WorldWideScience

Sample records for massive star formation

  1. Search of massive star formation with COMICS

    Science.gov (United States)

    Okamoto, Yoshiko K.

    2004-04-01

    Mid-infrared observations is useful for studies of massive star formation. Especially COMICS offers powerful tools: imaging survey of the circumstellar structures of forming massive stars such as massive disks and cavity structures, mass estimate from spectroscopy of fine structure lines, and high dispersion spectroscopy to census gas motion around formed stars. COMICS will open the next generation infrared studies of massive star formation.

  2. Black-hole-regulated star formation in massive galaxies

    Science.gov (United States)

    Martín-Navarro, Ignacio; Brodie, Jean P.; Romanowsky, Aaron J.; Ruiz-Lara, Tomás; van de Ven, Glenn

    2018-01-01

    Supermassive black holes, with masses more than a million times that of the Sun, seem to inhabit the centres of all massive galaxies. Cosmologically motivated theories of galaxy formation require feedback from these supermassive black holes to regulate star formation. In the absence of such feedback, state-of-the-art numerical simulations fail to reproduce the number density and properties of massive galaxies in the local Universe. There is, however, no observational evidence of this strongly coupled coevolution between supermassive black holes and star formation, impeding our understanding of baryonic processes within galaxies. Here we report that the star formation histories of nearby massive galaxies, as measured from their integrated optical spectra, depend on the mass of the central supermassive black hole. Our results indicate that the black-hole mass scales with the gas cooling rate in the early Universe. The subsequent quenching of star formation takes place earlier and more efficiently in galaxies that host higher-mass central black holes. The observed relation between black-hole mass and star formation efficiency applies to all generations of stars formed throughout the life of a galaxy, revealing a continuous interplay between black-hole activity and baryon cooling.

  3. Black-hole-regulated star formation in massive galaxies.

    Science.gov (United States)

    Martín-Navarro, Ignacio; Brodie, Jean P; Romanowsky, Aaron J; Ruiz-Lara, Tomás; van de Ven, Glenn

    2018-01-18

    Supermassive black holes, with masses more than a million times that of the Sun, seem to inhabit the centres of all massive galaxies. Cosmologically motivated theories of galaxy formation require feedback from these supermassive black holes to regulate star formation. In the absence of such feedback, state-of-the-art numerical simulations fail to reproduce the number density and properties of massive galaxies in the local Universe. There is, however, no observational evidence of this strongly coupled coevolution between supermassive black holes and star formation, impeding our understanding of baryonic processes within galaxies. Here we report that the star formation histories of nearby massive galaxies, as measured from their integrated optical spectra, depend on the mass of the central supermassive black hole. Our results indicate that the black-hole mass scales with the gas cooling rate in the early Universe. The subsequent quenching of star formation takes place earlier and more efficiently in galaxies that host higher-mass central black holes. The observed relation between black-hole mass and star formation efficiency applies to all generations of stars formed throughout the life of a galaxy, revealing a continuous interplay between black-hole activity and baryon cooling.

  4. The Destructive Birth of Massive Stars and Massive Star Clusters

    Science.gov (United States)

    Rosen, Anna; Krumholz, Mark; McKee, Christopher F.; Klein, Richard I.; Ramirez-Ruiz, Enrico

    2017-01-01

    Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium with their intense radiation fields dwarfs the contribution by their vastly more numerous low-mass cousins. Previous theoretical and observational studies have concluded that the feedback associated with massive stars' radiation fields is the dominant mechanism regulating massive star and massive star cluster (MSC) formation. Therefore detailed simulation of the formation of massive stars and MSCs, which host hundreds to thousands of massive stars, requires an accurate treatment of radiation. For this purpose, we have developed a new, highly accurate hybrid radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform a suite of three-dimensional radiation-hydrodynamic simulations of the formation of massive stars and MSCs. For individual massive stellar systems, we simulate the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channeled to the massive stellar system via gravitational and Rayleigh-Taylor (RT) instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of RT instability, but does not suppress it entirely provided the edges of the radiation-dominated bubbles are adequately resolved. RT instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. To model MSC formation, we simulate the collapse of a dense, turbulent, magnetized Mcl = 106 M⊙ molecular cloud. We find that the influence of the magnetic pressure and radiative feedback slows down star formation. Furthermore, we find that star formation is suppressed along dense filaments where the magnetic field is

  5. Magnetic fields and massive star formation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Qizhou; Keto, Eric; Ho, Paul T. P.; Ching, Tao-Chung; Chen, How-Huan [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Qiu, Keping [School of Astronomy and Space Science, Nanjing University, 22 Hankou Road, Nanjing 210093 (China); Girart, Josep M.; Juárez, Carmen [Institut de Ciències de l' Espai, (CSIC-IEEC), Campus UAB, Facultat de Ciències, C5p 2, E-08193 Bellaterra, Catalonia (Spain); Liu, Hauyu; Tang, Ya-Wen; Koch, Patrick M.; Rao, Ramprasad; Lai, Shih-Ping [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan (China); Li, Zhi-Yun [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States); Frau, Pau [Observatorio Astronómico Nacional, Alfonso XII, 3 E-28014 Madrid (Spain); Li, Hua-Bai [Department of Physics, The Chinese University of Hong Kong, Hong Kong (China); Padovani, Marco [Laboratoire de Radioastronomie Millimétrique, UMR 8112 du CNRS, École Normale Supérieure et Observatoire de Paris, 24 rue Lhomond, F-75231 Paris Cedex 05 (France); Bontemps, Sylvain [OASU/LAB-UMR5804, CNRS, Université Bordeaux 1, F-33270 Floirac (France); Csengeri, Timea, E-mail: qzhang@cfa.harvard.edu [Max Planck Institute for Radioastronomy, Auf dem Hügel 69, D-53121 Bonn (Germany)

    2014-09-10

    Massive stars (M > 8 M {sub ☉}) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 μm obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of ≲0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within 40° of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks (≲ 10{sup 3} AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample of massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scales of 0.01-0.1 pc in the context of massive star and cluster star formation.

  6. Multi-wavelength investigations on feedback of massive star formation

    Science.gov (United States)

    Yuan, Jinghua

    2014-05-01

    In the course of massive star formation, outflows, ionizing radiation and intense stellar winds could heavily affect their adjacent environs and natal clouds. There are several outstanding open questions related to these processes: i) whether they can drive turbulence in molecular clouds; ii) whether they are able to trigger star formation; iii) whether they can destroy natal clouds to terminate star formation at low efficiencies. This thesis investigates feedback in different stages of massive star formation. Influence of such feedback to the ambient medium has been revealed. A new type of millimeter methanol maser is detected for the first time. An uncommon bipolar outflow prominent in the mid-infrared is discovered. And features of triggered star formation are found on the border of an infrared bubble and in the surroundings of a Herbig Be star. Extended green objects (EGOs) are massive outflow candidates showing prominent shocked features in the mid-infrared. We have carried out a high resolution study of the EGO G22.04+0.22 (hereafter, G22) based on archived SMA data. Continuum and molecular lines at 1.3 mm reveal that G22 is still at a hot molecular core stage. A very young multi-polar outflow system is detected, which is interacting with the adjacent dense gas. Anomalous emission features from CH3OH (8,-1,8 - 7,0,7) and CH3OH (4,2,2 - 3,1,2) are proven to be millimeter masers. It is the first time that maser emission of CH3OH (8,-1,8 - 7,0,7) at 218.440 GHz is detected in a massive star-forming region. Bipolar outflows have been revealed and investigated almost always in the microwave or radio domain. It's sort of rare that hourglass-shaped morphology be discovered in the mid-infrared. Based on GLIMPSE data, we have discovered a bipolar object resembling an hourglass at 8.0 um. It is found to be associated with IRAS 18114-1825. Analysis based on fitted SED, optical spectroscopy, and infrared color indices suggests IRAS 18114-1825 is an uncommon bipolar

  7. Formation of massive stars in OB associations and giant molecular clouds

    International Nuclear Information System (INIS)

    Lada, C.J.

    1980-01-01

    Certain interesting patterns are being perceived in the morphology of the regions which have recently produced massive OB stars. In particular, current evidence seems to favour the notion that the formation of massive stars takes place at the edges and not the centres of large molecular cloud complexes. It is this aspect of the observations that is discussed in the present paper. The phenomena described here will pertain to massive stars only. Specifically, stars with spectral types earlier than B3 will be considered since it is usually only these stars that produce sufficient havoc (e.g., maser sources, CO bright spots, H II regions) to noticeably affect their early environments. The corresponding phenomena for lower mass stars could be entirely different. A review is first presented of what has been learned about the OB star formation process from studies of the visible OB stars themselves. Then, newly derived information pertaining to the most recent episodes of OB star birth in galactic molecular clouds is discussed. Finally, a short discussion of the significance of the results and their implications for possible star formation mechanisms will be made. (U.K.)

  8. Formation and pre-MS Evolution of Massive Stars with Growing Accretion

    Science.gov (United States)

    Maeder, A.; Behrend, R.

    2002-10-01

    We briefly describe the three existing scenarios for forming massive stars and emphasize that the arguments often used to reject the accretion scenario for massive stars are misleading. It is usually not accounted for the fact that the turbulent pressure associated to large turbulent velocities in clouds necessarily imply relatively high accretion rates for massive stars. We show the basic difference between the formation of low and high mass stars based on the values of the free fall time and of the Kelvin-Helmholtz timescale, and define the concept of birthline for massive stars. Due to D-burning, the radius and location of the birthline in the HR diagram, as well as the lifetimes are very sensitive to the accretion rate dM/dt(accr). If a form dM/dt(accr) propto A(M/Msun)phi is adopted, the observations in the HR diagram and the lifetimes support a value of A approx 10-5 Msun/yr and a value of phi > 1. Remarkably, such a law is consistent with the relation found by Churchwell and Henning et al. between the outflow rates and the luminosities of ultracompact HII regions, if we assume that a fraction 0.15 to 0.3 of the global inflow is accreted. The above relation implies high dM/dt(accr) approx 10-3 Msun/yr for the most massive stars. The physical possibility of such high dM/dt(accr) is supported by current numerical models. Finally, we give simple analytical arguments in favour of the growth of dM/dt(accr) with the already accreted mass. We also suggest that due to Bondi-Hoyle accretion, the formation of binary stars is largely favoured among massive stars in the accretion scenario.

  9. The Formation and Early Evolution of Embedded Massive Star Clusters

    Science.gov (United States)

    Barnes, Peter

    We propose to combine Spitzer, WISE, Herschel, and other archival spacecraft data with an existing ground- and space-based mm-wave to near-IR survey of molecular clouds over a large portion of the Milky Way, in order to systematically study the formation and early evolution of massive stars and star clusters, and provide new observational calibrations for a theoretical paradigm of this key astrophysical problem. Central Objectives: The Galactic Census of High- and Medium-mass Protostars (CHaMP) is a large, unbiased, uniform, and panchromatic survey of massive star and cluster formation and early evolution, covering 20°x6° of the Galactic Plane. Its uniqueness lies in the comprehensive molecular spectroscopy of 303 massive dense clumps, which have also been included in several archival spacecraft surveys. Our objective is a systematic demographic analysis of massive star and cluster formation, one which has not been possible without knowledge of our CHaMP cloud sample, including all clouds with embedded clusters as well as those that have not yet formed massive stars. For proto-clusters deeply embedded within dense molecular clouds, analysis of these space-based data will: 1. Yield a complete census of Young Stellar Objects in each cluster. 2. Allow systematic measurements of embedded cluster properties: spectral energy distributions, luminosity functions, protostellar and disk fractions, and how these vary with cluster mass, age, and density. Combined with other, similarly complete and unbiased infrared and mm data, CHaMP's goals include: 3. A detailed comparison of the embedded stellar populations with their natal dense gas to derive extinction maps, star formation efficiencies and feedback effects, and the kinematics, physics, and chemistry of the gas in and around the clusters. 4. Tying the demographics, age spreads, and timescales of the clusters, based on pre-Main Sequence evolution, to that of the dense gas clumps and Giant Molecular Clouds. 5. A

  10. EARLY-STAGE MASSIVE STAR FORMATION NEAR THE GALACTIC CENTER: Sgr C

    Energy Technology Data Exchange (ETDEWEB)

    Kendrew, S.; Johnston, K.; Beuther, H. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Ginsburg, A.; Bally, J.; Battersby, C. [CASA, University of Colorado at Boulder, UCB 389, Boulder, CO 80309 (United States); Cyganowski, C. J., E-mail: kendrew@mpia.de [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

    2013-10-01

    We present near-infrared spectroscopy and 1 mm line and continuum observations of a recently identified site of high mass star formation likely to be located in the Central Molecular Zone (CMZ) near Sgr C. Located on the outskirts of the massive evolved H II region associated with Sgr C, the area is characterized by an Extended Green Object (EGO) measuring ∼10'' in size (0.4 pc), whose observational characteristics suggest the presence of an embedded massive protostar driving an outflow. Our data confirm that early-stage star formation is taking place on the periphery of the Sgr C H II region, with detections of two protostellar cores and several knots of H{sub 2} and Brackett γ emission alongside a previously detected compact radio source. We calculate the cores' joint mass to be ∼10{sup 3} M {sub ☉}, with column densities of 1-2 × 10{sup 24} cm{sup –2}. We show the host molecular cloud to hold ∼10{sup 5} M {sub ☉} of gas and dust with temperatures and column densities favorable for massive star formation to occur, however, there is no evidence of star formation outside of the EGO, indicating that the cloud is predominantly quiescent. Given its mass, density, and temperature, the cloud is comparable to other remarkable non-star-forming clouds such as G0.253 in the eastern CMZ.

