated in LSB dwarf-irregular galaxies but not in BCD galaxies.

  12. Star-forming galaxies in the infrared

    Science.gov (United States)

    Weedman, Daniel W.

    1988-01-01

    The infrared properties from IRAS of galaxy samples previously observed in the optical and ultraviolet are summarized in order to predict quantitatively the infrared fluxes corresponding to galaxies of given fluxes in other wavebands. An infrared luminosity function of galaxies is presented and used to predict galaxy counts and redshift ranges at the flux limits expected for SIRTF. Depending on the precise limit and whether or not galaxies evolve, SIRTF will see as many as 2200 galaxies/sq deg at 30 microns.

  13. Joint Analysis of Galaxy-Galaxy Lensing and Galaxy Clustering: Methodology and Forecasts for DES

    CERN Document Server

    Park, Y; Dodelson, S; Jain, B; Amara, A; Becker, M R; Bridle, S L; Clampitt, J; Crocce, M; Fosalba, P; Gaztanaga, E; Honscheid, K; Rozo, E; Sobreira, F; Sánchez, C; Wechsler, R H; Abbott, T; Abdalla, F B; Allam, S; Benoit-Lévy, A; Bertin, E; Brooks, D; Buckley-Geer, E; Burke, D L; Rosell, A Carnero; Kind, M Carrasco; Carretero, J; Castander, F J; da Costa, L N; DePoy, D L; Desai, S; Dietrich, J P; Gerdes, D W; Gruen, D; Gruendl, R A; Gutierrez, G; James, D J; Kent, S; Kuehn, K; Kuropatkin, N; Lima, M; Maia, M A G; Marshall, J L; Melchior, P; Miller, C J; Sanchez, E; Scarpine, V; Schubnell, M; Sevilla-Noarbe, I; Soares-Santos, M; Suchyta, E; Swanson, M E C; Tarle, G; Thaler, J; Vikram, V; Walker, A R; Weller, J; Zuntz, J

    2015-01-01

    The joint analysis of galaxy-galaxy lensing and galaxy clustering is a promising method for inferring the growth function of large scale structure. This analysis will be carried out on data from the Dark Energy Survey (DES), with its measurements of both the distribution of galaxies and the tangential shears of background galaxies induced by these foreground lenses. We develop a practical approach to modeling the assumptions and systematic effects affecting small scale lensing, which provides halo masses, and large scale galaxy clustering. Introducing parameters that characterize the halo occupation distribution (HOD), photometric redshift uncertainties, and shear measurement errors, we study how external priors on different subsets of these parameters affect our growth constraints. Degeneracies within the HOD model, as well as between the HOD and the growth function, are identified as the dominant source of complication, with other systematic effects sub-dominant. The impact of HOD parameters and their degen...

  14. Star Formation Activity of Barred Spiral Galaxies

    Science.gov (United States)

    Kim, Eunbin; Hwang, Ho Seong; Chung, Haeun; Lee, Gwang-Ho; Park, Changbom; Cervantes Sodi, Bernardo; Kim, Sungsoo S.

    2017-08-01

    We study the star formation activity of nearby galaxies with bars using a sample of late-type galaxies at 0.02≤slant z≤slant 0.05489 and {M}rmass and redshift distributions similar to barred galaxies. We find that the star formation activity of strongly barred galaxies probed by starburstiness, g-r, {NUV}-r, and mid-infrared [3.4]-[12] colors is, on average, lower than that of non-barred galaxies. However, weakly barred galaxies do not show such a difference between barred and non-barred galaxies. The amounts of atomic and molecular gas in strongly barred galaxies are smaller than those in non-barred galaxies, and the gas metallicity is higher in strongly barred galaxies than in non-barred galaxies. The gas properties of weakly barred galaxies again show no difference from those of non-barred galaxies. We stack the optical spectra of barred and non-barred galaxies in several mass bins and fit to the stacked spectra with a spectral fitting code, STARLIGHT. We find no significant difference in stellar populations between barred and non-barred galaxies for both strongly and weakly barred galaxies. Our results are consistent with the idea that the star formation activity of barred galaxies was enhanced in the past along with significant gas consumption, and is currently lower than or similar to that of non-barred galaxies. The past star formation enhancement depends on the strength of bars.

  15. Physical Conditions of the Interstellar Medium in Star-forming Galaxies at z1.5

    Science.gov (United States)

    Hayashi, Masao; Ly, Chun; Shimasaku, Kazuhiro; Motohara, Kentaro; Malkan, Matthew A.; Nagao, Tohru; Kashikawa, Nobunari; Goto, Ryosuke; Naito, Yoshiaki

    2015-01-01

    We present results from Subaru/FMOS near-infrared (NIR) spectroscopy of 118 star-forming galaxies at z approximately equal to 1.5 in the Subaru Deep Field. These galaxies are selected as [O II] lambda 3727 emitters at z approximately equal to 1.47 and 1.62 from narrow-band imaging. We detect H alpha emission line in 115 galaxies, [O III] lambda 5007 emission line in 45 galaxies, and H Beta, [N II] lambda 6584, and [S II]lambda lambda 6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O II] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate physical conditions of the interstellar medium in star-forming galaxies at z approximately equal to 1.5. We find a tight correlation between H alpha and [O II], which suggests that [O II] can be a good star formation rate (SFR) indicator for galaxies at z approximately equal to 1.5. The line ratios of H alpha / [O II] are consistent with those of local galaxies. We also find that [O II] emitters have strong [O III] emission lines. The [O III]/[O II] ratios are larger than normal star-forming galaxies in the local Universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O III]/[O II] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

  16. A modified FitzHugh-Nagumo model for cardiac instabilities: The replacement of a conductance variable with Ca current as a slow variable

    Science.gov (United States)

    Osaka, Motohisa

    2013-02-01

    The FitzHugh-Nagumo model of nerve conduction is also used as a model of cardiac excitability. We propose the replacement of a gating variable of the conductance of K+ current with Ca2+ current as a slow variable of the model, in which plays a key role in the cardiac action potential. Since ion currents conduct transversely as well as longitudinally through gap junctions between myocytes, particularly in ischemia, a respective diffusion term is involved to both equations of a fast variable and a slow variable. We show that only a small increase of a coefficient of the diffusion term of Ca2+ current may cause cardiac instabilities, which are presumed to cause breakup of conduction and finally a lethal arrhythmia, ventricular fibrillation. Particularly, these instabilities do not occur without the diffusion term of Ca2+ current.

  17. Galaxy Zoo: Chiral correlation function of galaxy spins

    CERN Document Server

    Slosar, Anze; Bamford, Steven; Lintott, Chris; Andreescu, Dan; Murray, Phil; Nichol, Robert; Raddick, M Jordan; Schawinski, Kevin; Szalay, Alex; Thomas, Daniel; Vandenberg, Jan

    2008-01-01

    Galaxy Zoo is the first study of nearby galaxies that contains reliable information about the spiral sense of rotation of galaxy arms for a sizeable number of galaxies. We measure the correlation function of spin chirality (the sense in which galaxies appear to be spinning) of face-on spiral galaxies in angular, real and projected spaces. Our results indicate a hint of positive correlation at separations less than ~0.5 Mpc at a statistical significance of 2-3 sigma. This is the first experimental evidence for chiral correlation of spins. Within tidal torque theory it indicates that the inertia tensors of nearby galaxies are correlated. This is complementary to the studies of nearby spin axis correlations that probe the correlations of the tidal field. Theoretical interpretation is made difficult by the small distances at which the correlations are detected, implying that substructure might play a significant role, and our necessary selection of face-on spiral galaxies, rather than a general volume-limited sam...

  18. Dependence of Barred Galaxy Fraction on Galaxy Properties and Environment

    CERN Document Server

    Lee, Gwang-Ho; Lee, Myung Gyoon; Choi, Yun-Young

    2011-01-01

    We investigate the dependence of occurrence of bars in galaxies on galaxy properties and environment. We use a volume-limited sample of 33,391 galaxies brighter than $M_{r}=-19.5+5$log$h$ at $0.02\\le z\\le0.05489$, drawn from the SDSS DR 7. We classify the galaxies into early and late types, and identify bars by visual inspection. Among 10,674 late-type galaxies with axis ratio $b/a>0.60$, we find 3,240 barred galaxies ($f_{bar}=30.4%$) which divide into 2,542 strong bars ($f_{SB1}=23.8%$) and 698 weak bars ($f_{SB2}=6.5%$). We find that $f_{SB1}$ increases as $u-r$ color becomes redder, and that it has a maximum value at intermediate velocity dispersion ($\\sigma\\simeq$150 km s$^{-1}$). This trend suggests that strong bars are dominantly hosted by intermediate-mass systems. Weak bars prefer bluer galaxies with lower mass and lower concentration. In the case of strong bars, their dependence on the concentration index appears only for massive galaxies with $\\sigma>150$ km s${}^{-1}$. We also find that $f_{bar}$ ...

  19. The 1000 Brightest HIPASS Galaxies Newly Cataloged Galaxies

    CERN Document Server

    Ryan-Weber, E; Staveley-Smith, L; Jerjen, H; Kraan-Korteweg, R C; Ryder, S D; Barnes, D G; De Blok, W J G; Kilborn, V A

    2002-01-01

    The HI Parkes All-Sky Survey (HIPASS) is a blind 21-cm survey for extragalactic neutral hydrogen, covering the whole southern sky. The HIPASS Bright Galaxy Catalog (BGC; Koribalski et al. 2002) is a subset of HIPASS and contains the 1000 HI-brightest (peak flux density) galaxies. Here we present the 138 HIPASS BGC galaxies, which had no redshift measured prior to the Parkes multibeam HI surveys. Of the 138 galaxies, 87 are newly cataloged. Newly cataloged is defined as no optical (or infrared) counterpart in the NASA/IPAC Extragalactic Database. Using the Digitized Sky Survey we identify optical counterparts for almost half of the newly cataloged galaxies, which are typically of irregular or magellanic morphological type. Several HI sources appear to be associated with compact groups or pairs of galaxies rather than an individual galaxy. The majority (57) of the newly cataloged galaxies lie within ten degrees of the Galactic Plane and are missing from optical surveys due to confusion with stars or dust extinc...

  20. Haro15: Is it actually a low metallicity galaxy?

    CERN Document Server

    Firpo, V; Hagele, G; Díaz, A I; Morrell, N

    2009-01-01

    We present a detailed study of the physical properties of the nebular material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperature), ionic and total chemical abundances of several atoms, reddening and ionization structure. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission line ratios (the eta and eta' plots) in different regions of the galaxy. Applying direct and empirical methods for abundance determination, we perform a comparative analysis between these regions.

  1. Magnetic fields in spiral galaxies

    Science.gov (United States)

    Beck, Rainer

    2015-12-01

    Radio synchrotron emission, its polarization and Faraday rotation of the polarization angle are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 \\upmu G) and in central starburst regions (50-100 \\upmu G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15 \\upmu G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the intergalactic medium.—Faraday rotation measures of the diffuse polarized radio emission from galaxy disks reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by mean-field dynamos. "Magnetic arms" between gaseous spiral arms may also be products of dynamo action, but need a stable spiral pattern to develop. Helically twisted field loops winding around spiral arms were found in two galaxies so far. Large-scale field reversals, like the one found in the Milky Way, could not yet be detected in external galaxies. In radio halos around edge-on galaxies, ordered magnetic fields with X-shaped patterns are observed. The origin and evolution of cosmic magnetic fields, in particular their first occurrence in young galaxies and their dynamical importance during galaxy evolution, will be studied with

  2. Local Environmental Dependence of Galaxy Properties in a Volume-Limited Sample of Main Galaxies

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Using a volume-limited sample of Main Galaxies from SDSS Data Release 5, we investigate the dependence of galaxy properties on local environment. For each galaxy, a local three-dimensional density is calculated. We find that the galaxy morphological type depends strongly on the local environment: galaxies in dense environments have predominantly early type morphologies. Galaxy colors have only a weak dependence on the environment. This puts an important constraint on the process of galaxy formation.

  3. VLA Discovers Giant Rings Around Galaxy Cluster

    Science.gov (United States)

    2006-11-01

    Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have discovered giant, ring-like structures around a cluster of galaxies. The discovery provides tantalizing new information about how such galaxy clusters are assembled, about magnetic fields in the vast spaces between galaxy clusters, and possibly about the origin of cosmic rays. Radio-Optical Image of Cluster Galaxy Cluster Abell 3376 (Radio/Optical) CREDIT: Joydeep Bagchi, IUCAA, NRAO/AUI/NSF Above, a combined radio/optical image shows the galaxy cluster Abell 3376 in visible light (blue) and radio (red) images. The giant radio arcs surrounding the cluster were discovered using the Very Large Array. The visible-light image is from the Digitized Sky survey. Below, an X-ray image of Abell 3376 made using the European Space Agency's XMM-Newton telescope shows a spectacular, bullet-shaped region of X-rays coming from gas heated to 60 million degrees Kelvin. The bullet shape results from the supersonic collision of a smaller smaller galaxy subcluster with the main body of the larger cluster. Click on images for larger version. X-Ray Image of Cluster Galaxy Cluster Abell 3376 (X-Ray) CREDIT: Joydeep Bagchi, IUCAA, ESA "These giant, radio-emitting rings probably are the result of shock waves caused by violent collisions of smaller groups of galaxies within the cluster," said Joydeep Bagchi, of the Inter-University Centre for Astronomy and Astrophysics in Pune, India, who led an international research team. The scientists reported their findings in the November 3 edition of the journal Science. The newly-discovered ring segments, some 6 million light-years across, surround a galaxy cluster called Abell 3376, more than 600 million light-years from Earth. They were revealed because fast-moving electrons emitted radio waves as they spiraled around magnetic field lines in intergalactic space. "Even from this large distance, the feeble radio waves were easily picked up by the VLA

  4. Galaxy Zoo: Mergers - Dynamical Models of Interacting Galaxies

    CERN Document Server

    Holincheck, Anthony J; Borne, Kirk; Fortson, Lucy; Lintott, Chris; Smith, Arfon M; Bamford, Steven; Keel, William C; Parrish, Michael

    2016-01-01

    The dynamical history of most merging galaxies is not well understood. Correlations between galaxy interaction and star formation have been found in previous studies, but require the context of the physical history of merging systems for full insight into the processes that lead to enhanced star formation. We present the results of simulations that reconstruct the orbit trajectories and disturbed morphologies of pairs of interacting galaxies. With the use of a restricted three-body simulation code and the help of Citizen Scientists, we sample 10^5 points in parameter space for each system. We demonstrate a successful recreation of the morphologies of 62 pairs of interacting galaxies through the review of more than 3 million simulations. We examine the level of convergence and uniqueness of the dynamical properties of each system. These simulations represent the largest collection of models of interacting galaxies to date, providing a valuable resource for the investigation of mergers. This paper presents the ...

  5. Separating intrinsic alignment and galaxy-galaxy lensing

    CERN Document Server

    Blazek, Jonathan; Seljak, Uros; Nakajima, Reiko

    2012-01-01

    The coherent physical alignment of galaxies is an important systematic for gravitational lensing studies as well as a probe of the physical mechanisms involved in galaxy formation and evolution. We develop a formalism for treating this intrinsic alignment (IA) in the context of galaxy-galaxy lensing, and present an improved method for measuring IA contamination, which can arise when sources physically associated with the lens are placed behind the lens due to photometric redshift scatter. We apply the technique to recent Sloan Digital Sky Survey (SDSS) measurements of Luminous Red Galaxy lenses and sources with photometric redshifts selected from the SDSS imaging data. Compared to previous measurements, this method has the advantage of being fully self-consistent in its treatment of the IA and lensing signals, solving for the two simultaneously. We find an IA signal consistent with zero, placing tight constraints on both the magnitude of the IA effect and its potential contamination to the lensing signal. Whi...

  6. Automatic quantitative morphological analysis of interacting galaxies

    CERN Document Server

    Shamir, Lior; Wallin, John

    2013-01-01

    The large number of galaxies imaged by digital sky surveys reinforces the need for computational methods for analyzing galaxy morphology. While the morphology of most galaxies can be associated with a stage on the Hubble sequence, morphology of galaxy mergers is far more complex due to the combination of two or more galaxies with different morphologies and the interaction between them. Here we propose a computational method based on unsupervised machine learning that can quantitatively analyze morphologies of galaxy mergers and associate galaxies by their morphology. The method works by first generating multiple synthetic galaxy models for each galaxy merger, and then extracting a large set of numerical image content descriptors for each galaxy model. These numbers are weighted using Fisher discriminant scores, and then the similarities between the galaxy mergers are deduced using a variation of Weighted Nearest Neighbor analysis such that the Fisher scores are used as weights. The similarities between the ga...

  7. Empirical ugri-UBVRc Transformations for Galaxies

    CERN Document Server

    Cook, David O; Johnson, Benjamin D; Van Zee, Liese; Lee, Janice C; Kennicutt, Robert C; Calzetti, Daniela; Staudaher, Shawn M; Engelbracht, Charles W

    2014-01-01

    We present empirical color transformations between Sloan Digital Sky Survey ugri and Johnson-Cousins UBVRc photometry for nearby galaxies (D < 11 Mpc). We use the Local Volume Legacy (LVL) galaxy sample where there are 90 galaxies with overlapping observational coverage for these two filter sets. The LVL galaxy sample consists of normal, non-starbursting galaxies. We also examine how well the LVL galaxy colors are described by previous transformations derived from standard calibration stars and model-based galaxy templates. We find significant galaxy color scatter around most of the previous transformation relationships. In addition, the previous transformations show systematic offsets between transformed and observed galaxy colors which are visible in observed color-color trends. The LVL-based $galaxy$ transformations show no systematic color offsets and reproduce the observed color-color galaxy trends.

  8. The Nearby Field Galaxy Survey a spectrophotometric and photometric study of nearby galaxies

    CERN Document Server

    Jansen, R A

    2001-01-01

    We report on our observing program to obtain integrated spectrophotometry, intermediate and high resolution major axis spectra, and U,B,R surface photo- metry of a representative sample of ~200 galaxies in the nearby field. The main goal of this program is to provide a comparison sample for high redshift studies and to study the variation in star formation rates (SFR), star forma- tion history (SFH), excitation, metallicity, and internal kinematics over a large range in galaxy luminosity and morphological type. In particular, we extend the work of Kennicutt (1992) to lower luminosity systems. We present the main results of our analysis sofar. In these proceedings, we condense the presented two atlases of (1) images and radial surface brightness profiles and color profiles, and (2) of images and integrated spectra into several example images, profiles and spectra, showing the general trends observed. For the original atlasses we refer to the electronic version, available at http://www.astro.rug.nl/~nfgs/ .

  9. Dust tori in radio galaxies

    NARCIS (Netherlands)

    van der Wolk, G.; Barthel, P. D.; Peletier, R. F.; Pel, J. W.

    2010-01-01

    Aims: We investigate the quasar - radio galaxy unification scenario and detect dust tori within radio galaxies of various types. Methods: Using VISIR on the VLT, we acquired sub-arcsecond (~0.40 arcsec) resolution N-band images, at a wavelength of 11.85 μm, of the nuclei of a sample of 27 radio gala

  10. Nuclear activity in nearby galaxies

    NARCIS (Netherlands)

    Filho, Mercedes Esteves

    2003-01-01

    The main focus of this thesis has been the search for and study of low luminosity AGN. We have detected severa low luminosity AGN in nearby galaxies, revealing that this type of activity can occur in a broad range of galaxy types and powers. Furthermore, we have been able to establish importan const

  11. The Assembly of Galaxy Clusters

    CERN Document Server

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

    2008-01-01

    We study the formation of fifty-three galaxy cluster-size dark matter halos formed within a pair of cosmological LCDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host 0.1L* galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no pre-processing 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; and 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 like ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between clust...

  12. Viewing galaxies in 3D

    CERN Document Server

    Krajnović, Davor

    2016-01-01

    Thanks to a technique that reveals galaxies in 3D, astronomers can now show that many galaxies have been wrongly classified. Davor Krajnovi\\'c argues that the classification scheme proposed 85 years ago by Edwin Hubble now needs to be revised.

  13. Red galaxies at high redshift

    NARCIS (Netherlands)

    Wuyts, Stijn Elisabeth Raphaël

    2007-01-01

    From its origin at the center of a star to the edge, through the surrounding gas and dust in the distant galaxy, through the intergalactic medium, traveling billions of light years only to be reflected by a mirror and captured by a detector; the little amount of light observed from galaxies in the e

  14. Lenticular Galaxies and Their Environments

    CERN Document Server

    Bergh, Sidney van den

    2009-01-01

    It is widely believed that lenticular (S0) galaxies were initially spirals from which the gas has been removed by interactions with hot cluster gas, or by ram-pressure stripping of cool gas from spirals that are orbiting within rich clusters of galaxies. However, problems with this interpretation are that: (1) Some lenticulars, such as NGC 3115, are isolated field galaxies rather than cluster members. (2) The distribution of flattening values of S0 galaxies in clusters, in groups and in the field are statistically indistinguishable. This is surprising because one might have expected most of the progenitors of field S0 galaxies to have been flattened late-type galaxies, whereas lenticulars in clusters are thought to have mostly been derived from bulge-dominated early-type galaxies. (3) It should be hardest for ram-pressure to strip massive luminous galaxies with deep potential wells. However, no statistically significant differences are seen between the luminosity distributions of early-type Shapley-Ames galax...

  15. Magnetic fields in nearby galaxies

    NARCIS (Netherlands)

    Heald, G.; Braun, R.

    2009-01-01

    We describe a recent full-polarization radio continuum survey, performed using the Westerbork Synthesis Radio Telescope (WSRT), of several nearby galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The WSRT-SINGS survey has been utilized to study the polarized emission and

  16. Manganese in dwarf spheroidal galaxies

    NARCIS (Netherlands)

    North, P.; Cescutti, G.; Jablonka, P.; Hill, V.; Shetrone, M.; Letarte, B.; Lemasle, B.; Venn, K. A.; Battaglia, G.; Tolstoy, E.; Irwin, M. J.; Primas, F.; Francois, P.

    We provide manganese abundances (corrected for the effect of the hyperfine structure) for a large number of stars in the dwarf spheroidal galaxies Sculptor and Fornax, and for a smaller number in the Carina and Sextans dSph galaxies. Abundances had already been determined for a number of other

  17. Galaxies in the Early Universe

    DEFF Research Database (Denmark)

    Krogager, Jens-Kristian

    Understanding how galaxies evolved from the early Universe through cosmic time is a fundamental part of modern astrophysics. In order to study this evolution it is important to sample the galaxies at various times in a consistent way through time. In regular luminosity selected samples, our...

  18. Squelched Galaxies and Dark Halos

    NARCIS (Netherlands)

    Tully, R. Brent; Somerville, Rachel S.; Trentham, Neil; Verheijen, Marc A. W.