  11. Formation of new stellar populations from gas accreted by massive young star clusters.

    Science.gov (United States)

    Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

    2016-01-28

    Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

  12. The Galactic Distribution of Massive Star Formation from the Red MSX Source Survey

    Science.gov (United States)

    Figura, Charles C.; Urquhart, J. S.

    2013-01-01

    Massive stars inject enormous amounts of energy into their environments in the form of UV radiation and molecular outflows, creating HII regions and enriching local chemistry. These effects provide feedback mechanisms that aid in regulating star formation in the region, and may trigger the formation of subsequent generations of stars. Understanding the mechanics of massive star formation presents an important key to understanding this process and its role in shaping the dynamics of galactic structure. The Red MSX Source (RMS) survey is a multi-wavelength investigation of ~1200 massive young stellar objects (MYSO) and ultra-compact HII (UCHII) regions identified from a sample of colour-selected sources from the Midcourse Space Experiment (MSX) point source catalog and Two Micron All Sky Survey. We present a study of over 900 MYSO and UCHII regions investigated by the RMS survey. We review the methods used to determine distances, and investigate the radial galactocentric distribution of these sources in context with the observed structure of the galaxy. The distribution of MYSO and UCHII regions is found to be spatially correlated with the spiral arms and galactic bar. We examine the radial distribution of MYSOs and UCHII regions and find variations in the star formation rate between the inner and outer Galaxy and discuss the implications for star formation throughout the galactic disc.

  13. The formation of massive molecular filaments and massive stars triggered by a magnetohydrodynamic shock wave

    Science.gov (United States)

    Inoue, Tsuyoshi; Hennebelle, Patrick; Fukui, Yasuo; Matsumoto, Tomoaki; Iwasaki, Kazunari; Inutsuka, Shu-ichiro

    2018-05-01

    Recent observations suggest an that intensive molecular cloud collision can trigger massive star/cluster formation. The most important physical process caused by the collision is a shock compression. In this paper, the influence of a shock wave on the evolution of a molecular cloud is studied numerically by using isothermal magnetohydrodynamics simulations with the effect of self-gravity. Adaptive mesh refinement and sink particle techniques are used to follow the long-time evolution of the shocked cloud. We find that the shock compression of a turbulent inhomogeneous molecular cloud creates massive filaments, which lie perpendicularly to the background magnetic field, as we have pointed out in a previous paper. The massive filament shows global collapse along the filament, which feeds a sink particle located at the collapse center. We observe a high accretion rate \\dot{M}_acc> 10^{-4} M_{⊙}yr-1 that is high enough to allow the formation of even O-type stars. The most massive sink particle achieves M > 50 M_{⊙} in a few times 105 yr after the onset of the filament collapse.

  14. THE MILKY WAY PROJECT: A STATISTICAL STUDY OF MASSIVE STAR FORMATION ASSOCIATED WITH INFRARED BUBBLES

    International Nuclear Information System (INIS)

    Kendrew, S.; Robitaille, T. P.; Simpson, R.; Lintott, C. J.; Bressert, E.; Povich, M. S.; Sherman, R.; Schawinski, K.; Wolf-Chase, G.

    2012-01-01

    The Milky Way Project citizen science initiative recently increased the number of known infrared bubbles in the inner Galactic plane by an order of magnitude compared to previous studies. We present a detailed statistical analysis of this data set with the Red MSX Source (RMS) catalog of massive young stellar sources to investigate the association of these bubbles with massive star formation. We particularly address the question of massive triggered star formation near infrared bubbles. We find a strong positional correlation of massive young stellar objects (MYSOs) and H II regions with Milky Way Project bubbles at separations of <2 bubble radii. As bubble sizes increase, a statistically significant overdensity of massive young sources emerges in the region of the bubble rims, possibly indicating the occurrence of triggered star formation. Based on numbers of bubble-associated RMS sources, we find that 67% ± 3% of MYSOs and (ultra-)compact H II regions appear to be associated with a bubble. We estimate that approximately 22% ± 2% of massive young stars may have formed as a result of feedback from expanding H II regions. Using MYSO-bubble correlations, we serendipitously recovered the location of the recently discovered massive cluster Mercer 81, suggesting the potential of such analyses for discovery of heavily extincted distant clusters.

  15. THE MILKY WAY PROJECT: A STATISTICAL STUDY OF MASSIVE STAR FORMATION ASSOCIATED WITH INFRARED BUBBLES

    Energy Technology Data Exchange (ETDEWEB)

    Kendrew, S.; Robitaille, T. P. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Simpson, R.; Lintott, C. J. [Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Bressert, E. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Povich, M. S. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Sherman, R. [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637 (United States); Schawinski, K. [Yale Center for Astronomy and Astrophysics, Yale University, P.O. Box 208121, New Haven, CT 06520 (United States); Wolf-Chase, G., E-mail: kendrew@mpia.de [Astronomy Department, Adler Planetarium, 1300 S. Lake Shore Drive, Chicago, IL 60605 (United States)

    2012-08-10

    The Milky Way Project citizen science initiative recently increased the number of known infrared bubbles in the inner Galactic plane by an order of magnitude compared to previous studies. We present a detailed statistical analysis of this data set with the Red MSX Source (RMS) catalog of massive young stellar sources to investigate the association of these bubbles with massive star formation. We particularly address the question of massive triggered star formation near infrared bubbles. We find a strong positional correlation of massive young stellar objects (MYSOs) and H II regions with Milky Way Project bubbles at separations of <2 bubble radii. As bubble sizes increase, a statistically significant overdensity of massive young sources emerges in the region of the bubble rims, possibly indicating the occurrence of triggered star formation. Based on numbers of bubble-associated RMS sources, we find that 67% {+-} 3% of MYSOs and (ultra-)compact H II regions appear to be associated with a bubble. We estimate that approximately 22% {+-} 2% of massive young stars may have formed as a result of feedback from expanding H II regions. Using MYSO-bubble correlations, we serendipitously recovered the location of the recently discovered massive cluster Mercer 81, suggesting the potential of such analyses for discovery of heavily extincted distant clusters.

  16. Molecular Cloud Structures and Massive Star Formation in N159

    Science.gov (United States)

    Nayak, O.; Meixner, M.; Fukui, Y.; Tachihara, K.; Onishi, T.; Saigo, K.; Tokuda, K.; Harada, R.

    2018-02-01

    The N159 star-forming region is one of the most massive giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC). We show the 12CO, 13CO, CS molecular gas lines observed with ALMA in N159 west (N159W) and N159 east (N159E). We relate the structure of the gas clumps to the properties of 24 massive young stellar objects (YSOs) that include 10 newly identified YSOs based on our search. We use dendrogram analysis to identify properties of the molecular clumps, such as flux, mass, linewidth, size, and virial parameter. We relate the YSO properties to the molecular gas properties. We find that the CS gas clumps have a steeper size–linewidth relation than the 12CO or 13CO gas clumps. This larger slope could potentially occur if the CS gas is tracing shocks. The virial parameters of the 13CO gas clumps in N159W and N159E are low (<1). The threshold for massive star formation in N159W is 501 M ⊙ pc‑2, and the threshold for massive star formation in N159E is 794 M ⊙ pc‑2. We find that 13CO is more photodissociated in N159E than N159W. The most massive YSO in N159E has cleared out a molecular gas hole in its vicinity. All the massive YSO candidates in N159E have a more evolved spectral energy distribution type in comparison to the YSO candidates in N159W. These differences lead us to conclude that the giant molecular cloud complex in N159E is more evolved than the giant molecular cloud complex in N159W.

  17. THE SIZE-STAR FORMATION RELATION OF MASSIVE GALAXIES AT 1.5 < z < 2.5

    International Nuclear Information System (INIS)

    Toft, S.; Franx, M.; Van Dokkum, P.; Foerster Schreiber, N. M.; Labbe, I.; Wuyts, S.; Marchesini, D.

    2009-01-01

    We study the relation between size and star formation activity in a complete sample of 225 massive (M * > 5 x 10 10 M sun ) galaxies at 1.5 PSF ∼ 0.''45) ground-based ISAAC data, we confirm and improve the significance of the relation between star formation activity and compactness found in previous studies, using a large, complete mass-limited sample. At z ∼ 2, massive quiescent galaxies are significantly smaller than massive star-forming galaxies, and a median factor of 0.34 ± 0.02 smaller than galaxies of similar mass in the local universe. Thirteen percent of the quiescent galaxies are unresolved in the ISAAC data, corresponding to sizes <1 kpc, more than five times smaller than galaxies of similar mass locally. The quiescent galaxies span a Kormendy relation which, compared to the relation for local early types, is shifted to smaller sizes and brighter surface brightnesses and is incompatible with passive evolution. The progenitors of the quiescent galaxies were likely dominated by highly concentrated, intense nuclear starbursts at z ∼ 3-4, in contrast to star-forming galaxies at z ∼ 2 which are extended and dominated by distributed star formation.

  18. Formation of the First Star Clusters and Massive Star Binaries by Fragmentation of Filamentary Primordial Gas Clouds

    Science.gov (United States)

    Hirano, Shingo; Yoshida, Naoki; Sakurai, Yuya; Fujii, Michiko S.

    2018-03-01

    We perform a set of cosmological simulations of early structure formation incorporating baryonic streaming motions. We present a case where a significantly elongated gas cloud with ∼104 solar mass (M ⊙) is formed in a pre-galactic (∼107 M ⊙) dark halo. The gas streaming into the halo compresses and heats the massive filamentary cloud to a temperature of ∼10,000 Kelvin. The gas cloud cools rapidly by atomic hydrogen cooling, and then by molecular hydrogen cooling down to ∼400 Kelvin. The rapid decrease of the temperature and hence of the Jeans mass triggers fragmentation of the filament to yield multiple gas clumps with a few hundred solar masses. We estimate the mass of the primordial star formed in each fragment by adopting an analytic model based on a large set of radiation hydrodynamics simulations of protostellar evolution. The resulting stellar masses are in the range of ∼50–120 M ⊙. The massive stars gravitationally attract each other and form a compact star cluster. We follow the dynamics of the star cluster using a hybrid N-body simulation. We show that massive star binaries are formed in a few million years through multi-body interactions at the cluster center. The eventual formation of the remnant black holes will leave a massive black hole binary, which can be a progenitor of strong gravitational wave sources similar to those recently detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).

  19. Massive star formation by accretion. II. Rotation: how to circumvent the angular momentum barrier?

    Science.gov (United States)

    Haemmerlé, L.; Eggenberger, P.; Meynet, G.; Maeder, A.; Charbonnel, C.; Klessen, R. S.

    2017-06-01

    Context. Rotation plays a key role in the star-formation process, from pre-stellar cores to pre-main-sequence (PMS) objects. Understanding the formation of massive stars requires taking into account the accretion of angular momentum during their PMS phase. Aims: We study the PMS evolution of objects destined to become massive stars by accretion, focusing on the links between the physical conditions of the environment and the rotational properties of young stars. In particular, we look at the physical conditions that allow the production of massive stars by accretion. Methods: We present PMS models computed with a new version of the Geneva Stellar Evolution code self-consistently including accretion and rotation according to various accretion scenarios for mass and angular momentum. We describe the internal distribution of angular momentum in PMS stars accreting at high rates and we show how the various physical conditions impact their internal structures, evolutionary tracks, and rotation velocities during the PMS and the early main sequence. Results: We find that the smooth angular momentum accretion considered in previous studies leads to an angular momentum barrier and does not allow the formation of massive stars by accretion. A braking mechanism is needed in order to circumvent this angular momentum barrier. This mechanism has to be efficient enough to remove more than two thirds of the angular momentum from the inner accretion disc. Due to the weak efficiency of angular momentum transport by shear instability and meridional circulation during the accretion phase, the internal rotation profiles of accreting stars reflect essentially the angular momentum accretion history. As a consequence, careful choice of the angular momentum accretion history allows circumvention of any limitation in mass and velocity, and production of stars of any mass and velocity compatible with structure equations.

  20. Massive stars in galaxies

    International Nuclear Information System (INIS)

    Humphreys, R.M.