    2002-01-01

    There is accumulating evidence that the faint end of the galaxy luminosity function might be very different in different locations. The luminosity function might be rising in rich clusters and flat in regions of low density. If galaxies form according to the model of hierarchical clustering, then th

  19. Large-Scale Galaxy Bias

    CERN Document Server

    Desjacques, Vincent; Schmidt, Fabian

    2016-01-01

    This review presents a comprehensive overview of galaxy bias, that is, the statistical relation between the distribution of galaxies and matter. We focus on large scales where cosmic density fields are quasi-linear. On these scales, the clustering of galaxies can be described by a perturbative bias expansion, and the complicated physics of galaxy formation is absorbed by a finite set of coefficients of the expansion, called bias parameters. The review begins with a pedagogical proof of this very important result, which forms the basis of the rigorous perturbative description of galaxy clustering, under the assumptions of General Relativity and Gaussian, adiabatic initial conditions. Key components of the bias expansion are all leading local gravitational observables, which includes the matter density but also tidal fields and their time derivatives. We hence expand the definition of local bias to encompass all these contributions. This derivation is followed by a presentation of the peak-background split in i...

  20. Disrupted Stars in Unusual Galaxies

    Science.gov (United States)

    Kohler, Susanna

    2016-03-01

    Tidal disruption events (TDEs) occur when a star passes a little too close to a supermassive black hole at the center of a galaxy. Tidal forces from the black hole cause the passing star to be torn apart, resulting in a brief flare of radiation as the stars material accretes onto the black hole. A recent study asks the following question: do TDEs occur most frequently in an unusual type of galaxy?A Trend in DisruptionsSo far, we have data from eight candidate TDEs that peaked in optical and ultraviolet wavelengths. The spectra from these observations have shown an intriguing trend: many of these TDEs host galaxies exhibit weak line emission (indicating little or no current star-formation activity), and yet they show strong Balmer absorption lines (indicating star formation activity occurred within the last Gyr). These quiescent, Balmer-strong galaxies likely underwent a period of intense star formation that recently ended.To determine if TDEs are overrepresented in such galaxies, a team of scientists led by Decker French (Steward Observatory, University of Arizona) has quantified the fraction of galaxies in the Sloan Digital Sky Survey (SDSS) that exhibit similar properties to those of TDE hosts.Quantifying OverrepresentationSpectral characteristics of SDSS galaxies (gray) and TDE candidate host galaxies (colored points): line emission vs. Balmer absorption. The lower right-hand box identifies thequiescent, Balmer-strong galaxies which contain most TDE events, yet are uncommon among the galaxy sample as a whole. Click for a better look! [French et al. 2016]French and collaborators compare the optical spectra of the TDE host galaxies to those of nearly 600,000 SDSS galaxies, using two different cutoffs for the Balmer absorption the indicator of past star formation. Their strictest cut, filtering for very high Balmer absorption, selected only 0.2% of the SDSS galaxies, yet 38% of the TDEs are hosted in such galaxies. Using a more relaxed cutoff selects 2.3% of

  1. Magnetic Fields in Spiral Galaxies

    CERN Document Server

    Beck, Rainer

    2015-01-01

    Radio synchrotron emission is a powerful tool to study the strength and structure of magnetic fields in galaxies. Unpolarized synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30\\mu G) and in central starburst regions (50-100\\mu G). Such fields are dynamically important; they affect gas flows and drive gas inflows in central regions. Polarized emission traces ordered fields, which can be regular or anisotropic turbulent, where the latter originates from isotropic turbulent fields by the action of compression or shear. The strongest ordered fields (10-15\\mu G) are generally found in interarm regions. In galaxies with strong density waves, ordered fields are also observed at the inner edges of spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions. Ordered fields in interacting galaxies have asymmetric distributions and are a tracer of past interactions between galaxies or with the interg...

  2. Understanding Galaxy Formation and Evolution

    CERN Document Server

    Avila-Reese, V

    2006-01-01

    The old dream of integrating into one the study of micro and macrocosmos is now a reality. Cosmology, astrophysics, and particle physics intersect in a scenario (but still not a theory) of cosmic structure formation and evolution called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to explain the origin of galaxies. In these lecture notes, I first present a review of the main galaxy properties, highlighting the questions that any theory of galaxy formation should explain. Then, the cosmological framework and the main aspects of primordial perturbation generation and evolution are pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation, presenting a review on LCDM halo assembling and properties, and on the main candidates for non-baryonic dark matter. It is shown how the nature of elemental particles can influence on the features of galaxies and their systems. Finally, the complex processes of baryon dissipation inside the non-linearly evolving CDM halos, formation o...

  3. Galaxies in the Early Universe

    DEFF Research Database (Denmark)

    Krogager, Jens-Kristian

    analyses are biased towards the brightest galaxies at all times (as these are easier to observe and identify). A complementary method relies on the absorption imprint from neutral gas in galaxies, the so-called damped Ly absorbers (DLAs) seen towards distant bright objects. This thesis seeks to understand...... how the absorption selected galaxies relate to the emission selected galaxies by identifying the faint glow from the absorbing galaxies at redshift z 2. In Chapters 2 and 3, the emission properties of DLAs are studied in detail using state-of-the-art instrumentation. The specific DLA studied......), there might exist a bias against dusty foreground absorbers due to the reddening causing the background quasars to appear star-like in their optical colours. In Chapters 4 and 5, these hypothesized dusty absorbers are sought for through a combination of optical and near-infrared colour criteria. While a large...

  4. Relic galaxies: where are they?

    Science.gov (United States)

    Peralta de Arriba, P.; Quilis, V.; Trujillo, I.; Cebrián, M.; Balcells, M.

    2017-03-01

    The finding that massive galaxies grow with cosmic time fired the starting gun for the search of objects which could have survived up to the present day without suffering substantial changes (neither in their structures, neither in their stellar populations). Nevertheless, and despite the community efforts, up to now only one firm candidate to be considered one of these relics is known: NGC 1277. Curiously, this galaxy is located at the centre of one of the most rich near galaxy clusters: Perseus. Is its location a matter of chance? Should relic hunters focus their search on galaxy clusters? In order to reply this question, we have performed a simultaneous and analogous analysis using simulations (Millennium I-WMAP7) and observations (New York University Value-Added Galaxy Catalogue). Our results in both frameworks agree: it is more probable to find relics in high density environments.

  5. Galaxies as condensates

    CERN Document Server

    Bugg, D V

    2012-01-01

    A novel interpretation of MOND is presented. For galactic data, in addition to Newtonian acceleration, there is an attractive acceleration peaking at Milgrom's parameter a_0. The peak lies within experimental error where a_0 = cH_0/2\\pi and H_0 is the present-time value of the Hubble constant. This peaking may be understood in terms of quantum mechanical mixing between Newtonian gravitation and the Hubble mechanism. There are five pointers towards galaxies being Fermi-Dirac condensates.

  6. Lopsidedness in WHISP galaxies

    CERN Document Server

    Juette, Eva; Jog, Chanda; Dettmar, Ralf-Juergen; Stein, Yelena

    2010-01-01

    Observations of the stellar and gaseous components in disc galaxies often reveal asymmetries in the morphological and kinematic distribution. However, the origin of this effect is not well known to date, and quantitative studies are rare. Here, we present the first statistical investigation of a sample of 76 HI discs using the WHISP survey. We perform a Fourier analysis to study the morphological lopsidedness. This allows to trace the degree of asymmetry with radius. We further investigate the dependence on, e.g., the morphological type and the environment.

  7. TANGO I: Interstellar medium in nearby radio galaxies. Molecular gas

    Science.gov (United States)

    Ocaña Flaquer, B.; Leon, S.; Combes, F.; Lim, J.

    2010-07-01

    Context. Powerful radio-AGN are hosted by massive elliptical galaxies that are usually very poor in molecular gas. Nevertheless, gas is needed at their very center to feed the nuclear activity. Aims: We study the molecular gas properties (i.e., mass, kinematics, distribution, origin) of these objects, and compare them with results for other known samples. Methods: At the IRAM-30m telescope, we performed a survey of the CO(1-0) and CO(2-1) emission from the most powerful radio galaxies of the Local Universe, selected only on the basis of their radio continuum fluxes. Results: The main result of our survey is that the molecular gas content of these galaxies is very low compared to spiral or FIR-selected galaxies. The median value of the molecular gas mass, including detections and upper limits, is 2.2 × 108 M⊙. When separated into FR-I and FR-II types, a difference in their H2 masses is found. The median value of FR-I galaxies is about 1.9 × 108 M⊙ and higher for FR-II galaxies, at about 4.5 × 108 M⊙. Which is probably entirely because of a Malmquist bias. Our results contrast with those of previous surveys, whose targets were mainly selected by means of their FIR emission, implying that we measure higher observed masses of molecular gas. Moreover, the shape of CO spectra suggest that a central molecular gas disk exists in 30% of these radio galaxies, a lower rate than in other active galaxy samples. Conclusions: We find a low level of molecular gas in our sample of radio-selected AGNs, indicating that galaxies do not need much molecular gas to host an AGN. The presence of a molecular gas disk in some galaxies and the wide range of molecular gas masses may be indicative of different origins for the gas, which we can not exclude at present (e.g., minor/major mergers, stellar mass loss, or accretion). Appendices and Figure 15 are only available in electronic form at http://www.aanda.org

  8. FIR colours and SEDs of nearby galaxies observed with Herschel

    CERN Document Server

    Boselli, A; Buat, V; Cortese, L; Auld, R; Baes, M; Bendo, G J; Bianchi, S; Bock, J; Bomans, D J; Bradford, M; Castro-Rodriguez, N; Chanial, P; Charlot, S; Clemens, M; Clements, D; Corbelli, E; Cooray, A; Cormier, D; Dariush, A; Davies, J; De Looze, I; Alighieri, S di Serego; Dwek, E; Eales, S; Elbaz, D; Fadda, D; Fritz, J; Galametz, M; Galliano, F; Garcia-Appadoo, D A; Gavazzi, G; Gear, W; Giovanardi, C; Glenn, J; Gomez, H; Griffin, M; Grossi, M; Hony, S; Hughes, T M; Hunt, L; Isaak, K; Jones, A; Levenson, L; Lu, N; Madden, S C; O'Halloran, B; Okumura, K; Oliver, S; Page, M; Panuzzo, P; Papageorgiou, A; Parkin, T; Perez-Fournon, I; Pierini, D; Pohlen, M; Rangwala, N; Rigby, E; Roussel, H; Rykala, A; Sabatini, S; Sacchi, N; Sauvage, M; Schulz, B; Schirm, M; Smith, M W L; Spinoglio, L; Stevens, J; Sundar, S; Symeonidis, M; Trichas, M; Vaccari, M; Verstappen, J; Vigroux, L; Vlahakis, C; Wilson, C; Wozniak, H; Wright, G; Xilouris, E M; Zeilinger, W; Zibetti, S

    2010-01-01

    We present infrared colours (in the 25-500 mic spectral range) and UV to radio continuum spectral energy distributions of a sample of 51 nearby galaxies observed with SPIRE on Herschel. The observed sample includes all morphological classes, from quiescent ellipticals to active starbursts. Active galaxies have warmer colour temperatures than normal spirals. In ellipticals hosting a radio galaxy, the far-infrared (FIR) emission is dominated bynthe synchrotron nuclear emission. The colour temperature of the cold dust is higher in quiescent E-S0a than in star-forming systems probably because of the different nature of their dust heating sources (evolved stellar populations, X-ray, fast electrons) and dust grain properties. In contrast to the colour temperature of the warm dust, the f350/f500 index sensitive to the cold dust decreases with star formation and increases with metallicity, suggesting an overabundance of cold dust or an emissivity parameter beta<2 in low metallicity, active systems.

  9. Structures and components in galaxy clusters: observations and models

    CERN Document Server

    Bykov, A M; Ferrari, C; Forman, W R; Kaastra, J S; Klein, U; Markevitch, M; de Plaa, J

    2015-01-01

    Clusters of galaxies are the largest gravitationally bounded structures in the Universe dominated by dark matter. We review the observational appearance and physical models of plasma structures in clusters of galaxies. Bubbles of relativistic plasma which are inflated by supermassive black holes of AGNs, cooling and heating of the gas, large scale plasma shocks, cold fronts, non-thermal halos and relics are observed in clusters. These constituents are reflecting both the formation history and the dynamical properties of clusters of galaxies. We discuss X-ray spectroscopy as a tool to study the metal enrichment in clusters and fine spectroscopy of Fe X-ray lines as a powerful diagnostics of both the turbulent plasma motions and the energetics of the non-thermal electron populations. The knowledge of the complex dynamical and feedback processes is necessary to understand the energy and matter balance as well as to constrain the role of the non-thermal components of clusters.

  10. New fully empirical calibrations of strong-line metallicity indicators in star forming galaxies

    CERN Document Server

    Curti, M; Mannucci, F; Marconi, A; Maiolino, R; Esposito, S

    2016-01-01

    We derive new empirical calibrations for strong-line diagnostics of gas phase metallicity in local star forming galaxies by uniformly applying the Te method over the full metallicity range probed by the Sloan Digital Sky Survey (SDSS). To measure electron temperatures at high metallicity, where the auroral lines needed are not detected in single galaxies, we stacked spectra of more than 110,000 galaxies from the SDSS in bins of log[O II]/H$\\beta$ and log[O III]/H$\\beta$. This stacking scheme does not assume any dependence of metallicity on mass or star formation rate, but only that galaxies with the same line ratios have the same oxygen abundance. We provide calibrations which span more than 1 dex in metallicity and are entirely defined on a consistent absolute Te metallicity scale for galaxies. We apply our calibrations to the SDSS sample and find that they provide consistent metallicity estimates to within 0.05 dex.

  11. New fully empirical calibrations of strong-line metallicity indicators in star-forming galaxies

    Science.gov (United States)

    Curti, M.; Cresci, G.; Mannucci, F.; Marconi, A.; Maiolino, R.; Esposito, S.

    2017-02-01

    We derive new empirical calibrations for strong-line diagnostics of gas-phase metallicity in local star-forming galaxies by uniformly applying the Te method over the full metallicity range probed by the Sloan Digital Sky Survey (SDSS). To measure electron temperatures at high metallicity, where the auroral lines needed are not detected in single galaxies, we stacked spectra of more than 110 000 galaxies from the SDSS in bins of log[O II]/Hβ and log[O III]/Hβ. This stacking scheme does not assume any dependence of metallicity on mass or star formation rate, but only that galaxies with the same line ratios have the same oxygen abundance. We provide calibrations which span more than 1 dex in metallicity and are entirely defined on a consistent absolute Te metallicity scale for galaxies. We apply our calibrations to the SDSS sample and find that they provide consistent metallicity estimates to within 0.05 dex.

  12. Galaxy Zoo Hubble: Crowdsourced Morphologies for 169,944 Galaxies at 0

    Science.gov (United States)

    Willett, Kyle; Galloway, Melanie; Fortson, Lucy; Bamford, Steven; Masters, Karen; Lintott, Chris; Simmons, Brooke; Cheung, Edmond; Schawinski, Kevin; Scarlata, Claudia; Beck, Melanie; Galaxy Zoo volunteers

    2016-01-01

    The Galaxy Zoo project uses crowdsourced visual classifications to create large and statistically robust catalogs of detailed galaxy morphology. We present initial results for the Galaxy Zoo: Hubble dataset, which includes 169,944 images of galaxies selected from the AEGIS, COSMOS, GEMS, and GOODS surveys. The galaxies span a redshift range of 0Zoo: Hubble catalog.

  13. THE TULLY-FISHER RELATION FOR LOW SURFACE BRIGHTNESS GALAXIES - IMPLICATIONS FOR GALAXY EVOLUTION

    NARCIS (Netherlands)

    Zwaan, M.A.; VAN DER HULST, JM; DE BLOK, WJG; MCGAUGH, SS

    1995-01-01

    We present the B-band Tully-Fisher relation for low surface brightness (LSB) galaxies. These LSB galaxies follow the same Tully-Fisher relation as normal spiral galaxies. This implies that the mass-to-light ratio (M/L) of LSB galaxies is typically a factor of 2 larger than that of normal galaxies of

  14. A LABOCA survey of submillimeter galaxies behind galaxy clusters

    CERN Document Server

    Johansson, Daniel; Horellou, Cathy

    2011-01-01

    Context: Submillimeter galaxies are a population of dusty star-forming galaxies at high redshift. Measuring their properties will help relate them to other types of galaxies, both at high and low redshift. This is needed in order to understand the formation and evolution of galaxies. Aims: We use gravitational lensing by galaxy clusters to probe the faint and abundant submillimeter galaxy population down to a lower flux density level than what can be achieved in blank-field observations. Methods: We use the LABOCA bolometer camera on the APEX telescope to observe five cluster of galaxies at a wavelength of 870 micron. The final maps have an angular resolution of 27.5 arcsec and a point source noise level of 1.2-2.2 mJy. We model the mass distribution in the clusters as superpositions of spherical NFW halos and derive magnification maps that we use to calculate intrinsic flux densities as well as area-weighted number counts. We also use the positions of Spitzer MIPS 24 micron sources in four of the fields for ...

  15. A pseudo-spectrum analysis of galaxy-galaxy lensing

    CERN Document Server

    Hikage, Chiaki

    2016-01-01

    We present the application of the pseudo-spectrum method to galaxy-galaxy lensing. We derive explicit expressions for the pseudo-spectrum analysis of the galaxy-shear cross spectrum, which is the Fourier space counterpart of the stacked galaxy-galaxy lensing profile. The pseudo-spectrum method corrects observational issues such as the survey geometry, masks of bright stars and their spikes, and inhomogeneous noise, which distort the spectrum and also mix the E-mode and the B-mode signals. Using ray-tracing simulations in N-body simulations including realistic masks, we confirm that the pseudo-spectrum method successfully recovers the input galaxy-shear cross spectrum. We also investigate the covariance of the galaxy-shear cross spectrum using the ray-tracing simulations to show that there is an excess covariance relative to the Gaussian covariance at small scales where the shot noise is dominated in the Gaussian approximation. We find that the excess of the covariance is consistent with the expectation from t...

  16. Testing galaxy formation models with galaxy stellar mass functions

    Science.gov (United States)

    Lim, S. H.; Mo, H. J.; Lan, Ting-Wen; Ménard, Brice

    2016-10-01

    We compare predictions of a number of empirical models and numerical simulations of galaxy formation to the conditional stellar mass functions (CSMF) of galaxies in groups of different masses obtained recently by Lan et al. to test how well different models accommodate the data. The observational data clearly prefer a model in which star formation in low-mass halos changes behavior at a characteristic redshift zc ˜ 2. There is also tentative evidence that this characteristic redshift depends on environment, becoming zc ˜ 4 in regions that eventually evolve into rich clusters of galaxies. The constrained model is used to understand how galaxies form and evolve in dark matter halos, and to make predictions for other statistical properties of the galaxy population, such as the stellar mass functions of galaxies at high z, the star formation and stellar mass assembly histories in dark matter halos. A comparison of our model predictions with those of other empirical models shows that different models can make vastly different predictions, even though all of them are tuned to match the observed stellar mass functions of galaxies.

  17. Galaxy and Mass Assembly (GAMA): Projected Galaxy Clustering

    CERN Document Server

    Farrow, D J; Norberg, Peder; Metcalfe, N; Baldry, I; Bland-Hawthorn, Joss; Brown, Michael J I; Hopkins, A M; Lacey, Cedric G; Liske, J; Loveday, Jon; Palamara, David P; Robotham, A S G; Sridhar, Srivatsan

    2015-01-01

    We measure the projected 2-point correlation function of galaxies in the 180 deg$^2$ equatorial regions of the GAMA II survey, for four different redshift slices between z = 0.0 and z=0.5. To do this we further develop the Cole (2011) method of producing suitable random catalogues for the calculation of correlation functions. We find that more r-band luminous, more massive and redder galaxies are more clustered. We also find that red galaxies have stronger clustering on scales less than ~3 $h^{-1}$ Mpc. We compare to two different versions of the GALFORM galaxy formation model, Lacey et al (in prep.) and Gonzalez-Perez et al. (2014), and find that the models reproduce the trend of stronger clustering for more massive galaxies. However, the models under predict the clustering of blue galaxies, can incorrectly predict the correlation function on small scales and under predict the clustering in our sample of galaxies with ~3$L_r$ . We suggest possible avenues to explore to improve these cluster- ing predictions....

  18. Testing galaxy formation models with galaxy stellar mass functions

    Science.gov (United States)

    Lim, S. H.; Mo, H. J.; Lan, T.-W.; Ménard, B.

    2017-01-01

    We compare predictions of a number of empirical models and numerical simulations of galaxy formation to the conditional stellar mass functions of galaxies in groups of different masses obtained recently by Lan et al. to test how well different models accommodate the data. The observational data clearly prefer a model in which star formation in low-mass haloes changes behaviour at a characteristic redshift zc ˜ 2. There is also tentative evidence that this characteristic redshift depends on environment, becoming zc ˜ 4 in regions that eventually evolve into rich clusters of galaxies. The constrained model is used to understand how galaxies form and evolve in dark matter haloes, and to make predictions for other statistical properties of the galaxy population, such as the stellar mass functions of galaxies at high z, the star formation, and stellar mass assembly histories in dark matter haloes. A comparison of our model predictions with those of other empirical models shows that different models can make vastly different predictions, even though all of them are tuned to match the observed stellar mass functions of galaxies.

  19. The Dragonfly Nearby Galaxies Survey. II. Ultra-Diffuse Galaxies near the Elliptical Galaxy NGC 5485

    Science.gov (United States)

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

    2016-12-01

    We present the unexpected discovery of four ultra-diffuse galaxies (UDGs) in a group environment. We recently identified seven extremely low surface brightness galaxies in the vicinity of the spiral galaxy M101, using data from the Dragonfly Telephoto Array. The galaxies have effective radii of 10″-38″ and central surface brightnesses of 25.6-27.7 mag arcsec-2 in the g-band. We subsequently obtained follow-up observations with HST to constrain the distances to these galaxies. Four remain persistently unresolved even with the spatial resolution of HST/ACS, which implies distances of D\\gt 17.5 Mpc. We show that the galaxies are most likely associated with a background group at ˜27 Mpc containing the massive ellipticals NGC 5485 and NGC 5473. At this distance, the galaxies have sizes of 2.6-4.9 kpc, and are classified as UDGs, similar to the populations that have been revealed in clusters such as Coma, Virgo, and Fornax, yet even more diffuse. The discovery of four UDGs in a galaxy group demonstrates that the UDG phenomenon is not exclusive to cluster environments. Furthermore, their morphologies seem less regular than those of the cluster populations, which may suggest a different formation mechanism or be indicative of a threshold in surface density below which UDGs are unable to maintain stability.