    1987-01-01

    The relationship between the morphologic type of a galaxy and the evolution of its massive stars is explored, reviewing observational results for nearby galaxies. The data are presented in diagrams, and it is found that the massive-star populations of most Sc spiral galaxies and irregular galaxies are similar, while those of Sb spirals such as M 31 and M 81 may be affected by morphology (via differences in the initial mass function or star-formation rate). Consideration is also given to the stability-related upper luminosity limit in the H-R diagram of hypergiant stars (attributed to radiation pressure in hot stars and turbulence in cool stars) and the goals of future observation campaigns. 88 references

  1. MASSIVE STARS IN THE Cl 1813-178 CLUSTER: AN EPISODE OF MASSIVE STAR FORMATION IN THE W33 COMPLEX

    International Nuclear Information System (INIS)

    Messineo, Maria; Davies, Ben; Figer, Donald F.; Trombley, Christine; Kudritzki, R. P.; Valenti, Elena; Najarro, F.; Michael Rich, R.

    2011-01-01

    Young massive (M > 10 4 M sun ) stellar clusters are a good laboratory to study the evolution of massive stars. Only a dozen of such clusters are known in the Galaxy. Here, we report about a new young massive stellar cluster in the Milky Way. Near-infrared medium-resolution spectroscopy with UIST on the UKIRT telescope and NIRSPEC on the Keck telescope, and X-ray observations with the Chandra and XMM satellites, of the Cl 1813-178 cluster confirm a large number of massive stars. We detected 1 red supergiant, 2 Wolf-Rayet stars, 1 candidate luminous blue variable, 2 OIf, and 19 OB stars. Among the latter, twelve are likely supergiants, four giants, and the faintest three dwarf stars. We detected post-main-sequence stars with masses between 25 and 100 M sun . A population with age of 4-4.5 Myr and a mass of ∼10, 000 M sun can reproduce such a mixture of massive evolved stars. This massive stellar cluster is the first detection of a cluster in the W33 complex. Six supernova remnants and several other candidate clusters are found in the direction of the same complex.

  2. Induced massive star formation in the trifid nebula?

    Science.gov (United States)

    Cernicharo; Lefloch; Cox; Cesarsky; Esteban; Yusef-Zadeh; Mendez; Acosta-Pulido; Garcia Lopez RJ; Heras

    1998-10-16

    The Trifid nebula is a young (10(5) years) galactic HII region where several protostellar sources have been detected with the infrared space observatory. The sources are massive (17 to 60 solar masses) and are associated with molecular gas condensations at the edges or inside the nebula. They appear to be in an early evolutionary stage and may represent the most recent generation of stars in the Trifid. These sources range from dense, apparently still inactive cores to more evolved sources, undergoing violent mass ejection episodes, including a source that powers an optical jet. These observations suggest that the protostellar sources may have evolved by induced star formation in the Trifid nebula.

  3. Global and radial variations in the efficiency of massive star formation among galaxies

    International Nuclear Information System (INIS)

    Allen, L.E.; Young, J.S.

    1990-01-01

    In order to determine the regions within galaxies which give rise to the most efficient star formation and to test the hypothesis that galaxies with high infrared luminosities per unit molecular mass are efficiently producing high mass stars, researchers have undertaken an H alpha imaging survey in galaxies whose CO distributions have been measured as part of the Five College Radio Astronomy Observatory (FCRAO) Extragalactic CO Survey. From these images researchers have derived global H alpha fluxes and distributions for comparison with far infrared radiation (FIR) fluxes and CO fluxes and distributions. Here, researchers present results on the global massive star formation efficiency (SFE = L sub H sub alpha/M(H2)) as a function of morphological type and environment, and on the radial distribution of the SFE within both peculiar and isolated galaxies. On the basis of comparison of the global L sub H sub alpha/M(H2) and L sub FIR/M(H2) for 111 galaxies, researchers conclude that environment rather than morphological type has the strongest effect on the global efficiency of massive star formation. Based on their study of a small sample, they find that the largest radial gradients are observed in the interacting/peculiar galaxies, indicating that environment affects the star formation efficiency within galaxies as well

  4. WHAT SETS THE INITIAL ROTATION RATES OF MASSIVE STARS?

    International Nuclear Information System (INIS)

    Rosen, Anna L.; Krumholz, Mark R.; Ramirez-Ruiz, Enrico

    2012-01-01

    The physical mechanisms that set the initial rotation rates in massive stars are a crucial unknown in current star formation theory. Observations of young, massive stars provide evidence that they form in a similar fashion to their low-mass counterparts. The magnetic coupling between a star and its accretion disk may be sufficient to spin down low-mass pre-main-sequence (PMS) stars to well below breakup at the end stage of their formation when the accretion rate is low. However, we show that these magnetic torques are insufficient to spin down massive PMS stars due to their short formation times and high accretion rates. We develop a model for the angular momentum evolution of stars over a wide range in mass, considering both magnetic and gravitational torques. We find that magnetic torques are unable to spin down either low-mass or high-mass stars during the main accretion phase, and that massive stars cannot be spun down significantly by magnetic torques during the end stage of their formation either. Spin-down occurs only if massive stars' disk lifetimes are substantially longer or their magnetic fields are much stronger than current observations suggest.

  5. Hyper-massive cloud, shock and stellar formation efficiency

    International Nuclear Information System (INIS)

    Louvet, Fabien

    2014-01-01

    O and B types stars are of paramount importance in the energy budget of galaxies and play a crucial role enriching the interstellar medium. However, their formation, unlike that of solar-type stars, is still subject to debate, if not an enigma. The earliest stages of massive star formation and the formation of their parent cloud are still crucial astrophysical questions that drew a lot of attention in the community, both from the theoretical and observational perspective, during the last decade. It has been proposed that massive stars are born in massive dense cores that form through very dynamic processes, such as converging flows of gas. During my PhD, I conducted a thorough study of the formation of dense cores and massive stars in the W43-MM1 supermassive structure, located at 6 kpc from the sun. At first, I showed a direct correlation between the star formation efficiency and the volume gas density of molecular clouds, in contrast with scenarios suggested by previous studies. Indeed, the spatial distribution and mass function of the massive dense cores currently forming in W43-MM1 suggests that this supermassive filament is undergoing a star formation burst, increasing as one approaches its center. I compared these observational results with the most recent numerical and analytical models of star formation. This comparison not only provides new constraints on the formation of supermassive filaments, but also suggests that understanding star formation in high density, extreme ridges requires a detailed portrait of the structure of these exceptional objects. Second, having shown that the formation of massive stars depends strongly on the properties of the ridges where they form, I studied the formation processes of these filaments, thanks of the characterization of their global dynamics. Specifically, I used a tracer of shocks (SiO molecule) to disentangle the feedback of local star formation processes (bipolar jets and outflows) from shocks tracing the pristine

  6. Star formation

    International Nuclear Information System (INIS)

    Woodward, P.R.

    1978-01-01

    Theoretical models of star formation are discussed beginning with the earliest stages and ending in the formation of rotating, self-gravitating disks or rings. First a model of the implosion of very diffuse gas clouds is presented which relies upon a shock at the edge of a galactic spiral arm to drive the implosion. Second, models are presented for the formation of a second generation of massive stars in such a cloud once a first generation has formed. These models rely on the ionizing radiation from massive stars or on the supernova shocks produced when these stars explode. Finally, calculations of the gravitational collapse of rotating clouds are discussed with special focus on the question of whether rotating disks or rings are the result of such a collapse. 65 references

  7. THE MASSIVE STAR-FORMING REGION CYGNUS OB2. II. INTEGRATED STELLAR PROPERTIES AND THE STAR FORMATION HISTORY

    International Nuclear Information System (INIS)

    Wright, N. J.; Drake, J. J.; Drew, J. E.; Vink, J. S.

    2010-01-01

    Cygnus OB2 is the nearest example of a massive star-forming region (SFR), containing over 50 O-type stars and hundreds of B-type stars. We have analyzed the properties of young stars in two fields in Cyg OB2 using the recently published deep catalog of Chandra X-ray point sources with complementary optical and near-IR photometry. Our sample is complete to ∼1 M sun (excluding A- and B-type stars that do not emit X-rays), making this the deepest study of the stellar properties and star formation history in Cyg OB2 to date. From Siess et al. isochrone fits to the near-IR color-magnitude diagram, we derive ages of 3.5 +0.75 -1.0 and 5.25 +1.5 -1.0 Myr for sources in the two fields, both with considerable spreads around the pre-main-sequence isochrones. The presence of a stellar population somewhat older than the present-day O-type stars, also fits in with the low fraction of sources with inner circumstellar disks (as traced by the K-band excess) that we find to be very low, but appropriate for a population of age ∼5 Myr. We also find that the region lacks a population of highly embedded sources that is often observed in young SFRs, suggesting star formation in the vicinity has declined. We measure the stellar mass functions (MFs) in this limit and find a power-law slope of Γ = -1.09 ± 0.13, in good agreement with the global mean value estimated by Kroupa. A steepening of the slope at higher masses is observed and suggested as due to the presence of the previous generation of stars that have lost their most massive members. Finally, combining our MF and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ∼3 x 10 4 M sun , similar to that of many of our Galaxy's most massive SFRs.

  8. Limiting Accretion onto Massive Stars by Fragmentation-Induced Starvation

    Energy Technology Data Exchange (ETDEWEB)

    Peters, Thomas; /ZAH, Heidelberg; Klessen, Ralf S.; /ZAH, Heidelberg /KIPAC, Menlo Park; Mac Low, Mordecai-Mark; /Amer. Museum Natural Hist.; Banerjee, Robi; /ZAH, Heidelberg

    2010-08-25

    Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems that themselves belong to large clusters containing stars of all masses. The radiative heating does not prevent fragmentation, but does lead to a higher Jeans mass, resulting in fewer and more massive stars than would form without the heating. This mechanism reproduces the observed relation between the total stellar mass in the cluster and the mass of the largest star. It predicts strong clumping and filamentary structure in the center of collapsing cores, as has recently been observed. We speculate that a similar mechanism will act during primordial star formation.

  9. NGC 346: Looking in the Cradle of a Massive Star Cluster

    Science.gov (United States)

    Gouliermis, Dimitrios A.; Hony, Sacha

    2017-03-01

    How does a star cluster of more than few 10,000 solar masses form? We present the case of the cluster NGC 346 in the Small Magellanic Cloud, still embedded in its natal star-forming region N66, and we propose a scenario for its formation, based on observations of the rich stellar populations in the region. Young massive clusters host a high fraction of early-type stars, indicating an extremely high star formation efficiency. The Milky Way galaxy hosts several young massive clusters that fill the gap between young low-mass open clusters and old massive globular clusters. Only a handful, though, are young enough to study their formation. Moreover, the investigation of their gaseous natal environments suffers from contamination by the Galactic disk. Young massive clusters are very abundant in distant starburst and interacting galaxies, but the distance of their hosting galaxies do not also allow a detailed analysis of their formation. The Magellanic Clouds, on the other hand, host young massive clusters in a wide range of ages with the youngest being still embedded in their giant HII regions. Hubble Space Telescope imaging of such star-forming complexes provide a stellar sampling with a high dynamic range in stellar masses, allowing the detailed study of star formation at scales typical for molecular clouds. Our cluster analysis on the distribution of newly-born stars in N66 shows that star formation in the region proceeds in a clumpy hierarchical fashion, leading to the formation of both a dominant young massive cluster, hosting about half of the observed pre-main-sequence population, and a self-similar dispersed distribution of the remaining stars. We investigate the correlation between stellar surface density (and star formation rate derived from star-counts) and molecular gas surface density (derived from dust column density) in order to unravel the physical conditions that gave birth to NGC 346. A power law fit to the data yields a steep correlation between these

  10. Radiation pressure in super star cluster formation

    Science.gov (United States)

    Tsang, Benny T.-H.; Milosavljević, Miloš

    2018-05-01

    The physics of star formation at its extreme, in the nuclei of the densest and the most massive star clusters in the universe—potential massive black hole nurseries—has for decades eluded scrutiny. Spectroscopy of these systems has been scarce, whereas theoretical arguments suggest that radiation pressure on dust grains somehow inhibits star formation. Here, we harness an accelerated Monte Carlo radiation transport scheme to report a radiation hydrodynamical simulation of super star cluster formation in turbulent clouds. We find that radiation pressure reduces the global star formation efficiency by 30-35%, and the star formation rate by 15-50%, both relative to a radiation-free control run. Overall, radiation pressure does not terminate the gas supply for star formation and the final stellar mass of the most massive cluster is ˜1.3 × 106 M⊙. The limited impact as compared to in idealized theoretical models is attributed to a radiation-matter anti-correlation in the supersonically turbulent, gravitationally collapsing medium. In isolated regions outside massive clusters, where the gas distribution is less disturbed, radiation pressure is more effective in limiting star formation. The resulting stellar density at the cluster core is ≥108 M⊙ pc-3, with stellar velocity dispersion ≳ 70 km s-1. We conclude that the super star cluster nucleus is propitious to the formation of very massive stars via dynamical core collapse and stellar merging. We speculate that the very massive star may avoid the claimed catastrophic mass loss by continuing to accrete dense gas condensing from a gravitationally-confined ionized phase.