  20. The Dragonfly Nearby Galaxies Survey. II. Ultra diffuse galaxies near the elliptical galaxy NGC 5485

    CERN Document Server

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

    2016-01-01

    We present the unexpected discovery of four ultra diffuse galaxies (UDGs) in a group environment. We recently identified seven extremely low surface brightness galaxies in the vicinity of the spiral galaxy M101, using data from the Dragonfly Telephoto Array. The galaxies have effective radii of $10"-38"$ and central surface brightnesses of $25.6-27.7$ mag arcsec$^{-2}$ in g-band. We subsequently obtained follow-up observations with $HST$ to constrain the distances to these galaxies. Four remain persistently unresolved even with the spatial resolution of $HST$/ACS, which implies distances of $D > 17.5$ Mpc. We show that the galaxies are most likely associated with a background group at $\\sim 27$ Mpc containing the massive ellipticals NGC 5485 and NGC 5473. At this distance, the galaxies have sizes of $2.6-4.9$ kpc, and are classified as UDGs, similar to the populations that have been revealed in clusters such as Coma, Virgo and Fornax, yet even more diffuse. The discovery of four UDGs in a galaxy group demonst...

  1. Lopsided Collections of Satellite Galaxies

    Science.gov (United States)

    Kohler, Susanna

    2016-12-01

    You might think that small satellite galaxies would be distributed evenly around their larger galactic hosts but local evidence suggests otherwise. Are satellite distributions lopsided throughout the universe?Satellites in the Local GroupThe distribution of the satellite galaxies orbiting Andromeda, our neighboring galaxy, is puzzling: 21 out of 27 ( 80%) of its satellites are on the side of Andromeda closest to us. In a similar fashion, 4 of the 11 brightest Milky Way satellites are stacked on the side closest to Andromeda.It seems to be the case, then, that satellites around our pair of galaxies preferentially occupy the space between the two galaxies. But is this behavior specific to the Local Group? Or is it commonplace throughout the universe? In a recent study, a team of scientists led by Noam Libeskind (Leibniz Institute for Astrophysics Potsdam, Germany) set out to answer this question.Properties of the galaxies included in the authors sample. Left: redshifts for galaxy pairs. Right: Number of satellite galaxies around hosts. [Adapted from Libeskind et al. 2016]Asymmetry at LargeLibeskind and collaborators tested whether this behavior is common by searching through Sloan Digital Sky Survey observations for galaxy pairs that are similar to the Milky Way/Andromeda pair. The resulting sample consists of 12,210 pairs of galaxies, which have 46,043 potential satellites among them. The team then performed statistical tests on these observations to quantify the anisotropic distribution of the satellites around the host galaxies.Libeskind and collaborators find that roughly 8% more galaxies are seen within a 15 angle facing the other galaxy of a pair than would be expected in a uniform distribution. The odds that this asymmetric behavior is randomly produced, they show, are lower than 1 in 10 million indicating that the lopsidedness of satellites around galaxies in pairs is a real effect and occurs beyond just the Local Group.Caution for ModelingProbability that

  2. Star formation suppression in compact group galaxies

    DEFF Research Database (Denmark)

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

    2015-01-01

    on poststarburst galaxies with molecular reservoirs, indicates that galaxies do not need to expel their molecular reservoirs prior to quenching SF and transitioning from blue spirals to red early-type galaxies. This may imply that SF quenching can occur without the need to starve a galaxy of cold gas first....

  3. Stars, Galaxies and Quasars

    Directory of Open Access Journals (Sweden)

    Patrick Das Gupta

    2009-05-01

    Full Text Available This article provides a brief introduction to the basics of stars, galaxies and Quasi-stellar objects (QSOs. In stars, the central pressure and temperature must be high in order to halt the stellar gravitational collapse. High temperature leads to thermonuclear fusion in the stellar core, releasing thereby enormous amount of nuclear energy, making the star shine brilliantly. On the other hand, the QSOs are very bright nuclei lying in the centres of some galaxies. Many of these active galactic nuclei, which appear star-like when observed through a telescope and  whose power output are more than 1011 times that of the Sun, exhibit rapid time variability in their X-ray emissions.  Rapid variability along with the existence of a maximum speed limit, c, provide a strong argument in favour of a compact central engine model for QSOs in which a thick disc of hot gas going around a supermassive blackhole is what makes a QSO appear like a bright point source. Hence, unlike stars, QSOs are powered by gravitational potential energy.

  4. Galaxy cluster's rotation

    CERN Document Server

    Manolopoulou, Maria

    2016-01-01

    We study the possible rotation of cluster galaxies, developing, testing and applying a novel algorithm which identifies rotation, if such does exits, as well as its rotational centre, its axis orientation, rotational velocity amplitude and, finally, the clockwise or counterclockwise direction of rotation on the plane of the sky. To validate our algorithms we construct realistic Monte-Carlo mock rotating clusters and confirm that our method provides robust indications of rotation. We then apply our methodology on a sample of Abell clusters with z<~0.1 with member galaxies selected from the SDSS DR10 spectroscopic database. We find that ~35% of our clusters are rotating when using a set of strict criteria, while loosening the criteria we find this fraction increasing to ~48%. We correlate our rotation indicators with the cluster dynamical state, provided either by their Bautz-Morgan type or by their X-ray isophotal shape and find for those clusters showing rotation that the significance and strength of their...

  5. Relativistic Particles in Clusters of Galaxies

    CERN Document Server

    Ensslin, T A

    2002-01-01

    A brief overview on the theory and observations of relativistic particle populations in clusters of galaxies is given. The following topics are addressed: (i) the diffuse relativistic electron population within the intra-cluster medium (ICM) as seen in the cluster wide radio halos and possibly also seen in the high energy X-ray and extreme ultraviolet excess emissions of some clusters, (ii) the observed confined relativistic electrons within fresh and old radio plasma and their connection to cluster radio relics at cluster merger shock waves, (iii) the relativistic proton population within the ICM, and its observable consequences (if it exists), and (iv) the confined relativistic proton population (if it exists) within radio plasma. The importance of upcoming, sensitive gamma-ray telescopes for this research area is highlighted.

  6. Dark-ages reionization and galaxy formation simulation III: Modelling galaxy formation and the Epoch of Reionization

    CERN Document Server

    Mutch, Simon J; Poole, Gregory B; Angel, Paul W; Duffy, Alan R; Mesinger, Andrei; Wyithe, J Stuart B

    2015-01-01

    We introduce Meraxes, a new, purpose-built semi-analytic galaxy formation model designed for studying galaxy growth during reionization. Meraxes is the first model of its type to include a temporally- and spatially-coupled treatment of reionization and is built upon a custom (100 Mpc)$^3$ N-body simulation with high temporal and mass resolution, allowing us to resolve the galaxy and star formation physics relevant to early galaxy formation. Our fiducial model with supernova feedback reproduces the observed optical depth to electron scattering and evolution of the galaxy stellar mass function between $z$=5-7, predicting that a broad range of halo masses contribute to reionization. Using a constant escape fraction and global recombination rate, our model is unable to simultaneously match the observed ionizing emissivity at $z{\\lesssim}6$. However, the use of an evolving escape fraction of 0.05-0.1 at $z{\\sim}6$, increasing towards higher redshift, is able to satisfy these three constraints. We also demonstrate ...

  7. A machine-learning approach to measuring the escape of ionizing radiation from galaxies in the reionization epoch

    CERN Document Server

    Jensen, Hannes; Pelckmans, Kristiaan; Binggeli, Christian; Ausmees, Kristiina; Lundholm, Ulrika

    2016-01-01

    Recent observations of galaxies at $z \\gtrsim 7$, along with the low value of the electron scattering optical depth measured by the Planck mission, make galaxies plausible as dominant sources of ionizing photons during the epoch of reionization. However, scenarios of galaxy-driven reionization hinge on the assumption that the average escape fraction of ionizing photons is significantly higher for galaxies in the reionization epoch than in the local Universe. The NIRSpec instrument on the James Webb Space Telescope (JWST) will enable spectroscopic observations of large samples of reionization-epoch galaxies. While the leakage of ionizing photons will not be directly measurable from these spectra, the leakage is predicted to have an indirect effect on the spectral slope and the strength of nebular emission lines in the rest-frame ultraviolet and optical. Here, we apply a machine learning technique known as lasso regression on mock JWST/NIRSpec observations of simulated $z=7$ galaxies in order to obtain a model ...

  8. Dust tori in radio galaxies

    CERN Document Server

    van der Wolk, G; Peletier, R F; Pel, J W

    2009-01-01

    We investigate the validity of the quasar - radio galaxy unification scenario and determine the presence of dust tori among radio galaxies of various types. Actively accreting supermassive black holes in the centres of radio galaxies may be uncovered through their dust tori reradiating the optical and ultraviolet continuum in mid-infrared bands. Using VISIR on the VLT, we have obtained sub-arcsecond (~0.40") resolution N-band images, at a wavelength of 11.85 micron, of the nuclei of a sample of 27 radio galaxies of four types in the redshift range z=0.006-0.156. The sample consists of 8 edge-darkened, low-power Fanaroff-Riley class I (FR-I) radio galaxies, 6 edge-brightened, class II (FR-II) radio galaxies displaying low-excitation optical emission, 7 FR-IIs displaying high-excitation optical emission, and 6 FR-II broad emission line radio galaxies. Out of the sample of 27 objects, 10 nuclei are detected and several have constraining non-detections at 10 sigma sensitivities of 7 mJy. On the basis of the core ...

  9. The evolution of galaxy habitability

    CERN Document Server

    Gobat, R

    2016-01-01

    We combine a semi-analytic model of galaxy evolution with constraints on circumstellar habitable zones and the distribution of terrestrial planets to probe the suitability of galaxies of different mass and type to host habitable planets, as well as its evolution with time. We find that the fraction of stars with terrestrial planets in their habitable zone ("habitability") depends only weakly on galaxy mass, with a maximum around 4e10 Msun. We estimate that 0.7% of all stars in Milky Way type galaxies to host a terrestrial planet within their habitable zone, consistent with the value derived from Kepler observations. On the other hand, the habitability of passive galaxies is slightly but systematically higher, unless we assume an unrealistically high sensitivity of planets to supernovae. We find that the overall habitability of galaxies has not changed significantly in the last ~8 Gyr, with most of the habitable planets in local disk galaxies having formed ~1.5 Gyr before our own solar system. Finally, we expe...

  10. Effect of bars on the galaxy properties

    Science.gov (United States)

    Vera, Matias; Alonso, Sol; Coldwell, Georgina

    2016-10-01

    Aims: With the aim of assessing the effects of bars on disk galaxy properties, we present an analysis of different characteristics of spiral galaxies with strong bars, weak bars and without bars. Methods: We identified barred galaxies from the Sloan Digital Sky Survey (SDSS). By visual inspection of SDSS images we classified the face-on spiral galaxies brighter than glog (M∗/M⊙) processing, reflected in the significant changes in the physical properties of the host galaxies.

  11. The Assembly of Galaxy Clusters

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-05-16

    We study the formation of fifty-three galaxy cluster-size dark matter halos (M = 10{sup 14.0-14.76} M{sub {circle_dot}}) formed within a pair of cosmological {Lambda}CDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host {approx} 0.1L{sub *} galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no 'pre-processing' in the group environment prior to their accretion into the cluster. On average, {approx} 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; and less than {approx} 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 ({approx}< 6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like 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 {approx} 20% incorporated into the cluster halo more than 7 Gyr ago and {approx} 20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate time-scale for late-type to early-type transformation within the cluster environment to be {approx} 6 Gyr.

  12. Galaxy Collisions, Gas Stripping and Star Formation in the Evolution of Galaxies

    CERN Document Server

    Palous, J

    2004-01-01

    A review of gravitational and hydrodynamical processes during formation of clusters and evolution of galaxies is given. Early, at the advent of N-body computer simulations, the importance of tidal fields in galaxy encounters has been recognized. Orbits are crowded due to tides along spiral arms, where the star formation is enhanced. Low relative velocity encounters lead to galaxy mergers. The central dominating galaxies in future clusters form before the clusters in a merging process in galaxy groups. Galaxy clusters are composed in a hierarchical scenario due to relaxation processes between galaxies and galaxy groups. As soon as the overall cluster gravitational potential is built, high speed galaxy versus galaxy encounters start to play a role. These harassment events gradually thicken and shorten spiral galaxy disks leading to the formation of S0 galaxies and ellipticals. Another aspect of the high speed motion in the hot and diluted Intracluster Medium (ICM) is the ram pressure exerted on the Interstellar...

  13. Why Are Ring Galaxies Interesting?

    CERN Document Server

    Higdon, James L

    2010-01-01

    Compared with ordinary spirals, the ISM in ring galaxies experiences markedly different physical conditions and evolution. As a result, ring galaxies provide interesting perspectives on the triggering/quenching of large scale star formation and the destructive effects of massive stars on molecular cloud complexes. We use high resolution radio, sub-millimeter, infrared, and optical data to investigate the role of gravitational stability in star formation regulation, factors influencing the ISM's molecular fraction, and evidence of peculiar star formation laws and efficiencies in two highly evolved ring galaxies: Cartwheel and the Lindsay-Shapley ring.

  14. Samsung Galaxy Tabs for dummies

    CERN Document Server

    Gookin, Dan

    2013-01-01

    A colorful, entertaining, and informative guide to the Samsung Galaxy family of tablets Samsung's bestselling Galaxy Tabs may come in multiple sizes, but they all share the wildly popular Android operating system and are packed with tons of top-notch tablet features. This full-color book shows you how to enjoy all the things your Galaxy Tab can do, regardless of model: browse the web, handle e-mail, manage your social media, make phone calls and video chat, read e-books, take and share photos, play music, and more. Author Dan Gookin, famous for his skill in demystifying technology, takes you

  15. HII galaxies in 4D

    CERN Document Server

    Telles, Eduardo

    2014-01-01

    HII galaxies are clumpy and their gas kinematics can be mapped to show the global turbulent motions and the effect of massive star evolution. The distribution of their physical conditions is homogeneous and oxygen abundance is uniform. The presence of nebular HeII 4868 line seems to be higher in a low abundance galaxy, implying a harder ionization power probably due to stars in low metallicity. Innovative methods of data cube analysis, namely PCA tomography (nicknamed 4D), seem promising in revealing additional information not detected with the standard methods. I review some of our own recent work on the 3D spectroscopy of HII galaxies.

  16. Uncovering star formation feedback and magnetism in galaxies with radio continuum surveys

    Science.gov (United States)

    Tabatabaei, F. S.

    2017-03-01

    Recent studies show the importance of the star formation feedback in changing the energetic and structure of galaxies. Dissecting the physics of the feedback is hence crucial to understand the evolution of galaxies. Full polarization radio continuum surveys can be ideally performed to trace not only star formation but also the energetic components of the interstellar medium (ISM), the magnetic fields and cosmic ray electrons. Using the SKA precursors, we investigate the effect of the massive star formation on the ISM energy balance in nearby galaxies. Our multi-scale and multi-frequency surveys show that cosmic rays are injected in star forming regions and lose energy propagating away from their birth place. Due to the star formation feedback, cosmic ray electron population becomes younger and more energetic. Star formation also amplifies the turbulent magnetic field inserting a high pressure which is important in energy balance in the ISM and structure formation in the host galaxy.

  17. Uncovering star formation feedback and magnetism in galaxies with radio continuum surveys

    CERN Document Server

    Tabatabaei, Fatemeh S

    2016-01-01

    Recent studies show the importance of the star formation feedback in changing the energetic and structure of galaxies. Dissecting the physics of the feedback is hence crucial to understand the evolution of galaxies. Full polarization radio continuum surveys can be ideally performed to trace not only star formation but also the energetic components of the interstellar medium (ISM), the magnetic fields and cosmic ray electrons. Using the SKA precursors, we investigate the effect of the massive star formation on the ISM energy balance in nearby galaxies. Our multi-scale and multi-frequency surveys show that cosmic rays are injected in star forming regions and lose energy propagating away from their birth place. Due to the star formation feedback, cosmic ray electron population becomes younger and more energetic. Star formation also amplifies the turbulent magnetic field inserting a high pressure which is important in energy balance in the ISM and structure formation in the host galaxy.

  18. The influence of halo assembly on galaxies and galaxy groups

    CERN Document Server

    Zapata, Tatiana; Padilla, Nelson; Tissera, Patricia

    2008-01-01

    We study the variations of group galaxy properties according to their assembly history in groups identified in the SDSS-DR6 (hereafter SDSS) catalogue. Using mock SDSS group catalogues, we find that the isolation and concentration of a galaxy group are good observational discriminators of group assembly. However, analysing the mean spectral type of SDSS groups as a function of concentration and isolation, we find that while SDSS massive groups confirm the predicted correlation between concentration and age found in mock catalogues, they disagree with models in the isolation-age trend. This may be partially explained in terms of possible problems associated to the modelling of cold gas in satellite galaxies in semi-analytical models, which could be overestimating the effects of environment. We study properties of galaxies in groups of similar masses and different ages, finding important variations between model and observations. These variations can be explained in terms of the different isolation-age trends o...

  19. Observations and Models of Galaxy Assembly Bias

    Science.gov (United States)

    Campbell, Duncan A.

    2017-01-01

    The assembly history of dark matter haloes imparts various correlations between a halo’s physical properties and its large scale environment, i.e. assembly bias. It is common for models of the galaxy-halo connection to assume that galaxy properties are only a function of halo mass, implicitly ignoring how assembly bias may affect galaxies. Recently, programs to model and constrain the degree to which galaxy properties are influenced by assembly bias have been undertaken; however, the extent and character of galaxy assembly bias remains a mystery. Nevertheless, characterizing and modeling galaxy assembly bias is an important step in understanding galaxy evolution and limiting any systematic effects assembly bias may pose in cosmological measurements using galaxy surveys.I will present work on modeling and constraining the effect of assembly bias in two galaxy properties: stellar mass and star-formation rate. Conditional abundance matching allows for these galaxy properties to be tied to halo formation history to a variable degree, making studies of the relative strength of assembly bias possible. Galaxy-galaxy clustering and galactic conformity, the degree to which galaxy color is correlated between neighbors, are sensitive observational measures of galaxy assembly bias. I will show how these measurements can be used to constrain galaxy assembly bias and the peril of ignoring it.

  20. Metal Abundances of KISS Galaxies. V. Nebular Abundances of 15 Intermediate Luminosity Star-forming Galaxies

    Science.gov (United States)

    Hirschauer, Alec S.; Salzer, John J.; Bresolin, Fabio; Saviane, Ivo; Yegorova, Irina

    2015-09-01

    We present high signal-to-noise ratio spectroscopy of 15 emission-line galaxies cataloged in the KPNO International Spectroscopic Survey, selected for their possession of high equivalent width [O iii] lines. The primary goal of this study was to attempt to derive direct-method (Te) abundances for use in constraining the upper-metallicity branch of the {R}23 relation. The spectra cover the full optical region from [O ii]λλ3726,3729 to [S iii]λλ9069,9531 and include the measurement of [O iii]λ4363 in 13 objects. From these spectra, we determine abundance ratios of helium, nitrogen, oxygen, neon, sulfur, and argon. We find these galaxies to predominantly possess oxygen abundances in the range of 8.0 ≲ 12+log(O/H) ≲ 8.3. We present a comparison of direct-method abundances with empirical strong-emission-line techniques, revealing several discrepancies. We also present a comparison of direct-method oxygen abundance calculations using electron temperatures determined from emission lines of O++ and S++, finding a small systematic shift to lower Te (∼1184 K) and higher metallicity (∼0.14 dex) for sulfur-derived Te compared to oxygen-derived Te. Finally, we explore in some detail the different spectral activity types of targets in our sample, including regular star-forming galaxies, those with suspected AGN contamination, and a local pair of low-metallicity, high-luminosity compact objects.

  1. Galaxy Motions, Turbulence and Conduction in Clusters of Galaxies

    CERN Document Server

    Ruszkowski, M

    2010-01-01

    Unopposed radiative cooling in clusters of galaxies results in excessive mass deposition rates. However, the cool cores of galaxy clusters are continuously heated by thermal conduction and turbulent heat diffusion due to minor mergers or the galaxies orbiting the cluster center. These processes can either reduce the energy requirements for AGN heating of cool cores, or they can prevent overcooling altogether. We perform 3D MHD simulations including field-aligned thermal conduction and self-gravitating particles to model this in detail. Turbulence is not confined to the wakes of galaxies but is instead volume-filling, due to the excitation of large-scale g-modes. We systematically probe the parameter space of galaxy masses and numbers. For a wide range of observationally motivated galaxy parameters, the magnetic field is randomized by stirring motions, restoring the conductive heat flow to the core. The cooling catastrophe either does not occur or it is sufficiently delayed to allow the cluster to experience a...

  2. Galaxy-Galaxy Lensing in the DES Science Verification Data

    Energy Technology Data Exchange (ETDEWEB)

    Clampitt, J.; et al.

    2016-03-18

    We present galaxy-galaxy lensing results from 139 square degrees of Dark Energy Survey (DES) Science Verification (SV) data. Our lens sample consists of red galaxies, known as redMaGiC, which are specifically selected to have a low photometric redshift error and outlier rate. The lensing measurement has a total signal-to-noise of 29, including all lenses over a wide redshift range $0.2 < z < 0.8$. Dividing the lenses into three redshift bins, we find no evidence for evolution in the halo mass with redshift. We obtain consistent results for the lensing measurement with two independent shear pipelines, ngmix and im3shape. We perform a number of null tests on the shear and photometric redshift catalogs and quantify resulting systematic errors. Covariances from jackknife subsamples of the data are validated with a suite of 50 mock surveys. The results and systematics checks in this work provide a critical input for future cosmological and galaxy evolution studies with the DES data and redMaGiC galaxy samples. We fit a Halo Occupation Distribution (HOD) model, and demonstrate that our data constrains the mean halo mass of the lens galaxies, despite strong degeneracies between individual HOD parameters.

  3. Giant disk galaxies : Where environment trumps mass in galaxy evolution

    CERN Document Server

    Courtois, H M; Sorce, J G; Pomarede, D

    2015-01-01

    We identify some of the most HI massive and fastest rotating disk galaxies in the local universe with the aim of probing the processes that drive the formation of these extreme disk galaxies. By combining data from the Cosmic Flows project, which has consistently reanalyzed archival galaxy HI profiles, and 3.6$\\mu$m photometry obtained with the Spitzer Space Telescope, with which we can measure stellar mass, we use the baryonic Tully-Fisher (BTF) relationship to explore whether these massive galaxies are distinct. We discuss several results, but the most striking is the systematic offset of the HI-massive sample above the BTF. These galaxies have both more gas and more stars in their disks than the typical disk galaxy of similar rotational velocity. The "condensed" baryon fraction, $f_C$, the fraction of the baryons in a dark matter halo that settle either as cold gas or stars into the disk, is twice as high in the HI-massive sample than typical, and almost reaches the universal baryon fraction in some cases,...

  4. Fitting Galaxies on GPUs

    CERN Document Server

    Barsdell, Benjamin R; Fluke, Christopher J

    2011-01-01

    Structural parameters are normally extracted from observed galaxies by fitting analytic light profiles to the observations. Obtaining accurate fits to high-resolution images is a computationally expensive task, requiring many model evaluations and convolutions with the imaging point spread function. While these algorithms contain high degrees of parallelism, current implementations do not exploit this property. With evergrowing volumes of observational data, an inability to make use of advances in computing power can act as a constraint on scientific outcomes. This is the motivation behind our work, which aims to implement the model-fitting procedure on a graphics processing unit (GPU). We begin by analysing the algorithms involved in model evaluation with respect to their suitability for modern many-core computing architectures like GPUs, finding them to be well-placed to take advantage of the high memory bandwidth offered by this hardware. Following our analysis, we briefly describe a preliminary implementa...

  5. Outskirts of Galaxy Clusters

    CERN Document Server

    Reiprich, Thomas H; Ettori, Stefano; Israel, Holger; Lovisari, Lorenzo; Molendi, Silvano; Pointecouteau, Etienne; Roncarelli, Mauro

    2013-01-01

    Until recently, only about 10% of the total intracluster gas volume had been studied with high accuracy, leaving a vast region essentially unexplored. This is now changing and a wide area of hot gas physics and chemistry awaits discovery in galaxy cluster outskirts. Also, robust large-scale total mass profiles and maps are within reach. First observational and theoretical results in this emerging field have been achieved in recent years with sometimes surprising findings. Here, we summarize and illustrate the relevant underlying physical and chemical processes and review the recent progress in X-ray, Sunyaev--Zel'dovich, and weak gravitational lensing observations of cluster outskirts, including also brief discussions of technical challenges and possible future improvements.

  6. Galaxy Outflows Without Supernovae

    CERN Document Server

    Sur, Sharanya; Ostriker, Eve C

    2016-01-01

    High surface density, rapidly star-forming galaxies are observed to have $\\approx 50-100\\,{\\rm km\\,s^{-1}}$ line-of-sight velocity dispersions, which are much higher than expected from supernova driving alone, but may arise from large-scale gravitational instabilities. Using three-dimensional simulations of local regions of the interstellar medium, we explore the impact of high velocity dispersions that arise from these disk instabilities. Parametrizing disks by their surface densities and epicyclic frequencies, we conduct a series of simulations that probe a broad range of conditions. Turbulence is driven purely horizontally and on large scales, neglecting any energy input from supernovae. We find that such motions lead to strong global outflows in the highly-compact disks that were common at high redshifts, but weak or negligible mass loss in the more diffuse disks that are prevalent today. Substantial outflows are generated if the one-dimensional horizontal velocity dispersion exceeds $\\approx 35\\,{\\rm km\\...

  7. GREEN GALAXIES IN THE COSMOS FIELD

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Zhizheng; Kong, Xu; Fan, Lulu, E-mail: panzz@mail.ustc.edu.cn, E-mail: xkong@ustc.edu.cn [Center of Astrophysics, University of Science and Technology of China, Hefei 230026 (China)

    2013-10-10

    We present research on the morphologies, spectra, and environments of ≈2350 'green valley' galaxies at 0.2 < z < 1.0 in the COSMOS field. The bimodality of dust-corrected NUV–r {sup +} color is used to define 'green valley'; it removes dusty star-forming galaxies from galaxies that are truly transitioning between the blue cloud and the red sequence. Morphological parameters of green galaxies are intermediate between those of blue and red galaxy populations, both on the Gini-asymmetry and the Gini-M{sub 20} planes. Approximately 60%-70% of green disk galaxies have intermediate or big bulges, and only 5%-10% are pure disk systems, based on morphological classification using the Zurich Estimator of Structural Types. The obtained average spectra of green galaxies are intermediate between blue and red ones in terms of [O II], Hα, and Hβ emission lines. Stellar population synthesis on the average spectra shows that green galaxies are on average older than blue galaxies but younger than red galaxies. Green galaxies and blue galaxies have similar projected galaxy density (Σ{sub 10}) distributions at z > 0.7. At z < 0.7, the fractions of M{sub *} < 10{sup 10.0} M{sub ☉} green galaxies located in a dense environment are found to be significantly larger than those of blue galaxies. The morphological and spectral properties of green galaxies are consistent with the transitioning population between the blue cloud and the red sequence. The possible mechanisms for quenching star formation activities in green galaxies are discussed. The importance of active galactic nucleus feedback cannot be well constrained in our study. Finally, our findings suggest that environmental conditions, most likely starvation and harassment, significantly affect the transformation of M{sub *} < 10{sup 10.0} M{sub ☉} blue galaxies into red galaxies, especially at z < 0.5.

  8. Spectral Synthesis of SDSS Galaxies

    CERN Document Server

    Sodre, J; Mateus, A; Stasinska, G; Gomes, J M

    2005-01-01

    We investigate the power of spectral synthesis as a mean to estimate physical properties of galaxies. Spectral synthesis is nothing more than the decomposition of an observed spectrum in terms of a superposition of a base of simple stellar populations of various ages and metallicities (here from Bruzual & Charlot 2003), producing as output the star-formation and chemical histories of a galaxy, its extinction and velocity dispersion. We discuss the reliability of this approach and apply it to a volume limited sample of 50362 galaxies from the SDSS Data Release 2, producing a catalog of stellar population properties. A comparison with recent estimates of both observed and physical properties of these galaxies obtained by other groups shows good qualitative and quantitative agreement, despite substantial differences in the method of analysis. The confidence in the method is further strengthened by several empirical and astrophysically reasonable correlations between synthesis results and independent quantiti...

  9. Secular Evolution in Disk Galaxies

    Science.gov (United States)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  10. Thermal and Nonthermal Radio Galaxies

    CERN Document Server

    Antonucci, Robert

    2011-01-01

    Radio galaxies were discovered and mapped in the 1950s. The optical spectra showed little or no nuclear continuum light. Some also revealed powerful high ionization emission lines, while others showed at most weak low-ionization emission lines. Quasars were found in the 1960s, and their spectra were dominated by powerful continuum radiation which was subsequently identified with optically thick thermal radiation from copious accretion flows, as well as high ionization narrow emission lines, and powerful broad permitted lines. By the 1980s, data from optical polarization and statistics of the radio properties required that many radio galaxies contain hidden quasar nuclei, hidden from the line of sight by dusty, roughly toroidal gas distributions. The radio galaxies with hidden quasars are referred to as "thermal." Do all radio galaxies have powerful hidden quasars? We now know the answer using arguments based on radio, infrared, optical and X-ray properties. Near the top of the radio luminosity function, for F...

  11. Markarian 36: A young galaxy

    Science.gov (United States)

    Huchra, J.; Geller, M.; Hunter, D.; Gallagher, J.

    The UV, optical, and IR observations of three galaxies (NGC 4214, NGC4670 = Haro 9, and Markarian 36) are reported. The optical spectrum of Markarian 36, a dwarf galaxy, is dominated by strong emission lines. The UV spectrum however shows no strong emission lines, only weak C IV and Si absorption and a strong blue continuum that is still rising shortward of Lyman alpha. Combined UV, optical and IR observations show that the continuum is nearly Rayleigh-Jeans from 1100 A to 2.2 microns, with a slight excess in the optical due to free-free emission and recombination lines. This galaxy has few, if any, red stars. Combined with its low metal content, this lack of red stars is a very strong indication that this galaxy has only recently begun to form stars.

  12. Galaxy Zoo: Passive Red Spirals

    CERN Document Server

    Masters, Karen L; Romer, A Kathy; Nichol, Robert C; Bamford, Steven P; Schawinski, Kevin; Lintott, Chris J; Andreescu, Dan; Campbell, Heather C; Crowcroft, Ben; Doyle, Isabelle; Edmondson, Edward M; Murray, Phil; Raddick, M Jordan; Slosar, Anze; Szalay, Alexander S; Vandenberg, Jan

    2009-01-01

    We study the spectroscopic properties and environments of red spiral galaxies found by the Galaxy Zoo project. By carefully selecting face-on, disk dominated spirals we construct a sample of truly passive disks (not dust reddened, nor dominated by old stellar populations in a bulge). As such, our red spirals represent an interesting set of possible transition objects between normal blue spirals and red early types. We use SDSS data to investigate the physical processes which could have turned these objects red without disturbing their morphology. Red spirals prefer intermediate density regimes, however there are no obvious correlations between red spiral properties and environment - environment alone is not sufficient to determine if a galaxy will become a red spiral. Red spirals are a small fraction of spirals at low masses, but dominate at large stellar masses - massive galaxies are red independent of morphology. We confirm that red spirals have older stellar populations and less recent star formation than ...

  13. Normal Galaxies in the Infrared

    CERN Document Server

    Helou, G

    2000-01-01

    This review addresses what can be learned from infrared observations about galaxies powered predominantly by star formation. Infrared techniques mostly probe the interstellar medium of galaxies, yielding physical and chemical information on the medium out of which stars form, which is in turn affected by those stars. Methods traditionally used in the study of such normal galaxies at wavelengths longer than 3 microns are described, and major questions currently pursued in the field are outlined. The most prominent results from the IRAS survey are reviewed. Contributions by ISO in the field of broad-band photometry are then presented, followed by ISO results in spectrospcopy. Normal galaxy studies not directly concerned with the ISM are quickly reviewed. The outlook and challenges in pursuing the interpretation of infrared data on the ISM are discussed.

  14. Spiral Galaxies as Chiral Objects?

    CERN Document Server

    Capozziello, S; Capozziello, Salvatore; Lattanzi, Alessandra

    2005-01-01

    Spiral galaxies show axial symmetry and an intrinsic 2D-chirality. Environmental effects can influence the chirality of originally isolated stellar systems and a progressive loss of chirality can be recognised in the Hubble sequence. We point out a preferential modality for genetic galaxies as in microscopic systems like aminoacids, sugars or neutrinos. This feature could be the remnant of a primordial symmetry breaking characterizing systems at all scales.

  15. Cosmological models of galaxy formation

    Science.gov (United States)

    Menci, N.

    I review the present status of galaxy formation models within a cosmological framework. I focus on semi-analytic models based on the Cold Dark Matter scenario, discussing the role of the different physical process involving dark matter and baryons in determining the observed statistical properties of galaxies and their dependence on cosmic time and on environment evolution. I will highlight some present problems and briefly present the main effects of assuming a Warm Dark Matter scenario.

  16. The faintest star forming galaxies

    CERN Document Server

    Ranalli, P

    2003-01-01

    I briefly report on the X-ray detection of 10 radio sub-mJy sources in the 2 Ms Chandra observation of the Hubble Deep Field North region. These sources follow the same radio/X-ray luminosities relation which holds for nearby galaxies. Making use of this relation, X-ray number counts from star forming galaxies are predicted from the deep radio Log N-Log S's.

  17. Galaxy clusters as hydrodynamics laboratories

    Science.gov (United States)

    Roediger, Elke; Sheardown, Alexander; Fish, Thomas; ZuHone, John; Hunt, Matthew; Su, Yuanyuan; Kraft, Ralph P.; Nulsen, Paul; Forman, William R.; Churazov, Eugene; Randall, Scott W.; Jones, Christine; Machacek, Marie E.

    2017-08-01

    The intra-cluster medium (ICM) of galaxy clusters shows a wealth of hydrodynamical features that trace the growth of clusters via the infall of galaxies or smaller subclusters. Such hydrodynamical features include the wakes of the infalling objects as well as the interfaces between the host cluster’s ICM and the atmosphere of the infalling object. Furthermore, the cluster dynamics can be traced by merger shocks, bow shocks, and sloshing motions of the ICM.The characteristics of these dynamical features, e.g., the direction, length, brightness, and temperature of the galaxies' or subclusters' gas tails varies significantly between different objects. This could be due to either dynamical conditions or ICM transport coefficients such as viscosity and thermal conductivity. For example, the cool long gas tails of of some infalling galaxies and groups have been attributed to a substantial ICM viscosity suppressing mixing of the stripped galaxy or group gas with the hotter ambient ICM.Using hydrodynamical simulations of minor mergers we show, however, that these features can be explained naturally by the dynamical conditions of each particular galaxy or group infall. Specifically, we identify observable features to distinguish the first and second infall of a galaxy or group into its host cluster as well as characteristics during apocentre passage. Comparing our simulations with observations, we can explain several puzzling observations such as the long and cold tail of M86 in Virgo and the very long and tangentially oriented tail of the group LEDA 87445 in Hydra A.Using our simulations, we also assess the validity of the stagnation pressure method that is widely used to determine an infalling galaxy's velocity. We show that near pericentre passage the method gives reasonable results, but near apocentre it is not easily applicable.

  18. Massive star clusters in galaxies

    CERN Document Server

    Harris, William E

    2009-01-01

    The ensemble of all star clusters in a galaxy constitutes its star cluster system. In this review, the focus of the discussion is on the ability of star clusters, particularly the systems of old massive globular clusters (GCSs), to mark the early evolutionary history of galaxies. I review current themes and key findings in GCS research, and highlight some of the outstanding questions that are emerging from recent work.

  19. Gas-Rich Companions of Isolated Galaxies

    CERN Document Server

    Pisano, D J; Wilcots, Eric M.

    1999-01-01

    We have used the VLA to search for gaseous remnants of the galaxy formation process around six extremely isolated galaxies. We found two distinct HI clouds around each of two galaxies in our sample (UGC 9762 & UGC 11124). These clouds are rotating and appear to have optical counterparts, strongly implying that they are typical dwarf galaxies. The companions are currently weakly interacting with the primary galaxy, but have short dynamical friction timescales (~1 Gyr) suggesting that these triple galaxy systems will shortly collapse into one massive galaxy. Given that the companions are consistent with being in circular rotation about the primary galaxy, and that they have small relative masses, the resulting merger will be a minor one. The companions do, however, contain enough gas that the merger will represent a significant infusion of fuel to drive future star formation, bar formation, or central activity, while building up the mass of the disk thus making these systems important pieces of the galaxy f...

  20. The Environment of Galaxies at Low Redshift

    CERN Document Server

    Ivezic, Nicolas B Cowan Zeljko

    2008-01-01

    We compare environmental effects in two analogous samples of galaxies, one from the Sloan Digital Sky Survey (SDSS) and the other from a semi-analytic model (SAM) based on the Millennium Simulation (MS), to test to what extent current SAMs of galaxy formation are reproducing environmental effects. We estimate the large-scale environment of each galaxy using a Bayesian density estimator based on distances to all ten nearest neighbors and compare broad-band photometric properties of the two samples as a function of environment. The feedbacks implemented in the semi-analytic model produce a qualitatively correct galaxy population with similar environmental dependence as that seen in SDSS galaxies. In detail, however, the colors of MS galaxies exhibit an exaggerated dependence on environment: the field contains too many blue galaxies while clusters contain too many red galaxies, compared to the SDSS sample. We also find that the MS contains a population of highly clustered, relatively faint red galaxies with velo...

  1. The realm of the galaxy protoclusters

    CERN Document Server

    Overzier, R A

    2016-01-01

    The study of galaxy protoclusters is beginning to fill in unknown details of the important phase of the assembly of clusters and cluster galaxies. This review describes the current status of this field and highlights promising recent findings related to galaxy formation in the densest regions of the early universe. We discuss the main search techniques and the characteristic properties of protoclusters in observations and simulations, and show that protoclusters will have present-day masses similar to galaxy clusters when fully collapsed. We discuss the physical properties of galaxies in protoclusters, including (proto-)brightest cluster galaxies, and the forming red sequence. We highlight the fact that the most massive halos at high redshift are found in protoclusters, making these objects uniquely suited for testing important recent models of galaxy formation. We show that galaxies in protoclusters should be among the first galaxies at high redshift making the transition from a gas cooling regime dominated ...

  2. Galaxy alignments: Theory, modelling and simulations

    CERN Document Server

    Kiessling, Alina; Joachimi, Benjamin; Kirk, Donnacha; Kitching, Thomas D; Leonard, Adrienne; Mandelbaum, Rachel; Schäfer, Björn Malte; Sifón, Cristóbal; Brown, Michael L; Rassat, Anais

    2015-01-01

    The shapes of galaxies are not randomly oriented on the sky. During the galaxy formation and evolution process, environment has a strong influence, as tidal gravitational fields in large-scale structure tend to align the shapes and angular momenta of nearby galaxies. Additionally, events such as galaxy mergers affect the relative alignments of galaxies throughout their history. These "intrinsic galaxy alignments" are known to exist, but are still poorly understood. This review will offer a pedagogical introduction to the current theories that describe intrinsic galaxy alignments, including the apparent difference in intrinsic alignment between early- and late-type galaxies and the latest efforts to model them analytically. It will then describe the ongoing efforts to simulate intrinsic alignments using both $N$-body and hydrodynamic simulations. Due to the relative youth of this field, there is still much to be done to understand intrinsic galaxy alignments and this review summarises the current state of the ...

  3. The History of Star Formation in Galaxies

    CERN Document Server

    Brown, Thomas M; Calzetti, Daniela

    2009-01-01

    If we are to develop a comprehensive and predictive theory of galaxy formation and evolution, it is essential that we obtain an accurate assessment of how and when galaxies assemble their stellar populations, and how this assembly varies with environment. There is strong observational support for the hierarchical assembly of galaxies, but by definition the dwarf galaxies we see today are not the same as the dwarf galaxies and proto-galaxies that were disrupted during the assembly. Our only insight into those disrupted building blocks comes from sifting through the resolved field populations of the surviving giant galaxies to reconstruct the star formation history, chemical evolution, and kinematics of their various structures. To obtain the detailed distribution of stellar ages and metallicities over the entire life of a galaxy, one needs multi-band photometry reaching solar-luminosity main sequence stars. The Hubble Space Telescope can obtain such data in the outskirts of Local Group galaxies. To perform the...

  4. Measuring dark matter by modeling interacting galaxies

    CERN Document Server

    Petsch, H P; Theis, Ch

    2009-01-01

    The dark matter content of galaxies is usually determined from galaxies in dynamical equilibrium, mainly from rotationally supported galactic components. Such determinations restrict measurements to special regions in galaxies, e.g. the galactic plane(s), whereas other regions are not probed at all. Interacting galaxies offer an alternative, because extended tidal tails often probe outer or off-plane regions of galaxies. However, these systems are neither in dynamical equilibrium nor simple, because they are composed of two or more galaxies, by this increasing the associated parameter space.We present our genetic algorithm based modeling tool which allows to investigate the extended parameter space of interacting galaxies. From these studies, we derive the dynamical history of (well observed) galaxies. Among other parameters we constrain the dark matter content of the involved galaxies. We demonstrate the applicability of this strategy with examples ranging from stellar streams around theMilkyWay to extended ...

  5. Supersonic Motions of Galaxies in Clusters

    CERN Document Server

    Faltenbacher, A; Nagai, D; Gottlöber, S; Faltenbacher, Andreas; Kravtsov, Andrey V.; Nagai, Daisuke; Gottloeber, Stefan

    2004-01-01

    We study motions of galaxies in galaxy clusters formed in the concordance LCDM cosmology. We use high-resolution cosmological simulations that follow dynamics of dark matter and gas and include various physical processes critical for galaxy formation: gas cooling, heating and star formation. Analysing motions of galaxies and the properties of intracluster gas in the sample of eight simulated clusters at z=0, we study velocity dispersion profiles of the dark matter, gas, and galaxies. We measure the mean velocity of galaxy motions and gas sound speed as a function of radius and calculate the average Mach number of galaxy motions. The simulations show that galaxies, on average, move supersonically with the average Mach number of ~1.4, approximately independent of the cluster-centric radius. The supersonic motions of galaxies may potentially provide an important source of heating for the intracluster gas by driving weak shocks and via dynamical friction, although these heating processes appear to be inefficient ...

  6. Internal kinematics of modelled interacting disc galaxies

    CERN Document Server

    Kronberger, T; Schindler, S; Böhm, A; Kutdemir, E; Ziegler, B L

    2006-01-01

    We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of disc galaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, and galactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows the procedure applied in observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys significantly disturb the velocity fields and hence the RCs of the interacting galaxies, leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are rising or falling profiles in direction to the companion galaxy and bumps in the RCs. In addition, tidal tails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshift galaxies, on which we focus our investigations. The appearance of these distortions depends, however, strongly on the viewing angle. The velocity ...

  7. Star Formation in Tadpole Galaxies

    Directory of Open Access Journals (Sweden)

    Casiana Muñoz-Tuñon

    2014-12-01

    Full Text Available Tadpole Galaxies look like a star forming head with a tail structure to the side. They are also named cometaries. In a series of recent works we have discovered a number of issues that lead us to consider them extremely interesting targets. First, from images, they are disks with a lopsided starburst. This result is rmly  established with long slit spectroscopy in a nearby representative sample. They rotate with the head following the rotation pattern but displaced from the rotation center. Moreover, in a search for extremely metal poor (XMP galaxies, we identied tadpoles as the dominant shapes in the sample - nearly 80% of the local XMP galaxies have a tadpole morphology. In addition, the spatially resolved analysis of the metallicity shows the remarkable result that there is a metallicity drop right at the position of the head. This is contrary to what intuition would say and dicult to explain if star formation has happened from gas processed in the disk. The result could however be understood if the star formation is driven by pristine gas falling into the galaxy disk. If conrmed, we could be unveiling, for the rst time, cool  ows in action in our nearby world. The tadpole class is relatively frequent at high redshift - 10% of resolvable galaxies in the Hubble UDF but less than 1% in the local Universe. They are systems that could track cool ows and test models of galaxy formation.

  8. Galaxy Evolution in Rich Clusters

    Science.gov (United States)

    Schwarzkopf, U.; Hill, J. M.

    2000-12-01

    We present the first results of a study of the morphological and spectral evolution of galaxies within the dense cores of distant clusters at redshifts between z=0.4 and 1. The morphology, colors, concentration index, and asymmetry parameters of these cluster members are compared by using a combination of deep HST NICMOS and WFPC2 imaging, covering the rest-frame U and J bands. We also discuss the influence of dust obscuration on the derived measurements. Of particular interest is the morphology of galaxies at near-infrared wavelengths in rich clusters which show an excess of blue galaxies (Butcher-Oelmer effect), namely Abell 851 (z=0.4) and CL 1603+43 (z=0.92). We focus our study on optical/near-infrared measurements of galaxy asymmetry and central concentration, derived from a large number (>400) of objects detected within the core of Abell 851. The sensitivity and reliability of these parameters for galaxy classification and physical diagnostic purposes are tested. In conjunction with the use of recent source extraction software we are able to establish a fast, robust, and highly automated procedure of mapping the structural parameters of large galaxy samples. This work is supported by NASA, under contract NAS5-26555.

  9. A catalog of Kazarian galaxies

    Science.gov (United States)

    Kazarian, M. A.; Adibekyan, V. Zh.; McLean, B.; Allen, R. J.; Petrosian, A. R.