  11. EVIDENCE FOR DELAYED MASSIVE STAR FORMATION IN THE M17 PROTO-OB ASSOCIATION

    International Nuclear Information System (INIS)

    Povich, Matthew S.; Whitney, Barbara A.

    2010-01-01

    Through analysis of archival images and photometry from the Spitzer GLIMPSE and MIPSGAL surveys combined with Two Micron All Sky Survey and MSX data, we have identified 488 candidate young stellar objects (YSOs) in the giant molecular cloud M17 SWex, which extends ∼50 pc southwest from the prominent Galactic H II region M17. Our sample includes >200 YSOs with masses >3 M sun that will become B-type stars on the main sequence. Extrapolating over the stellar initial mass function (IMF), we find that M17 SWex contains >1.3 x 10 4 young stars, representing a proto-OB association. The YSO mass function is significantly steeper than the Salpeter IMF, and early O stars are conspicuously absent from M17 SWex. Assuming M17 SWex will form an OB association with a Salpeter IMF, these results reveal the combined effects of (1) more rapid circumstellar disk evolution in more massive YSOs and (2) delayed onset of massive star formation.

  12. Globular Cluster Formation at High Density: A Model for Elemental Enrichment with Fast Recycling of Massive-star Debris

    Energy Technology Data Exchange (ETDEWEB)

    Elmegreen, Bruce G., E-mail: bge@us.ibm.com [IBM Research Division, T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States)

    2017-02-10

    The self-enrichment of massive star clusters by p -processed elements is shown to increase significantly with increasing gas density as a result of enhanced star formation rates and stellar scatterings compared to the lifetime of a massive star. Considering the type of cloud core where a globular cluster (GC) might have formed, we follow the evolution and enrichment of the gas and the time dependence of stellar mass. A key assumption is that interactions between massive stars are important at high density, including interactions between massive stars and massive-star binaries that can shred stellar envelopes. Massive-star interactions should also scatter low-mass stars out of the cluster. Reasonable agreement with the observations is obtained for a cloud-core mass of ∼4 × 10{sup 6} M {sub ⊙} and a density of ∼2 × 10{sup 6} cm{sup −3}. The results depend primarily on a few dimensionless parameters, including, most importantly, the ratio of the gas consumption time to the lifetime of a massive star, which has to be low, ∼10%, and the efficiency of scattering low-mass stars per unit dynamical time, which has to be relatively large, such as a few percent. Also for these conditions, the velocity dispersions of embedded GCs should be comparable to the high gas dispersions of galaxies at that time, so that stellar ejection by multistar interactions could cause low-mass stars to leave a dwarf galaxy host altogether. This could solve the problem of missing first-generation stars in the halos of Fornax and WLM.

  13. FROM THE CONVERGENCE OF FILAMENTS TO DISK-OUTFLOW ACCRETION: MASSIVE STAR FORMATION IN W33A

    International Nuclear Information System (INIS)

    Galvan-Madrid, Roberto; Zhang Qizhou; Keto, Eric; Ho, Paul T. P.; Pineda, Jaime E.; Zapata, Luis A.; RodrIguez, Luis F.; Vazquez-Semadeni, Enrique

    2010-01-01

    Interferometric observations of the W33A massive star formation region, performed with the Submillimeter Array and the Very Large Array at resolutions from 5'' (0.1 pc) to 0.''5 (0.01 pc), are presented. Our three main findings are: (1) parsec-scale, filamentary structures of cold molecular gas are detected. Two filaments at different velocities intersect in the zone where the star formation is occurring. This is consistent with triggering of the star formation activity by the convergence of such filaments, as predicted by numerical simulations of star formation initiated by converging flows. (2) The two dusty cores (MM1 and MM2) at the intersection of the filaments are found to be at different evolutionary stages, and each of them is resolved into multiple condensations. MM1 and MM2 have markedly different temperatures, continuum spectral indices, molecular-line spectra, and masses of both stars and gas. (3) The dynamics of the 'hot-core' MM1 indicates the presence of a rotating disk in its center (MM1-Main) around a faint free-free source. The stellar mass is estimated to be ∼10 M sun . A massive molecular outflow is observed along the rotation axis of the disk.

  14. The onset of massive star formation: The evolution of temperature and density structure in an infrared dark cloud

    Energy Technology Data Exchange (ETDEWEB)

    Battersby, Cara [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ginsburg, Adam; Bally, John; Darling, Jeremy [Center for Astrophysics and Space Astronomy, University of Colorado, UCB 389, Boulder, CO 80309 (United States); Longmore, Steve [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom); Dunham, Miranda [Department of Astronomy, Yale University, New Haven, CT 06520 (United States)

    2014-06-01

    We present new NH{sub 3} (1, 1), (2, 2), and (4, 4) observations from the Karl G. Jansky Very Large Array compiled with work in the literature to explore the range of conditions observed in young, massive star-forming regions. To sample the effects of evolution independent from those of distance/resolution, abundance, and large-scale environment, we compare clumps in different evolutionary stages within a single infrared dark cloud (IRDC), G32.02+0.06. We find that the early stages of clustered star formation are characterized by dense, parsec-scale filamentary structures interspersed with complexes of dense cores (<0.1 pc cores clustered in complexes separated by ∼1 pc) with masses from about 10 to 100 M {sub ☉}. The most quiescent core is the most extended while the star forming cores are denser and more compact, showing very similar column density structure before and shortly after the onset of massive star formation, with peak surface densities Σ ≳ 1 g cm{sup –2}. Quiescent cores and filaments show smoothly varying temperatures from 10 to 20 K, rising to over 40 K in star-forming cores. We calculate virial parameters for 16 cores and find that the level of support provided by turbulence is generally insufficient to support them against gravitational collapse ((α{sub vir}) ∼ 0.6). The star-forming filaments show smooth velocity fields, punctuated by discontinuities at the sites of active star formation. We discuss the massive molecular filament (M ∼ 10{sup 5} M {sub ☉}, length >60 pc) hosting the IRDC, hypothesizing that it may have been shaped by previous generations of massive stars.

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

    Science.gov (United States)

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

    2015-01-01

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

  16. Small scale kinematics of massive star-forming cores

    NARCIS (Netherlands)

    Wang, Kuo-Song

    2013-01-01

    Unlike the formation of Solar-type stars, the formation of massive stars (M>8 Msun) is not yet well understood. For Solar-type protostars, the presence of circumstellar or protoplanetary disks which provide a path for mass accretion onto protostars is well established. However, to date only few

  17. Inferring the star-formation histories of the most massive and passive early-type galaxies at z < 0.3

    Science.gov (United States)

    Citro, Annalisa; Pozzetti, Lucia; Moresco, Michele; Cimatti, Andrea

    2016-07-01

    Context. In the Λ cold dark matter (ΛCDM) cosmological framework, massive galaxies are the end-points of the hierarchical evolution and are therefore key probes for understanding how the baryonic matter evolves within the dark matter halos. Aims: The aim of this work is to use the archaeological approach in order to infer the stellar population properties and star formation histories of the most massive (M > 1010.75 M⊙) and passive early-type galaxies (ETGs) at 0 tests have been performed to assess the reliability of STARLIGHT to retrieve the evolutionary properties of the ETG stellar populations such as the age, metallicity and star formation history. The results indicate that these properties can be derived with accuracy better than 10% at S/N ≳ 10-20, and also that the procedure of stacking galaxy spectra does not introduce significant biases into their retrieval. Results: Based on our spectral analysis, we found that the ETGs of our sample are very old systems - the most massive ones are almost as old as the Universe. The stellar metallicities are slightly supersolar, with a mean of Z ~ 0.027 ± 0.002 and Z ~ 0.029 ± 0.0015 (depending on the spectral synthesis models used for the fit) and do not depend on redshift. Dust extinction is very low, with a mean of AV ~ 0.08 ± 0.030 mag and AV ~ 0.16 ± 0.048 mag. The ETGs show an anti-hierarchical evolution (downsizing) where more massive galaxies are older. The SFHs can be approximated with a parametric function of the form SFR(t) ∝ τ- (c + 1)tc exp(-t/τ), with typical short e-folding times of τ ~ 0.6-0.8 Gyr (with a dispersion of ±0.1 Gyr) and c ~ 0.1 (with a dispersion of ±0.05). Based on the reconstructed SFHs, most of the stellar mass (≳75%) was assembled by z ~ 5 and ≲4% of it can be ascribed to stellar populations younger than ~1 Gyr. The inferred SFHs are also used to place constraints on the properties and evolution of the ETG progenitors. In particular, the ETGs of our samples should have

  18. An unstable truth: how massive stars get their mass

    Science.gov (United States)

    Rosen, Anna L.; Krumholz, Mark R.; McKee, Christopher F.; Klein, Richard I.

    2016-12-01

    The pressure exerted by massive stars' radiation fields is an important mechanism regulating their formation. Detailed simulation of massive star formation therefore requires an accurate treatment of radiation. However, all published simulations have either used a diffusion approximation of limited validity; have only been able to simulate a single star fixed in space, thereby suppressing potentially important instabilities; or did not provide adequate resolution at locations where instabilities may develop. To remedy this, we have developed a new, highly accurate radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform 3D radiation-hydrodynamic simulations of the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channelled to the stellar system via gravitational and Rayleigh-Taylor (RT) instabilities, in agreement with previous results using stars capable of moving, but in disagreement with methods where the star is held fixed or with simulations that do not adequately resolve the development of RT instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of instability, but does not suppress it entirely provided the edges of radiation-dominated bubbles are adequately resolved. Instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. Our results suggest that RT features should be present around accreting massive stars throughout their formation.

  19. The formation of massive primordial stars in the presence of moderate UV backgrounds

    Energy Technology Data Exchange (ETDEWEB)

    Latif, M. A.; Schleicher, D. R. G.; Bovino, S. [Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, D-37077 Göttingen (Germany); Grassi, T. [Centre for Star and Planet Formation, Natural History Museum of Denmark, Øster Voldgade 5-7, DK-1350 Copenhagen (Denmark); Spaans, M., E-mail: mlatif@astro.physik.uni-goettingen.de [Kapteyn Astronomical Institute, University of Groningen, 9700-AV Groningen (Netherlands)

    2014-09-01

    Radiative feedback produced by stellar populations played a vital role in early structure formation. In particular, photons below the Lyman limit can escape the star-forming regions and produce a background ultraviolet (UV) flux, which consequently may influence the pristine halos far away from the radiation sources. These photons can quench the formation of molecular hydrogen by photodetachment of H{sup –}. In this study, we explore the impact of such UV radiation on fragmentation in massive primordial halos of a few times 10{sup 7} M {sub ☉}. To accomplish this goal, we perform high resolution cosmological simulations for two distinct halos and vary the strength of the impinging background UV field in units of J {sub 21} assuming a blackbody radiation spectrum with a characteristic temperature of T {sub rad} = 10{sup 4} K. We further make use of sink particles to follow the evolution for 10,000 yr after reaching the maximum refinement level. No vigorous fragmentation is observed in UV-illuminated halos while the accretion rate changes according to the thermal properties. Our findings show that a few 10{sup 2}-10{sup 4} solar mass protostars are formed when halos are irradiated by J {sub 21} = 10-500 at z > 10 and suggest a strong relation between the strength of the UV flux and mass of a protostar. This mode of star formation is quite different from minihalos, as higher accretion rates of about 0.01-0.1 M {sub ☉} yr{sup –1} are observed by the end of our simulations. The resulting massive stars are potential cradles for the formation of intermediate-mass black holes at earlier cosmic times and contribute to the formation of a global X-ray background.

  20. THE HCN/HNC ABUNDANCE RATIO TOWARD DIFFERENT EVOLUTIONARY PHASES OF MASSIVE STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Mihwa; Lee, Jeong-Eun [School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of); Kim, Kee-Tae, E-mail: mihwajin.sf@gmail.com, E-mail: jeongeun.lee@khu.ac.kr, E-mail: ktkim@kasi.re.kr [Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 305-348 (Korea, Republic of)

    2015-07-20

    Using the H{sup 13}CN and HN{sup 13}C J = 1–0 line observations, the abundance ratio of HCN/HNC has been estimated for different evolutionary stages of massive star formation: infrared dark clouds (IRDCs), high-mass protostellar objects (HMPOs), and ultracompact H ii regions (UCH iis). IRDCs were divided into “quiescent IRDC cores (qIRDCc)” and “active IRDC cores (aIRDCc),” depending on star formation activity. The HCN/HNC ratio is known to be higher at active and high temperature regions related to ongoing star formation, compared to cold and quiescent regions. Our observations toward 8 qIRDCc, 16 aIRDCc, 23 HMPOs, and 31 UCH iis show consistent results; the ratio is 0.97 (±0.10), 2.65 (±0.88), 4.17 (±1.03), and 8.96 (±3.32) in these respective evolutionary stages, increasing from qIRDCc to UCH iis. The change of the HCN/HNC abundance ratio, therefore, seems directly associated with the evolutionary stages of star formation, which have different temperatures. One suggested explanation for this trend is the conversion of HNC to HCN, which occurs effectively at higher temperatures. To test the explanation, we performed a simple chemical model calculation. In order to fit the observed results, the energy barrier of the conversion must be much lower than the value provided by theoretical calculations.

  1. Star formation: Cosmic feast

    Science.gov (United States)

    Scaringi, Simone

    2017-03-01

    Low-mass stars form through a process known as disk accretion, eating up material that orbits in a disk around them. It turns out that the same mechanism also describes the formation of more massive stars.

  2. Hyperfast pulsars as the remnants of massive stars ejected from young star clusters

    Science.gov (United States)

    Gvaramadze, Vasilii V.; Gualandris, Alessia; Portegies Zwart, Simon

    2008-04-01

    Recent proper motion and parallax measurements for the pulsar PSR B1508+55 indicate a transverse velocity of ~1100kms-1, which exceeds earlier measurements for any neutron star. The spin-down characteristics of PSR B1508+55 are typical for a non-recycled pulsar, which implies that the velocity of the pulsar cannot have originated from the second supernova disruption of a massive binary system. The high velocity of PSR B1508+55 can be accounted for by assuming that it received a kick at birth or that the neutron star was accelerated after its formation in the supernova explosion. We propose an explanation for the origin of hyperfast neutron stars based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star which attained its peculiar velocity (similar to that of the pulsar) in the course of a strong dynamical three- or four-body encounter in the core of dense young star cluster. To check this hypothesis, we investigated three dynamical processes involving close encounters between: (i) two hard massive binaries, (ii) a hard binary and an intermediate-mass black hole (IMBH) and (iii) a single stars and a hard binary IMBH. We find that main-sequence O-type stars cannot be ejected from young massive star clusters with peculiar velocities high enough to explain the origin of hyperfast neutron stars, but lower mass main-sequence stars or the stripped helium cores of massive stars could be accelerated to hypervelocities. Our explanation for the origin of hyperfast pulsars requires a very dense stellar environment of the order of 106- 107starspc-3. Although such high densities may exist during the core collapse of young massive star clusters, we caution that they have never been observed.

  3. A Massive Star Census of the Starburst Cluster R136

    Science.gov (United States)

    Crowther, Paul

    2012-10-01

    We propose to carry out a comprehensive census of the most massive stars in the central parsec {4"} of the starburst cluster, R136, which powers the Tarantula Nebula in the LMC. R136 is both sufficiently massive that the upper mass function is richly populated and young enough that its most massive stars have yet to explode as supernovae. The identification of very massive stars in R136, up to 300 solar masses, raises general questions of star formation, binarity and feedback in young massive clusters. The proposed STIS spectral survey of 36 stars more massive than 50 solar masses within R136 is ground-breaking, of legacy value, and is specifically tailored to a} yield physical properties; b} detect the majority of binaries by splitting observations between Cycles 19 and 20; c} measure rotational velocities, relevant for predictions of rotational mixing; d} quantify mass-loss properties for very massive stars; e} determine surface compositions; f} measure radial velocities, relevant for runaway stars and cluster dynamics; g} quantify radiative and mechanical feedback. This census will enable the mass function of very massive stars to be measured for the first time, as a result of incomplete and inadequate spectroscopy to date. It will also perfectly complement our Tarantula Survey, a ground-based VLT Large Programme, by including the most massive stars that are inaccessible to ground-based visual spectroscopy due to severe crowding. These surveys, together with existing integrated UV and optical studies will enable 30 Doradus to serve as a bona-fide template for unresolved extragalactic starburst regions.

  4. MASSIVE INFANT STARS ROCK THEIR CRADLE

    Science.gov (United States)

    2002-01-01

    Extremely intense radiation from newly born, ultra-bright stars has blown a glowing spherical bubble in the nebula N83B, also known as NGC 1748. A new NASA Hubble Space Telescope image has helped to decipher the complex interplay of gas and radiation of a star-forming region in a nearby galaxy. The image graphically illustrates just how these massive stars sculpt their environment by generating powerful winds that alter the shape of the parent gaseous nebula. These processes are also seen in our Milky Way in regions like the Orion Nebula. The Hubble telescope is famous for its contribution to our knowledge about star formation in very distant galaxies. Although most of the stars in the Universe were born several billions of years ago, when the Universe was young, star formation still continues today. This new Hubble image shows a very compact star-forming region in a small part of one of our neighboring galaxies - the Large Magellanic Cloud. This galaxy lies only 165,000 light-years from our Milky Way and can easily be seen with the naked eye from the Southern Hemisphere. Young, massive, ultra-bright stars are seen here just as they are born and emerge from the shelter of their pre-natal molecular cloud. Catching these hefty stars at their birthplace is not as easy as it may seem. Their high mass means that the young stars evolve very rapidly and are hard to find at this critical stage. Furthermore, they spend a good fraction of their youth hidden from view, shrouded by large quantities of dust in a molecular cloud. The only chance is to observe them just as they start to emerge from their cocoon - and then only with very high-resolution telescopes. Astronomers from France, the U.S., and Germany have used Hubble to study the fascinating interplay between gas, dust, and radiation from the newly born stars in this nebula. Its peculiar and turbulent structure has been revealed for the first time. This high-resolution study has also uncovered several individual stars

  5. GRAVITATIONAL SLINGSHOT OF YOUNG MASSIVE STARS IN ORION

    Energy Technology Data Exchange (ETDEWEB)

    Chatterjee, Sourav; Tan, Jonathan C., E-mail: s.chatterjee@astro.ufl.edu, E-mail: jt@astro.ufl.edu [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)

    2012-08-01

    The Orion Nebula Cluster (ONC) is the nearest region of massive star formation and thus a crucial testing ground for theoretical models. Of particular interest among the ONC's {approx}1000 members are: {theta}{sup 1} Ori C, the most massive binary in the cluster with stars of masses 38 and 9 M{sub Sun }; the Becklin-Neugebauer (BN) object, a 30 km s{sup -1} runaway star of {approx}8 M{sub Sun }; and the Kleinmann-Low (KL) nebula protostar, a highly obscured, {approx}15 M{sub Sun} object still accreting gas while also driving a powerful, apparently 'explosive' outflow. The unusual behavior of BN and KL is much debated: How did BN acquire its high velocity? How is this related to massive star formation in the KL nebula? Here, we report the results of a systematic survey using {approx}10{sup 7} numerical experiments of gravitational interactions of the {theta}{sup 1}C and BN stars. We show that dynamical ejection of BN from this triple system at its observed velocity leaves behind a binary with total energy and eccentricity matching those observed for {theta}{sup 1}C. Five other observed properties of {theta}{sup 1}C are also consistent with it having ejected BN and altogether we estimate that there is only a {approx}< 10{sup -5} probability that {theta}{sup 1}C has these properties by chance. We conclude that BN was dynamically ejected from the {theta}{sup 1}C system about 4500 years ago. BN then plowed through the KL massive star-forming core within the last 1000 years causing its recently enhanced accretion and outflow activity.

  6. The evolution of massive stars

    International Nuclear Information System (INIS)

    Loore, C. de

    1980-01-01

    The evolution of stars with masses between 15 M 0 and 100 M 0 is considered. Stars in this mass range lose a considerable fraction of their matter during their evolution. The treatment of convection, semi-convection and the influence of mass loss by stellar winds at different evolutionary phases are analysed as well as the adopted opacities. Evolutionary sequences computed by various groups are examined and compared with observations, and the advanced evolution of a 15 M 0 and a 25 M 0 star from zero-age main sequence (ZAMS) through iron collapse is discussed. The effect of centrifugal forces on stellar wind mass loss and the influence of rotation on evolutionary models is examined. As a consequence of the outflow of matter deeper layers show up and when the mass loss rates are large enough layers with changed composition, due to interior nuclear reactions, appear on the surface. The evolution of massive close binaries as well during the phase of mass loss by stellar wind as during the mass exchange and mass loss phase due to Roche lobe overflow is treated in detail, and the value of the parameters governing mass and angular momentum losses are discussed. The problem of the Wolf-Rayet stars, their origin and the possibilities of their production either as single stars or as massive binaries is examined. Finally, the origin of X-ray binaries is discussed and the scenario for the formation of these objects (starting from massive ZAMS close binaries, through Wolf-Rayet binaries leading to OB-stars with a compact companion after a supernova explosion) is reviewed and completed, including stellar wind mass loss. (orig.)

  7. Grain processes in massive star formation

    International Nuclear Information System (INIS)

    Wolfire, M.G.; Cassinelli, J.P.

    1986-01-01

    Observational evidence suggests that stars greater than 100 M(solar) exist in the Galaxy and Large Magellanic Cloud (LMC), however classical star formation theory predicts stellar mass limits of only approx. 60 M(solar). A protostellar accretion flow consists of inflowing gas and dust. Grains are destroyed as they are near the central protostar creating a dust shell or cocoon. Radiation pressure acting on the grain can halt the inflow of material thereby limiting the amount of mass accumulated by the protostar. We first consider rather general constraints on the initial grain to gas ratio and mass accretion rates that permit inflow. We further constrain these results by constructing a numerical model. Radiative deceleration of grains and grain destruction processes are explicitly accounted for in an iterative solution of the radiation-hydrodynamic equations. Findings seem to suggest that star formation by spherical accretion requires rather extreme preconditioning of the grain and gas environment

  8. The SOFIA Massive (SOMA) Star Formation Survey. I. Overview and First Results

    Energy Technology Data Exchange (ETDEWEB)

    De Buizer, James M.; Shuping, Ralph [SOFIA-USRA, NASA Ames Research Center, MS 232-12, Moffett Field, CA 94035 (United States); Liu, Mengyao; Tan, Jonathan C.; Staff, Jan E.; Tanaka, Kei E. I. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Zhang, Yichen [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Beltrán, Maria T. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Whitney, Barbara [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St, Madison, WI 53706 (United States)

    2017-07-01

    We present an overview and first results of the Stratospheric Observatory For Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the FORCAST instrument to image massive protostars from ∼10 to 40 μ m. These wavelengths trace thermal emission from warm dust, which in Core Accretion models mainly emerges from the inner regions of protostellar outflow cavities. Dust in dense core envelopes also imprints characteristic extinction patterns at these wavelengths, causing intensity peaks to shift along the outflow axis and profiles to become more symmetric at longer wavelengths. We present observational results for the first eight protostars in the survey, i.e., multiwavelength images, including some ancillary ground-based mid-infrared (MIR) observations and archival Spitzer and Herschel data. These images generally show extended MIR/FIR emission along directions consistent with those of known outflows and with shorter wavelength peak flux positions displaced from the protostar along the blueshifted, near-facing sides, thus confirming qualitative predictions of Core Accretion models. We then compile spectral energy distributions and use these to derive protostellar properties by fitting theoretical radiative transfer models. Zhang and Tan models, based on the Turbulent Core Model of McKee and Tan, imply the sources have protostellar masses m {sub *} ∼ 10–50 M {sub ⊙} accreting at ∼10{sup −4}–10{sup −3} M {sub ⊙} yr{sup −1} inside cores of initial masses M {sub c} ∼ 30–500 M {sub ⊙} embedded in clumps with mass surface densities Σ{sub cl} ∼ 0.1–3 g cm{sup −2}. Fitting the Robitaille et al. models typically leads to slightly higher protostellar masses, but with disk accretion rates ∼100× smaller. We discuss reasons for these differences and overall implications of these first survey results for massive star formation theories.

  9. ENHANCED STAR FORMATION OF LESS MASSIVE GALAXIES IN A PROTOCLUSTER AT z = 2.5

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi, Masao; Kodama, Tadayuki [Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Tanaka, Ichi; Koyama, Yusei [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720 (United States); Shimakawa, Rhythm; Suzuki, Tomoko L.; Yamamoto, Moegi [Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), Mitaka, Tokyo 181-8588 (Japan); Tadaki, Ken-ichi, E-mail: masao.hayashi@nao.ac.jp [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany)

    2016-08-01

    We investigate a correlation between star formation rate (SFR) and stellar mass for H α emission-line galaxies (HAEs) in one of the richest protoclusters ever known at z∼2.5, the USS 1558-003 protocluster. This study is based on a 9.7 hr narrowband imaging data with MOIRCS on the Subaru telescope. We are able to construct a sample in combination with additional H -band data taken with WFC3 on the Hubble Space Telescope , of 100 HAEs reaching the dust-corrected SFRs down to 3 M {sub ⊙} yr{sup −1} and the stellar masses down to 10{sup 8.0} M {sub ⊙}. We find that while the star-forming galaxies with ≳10{sup 9.3} M {sub ⊙} are located on the universal SFR-mass main sequence (MS) irrespective of the environment, less massive star-forming galaxies with ≲10{sup 9.3} M {sub ⊙} show a significant upward scatter from the MS in this protocluster. This suggests that some less massive galaxies are in a starburst phase, although we do not know yet if this is due to environmental effects.