    2010-01-01

    The entire Kazarian galaxies (KG) catalog is presented, which combines extensive new measurements of their optical parameters with a literature and database search. The measurements were made using images extracted from the STScI Digitized Sky Survey (DSS) of Jpg(blue), Fpg(red), and Ipg(NIR) band photographic sky survey plates obtained by the Palomar and UK Schmidt telescopes. We provide accurate coordinates, morphological types, spectral and activity classes, blue apparent diameters, axial ratios, position angles, red, blue, and NIR apparent magnitudes, as well as counts of neighboring objects in a circle of radius 50 kpc from centers of KG. Special attention was paid to the individual descriptions of the galaxies in the original Kazarian lists, which clarified many cases of misidentifications of the objects, particularly among interacting systems. The total number of individual Kazarian objects in the database is now 706. We also include the redshifts, which are now available for 404 galaxies and the 2MASS infrared magnitudes for 598 KG. The database also includes extensive notes, which summarize information about the membership of Kazarian galaxies in different systems of galaxies and about revised activity classes and redshifts. An atlas of several interesting subclasses of Kazarian galaxies is also presented.

  10. Modelling nova populations in galaxies

    CERN Document Server

    Chen, Hai-Liang; Yungelson, L R; Gilfanov, M; Han, Zhanwen

    2016-01-01

    Theoretical modelling of the evolution of classical and recurrent novae plays an important role in studies of binary evolution, nucleosynthesis and accretion physics. However, from a theoretical perspective the observed statistical properties of novae remain poorly understood. In this paper, we have produced model populations of novae using a hybrid binary population synthesis approach for differing star formation histories (SFHs): a starburst case (elliptical-like galaxies), a constant star formation rate case (spiral-like galaxies) and a composite case (in line with the inferred SFH for M31). We found that the nova rate at 10\\;Gyr in an elliptical-like galaxy is $\\sim 10-20$ times smaller than a spiral-like galaxy with the same mass. The majority of novae in elliptical-like galaxies at the present epoch are characterized by low mass white dwarfs (WDs), long decay times, relatively faint absolute magnitudes and long recurrence periods. In contrast, the majority of novae in spiral-like galaxies at 10\\;Gyr hav...

  11. The rotation of Galaxy Clusters

    CERN Document Server

    Tovmassian, Hrant 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\\%, and clusters of BMI type with dominant cD galaxy, ~ 35%. 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 merging with other clusters and groups of galaxies, in the result of which the rotation has been prevented.

  12. Qualitative interpretation of galaxy spectra

    CERN Document Server

    Almeida, J Sanchez; Terlevich, E; Fernandes, R Cid; Morales-Luis, A B

    2012-01-01

    We describe a simple step-by-step guide to qualitative interpretation of galaxy spectra. Rather than an alternative to existing automated tools, it is put forward as an instrument for quick-look analysis, and for gaining physical insight when interpreting the outputs provided by automated tools. Though the recipe is of general application, it was developed for understanding the nature of the Automatic Spectroscopic K-means based (ASK) template spectra. They resulted from the classification of all the galaxy spectra in the Sloan Digital Sky Survey data release 7 (SDSS-DR7), thus being a comprehensive representation of the galaxy spectra in the local universe. Using the recipe, we give a description of the properties of the gas and the stars that characterize the ASK classes, from those corresponding to passively evolving galaxies, to HII galaxies undergoing a galaxy-wide starburst. The qualitative analysis is found to be in excellent agreement with quantitative analyses of the same spectra. A number of byprodu...

  13. Manganese in dwarf spheroidal galaxies

    CERN Document Server

    North, P; Jablonka, P; Hill, V; Shetrone, M; Letarte, B; Lemasle, B; Venn, K A; Battaglia, G; Tolstoy, E; Irwin, M J; Primas, F; Francois, P

    2012-01-01

    We provide manganese abundances (corrected for the effect of the hyperfine structure) for a large number of stars in the dwarf spheroidal galaxies Sculptor and Fornax, and for a smaller number in the Carina and Sextans dSph galaxies. Abundances had already been determined for a number of other elements in these galaxies, including alpha and iron-peak ones, which allowed us to build [Mn/Fe] and [Mn/alpha] versus [Fe/H] diagrams. The Mn abundances imply sub-solar [Mn/Fe] ratios for the stars in all four galaxies examined. In Sculptor, [Mn/Fe] stays roughly constant between [Fe/H]\\sim -1.8 and -1.4 and decreases at higher iron abundance. In Fornax, [Mn/Fe] does not vary in any significant way with [Fe/H]. The relation between [Mn/alpha] and [Fe/H] for the dSph galaxies is clearly systematically offset from that for the Milky Way, which reflects the different star formation histories of the respective galaxies. The [Mn/alpha] behavior can be interpreted as a result of the metal-dependent Mn yields of type II and ...

  14. Mercury in waters, soils, and sediments of the New Jersey Coastal Plain: A comparison of regional distribution and mobility with the mercury contamination at the William J. Hughes Technical Center, Atlantic County, New Jersey

    Science.gov (United States)

    Barringer, Julia L.; Szabo, Zoltan; Reilly, Pamela A.

    2012-01-01

    Mercury in soils, surface water, and groundwater at the William J. Hughes Technical Center , Atlantic County, New Jersey, has been found at levels that exceed established background concentrations in Coastal Plain waters, and, in some cases, New Jersey State standards for mercury in various media. As of 2012, it is not known whether this mercury is part of regional mercury contamination or whether it is related to former military activities. Regionally, groundwater supplying about 700 domestic wells in the New Jersey Coastal Plain is contaminated with mercury that appears to be derived from anthropogenic inputs, such as agricultural pesticide use and atmospheric deposition. High levels of mercury occasionally are found in Coastal Plain soils, but disturbance during residential development on former agricultural land is thought to have mobilized any mercury applied during farming, a hypothesis borne out by experiments leaching mercury from soils. In the unsewered residential areas with mercury-contaminated groundwater, septic-system effluent is believed to create reducing conditions in which mercury sorbed to subsoils is mobilized to groundwater. In comparing the levels of mercury found in soils, sediments, streamwater, and groundwater at the William J. Hughes Technical Center site with those found regionally, mercury concentrations in groundwater in the region are, in some cases, substantially higher than those found in groundwater at the William J. Hughes Technical Center site. Nevertheless, concentrations of mercury in streamwater at the site are, in some instances, higher than most found regionally. The mercury contents in soils and sediment at the William J. Hughes Technical Center site are substantially higher than those found to date (2012) in the region, indicating that a source other than regional sources may be present at the site.

  15. Submillimeter galaxies as progenitors of compact quiescent galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Toft, S.; Zirm, A.; Krogager, J.-K.; Man, A. W. S. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Mariesvej 30, DK-2100 Copenhagen (Denmark); Smolčić, V.; Krpan, J. [Physics Department, University of Zagreb, Bijenička cesta 32, 10002 Zagreb (Croatia); Magnelli, B.; Karim, A. [Argelander Institute for Astronomy, Auf dem Hügel 71, Bonn, D-53121 (Germany); Michalowski, M. [Scottish Universities Physics Alliance, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ (United Kingdom); Capak, P. [Spitzer Science Center, 314-6 Caltech, 1201 East California Boulevard, Pasadena, CA 91125 (United States); Sheth, K. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Schawinski, K. [ETH Zurich, Institute for Astronomy, Department of Physics, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich (Switzerland); Wuyts, S.; Lutz, D.; Staguhn, J.; Berta, S. [MPE, Postfach 1312, D-85741 Garching (Germany); Sanders, D. [Institute for Astronomy, 2680 Woodlawn Drive, University of Hawaii, Honolulu, HI 96822 (United States); Mccracken, H. [Institut dAstrophysique de Paris, UMR7095 CNRS, Universite Pierre et Marie Curie, 98 bis Boulevard Arago, F-75014 Paris (France); Riechers, D., E-mail: sune@dark-cosmology.dk [Department of Astronomy, Cornell University, 220 Space Sciences Building, Ithaca, NY 14853 (United States)

    2014-02-20

    Three billion years after the big bang (at redshift z = 2), half of the most massive galaxies were already old, quiescent systems with little to no residual star formation and extremely compact with stellar mass densities at least an order of magnitude larger than in low-redshift ellipticals, their descendants. Little is known about how they formed, but their evolved, dense stellar populations suggest formation within intense, compact starbursts 1-2 Gyr earlier (at 3 < z < 6). Simulations show that gas-rich major mergers can give rise to such starbursts, which produce dense remnants. Submillimeter-selected galaxies (SMGs) are prime examples of intense, gas-rich starbursts. With a new, representative spectroscopic sample of compact, quiescent galaxies at z = 2 and a statistically well-understood sample of SMGs, we show that z = 3-6 SMGs are consistent with being the progenitors of z = 2 quiescent galaxies, matching their formation redshifts and their distributions of sizes, stellar masses, and internal velocities. Assuming an evolutionary connection, their space densities also match if the mean duty cycle of SMG starbursts is 42{sub −29}{sup +40} Myr (consistent with independent estimates), which indicates that the bulk of stars in these massive galaxies were formed in a major, early surge of star formation. These results suggest a coherent picture of the formation history of the most massive galaxies in the universe, from their initial burst of violent star formation through their appearance as high stellar-density galaxy cores and to their ultimate fate as giant ellipticals.

  16. Do Galaxies Follow Darwinian Evolution?

    Science.gov (United States)

    2006-12-01

    Using VIMOS on ESO's Very Large Telescope, a team of French and Italian astronomers have shown the strong influence the environment exerts on the way galaxies form and evolve. The scientists have for the first time charted remote parts of the Universe, showing that the distribution of galaxies has considerably evolved with time, depending on the galaxies' immediate surroundings. This surprising discovery poses new challenges for theories of the formation and evolution of galaxies. The 'nature versus nurture' debate is a hot topic in human psychology. But astronomers too face similar conundrums, in particular when trying to solve a problem that goes to the very heart of cosmological theories: are the galaxies we see today simply the product of the primordial conditions in which they formed, or did experiences in the past change the path of their evolution? ESO PR Photo 17/06 ESO PR Photo 45/06 Galaxy Distribution in Space In a large, three-year long survey carried out with VIMOS [1], the Visible Imager and Multi-Object Spectrograph on ESO's VLT, astronomers studied more than 6,500 galaxies over a wide range of distances to investigate how their properties vary over different timescales, in different environments and for varying galaxy luminosities [2]. They were able to build an atlas of the Universe in three dimensions, going back more than 9 billion years. This new census reveals a surprising result. The colour-density relation, that describes the relationship between the properties of a galaxy and its environment, was markedly different 7 billion years ago. The astronomers thus found that the galaxies' luminosity, their initial genetic properties, and the environments they reside in have a profound impact on their evolution. "Our results indicate that environment is a key player in galaxy evolution, but there's no simple answer to the 'nature versus nurture' problem in galaxy evolution," said Olivier Le Fèvre from the Laboratoire d'Astrophysique de Marseille

  17. Galaxy bias from galaxy-galaxy lensing in the DES Science Verification Data

    Energy Technology Data Exchange (ETDEWEB)

    Prat, J.; et al.

    2016-09-26

    We present a measurement of galaxy-galaxy lensing around a magnitude-limited ($i_{AB} < 22.5$) sample of galaxies selected from the Dark Energy Survey Science Verification (DES-SV) data. We split these lenses into three photometric-redshift bins from 0.2 to 0.8, and determine the product of the galaxy bias $b$ and cross-correlation coefficient between the galaxy and dark matter overdensity fields $r$ in each bin, using scales above 4 Mpc/$h$ comoving, where we find the linear bias model to be valid given our current uncertainties. We compare our galaxy bias results from galaxy-galaxy lensing with those obtained from galaxy clustering (Crocce et al. 2016) and CMB lensing (Giannantonio et al. 2016) for the same sample of galaxies, and find our measurements to be in good agreement with those in Crocce et al. (2016), while, in the lowest redshift bin ($z\\sim0.3$), they show some tension with the findings in Giannantonio et al. (2016). Our results are found to be rather insensitive to a large range of systematic effects. We measure $b\\cdot r$ to be $0.87\\pm 0.11$, $1.12 \\pm 0.16$ and $1.24\\pm 0.23$, respectively for the three redshift bins of width $\\Delta z = 0.2$ in the range $0.2galaxy sample, except possibly at the lowest redshift bin ($z\\sim 0.3$), where we find $r = 0.71 \\pm 0.11$ when using TPZ, and $0.83 \\pm 0.12$ with BPZ, assuming the difference between the results from the two probes can be solely attributed to the cross-correlation parameter.

  18. FPGA implementation of a modified FitzHugh-Nagumo neuron based causal neural network for compact internal representation of dynamic environments

    Science.gov (United States)

    Salas-Paracuellos, L.; Alba, Luis; Villacorta-Atienza, Jose A.; Makarov, Valeri A.

    2011-05-01

    Animals for surviving have developed cognitive abilities allowing them an abstract representation of the environment. This internal representation (IR) may contain a huge amount of information concerning the evolution and interactions of the animal and its surroundings. The temporal information is needed for IRs of dynamic environments and is one of the most subtle points in its implementation as the information needed to generate the IR may eventually increase dramatically. Some recent studies have proposed the compaction of the spatiotemporal information into only space, leading to a stable structure suitable to be the base for complex cognitive processes in what has been called Compact Internal Representation (CIR). The Compact Internal Representation is especially suited to be implemented in autonomous robots as it provides global strategies for the interaction with real environments. This paper describes an FPGA implementation of a Causal Neural Network based on a modified FitzHugh-Nagumo neuron to generate a Compact Internal Representation of dynamic environments for roving robots, developed under the framework of SPARK and SPARK II European project, to avoid dynamic and static obstacles.

  19. Sir Hugh Cairns and World War II British advances in head injury management, diffuse brain injury, and concussion: an Oxford tale.

    Science.gov (United States)

    Stone, James L; Patel, Vimal; Bailes, Julian E

    2016-11-01

    The authors trace the Oxford, England, roots of World War II (WWII)-related advances in head injury management, the biomechanics of concussion and brain injury, and postwar delineation of pathological findings in severe concussion and diffuse brain injury in man. The prominent figure in these developments was the charismatic and innovative Harvey Cushing-trained neurosurgeon Sir Hugh Cairns. Cairns, who was to closely emulate Cushing's surgical and scholarly approach, is credited with saving thousands of lives during WWII by introducing and implementing innovative programs such as helmets for motorcyclists, mobile neurosurgical units near battle zones, and the military usage of penicillin. In addition, he inspired and taught a generation of neurosurgeons, neurologists, and neurological nurses in the care of brain and spinal cord injuries at Oxford's Military Hospital for Head Injuries. During this time Cairns also trained the first full-time female neurosurgeon. Pivotal in supporting animal research demonstrating the critical role of acceleration in the causation of concussion, Cairns recruited the physicist Hylas Holbourn, whose research implicated rotary acceleration and shear strains as particularly damaging. Cairns' work in military medicine and head injury remain highly influential in efforts to mitigate and manage brain injury.

  20. Gas Stripping in the Simulated Pegasus Galaxy

    Science.gov (United States)

    Mercado, Francisco Javier; Samaniego, Alejandro; Wheeler, Coral; Bullock, James

    2017-01-01

    We utilize the hydrodynamic simulation code GIZMO to construct a non-cosmological idealized dwarf galaxy built to match the parameters of the observed Pegasus dwarf galaxy. This simulated galaxy will be used in a series of tests in which we will implement different methods of removing the dwarf’s gas in order to emulate the ram pressure stripping mechanism encountered by dwarf galaxies as they fall into more massive companion galaxies. These scenarios will be analyzed in order to determine the role that the removal of gas plays in rotational vs. dispersion support (Vrot/σ) of our galaxy.

  1. The Local Universe: Galaxies in 3D

    CERN Document Server

    Koribalski, B S

    2016-01-01

    Here I present results from individual galaxy studies and galaxy surveys in the Local Universe with particular emphasis on the spatially resolved properties of neutral hydrogen gas. The 3D nature of the data allows detailed studies of the galaxy morphology and kinematics, their relation to local and global star formation as well as galaxy environments. I use new 3D visualisation tools to present multi-wavelength data, aided by tilted-ring models of the warped galaxy disks. Many of the algorithms and tools currently under development are essential for the exploration of upcoming large survey data, but are also highly beneficial for the analysis of current galaxy surveys.

  2. Globular Clusters for Faint Galaxies

    Science.gov (United States)

    Kohler, Susanna

    2017-07-01

    The origin of ultra-diffuse galaxies (UDGs) has posed a long-standing mystery for astronomers. New observations of several of these faint giants with the Hubble Space Telescope are now lending support to one theory.Faint-Galaxy MysteryHubble images of Dragonfly 44 (top) and DFX1 (bottom). The right panels show the data with greater contrast and extended objects masked. [van Dokkum et al. 2017]UDGs large, extremely faint spheroidal objects were first discovered in the Virgo galaxy cluster roughly three decades ago. Modern telescope capabilities have resulted in many more discoveries of similar faint galaxies in recent years, suggesting that they are a much more common phenomenon than we originally thought.Despite the many observations, UDGs still pose a number of unanswered questions. Chief among them: what are UDGs? Why are these objects the size of normal galaxies, yet so dim? There are two primary models that explain UDGs:UDGs were originally small galaxies, hence their low luminosity. Tidal interactions then puffed them up to the large size we observe today.UDGs are effectively failed galaxies. They formed the same way as normal galaxies of their large size, but something truncated their star formation early, preventing them from gaining the brightness that we would expect for galaxies of their size.Now a team of scientists led by Pieter van Dokkum (Yale University) has made some intriguing observations with Hubble that lend weight to one of these models.Globulars observed in 16 Coma-cluster UDGs by Hubble. The top right panel shows the galaxy identifications. The top left panel shows the derived number of globular clusters in each galaxy. [van Dokkum et al. 2017]Globulars GaloreVan Dokkum and collaborators imaged two UDGs with Hubble: Dragonfly 44 and DFX1, both located in the Coma galaxy cluster. These faint galaxies are both smooth and elongated, with no obvious irregular features, spiral arms, star-forming regions, or other indications of tidal interactions

  3. SAMI Galaxy Survey: Spectrally Dissecting 3400 Galaxies By the Dozen

    Science.gov (United States)

    Cecil, Gerald N.; Croom, S.; The SAMI Galaxy Survey Team

    2014-01-01

    More than 440 mapped, less than 3000 to go in the Sydney-AAO Multi-object IFU (SAMI) Galaxy Survey! SAMI uses novel, photonic fused-optical fiber “hexabundles” that were developed successfully at The University of Sydney and the Australian Astronomical Observatory AAO), with support from the Australian Research Council Centre of Excellence for All-Sky Astrophysics (CAASTRO). The SAMI Galaxy Survey, led by Assoc. Prof. Croom, is backed by an international team. This spectro-bolometric survey mitigates against “aperture effects” that may mislead when stacking single-fiber galaxy spectra. We seek to answer questions such as “what is the physical role of environment in galaxy evolution? How is stellar mass growth and angular momentum development related in galaxies? How does gas get into and out of galaxies, and how do such flows drive star formation?” SAMI maps stellar and gas properties with 13 integral-field units (IFU) plugged onto a dozen galaxies over the 1° field of the AAT prime-focus corrector. 78% of each bundle's area is filled by sixty-one 1.6-arcsec diameter fibers that are packed closely into concentric circles then their etched, thinned cladding is fused without deforming their cores. The fiber hexabundles route to the bench-mounted AAOmega double-beam spectrograph to cover simultaneously 373-570 nm at R=1730 and 620-735 nm at R=4500. Full spatial resolution of the observing site is recovered by dithered exposures totaling 3.5 hours per field. Target stellar masses generally exceed 108 M⊙, and span a range of environments: ˜650 are within clusters of virial mass 1014-15 M⊙ at 0.03 team, from rotation curve dependence on group halo mass, through galaxy winds and AGN feedback mechanisms, to oxygen abundance gradients, kinematic decomposition of galaxies into structural components to refine the T-F and FP scaling relations, and aperture effects. Our large sample size enables study of environmental dependencies. As the SAMI survey executes

  4. A Galaxy is Born in a Swirling Hydrogen Cloud

    Science.gov (United States)

    1995-10-01

    radio images are combined, it is seen that a radio `jet' emerges from the centre of the galaxy and interacts vigorously with the inner region of the gas cloud. This jet is believed to be a narrow stream of high-energy electrons spewed out at the edge of a black hole located at the center of the galaxy. Such jets are often seen in distant radio galaxies. But the most intriguing property of 1243+036 is revealed by the faint glow from the hydrogen atoms in the outer regions of the gas cloud, now detected on the EMMI spectra. The extent of this faint light shows that the size of the gas cloud is almost 500,000 light years, i.e. many times larger than the clouds seen around normal galaxies. The mass of this enormous cloud probably exceeds 10,000 million times that of the Sun. This Press Release is accompanied by ESO Press Photo 32/95 [86K] with an explanatory text that shows these features. The Giant Hydrogen Cloud Rotates ! Even more exciting, the astronomers also found that the measured wavelength of the Lyman-alpha emission from the hydrogen gas differs slightly, but systematically from one side of the cloud to the other. The difference implies that the two extremities of the cloud are rushing away from us with speeds that differ by 450 km/s. This is the first time ever that organized motion in such a large and distant structure has been detected and measured. According to van Ojik and his colleagues, the most likely explanation of the variation in speed is that the huge gas cloud rotates in such a way that the Northwest edge is receding and the Southeast edge is approaching, relative to the embedded galaxy at its centre. The measured size of the cloud and the rotation velocity indicate that it has made about one complete revolution since the Big Bang. The cloud around 1243+036 may be a relic of the earliest stages of formation of this galaxy. The observed motion may in fact represent a typical state of the gas around primeval galaxies in the young Universe, before it is

  5. Quenching of Satellite Galaxies at the Outskirts of Galaxy Clusters

    CERN Document Server

    Zinger, Elad; Kravtsov, Andrey V; Nagai, Daisuke

    2016-01-01

    We find, using cosmological simulations of galaxy clusters, that the hot X-ray emitting intra-cluster medium (ICM) enclosed within the outer accretion shock extends out to $R_{\\rm shock}\\sim(2 - 3) R_{\\rm vir}$, where $R_{\\rm vir}$ is the standard virial radius of the halo. Using a simple analytic model for satellite galaxies in the cluster, we evaluate the effect of ram-pressure stripping on the gas in the inner discs and in the haloes at different distances from the cluster centre. We find that significant removal of star-forming disc gas occurs only at $r \\lesssim 0.5 R_{\\rm vir}$, while gas removal from the satellite halo is also efficient between $R_{\\rm vir}$ and $R_{\\rm shock}$. This leads to quenching of star formation by starvation over $2-3\\,{\\rm Gyr}$, prior to the satellite entry to the inner cluster halo. This can explain the presence of quenched galaxies, preferentially discs, at the outskirts of galaxy clusters, and the delayed quenching of satellites compared to central galaxies.