  10. The incidence of stellar mergers and mass gainers among massive stars

    International Nuclear Information System (INIS)

    De Mink, S. E.; Sana, H.; Langer, N.; Izzard, R. G.; Schneider, F. R. N.

    2014-01-01

    Because the majority of massive stars are born as members of close binary systems, populations of massive main-sequence stars contain stellar mergers and products of binary mass transfer. We simulate populations of massive stars accounting for all major binary evolution effects based on the most recent binary parameter statistics and extensively evaluate the effect of model uncertainties. Assuming constant star formation, we find that 8 −4 +9 % of a sample of early-type stars are the products of a merger resulting from a close binary system. In total we find that 30 −15 +10 % of massive main-sequence stars are the products of binary interaction. We show that the commonly adopted approach to minimize the effects of binaries on an observed sample by excluding systems detected as binaries through radial velocity campaigns can be counterproductive. Systems with significant radial velocity variations are mostly pre-interaction systems. Excluding them substantially enhances the relative incidence of mergers and binary products in the non-radial velocity variable sample. This poses a challenge for testing single stellar evolutionary models. It also raises the question of whether certain peculiar classes of stars, such as magnetic O stars, are the result of binary interaction and it emphasizes the need to further study the effect of binarity on the diagnostics that are used to derive the fundamental properties (star-formation history, initial mass function, mass-to-light ratio) of stellar populations nearby and at high redshift.

  11. Spitzer view of massive star formation in the tidally stripped Magellanic Bridge

    International Nuclear Information System (INIS)

    Chen, C.-H. Rosie; Indebetouw, Remy; Muller, Erik; Kawamura, Akiko; Gordon, Karl D.; Meixner, Margaret; Seale, Jonathan P.; Shiao, Bernie; Sewiło, Marta; Whitney, Barbara A.; Meade, Marilyn R.; Fukui, Yasuo; Madden, Suzanne C.; Oliveira, Joana M.; Van Loon, Jacco Th.; Robitaille, Thomas P.

    2014-01-01

    The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper, we present an analysis of candidate massive young stellar objects (YSOs), i.e., in situ, current massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are ∼10 M ☉ , <<45 M ☉ found in the LMC. The intensity of MSF in the Bridge also appears to be decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given H I column density, N(H I). We found that the LMC has ∼3 × higher probability than the Bridge for N(H I) >12 × 10 20 cm –2 , but the trend reverses at lower N(H I). Investigating whether this lower efficiency relative to H I is due to less efficient molecular cloud formation or to less efficient cloud collapse, or to both, will require sensitive molecular gas observations.

  12. Spitzer view of massive star formation in the tidally stripped Magellanic Bridge

    Energy Technology Data Exchange (ETDEWEB)

    Chen, C.-H. Rosie; Indebetouw, Remy [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Muller, Erik; Kawamura, Akiko [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Gordon, Karl D.; Meixner, Margaret; Seale, Jonathan P.; Shiao, Bernie [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Sewiło, Marta [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Whitney, Barbara A.; Meade, Marilyn R. [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States); Fukui, Yasuo [Department of Astrophysics, Nagoya University, Furocho, Chikusaku, Nagoya 464-8602 (Japan); Madden, Suzanne C. [CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France); Oliveira, Joana M.; Van Loon, Jacco Th. [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Keele, Staffordshire ST5 5BG (United Kingdom); Robitaille, Thomas P., E-mail: rchen@mpifr-bonn.mpg.de [Max Planck Institute for Astronomy, D-69117 Heidelberg (Germany)

    2014-04-20

    The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper, we present an analysis of candidate massive young stellar objects (YSOs), i.e., in situ, current massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are ∼10 M {sub ☉}, <<45 M {sub ☉} found in the LMC. The intensity of MSF in the Bridge also appears to be decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given H I column density, N(H I). We found that the LMC has ∼3 × higher probability than the Bridge for N(H I) >12 × 10{sup 20} cm{sup –2}, but the trend reverses at lower N(H I). Investigating whether this lower efficiency relative to H I is due to less efficient molecular cloud formation or to less efficient cloud collapse, or to both, will require sensitive molecular gas observations.

  13. SPITZER VIEW OF YOUNG MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD H II COMPLEXES. II. N 159

    International Nuclear Information System (INIS)

    Chen, C.-H. Rosie; Indebetouw, Remy; Chu, You-Hua; Gruendl, Robert A.; Seale, Jonathan P.; Testor, Gerard; Heitsch, Fabian; Meixner, Margaret; Sewilo, Marta

    2010-01-01

    The H II complex N 159 in the Large Magellanic Cloud is used to study massive star formation in different environments, as it contains three giant molecular clouds (GMCs) that have similar sizes and masses but exhibit different intensities of star formation. We identify candidate massive young stellar objects (YSOs) using infrared photometry, and model their spectral energy distributions to constrain mass and evolutionary state. Good fits are obtained for less evolved Type I, I/II, and II sources. Our analysis suggests that there are massive embedded YSOs in N 159B, a maser source, and several ultracompact H II regions. Massive O-type YSOs are found in GMCs N 159-E and N 159-W, which are associated with ionized gas, i.e., where massive stars formed a few Myr ago. The third GMC, N 159-S, has neither O-type YSOs nor evidence of previous massive star formation. This correlation between current and antecedent formation of massive stars suggests that energy feedback is relevant. We present evidence that N 159-W is forming YSOs spontaneously, while collapse in N 159-E may be triggered. Finally, we compare star formation rates determined from YSO counts with those from integrated Hα and 24 μm luminosities and expected from gas surface densities. Detailed dissection of extragalactic GMCs like the one presented here is key to revealing the physics underlying commonly used star formation scaling laws.

  14. Formation of Massive Molecular Cloud Cores by Cloud-cloud Collision

    OpenAIRE

    Inoue, Tsuyoshi; Fukui, Yasuo

    2013-01-01

    Recent observations of molecular clouds around rich massive star clusters including NGC3603, Westerlund 2, and M20 revealed that the formation of massive stars could be triggered by a cloud-cloud collision. By using three-dimensional, isothermal, magnetohydrodynamics simulations with the effect of self-gravity, we demonstrate that massive, gravitationally unstable, molecular cloud cores are formed behind the strong shock waves induced by the cloud-cloud collision. We find that the massive mol...

  15. Star Cluster Structure from Hierarchical Star Formation

    Science.gov (United States)

    Grudic, Michael; Hopkins, Philip; Murray, Norman; Lamberts, Astrid; Guszejnov, David; Schmitz, Denise; Boylan-Kolchin, Michael

    2018-01-01

    Young massive star clusters (YMCs) spanning 104-108 M⊙ in mass generally have similar radial surface density profiles, with an outer power-law index typically between -2 and -3. This similarity suggests that they are shaped by scale-free physics at formation. Recent multi-physics MHD simulations of YMC formation have also produced populations of YMCs with this type of surface density profile, allowing us to narrow down the physics necessary to form a YMC with properties as observed. We show that the shallow density profiles of YMCs are a natural result of phase-space mixing that occurs as they assemble from the clumpy, hierarchically-clustered configuration imprinted by the star formation process. We develop physical intuition for this process via analytic arguments and collisionless N-body experiments, elucidating the connection between star formation physics and star cluster structure. This has implications for the early-time structure and evolution of proto-globular clusters, and prospects for simulating their formation in the FIRE cosmological zoom-in simulations.

  16. STAR CLUSTER FORMATION WITH STELLAR FEEDBACK AND LARGE-SCALE INFLOW

    International Nuclear Information System (INIS)

    Matzner, Christopher D.; Jumper, Peter H.

    2015-01-01

    During star cluster formation, ongoing mass accretion is resisted by stellar feedback in the form of protostellar outflows from the low-mass stars and photo-ionization and radiation pressure feedback from the massive stars. We model the evolution of cluster-forming regions during a phase in which both accretion and feedback are present and use these models to investigate how star cluster formation might terminate. Protostellar outflows are the strongest form of feedback in low-mass regions, but these cannot stop cluster formation if matter continues to flow in. In more massive clusters, radiation pressure and photo-ionization rapidly clear the cluster-forming gas when its column density is too small. We assess the rates of dynamical mass ejection and of evaporation, while accounting for the important effect of dust opacity on photo-ionization. Our models are consistent with the census of protostellar outflows in NGC 1333 and Serpens South and with the dust temperatures observed in regions of massive star formation. Comparing observations of massive cluster-forming regions against our model parameter space, and against our expectations for accretion-driven evolution, we infer that massive-star feedback is a likely cause of gas disruption in regions with velocity dispersions less than a few kilometers per second, but that more massive and more turbulent regions are too strongly bound for stellar feedback to be disruptive

  17. Wide-Field Infrared Survey Explorer Observations of the Evolution of Massive Star-Forming Regions

    Science.gov (United States)

    Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Rebull, L. M.; Padgett, D. L.; Asslef, R. J.

    2012-01-01

    We present the results of a mid-infrared survey of II outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the "fireworks hypothesis" since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

  18. WIDE-FIELD INFRARED SURVEY EXPLORER OBSERVATIONS OF THE EVOLUTION OF MASSIVE STAR-FORMING REGIONS

    International Nuclear Information System (INIS)

    Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Padgett, D. L.; Rebull, L. M.; Assef, R. J.

    2012-01-01

    We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the 'fireworks hypothesis' since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

  19. Stellar Feedback in Massive Star-Forming Regions

    Science.gov (United States)

    Baldwin, Jack; Pellegrini, Eric; Ferland, Gary; Murray, Norm; Hanson, Margaret

    2008-02-01

    Star formation rates and chemical evolution are controlled in part by the interaction of stellar radiation and winds with the remnant molecular gas from which the stars have formed. We are carrying out a detailed, panchromatic study in the two nearest giant star-forming regions to nail down the physics that produces the 10-20 parsec bubbles seen to surround young massive clusters in the Milky Way. This will determine if and how the clusters disrupt their natal giant molecular clouds (GMCs). Here we request 4 nights on the Blanco telescope to obtain dense grids of optical long-slit spectra criss-crossing each nebula. These will cover the [S II] doublet (to measure N_e) and also [O III], H(beta), [O I], H(alpha) and [N II] to measure the ionization mechanism and ionization parameter, at ~3000 different spots in each nebula. From this we can determine a number of dynamically important quantities, such as the gas density and temperature, hence pressure in and around these bubbles. These quantities can be compared to the dynamical (gravitationally induced) pressure, and the radiation pressure. All can be employed in dynamical models for the evolution of a GMC under the influence of an embedded massive star cluster. This research will elucidate the detailed workings of the star-forming regions which dominate the star formation rate in the Milky Way, and also will steadily improve our calibration and understanding of more distant, less well-resolved objects such as ULIRGS, Lyman break, and submillimeter galaxies.

  20. Massive Star Formation: Accreting from Companion X. Chen1 ...

    Indian Academy of Sciences (India)

    Abstract. We report the possible accretion from companion in the mas- sive star forming region (G350.69–0.49). This region seems to be a binary system composed of a diffuse object (possible nebulae or UC HII region) and a Massive Young Stellar Object (MYSO) seen in Spitzer IRAC image. The diffuse object and MYSO ...

  1. Molecular line study of massive star-forming regions from the Red MSX Source survey

    Science.gov (United States)

    Yu, Naiping; Wang, Jun-Jie

    2014-05-01

    In this paper, we have selected a sample of massive star-forming regions from the Red MSX Source survey, in order to study star formation activities (mainly outflow and inflow signatures). We have focused on three molecular lines from the Millimeter Astronomy Legacy Team Survey at 90 GHz: HCO+(1-0), H13CO+(1-0) and SiO(2-1). According to previous observations, our sources can be divided into two groups: nine massive young stellar object candidates (radio-quiet) and 10 H II regions (which have spherical or unresolved radio emissions). Outflow activities have been found in 11 sources, while only three show inflow signatures in all. The high outflow detection rate means that outflows are common in massive star-forming regions. The inflow detection rate was relatively low. We suggest that this was because of the beam dilution of the telescope. All three inflow candidates have outflow(s). The outward radiation and thermal pressure from the central massive star(s) do not seem to be strong enough to halt accretion in G345.0034-00.2240. Our simple model of G318.9480-00.1969 shows that it has an infall velocity of about 1.8 km s-1. The spectral energy distribution analysis agrees our sources are massive and intermediate-massive star formation regions.

  2. The formation and gravitational-wave detection of massive stellar black hole binaries

    International Nuclear Information System (INIS)

    Belczynski, Krzysztof; Walczak, Marek; Buonanno, Alessandra; Cantiello, Matteo; Fryer, Chris L.; Holz, Daniel E.; Mandel, Ilya; Miller, M. Coleman

    2014-01-01

    If binaries consisting of two ∼100 M ☉ black holes exist, they would serve as extraordinarily powerful gravitational-wave sources, detectable to redshifts of z ∼ 2 with the advanced LIGO/Virgo ground-based detectors. Large uncertainties about the evolution of massive stars preclude definitive rate predictions for mergers of these massive black holes. We show that rates as high as hundreds of detections per year, or as low as no detections whatsoever, are both possible. It was thought that the only way to produce these massive binaries was via dynamical interactions in dense stellar systems. This view has been challenged by the recent discovery of several ≳ 150 M ☉ stars in the R136 region of the Large Magellanic Cloud. Current models predict that when stars of this mass leave the main sequence, their expansion is insufficient to allow common envelope evolution to efficiently reduce the orbital separation. The resulting black hole-black hole binary remains too wide to be able to coalesce within a Hubble time. If this assessment is correct, isolated very massive binaries do not evolve to be gravitational-wave sources. However, other formation channels exist. For example, the high multiplicity of massive stars, and their common formation in relatively dense stellar associations, opens up dynamical channels for massive black hole mergers (e.g., via Kozai cycles or repeated binary-single interactions). We identify key physical factors that shape the population of very massive black hole-black hole binaries. Advanced gravitational-wave detectors will provide important constraints on the formation and evolution of very massive stars.

  3. Observational tests for the evolution of massive stars in nearby galaxies

    International Nuclear Information System (INIS)

    Leitherer, C.

    1990-01-01

    Population synthesis calculations applicable to the massive stellar content in nearby galaxies are presented. Stellar evolution calculations are combined with mass loss, model atmospheres with line blanketing, and a spectral type calibration to compute observable parameters of massive stars as a function of the star formation rate and the initial mass function slope. The number of O stars of given spectral types, the number of W-R stars, supernova rates, and fluxes of ionizing photons are predicted. Important constraints for the theories of stellar atmospheres and stellar evolution can be derived from observations if stellar number counts and ionizing flux data are available. 94 refs

  4. THE PREVALENCE AND IMPACT OF WOLF–RAYET STARS IN EMERGING MASSIVE STAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Sokal, Kimberly R.; Johnson, Kelsey E.; Indebetouw, Rémy [Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903 (United States); Massey, Philip, E-mail: krs9tb@virginia.edu [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States)

    2016-08-01

    We investigate Wolf–Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point in the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4 m Mayall Telescope at Kitt Peak National Observatory and the 6.5 m MMT.{sup 4} We identify 21 sources with significantly detected WR signatures, which we term “emerging WR clusters.” WR features are detected in ∼50% of the radio-selected sample, and thus we find that WR stars are commonly present in currently emerging massive star clusters. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process.

  5. A mathematical model of star formation in the Galaxy

    Directory of Open Access Journals (Sweden)

    M.A. Sharaf

    2012-06-01

    Full Text Available This paper is generally concerned with star formation in the Galaxy, especially blue stars. Blue stars are the most luminous, massive and the largest in radius. A simple mathematical model of the formation of the stars is established and put in computational algorithm. This algorithm enables us to know more about the formation of the star. Some real and artificial examples had been used to justify this model.

  6. DISCOVERY OF MASSIVE, MOSTLY STAR FORMATION QUENCHED GALAXIES WITH EXTREMELY LARGE Lyα EQUIVALENT WIDTHS AT z ∼ 3

    Energy Technology Data Exchange (ETDEWEB)

    Taniguchi, Yoshiaki; Kajisawa, Masaru; Kobayashi, Masakazu A. R.; Nagao, Tohru; Shioya, Yasuhiro [Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho, Matsuyama 790-8577 (Japan); Scoville, Nick Z.; Capak, Peter L. [Department of Astronomy, California Institute of Technology, MS 105-24, Pasadena, CA 91125 (United States); Sanders, David B. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Koekemoer, Anton M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Toft, Sune [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Mariesvej 30, DK-2100 Copenhagen (Denmark); McCracken, Henry J. [Institut d’Astrophysique de Paris, UMR7095 CNRS, Université Pierre et Marie Curie, 98 bis Boulevard Arago, F-75014 Paris (France); Le Fèvre, Olivier; Tasca, Lidia; Ilbert, Olivier [Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, F-13388 Marseille (France); Sheth, Kartik [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Renzini, Alvio [Dipartimento di Astronomia, Universita di Padova, vicolo dell’Osservatorio 2, I-35122 Padua (Italy); Lilly, Simon; Carollo, Marcella; Kovač, Katarina [Department of Physics, ETH Zurich, 8093 Zurich (Switzerland); Schinnerer, Eva, E-mail: tani@cosmos.phys.sci.ehime-u.ac.jp [MPI for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); and others

    2015-08-10

    We report a discovery of six massive galaxies with both extremely large Lyα equivalent widths (EWs) and evolved stellar populations at z ∼ 3. These MAssive Extremely STrong Lyα emitting Objects (MAESTLOs) have been discovered in our large-volume systematic survey for strong Lyα emitters (LAEs) with 12 optical intermediate-band data taken with Subaru/Suprime-Cam in the COSMOS field. Based on the spectral energy distribution fitting analysis for these LAEs, it is found that these MAESTLOs have (1) large rest-frame EWs of EW{sub 0} (Lyα) ∼ 100–300 Å, (2) M{sub ⋆} ∼ 10{sup 10.5}–10{sup 11.1} M{sub ⊙}, and (3) relatively low specific star formation rates of SFR/M{sub ⋆} ∼ 0.03–1 Gyr{sup −1}. Three of the six MAESTLOs have extended Lyα emission with a radius of several kiloparsecs, although they show very compact morphology in the HST/ACS images, which correspond to the rest-frame UV continuum. Since the MAESTLOs do not show any evidence for active galactic nuclei, the observed extended Lyα emission is likely to be caused by a star formation process including the superwind activity. We suggest that this new class of LAEs, MAESTLOs, provides a missing link from star-forming to passively evolving galaxies at the peak era of the cosmic star formation history.

  7. A dearth of short-period massive binaries in the young massive star forming region M 17. Evidence for a large orbital separation at birth?

    Science.gov (United States)

    Sana, H.; Ramírez-Tannus, M. C.; de Koter, A.; Kaper, L.; Tramper, F.; Bik, A.

    2017-03-01

    Aims: The formation of massive stars remains poorly understood and little is known about their birth multiplicity properties. Here, we aim to quantitatively investigate the strikingly low radial-velocity dispersion measured for a sample of 11 massive pre- and near-main-sequence stars (σ1D= 5.6 ± 0.2 km s-1) in the very young massive star forming region M 17, in order to obtain first constraints on the multiplicity properties of young massive stellar objects. Methods: We compute the radial-velocity dispersion of synthetic populations of massive stars for various multiplicity properties and we compare the obtained σ1D distributions to the observed value. We specifically investigate two scenarios: a low binary fraction and a dearth of short-period binary systems. Results: Simulated populations with low binary fractions () or with truncated period distributions (Pcutoff > 9 months) are able to reproduce the low σ1D observed within their 68%-confidence intervals. Furthermore, parent populations with fbin > 0.42 or Pcutoff < 47 d can be rejected at the 5%-significance level. Both constraints are in stark contrast with the high binary fraction and plethora of short-period systems in few Myr-old, well characterized OB-type populations. To explain the difference in the context of the first scenario would require a variation of the outcome of the massive star formation process. In the context of the second scenario, compact binaries must form later on, and the cut-off period may be related to physical length-scales representative of the bloated pre-main-sequence stellar radii or of their accretion disks. Conclusions: If the obtained constraints for the M 17's massive-star population are representative of the multiplicity properties of massive young stellar objects, our results may provide support to a massive star formation process in which binaries are initially formed at larger separations, then harden or migrate to produce the typical (untruncated) power-law period

  8. Kinematic evidence for feedback-driven star formation in NGC 1893

    Science.gov (United States)

    Lim, Beomdu; Sung, Hwankyung; Bessell, Michael S.; Lee, Sangwoo; Lee, Jae Joon; Oh, Heeyoung; Hwang, Narae; Park, Byeong-Gon; Hur, Hyeonoh; Hong, Kyeongsoo; Park, Sunkyung

    2018-06-01

    OB associations are the prevailing star-forming sites in the Galaxy. Up to now, the process of how OB associations were formed remained a mystery. A possible process is self-regulating star formation driven by feedback from massive stars. However, although a number of observational studies uncovered various signposts of feedback-driven star formation, the effectiveness of such feedback has been questioned. Stellar and gas kinematics is a promising tool to capture the relative motion of newborn stars and gas away from ionizing sources. We present high-resolution spectroscopy of stars and gas in the young open cluster NGC 1893. Our findings show that newborn stars and the tadpole nebula Sim 130 are moving away from the central cluster containing two O-type stars, and that the time-scale of sequential star formation is about 1 Myr within a 9 pc distance. The newborn stars formed by feedback from massive stars account for at least 18 per cent of the total stellar population in the cluster, suggesting that this process can play an important role in the formation of OB associations. These results support the self-regulating star formation model.

  9. Very massive runaway stars from three-body encounters

    Science.gov (United States)

    Gvaramadze, Vasilii V.; Gualandris, Alessia

    2011-01-01

    Very massive stars preferentially reside in the cores of their parent clusters and form binary or multiple systems. We study the role of tight very massive binaries in the origin of the field population of very massive stars. We performed numerical simulations of dynamical encounters between single (massive) stars and a very massive binary with parameters similar to those of the most massive known Galactic binaries, WR 20a and NGC 3603-A1. We found that these three-body encounters could be responsible for the origin of high peculiar velocities (≥70 km s-1) observed for some very massive (≥60-70 M⊙) runaway stars in the Milky Way and the Large Magellanic Cloud (e.g. λ Cep, BD+43°3654, Sk -67°22, BI 237, 30 Dor 016), which can hardly be explained within the framework of the binary-supernova scenario. The production of high-velocity massive stars via three-body encounters is accompanied by the recoil of the binary in the opposite direction to the ejected star. We show that the relative position of the very massive binary R145 and the runaway early B-type star Sk-69°206 on the sky is consistent with the possibility that both objects were ejected from the central cluster, R136, of the star-forming region 30 Doradus via the same dynamical event - a three-body encounter.

  10. A Submillimetre Study of Massive Star Formation Within the W51 Complex and Infrared Dark Clouds

    Science.gov (United States)

    Parsons, Harriet Alice Louise

    Despite its importance the fundamental question of how massive stars form remains unanswered, with improvements to both models and observations having crucial roles to play. To quote Bate et al. (2003) computational models of star formation are limited because "conditions in molecular clouds are not sufficiently well understood to be able to select a representative sample of cloud cores for the initial conditions". It is this notion that motivates the study of the environments within Giant Molecular Clouds (GMCs) and Infrared Dark Clouds (IRDCs), known sites of massive star formation, at the clump and core level. By studying large populations of these objects, it is possible to make conclusions based on global properties. With this in mind I study the dense molecular clumps within one of the most massive GMCs in the Galaxy: the W51 GMC. New observations of the W51 GMC in the 12CO, 13CO and C18O (3-2) transitions using the HARP instrument on the JCMT are presented. With the help of the clump finding algorithm CLUMPFIND a total of 1575 dense clumps are identified of which 1130 are associated with the W51 GMC, yielding a dense mass reservoir of 1.5 × 10^5 M contained within these clumps. Of these clumps only 1% by number are found to be super-critical, yielding a super-critical clump formation efficiency of 0.5%, below current SFE estimates of the region. This indicates star formation within the W51 GMC will diminish over time although evidence from the first search for molecular outflows presents the W51 GMC in an active light with a lower limit of 14 outflows. The distribution of the outflows within the region searched found them concentrated towards the W51A region. Having much smaller sizes and masses, obtaining global properties of clumps and cores within IRDCs required studying a large sample of these objects. To do this pre-existing data from the SCUBA Legacy Catalogue was utilised to study IRDCs within a catalogues based on 8 μm data. This data identified

  11. The interstellar medium, expanding nebulae and triggered star formation theory and simulations

    CERN Document Server

    Bisbas, Thomas G

    2016-01-01

    This brief brings together the theoretical aspects of star formation and ionized regions with the most up-to-date simulations and observations. Beginning with the basic theory of star formation, the physics of expanding HII regions is reviewed in detail and a discussion on how a massive star can give birth to tens or hundreds of other stars follows. The theoretical description of star formation is shown in simplified and state-of-the-art numerical simulations, describing in a more clear way how feedback from massive stars can trigger star and planet formation. This is also combined with spectacular images of nebulae taken by talented amateur astronomers. The latter is very likely to stimulate the reader to observe the structure of nebulae from a different point of view, and better understand the associated star formation therein.