  6. Galaxy-Galaxy Lensing in the DES Science Verification Data

    CERN Document Server

    Clampitt, J; Kwan, J; Krause, E; MacCrann, N; Park, Y; Troxel, M A; Jain, B; Rozo, E; Rykoff, E S; Wechsler, R H; Blazek, J; Bonnett, C; Crocce, M; Fang, Y; Gaztanaga, E; Gruen, D; Jarvis, M; Miquel, R; Prat, J; Ross, A J; Sheldon, E; Zuntz, J; Abbott, T M C; Abdalla, F B; Armstrong, R; Becker, M R; Benoit-Lévy, A; Bernstein, G M; Bertin, E; Brooks, D; Burke, D L; Rosell, A Carnero; Kind, M Carrasco; Cunha, C E; D'Andrea, C B; da Costa, L N; Desai, S; Diehl, H T; Dietrich, J P; Doel, P; Estrada, J; Evrard, A E; Neto, A Fausti; Flaugher, B; Fosalba, P; Frieman, J; Gruendl, R A; Honscheid, K; James, D J; Kuehn, K; Kuropatkin, N; Lima, M; March, M; Marshall, J L; Martini, P; Melchior, P; Mohr, J J; Nichol, R C; Nord, B; Plazas, A A; Romer, A K; Sanchez, E; Scarpine, V; Schubnell, M; Sevilla-Noarbe, I; Smith, R C; Soares-Santos, M; Sobreira, F; Suchyta, E; Swanson, M E C; Tarle, G; Thomas, D; Vikram, V; Walker, A R

    2016-01-01

    We present galaxy-galaxy lensing results from 139 square degrees of Dark Energy Survey (DES) Science Verification (SV) data. Our lens sample consists of red galaxies, known as redMaGiC, which are specifically selected to have a low photometric redshift error and outlier rate. The lensing measurement has a total signal-to-noise of 29, including all lenses over a wide redshift range $0.2 < z < 0.8$. Dividing the lenses into three redshift bins, we find no evidence for evolution in the halo mass with redshift. We obtain consistent results for the lensing measurement with two independent shear pipelines, ngmix and im3shape. We perform a number of null tests on the shear and photometric redshift catalogs and quantify resulting systematic errors. Covariances from jackknife subsamples of the data are validated with a suite of 50 mock surveys. The results and systematics checks in this work provide a critical input for future cosmological and galaxy evolution studies with the DES data and redMaGiC galaxy sample...

  7. Satellites of spiral galaxies

    Science.gov (United States)

    Zaritsky, Dennis; Smith, Rodney; Frenk, Carlos; White, Simon D. M.

    1993-01-01

    We present a survey of satellites around a homogeneous set of late-type spirals with luminosity similar to that of the Milky Way. On average, we find fewer than 1.5 satellites per primary, but we argue that we can treat the survey as an ensemble and so derive the properties of the halo of a 'typical' isolated spiral. The projected density profile of the ensemble falls off approximately as 1/r. Within 50 kpc the azimuthal distribution of satellites shows some evidence for the 'Holmberg effect', an excess near the minor axis of the primary; however, at larger projected distances, the distribution appears isotropic. There is a weak but significant correlation between the size of a satellite and its distance from its primary, as expected if satellites are tidally truncated. Neither Hubble type nor spectral characteristics correlate with apparent separation. The ensemble of satellites appears to be rotating at about 30 km/s in the same direction as the galactic disk. Satellites on prograde orbits tend to be brighter than those on retrograde orbits. The typical velocity difference between a satellite and its primary shows no clear dependence either on apparent separation, or on the rotation speed of the primary. Thus our survey demonstrates that isolated spiral galaxies have massive halos that extend to many optical radii.

  8. Fitting Galaxies on GPUs

    Science.gov (United States)

    Barsdell, B. R.; Barnes, D. G.; Fluke, C. J.

    2011-07-01

    Structural parameters are normally extracted from observed galaxies by fitting analytic light profiles to the observations. Obtaining accurate fits to high-resolution images is a computationally expensive task, requiring many model evaluations and convolutions with the imaging point spread function. While these algorithms contain high degrees of parallelism, current implementations do not exploit this property. With ever-growing volumes of observational data, an inability to make use of advances in computing power can act as a constraint on scientific outcomes. This is the motivation behind our work, which aims to implement the model-fitting procedure on a graphics processing unit (GPU). We begin by analysing the algorithms involved in model evaluation with respect to their suitability for modern many-core computing architectures like GPUs, finding them to be well-placed to take advantage of the high memory bandwidth offered by this hardware. Following our analysis, we briefly describe a preliminary implementation of the model fitting procedure using freely-available GPU libraries. Early results suggest a speed-up of around 10× over a CPU implementation. We discuss the opportunities such a speed-up could provide, including the ability to use more computationally expensive but better-performing fitting routines to increase the quality and robustness of fits.

  9. A galaxy of folds.

    Science.gov (United States)

    Alva, Vikram; Remmert, Michael; Biegert, Andreas; Lupas, Andrei N; Söding, Johannes

    2010-01-01

    Many protein classification systems capture homologous relationships by grouping domains into families and superfamilies on the basis of sequence similarity. Superfamilies with similar 3D structures are further grouped into folds. In the absence of discernable sequence similarity, these structural similarities were long thought to have originated independently, by convergent evolution. However, the growth of databases and advances in sequence comparison methods have led to the discovery of many distant evolutionary relationships that transcend the boundaries of superfamilies and folds. To investigate the contributions of convergent versus divergent evolution in the origin of protein folds, we clustered representative domains of known structure by their sequence similarity, treating them as point masses in a virtual 2D space which attract or repel each other depending on their pairwise sequence similarities. As expected, families in the same superfamily form tight clusters. But often, superfamilies of the same fold are linked with each other, suggesting that the entire fold evolved from an ancient prototype. Strikingly, some links connect superfamilies with different folds. They arise from modular peptide fragments of between 20 and 40 residues that co-occur in the connected folds in disparate structural contexts. These may be descendants of an ancestral pool of peptide modules that evolved as cofactors in the RNA world and from which the first folded proteins arose by amplification and recombination. Our galaxy of folds summarizes, in a single image, most known and many yet undescribed homologous relationships between protein superfamilies, providing new insights into the evolution of protein domains.

  10. Binary Satellite Galaxies

    CERN Document Server

    Evslin, Jarah

    2013-01-01

    Suggestions have appeared in the literature that the following five pairs of Milky Way and Andromeda satellite galaxies are gravitationally bound: Draco and Ursa Minor, Leo IV and V, Andromeda I and III, NGC 147 and 185, and the Magellanic clouds. Under the assumption that a given pair is gravitationally bound, the Virial theorem provides an estimate of its total mass and so its instantaneous tidal radius. For all of these pairs except for the Magellanic clouds the resulting total mass is 2 to 4 orders of magnitude higher than that within the half light radius. Furthermore in the case of each pair except for Leo IV and Leo V, the estimated tidal radius is inferior to the separation between the two satellites. Therefore all or almost all of these systems are not gravitationally bound. We note several possible explanations for the proximities and similar radial velocities of the satellites in each pair, for example they may have condensed from the same infalling structure or they may be bound by a nongravitatio...

  11. Nomads of the Galaxy

    CERN Document Server

    Strigari, Louis E; Marshall, Philip J; Blandford, Roger D

    2012-01-01

    We estimate that there may be up to ~10^5 compact objects in the mass range 10^{-8} -10^{-2} solar mass per main sequence star that are unbound to a host star in the Galaxy. We refer to these objects as nomads; in the literature a subset of these are sometimes called free-floating or rogue planets. Our estimate for the number of Galactic nomads is consistent with a smooth extrapolation of the mass function of unbound objects above the Jupiter-mass scale, the stellar mass density limit, and the metallicity of the interstellar medium. We analyze the prospects for detecting nomads via Galactic microlensing. The Wide-Field Infrared Survey Telescope (WFIRST) will measure the number of nomads per main sequence star greater than the mass of Jupiter to ~ 13%, and the corresponding number greater than the mass of Mars to ~25%. All-sky surveys such as GAIA and LSST can identify nomads greater than about the mass of Jupiter. We suggest a dedicated drift scanning telescope that covers approximately 100 square degrees in ...

  12. Astrophysics of galaxy clusters

    Science.gov (United States)

    Ettori, Stefano

    2016-07-01

    As the nodes of the cosmic web, clusters of galaxies trace the large-scale distribution of matter in the Universe. They are thus privileged sites in which to investigate the complex physics of structure formation. However, the complete story of how these structures grow, and how they dissipate the gravitational and non-thermal components of their energy budget over cosmic time, is still beyond our grasp. Most of the baryons gravitationally bound to the cluster's halo is in the form of a diffuse, hot, metal-enriched plasma that radiates primarily in the X-ray band. X-ray observations of the evolving cluster population provide a unique opportunity to address such fundamental open questions as: How do hot diffuse baryons accrete and dynamically evolve in dark matter potentials? How and when was the energy that we observe in the ICM generated and distributed? Where and when are heavy elements produced and how are they circulated? We will present the ongoing activities to define the strategy on how an X-ray observatory with large collecting area and an unprecedented combination of high spectral and angular resolution, such as Athena, can address these questions.

  13. Galaxies Probing Galaxies: Cool Halo Gas from a z = 0.47 Post-Starburst Galaxy

    Science.gov (United States)

    Rubin, Kate H. R.; Prochaska, J. Xavier; Koo, David C.; Phillips, Andrew C.; Weiner, Benjamin J.

    2010-03-01

    We study the cool gas around a galaxy at z = 0.4729 using Keck/LRIS spectroscopy of a bright (B = 21.7) background galaxy at z = 0.6942 at a transverse distance of 16.5h -1 70 kpc. The background galaxy spectrum reveals strong Fe II, Mg II, Mg I, and Ca II absorption at the redshift of the foreground galaxy, with an Mg II λ2796 rest equivalent width of 3.93 ± 0.08 Å, indicative of a velocity width exceeding 400 km s-1. Because the background galaxy is large (>4h -1 70 kpc), the high covering fraction of the absorbing gas suggests that it arises in a spatially extended complex of cool clouds with large velocity dispersion. Spectroscopy of the massive (log M */M sun = 11.15 ± 0.08) host galaxy reveals that it experienced a burst of star formation about 1 Gyr ago and that it harbors a weak active galactic nucleus. We discuss the possible origins of the cool gas in its halo, including multiphase cooling of hot halo gas, cold inflow, tidal interactions, and galactic winds. We conclude that the absorbing gas was most likely ejected or tidally stripped from the interstellar medium of the host galaxy or its progenitors during the past starburst event. Adopting the latter interpretation, these results place one of only a few constraints on the radial extent of cool gas driven or stripped from a galaxy in the distant universe. Future studies with integral field unit spectroscopy of spatially extended background galaxies will provide multiple sight lines through foreground absorbers and permit analysis of the morphology and kinematics of the gas surrounding galaxies with a diverse set of properties and environments. 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.

  14. Galaxy-galaxy lensing estimators and their covariance properties

    CERN Document Server

    Singh, Sukhdeep; Seljak, Uroš; Slosar, Anže; Gonzalez, Jose Vazquez

    2016-01-01

    We study the covariance properties of real space correlation function estimators -- primarily galaxy-shear correlations, or galaxy-galaxy lensing -- using SDSS data for both shear catalogs and lenses (specifically the BOSS LOWZ sample). Using mock catalogs of lenses and sources, we disentangle the various contributions to the covariance matrix and compare them with a simple analytical model. We show that not subtracting the lensing measurement around random points from the measurement around the lens sample is equivalent to performing the measurement using the density field instead of the over-density field, and that this leads to a significant error increase due to an additional term in the covariance. Therefore, this subtraction should be performed regardless of its beneficial effects on systematics. Comparing the error estimates from data and mocks for estimators that involve the over-density, we find that the errors are dominated by the shape noise and lens clustering, that empirically estimated covarianc...

  15. Galaxy Zoo: Reproducing Galaxy Morphologies Via Machine Learning

    CERN Document Server

    Banerji, Manda; Lintott, Chris J; Abdalla, Filipe B; Schawinski, Kevin; Andreescu, Dan; Bamford, Steven; Murray, Phil; Raddick, M Jordan; Slosar, Anze; Szalay, Alex; Thomas, Daniel; Vandenberg, Jan

    2009-01-01

    We present morphological classifications obtained using machine learning for objects in SDSS DR7 that have been classified by Galaxy Zoo into three classes namely spirals, ellipticals and stars/unique objects. An artificial neural network is trained on a subset of objects classified by the human eye and we test whether the machine learning algorithm can reproduce the human classifications for the rest of the sample. We find that the success of the neural network in matching the human classifications depends crucially on the set of input parameters chosen for the machine-learning algorithm. The colours, concentrations and parameters associated with profile-fitting are reasonable in seperating the stars and galaxies into three classes. However, these results are considerably improved when adding adaptive shape parameters as well as texture. The adaptive moments and texture parameters alone cannot distinguish between stars and elliptical galaxies. Using a set of thirteen distance-independant parameters, the neur...

  16. Large-scale environmental dependence of gas-phase metallicity in dwarf galaxies

    CERN Document Server

    Douglass, Kelly A

    2016-01-01

    We study how the cosmic environment affects galaxy evolution in the Universe by comparing the metallicities of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the fluxes of emission lines, particularly those of the forbidden [OIII] and [SII] transitions, provide estimates of a region's electron temperature and number density. From these two quantities and the emission line fluxes [OII] 3727, [OIII] 4363, and [OIII] 4959,5007, we estimate the abundance of oxygen with the Direct Te method. We estimate the metallicity of 37 void dwarf galaxies and 75 dwarf galaxies in more dense regions using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, as re-processed in the MPA-JHU value-added catalog. We find very little difference between the two sets of galaxies, indicating little influence from the large-scale environment on their chemical evolution. Of particular interest are a number of extremely metal-poor dwarf galaxies that are equally abundant in both voids...

  17. Optical and X-ray profiles in the REXCESS sample of galaxy clusters

    CERN Document Server

    Holland, John G; Chon, Gayoung; Pierini, Daniele

    2015-01-01

    Galaxy clusters' structure, dominated by dark matter, is traced by member galaxies in the optical and hot intra-cluster medium (ICM) in X-rays. We compare the radial distribution of these components and determine the mass-to-light ratio vs. system mass relation. We use 14 clusters from the REXCESS sample which is representative of clusters detected in X-ray surveys. Photometric observations with the Wide Field Imager on the 2.2m MPG/ESO telescope are used to determine the number density profiles of the galaxy distribution out to $r_{200}$. These are compared to electron density profiles of the ICM obtained using XMM-Newton, and dark matter profiles inferred from scaling relations and an NFW model. While red sequence galaxies trace the total matter profile, the blue galaxy distribution is much shallower. We see a deficit of faint galaxies in the central regions of massive and regular clusters, and strong suppression of bright and faint blue galaxies in the centres of cool-core clusters, attributable to ram pre...

  18. Cosmological MHD Simulations of Galaxy Cluster Radio Relics: Insights and Warnings for Observations

    CERN Document Server

    Skillman, Samuel W; Hallman, Eric J; O'Shea, Brian W; Burns, Jack O; Li, Hui; Collins, David C; Norman, Michael L

    2012-01-01

    Non-thermal radio emission from cosmic ray electrons in the vicinity of merging galaxy clusters is an important tracer of cluster merger activity, and is the result of complex physical processes that involve magnetic fields, particle acceleration, gas dynamics, and radiation. In particular, objects known as radio relics are thought to be the result of shock-accelerated electrons that, when embedded in a magnetic field, emit synchrotron radiation in the radio wavelengths. In order to properly model this emission, we utilize the adaptive mesh refinement simulation of the magnetohydrodynamic evolution of a galaxy cluster from cosmological initial conditions. We locate shock fronts and apply models of cosmic ray electron acceleration that are then input into radio emission models. We have determined the thermodynamic properties of this radio-emitting plasma and constructed synthetic radio observations to compare to observed galaxy clusters. We find a significant dependence of the observed morphology and radio rel...

  19. The Equipartition Magnetic Field Formula in Starburst Galaxies: Accounting for Pionic Secondaries and Strong Energy Losses

    CERN Document Server

    Lacki, Brian C

    2013-01-01

    Equipartition arguments provide an easy way to find a characteristic scale for the magnetic field from radio emission, by assuming the energy densities in cosmic rays and magnetic fields are the same. Yet most of the cosmic ray content in star-forming galaxies is in protons, which are invisible in radio emission. Therefore, the argument needs assumptions about the proton spectrum, typically that of a constant proton/electron ratio. In some environments, particularly starburst galaxies, the reasoning behind these assumptions does not necessarily hold: secondary pionic positrons and electrons may be responsible for most of the radio emission, and strong energy losses can alter the proton/electron ratio. We derive an equipartition expression that should work in a hadronic loss-dominated environment like starburst galaxies. Surprisingly, despite the radically different assumptions from the classical equipartition formula, numerically the results for starburst magnetic fields are similar. We explain this fortuitou...

  20. Unveiling The Physics of Star Formation and Feedback in Galaxies

    CERN Document Server

    Tabatabaei, F S; Kramer, C; Schinnerer, E; Beckman, J; Knapen, J

    2016-01-01

    Recent studies show the importance of feedback in the evolution of the star formation rate in the Universe. However, the nature and physics of the feedback are still pressing questions. Radio continuum observations can provide unique dust-unbiased tracers of massive star formation and of the interstellar medium (ISM) and hence are ideal to address the regulation of star formation in galaxies. Our multi-frequency and multi-resolution radio surveys in nearby galaxies enable us to trace various phases of star formation and dissect the thermal and nonthermal ISM in galaxies. Mapping the cosmic ray electron energy index and magnetic field strength, we have found observational evidence that massive star formation significantly affects the energy balance in the ISM through the injection and acceleration of cosmic rays and the amplification of magnetic fields. How the next generation of stars could form in such a magnetized and turbulent ISM will be addressed in our 'EVLA cloud-scale survey of the local group galaxy ...

  1. Integral Field Spectroscopy of Blue Compact Dwarf Galaxies

    CERN Document Server

    Garcia-Lorenzo, Begona; Caon, Nicola; Monreal-Ibero, Ana; Kehrig, Carolina

    2008-01-01

    We present results on integral-field optical spectroscopy of five luminous Blue Compact Dwarf galaxies. The data were obtained using the fiber system INTEGRAL attached at the William Herschel telescope. The galaxies Mrk 370, Mrk 35, Mrk 297, Mrk 314 and III Zw 102 were observed. The central 33"x29" regions of the galaxies were mapped with a spatial resolution of 2"/spaxel, except for Mrk 314, in which we observed the central 16"x12" region with a resolution of 0.9"/spaxel$. We use high-resolution optical images to isolate the star-forming knots in the objects; line ratios, electron densities and oxygen abundances in each of these regions are computed. We build continuum and emission-line intensity maps as well as maps of the most relevant line ratios: [OIII]5007\\Hb, [NII]6584\\Ha, and Ha\\Hb, which allow us to obtain spatial information on the ionization structure and mechanisms. We also derive the gas velocity field from the Ha and [OIII]5007 emission lines. We find that all the five galaxies are in the high e...

  2. Radio properties of fossil galaxy groups

    Science.gov (United States)

    Miraghaei, H.; Khosroshahi, H. G.

    2016-09-01

    We study 1.4 GHz radio properties of a sample of fossil galaxy groups using GMRT radio observations and the FIRST survey catalog. Fossil galaxy groups, having no recent major mergers in their dominant galaxies and also group scale mergers, give us the opportunity to investigate the effect of galaxy merger on AGN activity. In this work, we compare the radio properties of a rich sample of fossil groups with a sample of normal galaxy groups and clusters and show that the brightest group galaxies in fossil groups are under luminous at 1.4 GHz, relative to the general population of the brightest group galaxies, indicating that the dynamically relaxed nature of fossil groups has influenced the AGN activity in their dominant galaxy.

  3. DATA MINING THE GALAXY ZOO MERGERS

    Data.gov (United States)

    National Aeronautics and Space Administration — DATA MINING THE GALAXY ZOO MERGERS STEVEN BAEHR, ARUN VEDACHALAM, KIRK BORNE, AND DANIEL SPONSELLER Abstract. Collisions between pairs of galaxies usually end in the...

  4. How do galaxies get their baryons?

    CERN Document Server

    Conselice, Christopher J

    2011-01-01

    Understanding how galaxies obtain baryons, their stars and gas, over cosmic time is traditionally approached in two different ways - theoretically and observationally. In general, observational approaches to galaxy formation include measuring basic galaxy properties, such as luminosities, stellar masses, rotation speeds, star formation rates and how these features evolve through time. Theoretically, cosmologically based models collate the physical effects driving galaxy assembly - mergers of galaxies, accretion of gas, star formation, and feedback, amongst others, to form predictions which are matched to galaxy observables. An alternative approach is to examine directly, in an observational way, the processes driving galaxy assembly, including the effects of feedback. This is a new `third way' towards understanding how galaxies are forming from gas accretion and mergers, and directly probes these effects instead of relying on simulations designed to reproduce observations. This empirical approach towards unde...

  5. First phylogenetic analyses of galaxy evolution

    CERN Document Server

    Fraix-Burnet, D

    2004-01-01

    The Hubble tuning fork diagram, based on morphology, has always been the preferred scheme for classification of galaxies and is still the only one originally built from historical/evolutionary relationships. At the opposite, biologists have long taken into account the parenthood links of living entities for classification purposes. Assuming branching evolution of galaxies as a "descent with modification", we show that the concepts and tools of phylogenetic systematics widely used in biology can be heuristically transposed to the case of galaxies. This approach that we call "astrocladistics" has been first applied to Dwarf Galaxies of the Local Group and provides the first evolutionary galaxy tree. The cladogram is sufficiently solid to support the existence of a hierarchical organization in the diversity of galaxies, making it possible to track ancestral types of galaxies. We also find that morphology is a summary of more fundamental properties. Astrocladistics applied to cosmology simulated galaxies can, uns...

  6. The Formation of Polar Disk Galaxies

    CERN Document Server

    Brook, Chris B; Quinn, Thomas; Wadsley, James; Brooks, Alyson M; Willman, Beth; Stilp, Adrienne; Jonsson, Patrik

    2008-01-01

    Polar Ring Galaxies, such as NGC4650A, are a class of galaxy which have two kinematically distinct components that are inclined by almost 90 degrees to each other. These striking galaxies challenge our understanding of how galaxies form; the origin of their distinct components has remained uncertain, and the subject of much debate. We use high-resolution cosmological simulations of galaxy formation to show that Polar Ring Galaxies are simply an extreme example of the angular moment misalignment that occurs during the hierarchical structure formation characteristic of Cold Dark Matter cosmology. In our model, Polar Ring Galaxies form through the continuous accretion of gas whose angular momentum is misaligned with the central galaxy.

  7. Collisionless evaporation from cluster elliptical galaxies

    CERN Document Server

    Muccione, V

    2003-01-01

    We describe a particular aspect of the effects of the parent cluster tidal field (CTF) on stellar orbits inside cluster Elliptical galaxies. In particular we discuss, with the aid of a simple numerical model, the possibility that collisionless stellar evaporation from elliptical galaxies is an effective mechanism for the production of the recently discovered intracluster stellar populations. A preliminary investigation, based on very idealized galaxy density profiles (Ferrers density distributions), showed that over an Hubble time, the amount of stars lost by a representative galaxy may sum up to the 10% of the initial galaxy mass, a fraction in interesting agreement with observational data. The effectiveness of this mechanism is due to the fact that the galaxy oscillation periods near equilibrium configurations in the CTF are comparable to stellar orbital times in the external galaxy regions. Here we extend our previous study to more realistic galaxy density profiles, in particular by adopting a triaxial Her...

  8. The Current Status of Galaxy Formation

    CERN Document Server

    Silk, Joe

    2012-01-01

    Understanding galaxy formation is one of the most pressing issues in cosmology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarise the prospects for future advances.

  9. Spherical Accretion in Nearby Weakly Active Galaxies

    CERN Document Server

    Moscibrodzka, M A

    2005-01-01

    We consider the sample of weakly active galaxies situated in 'Local Universe' collected in the paper of Pellegrini (2005) with inferred accretion efficiencies from $10^{-2}$ to $10^{-7}$. We apply a model of spherically symmetrical Bondi accretion for given parameters ($M_{BH}$,$T_{\\infty}$,$\\rho_{\\infty}$,) taken from observation. We calculate spectra emitted by the gas accreting onto its central objects using Monte Carlo method including synchrotron and bremsstrahlung photons as seed photons. We compare our results with observed nuclear X-ray luminosities $L_{X,nuc}$ (0.3-10 keV) of the sample. Model is also tested for different external medium parameters ($\\rho_{\\infty}$ and $T_{\\infty}$) and different free parameters of the model. Our model is able to explain most of the observed nuclear luminosities $L_X$ under an assumption that half of the compresion energy is transfered directly to the electrons.

  10. The CALIFA survey across the Hubble sequence. Spatially resolved stellar population properties in galaxies

    Science.gov (United States)

    González Delgado, R. M.; García-Benito, R.; Pérez, E.; Cid Fernandes, R.; de Amorim, A. L.; Cortijo-Ferrero, C.; Lacerda, E. A. D.; López Fernández, R.; Vale-Asari, N.; Sánchez, S. F.; Mollá, M.; Ruiz-Lara, T.; Sánchez-Blázquez, P.; Walcher, C. J.; Alves, J.; Aguerri, J. A. L.; Bekeraité, S.; Bland-Hawthorn, J.; Galbany, L.; Gallazzi, A.; Husemann, B.; Iglesias-Páramo, J.; Kalinova, V.; López-Sánchez, A. R.; Marino, R. A.; Márquez, I.; Masegosa, J.; Mast, D.; Méndez-Abreu, J.; Mendoza, A.; del Olmo, A.; Pérez, I.; Quirrenbach, A.; Zibetti, S.

    2015-09-01

    correlated and with disks covering a wider range of ages, and late-type spirals hosting younger disks. However, age gradients are only mildly negative or flat beyond R ~ 2 HLR (half light radius), indicating that star formation is more uniformly distributed or that stellar migration is important at these distances. The gradients in stellar mass surface density depend mostly on stellar mass, in the sense that more massive galaxies are more centrally concentrated. Whatever sets the concentration indices of galaxies obviously depends less on quenching/morphology than on the depth of the potential well. There is a secondary correlation in the sense that at the same M⋆ early-type galaxies have steeper gradients. The μ⋆ gradients outside 1 HLR show no dependence on Hubble type. We find mildly negative ⟨log Z⋆⟩M gradients, which are shallower than predicted from models of galaxy evolution in isolation. In general, metallicity gradients depend on stellar mass, and less on morphology, hinting that metallicity is affected by both - the depth of the potential well and morphology/quenching. Thus, the largest ⟨log Z⋆⟩M gradients occur in Milky Way-like Sb-Sbc galaxies, and are similar to those measured above the Galactic disk. Sc spirals show flatter ⟨log Z⋆⟩M gradients, possibly indicating a larger contribution from secular evolution in disks. The galaxies from the sample have decreasing-outward stellar extinction; all spirals show similar radial profiles, independent from the stellar mass, but redder than E and S0. Overall, we conclude that quenching processes act in manners that are independent of mass, while metallicity and galaxy structure are influenced by mass-dependent processes. Appendices are available in electronic form at http://www.aanda.org

  11. The Galaxy Cosmological Mass Function

    CERN Document Server

    Lopes, Amanda R; Ribeiro, Marcelo B; Stoeger, William R

    2014-01-01

    We study the galaxy cosmological mass function (GCMF) in a semi-empirical relativistic approach using observational data provided by galaxy redshift surveys. Starting from the theory of Ribeiro & Stoeger (2003, arXiv:astro-ph/0304094) between the mass-to-light ratio, the selection function obtained from the luminosity function (LF) data and the luminosity density, the average luminosity $L$ and the average galactic mass $\\mathcal{M}_g$ are computed in terms of the redshift. $\\mathcal{M}_g$ is also alternatively estimated by a method that uses the galaxy stellar mass function (GSMF). Comparison of these two forms of deriving the average galactic mass allows us to infer a possible bias introduced by the selection criteria of the survey. We used the FORS Deep Field galaxy survey sample of 5558 galaxies in the redshift range $0.5 < z < 5.0$ and its LF Schechter parameters in the B-band, as well as this sample's stellar mass-to-light ratio and its GSMF data. Assuming ${\\mathcal{M}_{g_0}} \\approx 10^{11} ...

  12. Counting pairs of faint galaxies

    CERN Document Server

    Woods, D; Richer, H B; Woods, David; Fahlman, Gregory G; Richer, Harvey B

    1995-01-01

    The number of close pairs of galaxies observed to faint magnitude limits, when compared to nearby samples, determines the interaction or merger rate as a function of redshift. The prevalence of mergers at intermediate redshifts is fundamental to understanding how galaxies evolve and the relative population of galaxy types. Mergers have been used to explain the excess of galaxies in faint blue counts above the numbers expected from no-evolution models. Using deep CFHT (I\\leq24) imaging of a ``blank'' field we find a pair fraction which is consistent with the galaxies in our sample being randomly distributed with no significant excess of ``physical'' close pairs. This is contrary to the pair fraction of 34\\%\\pm9\\% found by Burkey {\\it et al.} for similar magnitude limits and using an identical approach to the pair analysis. Various reasons for this discrepancy are discussed. Colors and morphologies of our close pairs are consistent with the bulk of them being random superpositions although, as indicators of int...

  13. Characterising Nearby Luminous Infrared Galaxies

    Science.gov (United States)

    Ramphul, R.; Vaisanen, P.; Van der Heyden, K.

    2017-06-01

    Luminous InfraRed Galaxies (LIRGs) in the local universe are known to be highly interacting galaxies with strong star-formation in obscured environments. LIRGs have diversity in terms of morphology and mode and location of SF, while their even more energetic counterparts, the Ultra-Luminous IR galaxies, ULIRGs, (LIR ≥ 10^12 Lsol ) are normally (remnants of) gas rich major mergers with centralised starbursts and AGN. I will present ongoing work on a survey of >40 (U)LIRGs, in a distance range of 40 to 300Mpc, observed with SALT/RSS in long-slit mode. The sample of galaxies are in various stages of interaction and merging, some with strong AGN contribution. The reduction of the SALT/RSS data, was performed efficiently with our custom-built pipeline written in python/iraf/pyraf and handles error-frames propagation. We are performing a rigorous stellar populations analysis of our sample using Starlight (Cid Fernandes, 2005) which will ultimately lead to understanding the star formation history of these galaxies. We also use automatic line intensity measurements to derive chemical abundances, star formation rates, metallicity and emission line diagnostic. The talk will showcase the latest results that we just obtained for this dataset and discuss some of the future works.

  14. 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...

  15. How to quench a galaxy

    CERN Document Server

    Pontzen, Andrew; Roth, Nina; Peiris, Hiranya V; Saintonge, Amélie; Volonteri, Marta; Quinn, Tom; Governato, Fabio

    2016-01-01

    We show how the interplay between active galactic nuclei (AGN) and merger history determines whether a galaxy quenches star formation at high redshift. We first simulate, in a full cosmological context, a galaxy of total dynamical mass $10^{12}\\,M_{\\odot}$ at $z=2$. Then we systematically alter the accretion history of the galaxy by minimally changing the linear overdensity in the initial conditions. This "genetic modification" approach allows the generation of three sets of $\\Lambda$CDM initial conditions leading to maximum merger ratios of 1:10, 1:5 and 2:3 respectively. The changes leave the final halo mass, large scale structure and local environment unchanged, providing a controlled numerical experiment. Interaction between the AGN physics and mergers in the three cases lead respectively to a star-forming, temporarily-quenched and permanently-quenched galaxy. However the differences do not primarily lie in the black hole accretion rates, but in the kinetic effects of the merger: the galaxy is resilient a...

  16. Jellyfish galaxies at low redshift

    CERN Document Server

    Poggianti, B M; Omizzolo, A; Gullieuszik, M; Bettoni, D; Moretti, A; Paccagnella, A; Jaffe', Y L; Vulcani, B; Fritz, J; Couch, W; D'Onofrio, M

    2015-01-01

    Jellyfish galaxies are galaxies that exhibit tentacles of debris material suggestive of gas stripping. We have conducted the first systematic search for jellyfish galaxies at low-z (z=0.04-0.07) in different environments. We have visually inspected B and V-band images and identified 241+153 candidates in 41+31 galaxy clusters of the OMEGAWINGS+WINGS sample and 99 candidates in groups and lower mass structures in the PM2GC sample. This large sample is well suited for follow-up studies of the gas and for a detailed analysis of the environments where such episodes of gas stripping occur. We present here the atlas of jellyfish candidates, a first analysis of their environment and their basic properties, such as morphologies, star formation rates and galaxy stellar masses. Jellyfish candidates are found in all clusters and at all clustercentric radii, and their number does not correlate with the cluster velocity dispersion or X-ray luminosity. Interestingly, convincing cases of jellyfish candidates are also found ...

  17. Power Spectra for Galaxy Shape Correlations

    OpenAIRE

    Mackey, Jonathan

    2001-01-01

    It has recently been argued that the observed ellipticities of galaxies may be determined at least in part by the primordial tidal gravitational field in which the galaxy formed. Long-range correlations in the tidal field could thus lead to an ellipticity-ellipticity correlation for widely separated galaxies. I present results of a calculation of the angular power spectrum of intrinsic galaxy shape correlations using a new model relating ellipticity to angular momentum. I show that for low re...

  18. Initial luminosity functions of starburst galaxies

    Science.gov (United States)

    Parnovsky, S.; Izotova, I.

    2016-12-01

    For the sample of about 800 starburst galaxies the initial luminosity functions which appear the distributions of galaxy luminosities at zero starburst age are considered based on the data of luminosities of galaxies in the recombination Hα emission line in the regions of ionised hydrogen and the ultraviolet continuum. We find the initial luminosity functions for the starburst galaxies with Hα emission and ultraviolet continuum are satisfactory approximated with log-normal function.

  19. On Three-Dimensional Spiral Galaxies

    Institute of Scientific and Technical Information of China (English)

    LUO Xin-Lian; PENG Qiu-He; LONG Min; PENG Fang; ZOU Zhi-Gang

    2000-01-01

    Density waves in 3D spiral galaxies are studied. In order to eliminate the forbidden region near the corotation in the grand-design galaxies, we assume that the perturbation satisfies the stable condition Q(r) > 1 over all the disk except that at the corotation. Then, a new method is put forward here to determine some basic parameters of spiral galaxies. We apply it to our Galaxy, and the results are in good agreement with the previous results.

  20. Machine Learning for Galaxy Morphology Classification

    CERN Document Server

    Gauci, Adam; Abela, John; Magro, Alessio

    2010-01-01

    In this work, decision tree learning algorithms and fuzzy inferencing systems are applied for galaxy morphology classification. In particular, the CART, the C4.5, the Random Forest and fuzzy logic algorithms are studied and reliable classifiers are developed to distinguish between spiral galaxies, elliptical galaxies or star/unknown galactic objects. Morphology information for the training and testing datasets is obtained from the Galaxy Zoo project while the corresponding photometric and spectra parameters are downloaded from the SDSS DR7 catalogue.

  1. Searching for metal-deficient emission-line galaxy candidates: the final sample of the SDSS DR12 galaxies

    CERN Document Server

    Guseva, N G; Fricke, K J; Henkel, C

    2016-01-01

    We present a spectroscopic study of metal-deficient dwarf galaxy candidates, selected from the SDSS DR12. The oxygen abundances were derived using the direct method in galaxies with the electron temperature-sensitive emission line [OIII]4363A measured with an accuracy better than 30%. The oxygen abundances for the remaining galaxies with larger uncertainties of the [OIII]4363A line fluxes were calculated using a strong-line semi-empirical method by Izotov and Thuan. The resulting sample consists of 287 low-metallicity candidates with oxygen abundances below 12+logO/H=7.65 including 23 extremely metal-deficient (XMD) candidates with 12+log O/H<7.35. Ten out of sixteen XMDs known so far (or ~60%) have been discovered by our team using the direct method. Three XMDs were found in the present study. We study relations between global parameters of low-metallicity galaxies, including absolute optical magnitudes, Hbeta luminosities (or equivalently star formation rates), stellar masses, mid-infrared colours, and o...

  2. The AGN Population in Nearby Galaxies

    NARCIS (Netherlands)

    Filho, Mercedes; Barthel, Peter; Ho, Luis

    2006-01-01

    In order to determine the incidence of black hole accretion-driven nuclear activity in nearby galaxies, we have compiled radio data for the LINERs, composite LINER,/Hn and Seyfert galaxies from a complete magnitude-limited sample of bright nearby galaxies (Palomar sample). Our results show an overal

  3. 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 rece

  4. Dark matter in low surface brightness galaxies

    NARCIS (Netherlands)

    de Blok, WJG; McGaugh, SS; Persic, M; Salucci, P

    1997-01-01

    Low Surface Brightness (LSB) galaxies form a large population of disc galaxies that extend the Hubble sequence towards extreme late-types. They are only slowly evolving, and still in an early evolutionary state. The Tully-Fisher relation and rotation curves of LSB galaxies both show that LSB

  5. Evolving Galaxies in a Hierachical Universe

    Science.gov (United States)

    Hahn, Changhoon

    2017-01-01

    Observations of galaxies using large surveys (SDSS, COSMOS, PRIMUS, etc.) have firmly established a global view of galaxy properties out to z~1. Galaxies are broadly divided into two classes: blue, typically disk-like star forming galaxies and red, typically elliptical quiescent ones with little star formation. The star formation rates (SFR) and stellar masses of star forming galaxies form an empirical relationship referred to as the "star formation main sequence". Over cosmic time, this sequence undergoes significant decline in SFR and causes the overall cosmic star formation decline. Simultaneously, physical processes cause significant fractions of star forming galaxies to "quench" their star formation. Hierarchical structure formation and cosmological models provide precise predictions of the evolution of the underying dark matter, which serve as the foundation for these detailed trends and their evolution. Whatever trends we observe in galaxy properties can be interpreted within the narrative of the underlying dark matter and halo occupation framework. More importantly, through careful statistical treatment and precise measurements, this connection can be utilized to better constrain and understand key elements of galaxy evolution. In this spirit, for my dissertation I connect observations of evolving galaxy properties to the framework of the hierarchical Universe and use it to better understand physical processes responsible for the cessation of star formation in galaxies. For instance, through this approach, I constrain the quenching timescale of central galaxies and find that they are significantly longer than the quenching timescale of satellite galaxies.

  6. The Evolution of Galaxies and Their Environment

    Science.gov (United States)

    Hollenbach, David (Editor); Thronson, Harley A. (Editor); Shull, J. Michael (Editor)

    1993-01-01

    The Third Teton Summer School on Astrophysics discussed the formation of galaxies, star formation in galaxies, galaxies and quasars at high red shift, and the intergalactic and intercluster medium and cooling flows. Observation and theoretical research on these topics was presented at the meeting and summaries of the contributed papers are included in this volume.

  7. The Metallicity of Void Dwarf Galaxies

    NARCIS (Netherlands)

    Kreckel, K.; Croxall, K.; Groves, B.; van de Weygaert, R.; Pogge, R. W.

    2015-01-01

    The current ΛCDM cosmological model predicts that galaxy evolution proceeds more slowly in lower density environments, suggesting that voids are a prime location to search for relatively pristine galaxies that are representative of the building blocks of early massive galaxies. To test the assumptio

  8. 10 billion years of massive Galaxies

    NARCIS (Netherlands)

    Taylor, Edward Nairne Cunningham

    2009-01-01

    The most massive galaxies in the local universe are not forming new stars -- but we don’t know why. As a step towards figuring out why big galaxies stop forming stars, we set out to measure when they stop forming stars. By looking at the colors of massive galaxies have changed over 10 billion year

  9. The stellar halo of the Galaxy

    NARCIS (Netherlands)

    Helmi, Amina

    2008-01-01

    Stellar halos may hold some of the best preserved fossils of the formation history of galaxies. They are a natural product of the merging processes that probably take place during the assembly of a galaxy, and hence may well be the most ubiquitous component of galaxies, independently of their Hubble

  10. Interacting galaxies and cosmological parameters

    CERN Document Server

    Reboul, H

    2006-01-01

    We propose a (physical)-geometrical method to measure the present rates of the density cosmological parameters for a Friedmann-Lemaitre universe. The distribution of linear separations between two interacting galaxies,when both of them undergo a first massive starburst, is used as a standard of length. Statistical properties of the linear separations of such pairs of ``interactivated'' galaxies are estimated from the data in the Two Degree Field Galaxy Redshift Survey. Synthetic samples of interactivated pairs are generated with random orientations and a likely distribution of redshifts. The resolution of the inverse problem provides the probability densities of the retrieved cosmological parameters. The accuracies that can be achieved by that method on matter and cosmological constant densities parameters are computed depending on the size of ongoing real samples. Observational prospects are investigated as the foreseeable surface densities on the sky and magnitudes of those objects.

  11. Galaxies and Cosmology with DENIS

    CERN Document Server

    Mamon, G A; Bonin, W; Banchet, V

    1997-01-01

    The DENIS survey is currently imaging 21334 deg^2 of the mainly southern sky in the IJK and the observations are expected to go on until mid 2000. The expectations for extragalactic and cosmological research are outlined, including a quantitative assessment of the effects of recent star formation on the measured fluxes of galaxies. The galaxy extraction is much improved with the modeling of the PSF across the 12'x12' frames and the reliability of star/galaxy separation (currently based upon a combination of classical and neural-network based methods) is measured from visual inspection to be >90% at I = 16. The I band counts follow the high bright-end normalization and the J differential counts follow N(J) \\simeq 11 \\times dex [0.6 (J-14)] deg^{-2} mag^{-1} and are expected to be complete, reliable and photometrically accurate

  12. Morphological Mutations of Dwarf Galaxies

    CERN Document Server

    Hensler, Gerhard

    2012-01-01

    Dwarf galaxies (DGs) are extremely challenging objects in extragalactic astrophysics. They are expected to originate as the first units in Cold Dark-Matter cosmology. They are the galaxy type most sensitive to environmental influences and their division into multiple types with various properties have invoked the picture of their variant morphological transformations. Detailed observations reveal characteristics which allow to deduce the evolutionary paths and to witness how the environment has affected the evolution. Here we review peculiarities of general morphological DG types and refer to processes which can deplete gas-rich irregular DGs leading to dwarf ellipticals, while gas replenishment implies an evolutionary cycling. Finally, as the less understood DG types the Milky Way satellite dwarf spheroidal galaxies are discussed in the context of transformation.

  13. The Laniakea supercluster of galaxies

    CERN Document Server

    Tully, R Brent; Hoffman, Yehuda; Pomarède, Daniel

    2014-01-01

    Galaxies congregate in clusters and along filaments, and are missing from large regions referred to as voids. These structures are seen in maps derived from spectroscopic surveys that reveal networks of structure that are interconnected with no clear boundaries. Extended regions with a high concentration of galaxies are called 'superclusters', although this term is not precise. There is, however, another way to analyse the structure. If the distance to each galaxy from Earth is directly measured, then the peculiar velocity can be derived from the subtraction of the mean cosmic expansion, the product of distance times the Hubble constant, from observed velocity. The peculiar velocity is the line-of-sight departure from the cosmic expansion and arises from gravitational perturbations; a map of peculiar velocities can be translated into a map of the distribution of matter. Here we report a map of structure made using a catalogue of peculiar velocities. We find locations where peculiar velocity flows diverge, as ...

  14. Percolation technique for galaxy clustering

    Science.gov (United States)

    Klypin, Anatoly; Shandarin, Sergei F.

    1993-01-01

    We study percolation in mass and galaxy distributions obtained in 3D simulations of the CDM, C + HDM, and the power law (n = -1) models in the Omega = 1 universe. Percolation statistics is used here as a quantitative measure of the degree to which a mass or galaxy distribution is of a filamentary or cellular type. The very fast code used calculates the statistics of clusters along with the direct detection of percolation. We found that the two parameters mu(infinity), characterizing the size of the largest cluster, and mu-squared, characterizing the weighted mean size of all clusters excluding the largest one, are extremely useful for evaluating the percolation threshold. An advantage of using these parameters is their low sensitivity to boundary effects. We show that both the CDM and the C + HDM models are extremely filamentary both in mass and galaxy distribution. The percolation thresholds for the mass distributions are determined.

  15. A catalog of Kazarian galaxies

    CERN Document Server

    Kazarian, M A; McLean, B; Allen, R J; Petrosian, A R

    2009-01-01

    The entire Kazarian galaxies (KG) catalog is presented which combines extensive new measurements of their optical parameters with a literature and database search. The measurements were made using images extracted from the STScI Digitized Sky Survey (DSS) of Jpg(blue), Fpg(red) and Ipg(NIR) band photographic sky survey plates obtained by the Palomar and UK Schmidt telescopes. We provide accurate coordinates, morphological type, spectral and activity classes, blue apparent diameters, axial ratios, position angles, red, blue and NIR apparent magnitudes, as well as counts of neighboring objects in a circle of radius 50 kpc from centers of KG. Special attention was paid to the individual descriptions of the galaxies in the original Kazarian lists, which clarified many cases of misidentifications of the objects, particularly among interacting systems. The total number of individual Kazarian objects in the database is now 706. We also include the redshifts which are now available for 404 galaxies and the 2MASS infr...

  16. Statistics of the galaxy distribution

    CERN Document Server

    Martinez, Vicent J

    2001-01-01

    Over the last decade, statisticians have developed new statistical tools in the field of spatial point processes. At the same time, observational efforts have yielded a huge amount of new cosmological data to analyze. Although the main tools in astronomy for comparing theoretical results with observation are statistical, in recent years, cosmologists have not been generally aware of the developments in statistics and vice versa.Statistics of the Galaxy Distribution describes both the available observational data on the distribution of galaxies and the applications of spatial statistics in cosmology. It gives a detailed derivation of the statistical methods used to study the galaxy distribution and the cosmological physics needed to formulate the statistical models. Because the prevalent approach in cosmological statistics has been frequentist, the authors focus on the most widely used of these methods, but they also explore Bayesian techniques that have become popular in large-scale structure studies.Describi...

  17. Neutral Hydrogen in Galaxy Groups

    CERN Document Server

    McKay, N P F; Brough, S; Forbes, D A; Barnes, D G

    2002-01-01

    We present preliminary results from a study of the neutral hydrogen (HI) properties of an X-ray selected sample of nearby loose galaxy groups. This forms part of a multi-wavelength investigation (X-ray, optical and radio) of the formation and evolution of galaxies within a group environment. Some initial findings of an ATNF Parkes Multibeam wide-area neutral hydrogen imaging survey of 17 nearby galaxy groups include two new, potentially isolated clouds of HI in the NGC 1052 and NGC 5044 groups and significant amounts of HI within the group virial radii of groups NGC 3557 and IC 1459 - two groups with complex X-ray structures that suggest they may still be in the act of virialisation. Here we present ATCA high-resolution synthesis-imaging follow-up observations of the distribution and kinematics of HI in these four groups.

  18. Secular Evolution in Disk Galaxies

    CERN Document Server

    Kormendy, John

    2013-01-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via available evolution processes. The inner parts shrink and the outer parts expand, provided that some physical process transports energy or angular momentum outward. The evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks, and galaxy disks are all fundamentally similar. These processes for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. Part 1 discusses formation, growth, and death of bars. Part 2 details the slow ("secular") rearrangement of angular momentum that results from interactions between stars or gas and nonaxisymmetries such as bars. We have a heuristic understanding of how this forms outer rings, inner rings, and stuff dumped into the center. Observations show that barred galaxies have central concentrations of gas and star formation. Timescales imply that they grow central "pseudobulges" that get mistaken for ellip...

  19. Optical radii of galaxy clusters

    CERN Document Server

    Girardi, M; Giuricin, G; Mardirossian, F; Mezzetti, M; Girardi, M; Biviano, A; Giuricin, G; Mardirossian, F; Mezzetti, M

    1994-01-01

    We analyze the density profiles and virial radii for a sample of 90 nearby clusters, using galaxies with available redshifts and positions. Each cluster has at least 20 redshifts measured within an Abell radius, and all the results come from galaxy sets of at least 20 members. Most of the density profiles of our clusters are well fitted by hydrostatic-isothermal-like profiles. The slopes we find for many cluster density profiles are consistent with the hypothesis that the galaxies are in equilibrium with the binding cluster potential. The virial radii correlate with the core radii at a very high significance level. The observed relationship between the two size estimates is in agreement with the theoretical one computed by using the median values of the density profile parameters fitted on our clusters. After correcting for incompleteness in our cluster sample, we provide the universal distributions functions of core and virial radii (obtained within half an Abell radius).

  20. New Eyes for Galaxies Investigation

    Science.gov (United States)

    D'Onofrio, Mauro; Zaggia, Simone; Rampazzo, Roberto; Vallenari, Antonella; Gilmore, Gerald F.; Marziani, Paola; Stiavelli, Massimo; Calzetti, Daniela; Bianchi, Luciana; Trinchieri, Ginevra; Bromm, Volker; Bland-Hawthorn, Jonathan; Kaifu, Norio; Combes, Françoise; Moss, David L.; Paturel, George

    The observational data for the extragalactic research are evolved across this century. While the first studies on galaxies were essentially based on images and spectra taken in the optical waveband and registered after hours of work at the telescope on glass photographic plates, today we receive pre-reduced multiwavelength images and spectra directly on our computers. The work of astronomers is changed completely with the technological progress. Only 30 years ago, 4-5 photographic images of galaxies, or a few spectra, were the best one can hope to get after a night of hard work at the telescope. Today, space and ground-based telescopes with big diameters and field of view are pointed toward the sky every night, collecting gigabytes of data for thousand of galaxies, that we bring with us in our laptop computers.

  1. Deciphering the Galaxy Guppy phenotype

    Directory of Open Access Journals (Sweden)

    Philip Shaddock

    2011-01-01

    Full Text Available Animal breeding hobbyists have been useful to science because they identify and isolate colorcoat mutations that geneticists can in turn use in their studies of the development and differentiation ofcolor cells. This paper discusses a very interesting color mutant, the Japanese Galaxy, tracing its creationfrom back to a self-educated genetics hobbyist, Hoskiki Tsutsui. The paper discusses a constituent genepreviously studied by Dr. Violet Phang, the snakeskin gene (the linked body and fin genes Ssb and Sst.And it discusses a gene previously unknown to science, the Schimmelpfennig Platinum gene (Sc.Through crossing experiments, the author determines that the combination of these two genes producesan intermediate phenotype, the Medusa. Incorporating the Grass (Gr, another gene unknown to sciencegene into the Medusa through a crossover produces the Galaxy phenotype. Microscope studies of thesnakeskin pattern in Galaxies and snakeskins reveals some parallels with similar studies made of theZebrafish Danio.

  2. GALAXY OUTFLOWS WITHOUT SUPERNOVAE

    Energy Technology Data Exchange (ETDEWEB)

    Sur, Sharanya [Indian Institute of Astrophysics, 2nd Block, Koramangala, Bangalore 560034 (India); Scannapieco, Evan [School of Earth and Space Exploration, Arizona State University, P.O. Box 876004, Tempe-85287 (United States); Ostriker, Eve C., E-mail: sharanya.sur@iiap.res.in, E-mail: sharanya.sur@asu.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

    2016-02-10

    High surface density, rapidly star-forming galaxies are observed to have ≈50–100 km s{sup −1} line of sight velocity dispersions, which are much higher than expected from supernova driving alone, but may arise from large-scale gravitational instabilities. Using three-dimensional simulations of local regions of the interstellar medium, we explore the impact of high velocity dispersions that arise from these disk instabilities. Parametrizing disks by their surface densities and epicyclic frequencies, we conduct a series of simulations that probe a broad range of conditions. Turbulence is driven purely horizontally and on large scales, neglecting any energy input from supernovae. We find that such motions lead to strong global outflows in the highly compact disks that were common at high redshifts, but weak or negligible mass loss in the more diffuse disks that are prevalent today. Substantial outflows are generated if the one-dimensional horizontal velocity dispersion exceeds ≈35 km s{sup −1}, as occurs in the dense disks that have star-formation rate (SFR) densities above ≈0.1 M{sub ⊙} yr{sup −1} kpc{sup −2}. These outflows are triggered by a thermal runaway, arising from the inefficient cooling of hot material coupled with successive heating from turbulent driving. Thus, even in the absence of stellar feedback, a critical value of the SFR density for outflow generation can arise due to a turbulent heating instability. This suggests that in strongly self-gravitating disks, outflows may be enhanced by, but need not caused by, energy input from supernovae.

  3. Galaxy-galaxy and galaxy-cluster lensing with the SDSS and the FIRST surveys

    CERN Document Server

    Demetroullas, Constantinos

    2016-01-01

    We perform a galaxy-galaxy lensing study by correlating the shapes of $\\sim$2.7 $\\times$ 10$^5$ galaxies selected from the VLA FIRST radio survey with the positions of $\\sim$38.5 million SDSS galaxies, $\\sim$132000 BCGs and $\\sim$78000 SDSS galaxies that are also detected in the VLA FIRST survey. The measurements are conducted on angular scales ${\\theta}$ $\\lesssim$ 1200 arcsec. On scales ${\\theta}$ $\\lesssim$ 200 arcsec we find that the measurements are corrupted by residual systematic effects associated with the instrumental beam of the VLA data. Using simulations we show that we can successfully apply a correction for these effects. Using the three lens samples (the SDSS DR10 sample, the BCG sample and the SDSS-FIRST matched object sample) we measure a tangential shear signal that is inconsistent with zero at the 10${\\sigma}$, 3.8${\\sigma}$ and 9${\\sigma}$ level respectively. Fitting an NFW model to the detected signals we find that the ensemble mass profile of the BCG sample agrees with the values in the ...

  4. Escape of ionizing radiation from star-forming regions in Young galaxies

    DEFF Research Database (Denmark)

    Razoumov, A; Sommer-Larsen, Jesper

    2006-01-01

    Galaxies: Formation, Galaxies: Intergalactic Medium, ISM: H II Regions, Radiative Transfer Udgivelsesdato: Nov. 10......Galaxies: Formation, Galaxies: Intergalactic Medium, ISM: H II Regions, Radiative Transfer Udgivelsesdato: Nov. 10...

  5. 苹果优良砧木资源--变叶海棠%MALUS TORINGOIDES (REHD.) HUGHES - A PROMISING STOCK FOR APPLE TREES

    Institute of Scientific and Technical Information of China (English)

    石胜友; 成明昊; 梁国鲁

    2004-01-01

    变叶海棠(Malus toringoides (Rehd.) Hughes)的形态特征、种质特性、分布的生态环境具有极其复杂的多样性,也是苹果属植物中具有多种高抗性的种类.作苹果砧木利用,嫁接亲和性好,嫁接树半矮化,进入结果期早,果实品质好,是极重要的苹果砧木资源.变叶海棠种群是变叶海棠与陇东海棠和花叶海棠3 个种的杂交复合体,由于杂种的全部或部分能育子代中发生的基因重组和增加基因的突变率,丰富了物种的基因库,从而深入的揭示了变叶海棠具有高抗性的遗传机理.变叶海棠是横断山脉地区特有种,是极珍贵的种质资源.因此,对变叶海棠及其近缘种(陇东海棠和花叶海棠)的保护,对于研究物种生物学理论以及资源利用都具有重要的科学意义和应用前景.

  6. The IRAS Galaxy Atlas (IGA)

    Science.gov (United States)

    Prince, Thomas A.; Oliversen, R. (Technical Monitor)

    1999-01-01

    In 1993 we proposed a project to NASA having the goal of producing a new infrared map of our Galaxy. In particular, we proposed to reprocess the IRAS data taken in the early 1980's using modern image processing algorithms and the large Intel parallel computers of the Center for Advanced Computing Research, (at that time called the Caltech Concurrent Supercomputing Facilities - CCSF). The rationale was simple: what took approximately 100 days on a typical workstation would take less than a day on the multi-processor parallel computers, thus making a high-resolution infrared atlas of the Galaxy feasible.

  7. X-ray emission from star-forming galaxies - signatures of cosmic rays and magnetic fields

    Science.gov (United States)

    Schober, J.; Schleicher, D. R. G.; Klessen, R. S.

    2015-01-01

    The evolution of magnetic fields in galaxies is still an open problem in astrophysics. In nearby galaxies the far-infrared-radio correlation indicates the coupling between magnetic fields and star formation. The correlation arises from the synchrotron emission of cosmic ray electrons travelling through the interstellar magnetic fields. However, with an increase of the interstellar radiation field (ISRF), inverse Compton scattering becomes the dominant energy loss mechanism of cosmic ray electrons with a typical emission frequency in the X-ray regime. The ISRF depends on the one hand on the star formation rate and becomes stronger in starburst galaxies, and on the other hand increases with redshift due to the higher temperature of the cosmic microwave background. With a model for the star formation rate of galaxies, the ISRF, and the cosmic ray spectrum, we can calculate the expected X-ray luminosity resulting from the inverse Compton emission. Except for galaxies with an active galactic nucleus the main additional contribution to the X-ray luminosity comes from X-ray binaries. We estimate this contribution with an analytical model as well as with an observational relation, and compare it to the pure inverse Compton luminosity. Using data from the Chandra Deep Field Survey and far-infrared observations from Atacama Large Millimeter/Submillimeter Array, we then determine upper limits for the cosmic ray energy. Assuming that the magnetic energy in a galaxy is in equipartition with the energy density of the cosmic rays, we obtain upper limits for the magnetic field strength. Our results suggest that the mean magnetic energy of young galaxies is similar to the one in local galaxies. This points towards an early generation of galactic magnetic fields, which is in agreement with current dynamo evolution models.

  8. Particle acceleration and dynamics of double-double radio galaxies: theory versus observations

    Science.gov (United States)

    Konar, C.; Hardcastle, M. J.

    2013-12-01

    In this paper, we show that a small sample of radio galaxies with evidence for multiple epochs of jet activity (so-called double-double radio galaxies) have the same electron injection spectral index in the two activity episodes, a result which might be considered surprising given the very different lobe dynamics expected in the first and second episode. We construct models for the dynamics of radio galaxies, with an emphasis on their episodic behaviour, and show that hotspot formation and confinement of lobes for the inner double of double-double radio galaxies are possible even without any thermal matter in the outer cocoon. We argue that (i) the observed similar injection spectral indices are due to similar jet powers in the two episodes, (ii) the `spectral index-radio power' correlation of a flux limited sample of radio galaxies is the primary one, and not the `spectral index-redshift correlation', (iii) jets are made of pair plasma and not electron-proton and (iv) the Lorentz factor of the spine of the jet should be ≳ 10 to explain the observations. Furthermore, we argue that the observations show that higher power radio galaxies do not have a higher jet bulk Lorentz factors, but instead simply have a higher number density of particles in the jet rest frame. A consequence of our models is that aligned double-double radio galaxies with very old ( ≳ 108 yr) outer doubles, or misaligned double-double radio galaxies, are statistically more likely to have dissimilar injection indices in two different episodes, as they will probably have different jet powers.

  9. Mapping stellar content to dark matter halos using galaxy clustering and galaxy-galaxy lensing in the SDSS DR7

    CERN Document Server

    Zu, Ying

    2015-01-01

    The mapping between the distributions of the observed galaxy stellar mass and the underlying dark matter halos provides the crucial link from theories of large-scale structure formation to interpreting the complex phenomena of galaxy formation and evolution. We develop a novel statistical method, based on the Halo Occupation Distribution model (HOD), to solve for this mapping by jointly fitting the galaxy clustering and the galaxy-galaxy lensing measured from the Sloan Digital Sky Survey (SDSS). The method, called the iHOD model, extracts maximum information from the survey by including ~80% more galaxies than the traditional HOD methods, and takes into account the incompleteness of the stellar mass samples in a statistically consistent manner. The derived stellar-to-halo mass relation not only explains the clustering and lensing of SDSS galaxies over almost four decades in stellar mass, but also successfully predicts the stellar mass functions observed in SDSS. Due to its capability of modelling significantl...

  10. Sub-millimeter galaxies as progenitors of compact quiescent galaxies

    CERN Document Server

    Toft, S; Magnelli, B; Karim, A; Zirm, A; Michalowski, M; Capak, P; Sheth, K; Schawinski, K; Krogager, J -K; Wuyts, S; Sanders, D; Man, A W S; Lutz, D; Staguhn, J; Berta, S; Mccracken, H; Krpan, J; Riechers, D

    2014-01-01

    Three billion years after the big bang (at redshift z=2), half of the most massive galaxies were already old, quiescent systems with little to no residual star formation and extremely compact with stellar mass densities at least an order of magnitude larger than in low redshift ellipticals, their descendants. Little is known about how they formed, but their evolved, dense stellar populations suggest formation within intense, compact starbursts 1-2 Gyr earlier (at 3galaxies (SMGs) are prime examples of intense, gas-rich, starbursts. With a new, representative spectroscopic sample of compact quiescent galaxies at z=2 and a statistically well-understood sample of SMGs, we show that z=3-6 SMGs are consistent with being the progenitors of z=2 quiescent galaxies, matching their formation redshifts and their distributions of sizes, stellar masses and internal velocities. As...

  11. The Intrinsic Shape of Galaxies in SDSS/Galaxy Zoo

    CERN Document Server

    Rodríguez, Silvio

    2013-01-01

    By modelling the axis ratio distribution of SDSS DR8 galaxies we find the intrinsic 3D shapes of spirals and ellipticals. We use morphological information from the Galaxy Zoo project and assume a non-parametric distribution intrinsic of shapes, while taking into account dust extinction. We measure the dust extinction of the full sample of spiral galaxies and find a smaller value than previous estimations, with an edge-on extinction of $E_0 = 0.284^{+0.015}_{-0.026}$ in the SDSS r band. We also find that the distribution of minor to major axis ratio has a mean value of $ 0.267 \\pm 0.009 $, slightly larger than previous estimates mainly due to the lower extinction used; the same affects the circularity of galactic discs, which are found to be less round in shape than in previous studies, with a mean ellipticity of $0.215 \\pm 0.013$. For elliptical galaxies, we find that the minor to major axis ratio, with a mean value of $0.584 \\pm 0.006$, is larger than previous estimations due to the removal of spiral interlo...

  12. Galaxy and Mass Assembly (GAMA): merging galaxies and their properties

    CERN Document Server

    De Propris, Roberto; Bland-Hawthorn, Joss; Brough, Sarah; Driver, Simon P; Hopkins, Andrew M; Kelvin, Lee; Loveday, Jon; Phillipps, Steve; Robotham, Aaron

    2014-01-01

    We derive the close pair fractions and volume merger rates as a function of luminosity and morphology for galaxies in the GAMA survey with -23 < M(r) < -17 at 0.01 < z < 0.22. The merger fraction is about 0.015 at all luminosities (assuming 1/2 of pairs merge) and the volume merger rate is about 0.00035 per cubic Mpc per Gyr. Dry mergers (between red or spheroidal galaxies) are uncommon and decrease with decreasing luminosity. Fainter mergers are wet, between blue or disky galaxies. Damp mergers (one of each type) follow the average of dry and wet mergers. In the brighter luminosity bin (-23 < M(r) < -20) the merger rate evolution is flat, irrespective of colour or morphology. The makeup of the merging population does not change since z = 0.2. Major mergers and dry mergers appear comparatively unimportant in the buildup of the red sequence over the past 2 Gyr. We compare the colour, morphology, environmental density and degree of activity of galaxies in pairs to those of more isolated object...

  13. The Arecibo Galaxy Environment Survey IX: The Isolated Galaxy Sample

    CERN Document Server

    Minchin, R F; Davies, J I; Karachentsev, I D; Keenan, O C; Momjian, E; Rodriguez, R; Taber, T; Taylor, R

    2015-01-01

    We have used the Arecibo L-band Feed Array to map three regions, each of 5 square degrees, around the isolated galaxies NGC 1156, UGC 2082, and NGC 5523. In the vicinity of these galaxies we have detected two dwarf companions: one near UGC 2082, previously discovered by ALFALFA, and one near NGC 1156, discovered by this project and reported in an earlier paper. This is significantly fewer than the 15.4 $^{+1.7}_{-1.5}$ that would be expected from the field HI mass function from ALFALFA or the 8.9 $\\pm$ 1.2 expected if the HI mass function from the Local Group applied in these regions. The number of dwarf companions detected is, however, consistent with a flat or declining HI mass function as seen by a previous, shallower, HI search for companions to isolated galaxies.We attribute this difference in Hi mass functions to the different environments in which they are measured. This agrees with the general observation that lower ratios of dwarf to giant galaxies are found in lower density environments.

  14. NGC 3934: a shell galaxy in a compact galaxy environment

    CERN Document Server

    Bettoni, D; Rampazzo, R; Marino, A; Mazzei, P; Buson, L M

    2011-01-01

    We investigate the NGC 3933 poor galaxy association, that contains NGC 3934, which is classified as a polar-ring galaxy. The multi-band photometric analysis of NGC 3934 allows us to investigate the nature of this galaxy and to re-define the NGC 3933 group members with the aim to characterize the group dynamical properties and its evolutionary phase. We imaged the group in the far (FUV,lambda = 1530A) and near (NUV, lambda=2316A) ultraviolet (UV) bands of the Galaxy Evolution Explorer (GALEX). From the deep optical imaging we determined the fine structure of NGC 3934. We measured the recession velocity of PGC 213894 which shows that it belongs to the NGC 3933 group. We derived the spectral energy distribution (SED) from FUV (GALEX) to far-IR emission of the two brightest members of the group. We compared a grid of smooth particle hydrodynamical (SPH) chemo-photometric simulations with the SED and the integrated properties of NGC 3934 and NGC 3933 to devise their possible formation/evolutionary scenarios. The N...

  15. Reconstructing Galaxy Histories from Globular Clusters

    CERN Document Server

    West, M J; Marzke, R O; Jordan, A; West, Michael J.; Cote, Patrick; Marzke, Ronald O.; Jordan, Andres

    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. 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.

  16. Galaxy Evolution in Clusters Since z ~ 1

    Science.gov (United States)

    Aragón-Salamanca, A.

    Galaxy clusters provide some of the most extreme environments in which galaxies evolve, making them excellent laboratories to study the age old question of "nature" vs. "nurture" in galaxy evolution. Here I review some of the key observational results obtained during the last decade on the evolution of the morphology, structure, dynamics, star-formation history and stellar populations of cluster galaxies since the time when the Universe was half its present age. Many of the results presented here have been obtained within the ESO Distant Cluster Survey (EDisCS) and Space Telescope A901/02 Galaxy Evolution Survey (STAGES) collaborations.

  17. Environmental Dependence of Warps in Spiral Galaxies

    Science.gov (United States)

    Ann, Hong Bae; Bae, Hyun Jeong

    2016-12-01

    We determined the warp parameters of 192 warped galaxies which are selected from 340 edge-on galaxies using color images as well as r-band isophotal maps. We derive the local background density (Σ_{n}) to examine the dependence of the warp amplitudes on the galaxy environment. We find a clear trend that strongly warped galaxies are likely to be found in high density regions where tidal interactions are supposed to be frequent. However, the correlation between α_{w} and Σ_{n} is too weak for weakly warped galaxies (α_{w} decisive role in the formation of weak warps.}

  18. AGN Host Galaxy Properties And Mass Function

    Science.gov (United States)

    Bongiorno, Angela

    2016-10-01

    Supermassive black hole growth, nuclear activity, and galaxy evolution have been found to be closely related. In the context of AGN-galaxy coevolution, I will discuss about the relation found between the host galaxy properties and the central BH and I will present the latest determination of the host galaxy stellar mass function (HGMF), and the specific accretion rate distribution function (SARDF), derived from the XMM-COSMOS sample up to z˜2.5, with particular focus on AGN feedback as possible responsible mechanism for galaxy quenching.

  19. Missing Mass in Collisional Debris from Galaxies

    CERN Document Server

    Bournaud, F; Brinks, E; Boquien, M; Amram, P; Lisenfeld, U; Koribalski, B S; Walter, F; Charmandaris, V

    2007-01-01

    Recycled dwarf galaxies can form in the collisional debris of massive galaxies. Theoretical models predict that, contrary to classical galaxies, they should be free of non-baryonic Dark Matter. Analyzing the observed gas kinematics of such recycled galaxies with the help of a numerical model, we demonstrate that they do contain a massive dark component amounting to about twice the visible matter. Staying within the standard cosmological framework, this result most likely indicates the presence of large amounts of unseen, presumably cold, molecular gas. This additional mass should be present in the disks of their progenitor spiral galaxies, accounting for a significant part of the so-called missing baryons.

  20. The formation of compact groups of galaxies

    Institute of Scientific and Technical Information of China (English)

    马駬; 俞允强

    1999-01-01

    In the compact group of galaxies the galaxies can merge into a few massive ones in a very short time, so they must be formed very recently. On the other hand, according to the theory of structure formation, the denser system should form earlier. By analyzing the apparent paradox, we suggest that the merging process of CDM halo plays an important role in the formation of the compact groups of galaxies: it delays the formation of compact groups of galaxies, and makes the groups of galaxies much denser.