  12. Curtain-Lifting Winds Allow Rare Glimpse into Massive Star Factory

    Science.gov (United States)

    2003-06-01

    Formation of Exceedingly Luminous and Hot Stars in Young Stellar Cluster Observed Directly Summary Based on a vast observational effort with different telescopes and instruments, ESO-astronomer Dieter Nürnberger has obtained a first glimpse of the very first stages in the formation of heavy stars. These critical phases of stellar evolution are normally hidden from the view, because massive protostars are deeply embedded in their native clouds of dust and gas, impenetrable barriers to observations at all but the longest wavelengths. In particular, no visual or infrared observations have yet "caught" nascent heavy stars in the act and little is therefore known so far about the related processes. Profiting from the cloud-ripping effect of strong stellar winds from adjacent, hot stars in a young stellar cluster at the center of the NGC 3603 complex, several objects located near a giant molecular cloud were found to be bona-fide massive protostars, only about 100,000 years old and still growing. Three of these objects, designated IRS 9A-C, could be studied in more detail. They are very luminous (IRS 9A is about 100,000 times intrinsically brighter than the Sun), massive (more than 10 times the mass of the Sun) and hot (about 20,000 degrees). They are surrounded by relative cold dust (about 0°C), probably partly arranged in disks around these very young objects. Two possible scenarios for the formation of massive stars are currently proposed, by accretion of large amounts of circumstellar material or by collision (coalescence) of protostars of intermediate masses. The new observations favour accretion, i.e. the same process that is active during the formation of stars of smaller masses. PR Photo 16a/03: Stellar cluster and star-forming region NGC 3603. PR Photo 16b/03: Region near very young, massive stars IRS 9A-C in NGC 3603 (8 bands from J to Q). How do massive stars form? This question is easy to pose, but so far very difficult to answer. In fact, the processes

  13. Evolution of massive close binaries and formation of neutron stars and black holes

    International Nuclear Information System (INIS)

    Massevitch, A.G.; Tutukov, A.V.; Yungelson, L.R.

    1976-01-01

    Main results of computations of evolution for massive close binaries (10 M(Sun)+9.4 M(Sun), 16 M(Sun)+15 M(Sun), 32 M(Sun)+30 M(Sun), 64 M(Sun)+60 M(Sun)) up to oxygen exhaustion in the core are described. Mass exchange starting in core hydrogen, shell hydrogen and core helium burning stages was studied. Computations were performed assuming both the Ledoux and Schwarzschild stability criteria for semiconvection. The influence of UFI-neutrino emission on evolution of close binaries was investigated. The results obtained allow to outline the following evolutionary chain: two detached Main-Sequence stars - mass exchange - Wolf-Rayet star or blue supergiant plus main sequence star - explosion of the initially more massive star appearing as a supernova event - collapsed or neutron star plus Main-Sequence star, that may be observed as a 'runaway star' - mass exchange leading to X-rays emission - collapsed or neutron star plus WR-star or blue supergiant - second explosion of supernova that preferentially disrupts the system and gives birth to two single high spatial velocity pulsars. Numerical estimates concerning the number and properties of WR-stars, pulsars and X-ray sources are presented. The results are in favour of the existence of UFI-neutrino and of the Ledoux criterion for describing semiconvection. Properties of several well-known X-ray sources and the binary pulsar are discussed on base of evolutionary chain of close binaries. (Auth.)

  14. Ionizing feedback from massive stars in massive clusters: fake bubbles and untriggered star formation

    Czech Academy of Sciences Publication Activity Database

    Dale, James E.; Bonnell, Ian A.

    2011-01-01

    Roč. 414, č. 1 (2011), s. 321-328 ISSN 0035-8711 R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars formation * H II regions Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.900, year: 2011

  15. THE ROTATION RATES OF MASSIVE STARS: THE ROLE OF BINARY INTERACTION THROUGH TIDES, MASS TRANSFER, AND MERGERS

    Energy Technology Data Exchange (ETDEWEB)

    De Mink, S. E. [Space Telescope Science Institute, Baltimore, MD (United States); Langer, N.; Izzard, R. G. [Argelander-Institut fuer Astronomie der Universitaet Bonn, D-53121 Bonn (Germany); Sana, H.; De Koter, A. [Astronomical Institute Anton Pannekoek, University of Amsterdam, 1098 XH Amsterdam (Netherlands)

    2013-02-20

    Rotation is thought to be a major factor in the evolution of massive stars-especially at low metallicity-with consequences for their chemical yields, ionizing flux, and final fate. Deriving the birth spin distribution is of high priority given its importance as a constraint on theories of massive star formation and as input for models of stellar populations in the local universe and at high redshift. Recently, it has become clear that the majority of massive stars interact with a binary companion before they die. We investigate how this affects the distribution of rotation rates, through stellar winds, expansion, tides, mass transfer, and mergers. For this purpose, we simulate a massive binary-star population typical for our Galaxy assuming continuous star formation. We find that, because of binary interaction, 20{sup +5} {sub -10}% of all massive main-sequence stars have projected rotational velocities in excess of 200 km s{sup -1}. We evaluate the effect of uncertain input distributions and physical processes and conclude that the main uncertainties are the mass transfer efficiency and the possible effect of magnetic braking, especially if magnetic fields are generated or amplified during mass accretion and stellar mergers. The fraction of rapid rotators we derive is similar to that observed. If indeed mass transfer and mergers are the main cause for rapid rotation in massive stars, little room remains for rapidly rotating stars that are born single. This implies that spin-down during star formation is even more efficient than previously thought. In addition, this raises questions about the interpretation of the surface abundances of rapidly rotating stars as evidence for rotational mixing. Furthermore, our results allow for the possibility that all early-type Be stars result from binary interactions and suggest that evidence for rotation in explosions, such as long gamma-ray bursts, points to a binary origin.

  16. KMOS"3"D Reveals Low-level Star Formation Activity in Massive Quiescent Galaxies at 0.7 < z < 2.7

    International Nuclear Information System (INIS)

    Belli, Sirio; Genzel, Reinhard; Förster Schreiber, Natascha M.; Wisnioski, Emily; Wilman, David J.; Mendel, J. Trevor; Beifiori, Alessandra; Bender, Ralf; Burkert, Andreas; Chan, Jeffrey; Davies, Rebecca L.; Davies, Ric; Fabricius, Maximilian; Fossati, Matteo; Galametz, Audrey; Lang, Philipp; Lutz, Dieter; Wuyts, Stijn; Brammer, Gabriel B.; Momcheva, Ivelina G.

    2017-01-01

    We explore the H α emission in the massive quiescent galaxies observed by the KMOS"3"D survey at 0.7 < z < 2.7. The H α line is robustly detected in 20 out of 120 UVJ -selected quiescent galaxies, and we classify the emission mechanism using the H α line width and the [N ii]/H α line ratio. We find that AGNs are likely to be responsible for the line emission in more than half of the cases. We also find robust evidence for star formation activity in nine quiescent galaxies, which we explore in detail. The H α kinematics reveal rotating disks in five of the nine galaxies. The dust-corrected H α star formation rates are low (0.2–7 M _⊙ yr"−"1), and place these systems significantly below the main sequence. The 24 μ m-based, infrared luminosities, instead, overestimate the star formation rates. These galaxies present a lower gas-phase metallicity compared to star-forming objects with similar stellar mass, and many of them have close companions. We therefore conclude that the low-level star formation activity in these nine quiescent galaxies is likely to be fueled by inflowing gas or minor mergers, and could be a sign of rejuvenation events.

  17. The VLT-FLAMES survey of massive stars

    NARCIS (Netherlands)

    Evans, C.; Langer, N.; Brott, I.; Hunter, I.; Smartt, S.J.; Lennon, D.J.

    2008-01-01

    The VLT-FLAMES Survey of Massive Stars was an ESO Large Programme to understand rotational mixing and stellar mass loss in different metallicity environments, in order to better constrain massive star evolution. We gathered high-quality spectra of over 800 stars in the Galaxy and in the Magellanic

  18. Kinematics of the inner thousand AU region around the young massive star AFGL 2591-VLA3: a massive disk candidate?

    NARCIS (Netherlands)

    Wang, K. -S.; van der Tak, F. F. S.; Hogerheijde, M. R.

    Context. Recent detections of disks around young high-mass stars support the idea of massive star formation through accretion rather than coalescence, but the detailed kinematics in the equatorial region of the disk candidates is not well known, which limits our understanding of the accretion

  19. Massive-Star Magnetospheres: Now in 3-D!

    Science.gov (United States)

    Townsend, Richard

    Magnetic fields are unexpected in massive stars, due to the absence of a dynamo convection zone beneath their surface layers. Nevertheless, kilogauss-strength, ordered fields were detected in a small subset of these stars over three decades ago, and the intervening years have witnessed the steady expansion of this subset. A distinctive feature of magnetic massive stars is that they harbor magnetospheres --- circumstellar environments where the magnetic field interacts strongly with the star's radiation-driven wind, confining it and channelling it into energetic shocks. A wide range of observational signatures are associated with these magnetospheres, in diagnostics ranging from X-rays all the way through to radio emission. Moreover, these magnetospheres can play an important role in massive-star evolution, by amplifying angular momentum loss in the wind. Recent progress in understanding massive-star magnetospheres has largely been driven by magnetohydrodynamical (MHD) simulations. However, these have been restricted to two- dimensional axisymmetric configurations, with three-dimensional configurations possible only in certain special cases. These restrictions are limiting further progress; we therefore propose to develop completely general three-dimensional models for the magnetospheres of massive stars, on the one hand to understand their observational properties and exploit them as plasma-physics laboratories, and on the other to gain a comprehensive understanding of how they influence the evolution of their host star. For weak- and intermediate-field stars, the models will be based on 3-D MHD simulations using a modified version of the ZEUS-MP code. For strong-field stars, we will extend our existing Rigid Field Hydrodynamics (RFHD) code to handle completely arbitrary field topologies. To explore a putative 'photoionization-moderated mass loss' mechanism for massive-star magnetospheres, we will also further develop a photoionization code we have recently

  20. High molecular gas fractions in normal massive star-forming galaxies in the young Universe.

    Science.gov (United States)

    Tacconi, L J; Genzel, R; Neri, R; Cox, P; Cooper, M C; Shapiro, K; Bolatto, A; Bouché, N; Bournaud, F; Burkert, A; Combes, F; Comerford, J; Davis, M; Schreiber, N M Förster; Garcia-Burillo, S; Gracia-Carpio, J; Lutz, D; Naab, T; Omont, A; Shapley, A; Sternberg, A; Weiner, B

    2010-02-11

    Stars form from cold molecular interstellar gas. As this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more molecular-gas rich. Molecular gas observations in the distant Universe have so far largely been restricted to very luminous, rare objects, including mergers and quasars, and accordingly we do not yet have a clear idea about the gas content of more normal (albeit massive) galaxies. Here we report the results of a survey of molecular gas in samples of typical massive-star-forming galaxies at mean redshifts of about 1.2 and 2.3, when the Universe was respectively 40% and 24% of its current age. Our measurements reveal that distant star forming galaxies were indeed gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z = 2.3 and z = 1.2 is respectively about 44% and 34%, three to ten times higher than in today's massive spiral galaxies. The slow decrease between z approximately 2 and z approximately 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies.

  1. Global Infrared–Radio Spectral Energy Distributions of Galactic Massive Star-Forming Regions

    Science.gov (United States)

    Povich, Matthew Samuel; Binder, Breanna Arlene

    2018-01-01

    We present a multiwavelength study of 30 Galactic massive star-forming regions. We fit multicomponent dust, blackbody, and power-law continuum models to 3.6 µm through 10 mm spectral energy distributions obtained from Spitzer, MSX, IRAS, Herschel, and Planck archival survey data. Averaged across our sample, ~20% of Lyman continuum photons emitted by massive stars are absorbed by dust before contributing to the ionization of H II regions, while ~50% of the stellar bolometric luminosity is absorbed and reprocessed by dust in the H II regions and surrounding photodissociation regions. The most luminous, infrared-bright regions that fully sample the upper stellar initial mass function (ionizing photon rates NC ≥ 1050 s–1 and total infrared luminosity LTIR ≥ 106.8 L⊙) have higher percentages of absorbed Lyman continuum photons (~40%) and dust-reprocessed starlight (~80%). The monochromatic 70-µm luminosity L70 is linearly correlated with LTIR, and on average L70/LTIR = 50%, in good agreement with extragalactic studies. Calibrated against the known massive stellar content in our sampled H II regions, we find that star formation rates based on L70 are in reasonably good agreement with extragalactic calibrations, when corrected for the smaller physical sizes of the Galactic regions. We caution that absorption of Lyman continuum photons prior to contributing to the observed ionizing photon rate may reduce the attenuation-corrected Hα emission, systematically biasing extragalactic calibrations toward lower star formation rates when applied to spatially-resolved studies of obscured star formation.This work was supported by the National Science Foundation under award CAREER-1454333.

  2. Supernovae from massive AGB stars

    NARCIS (Netherlands)

    Poelarends, A.J.T.; Izzard, R.G.; Herwig, F.; Langer, N.; Heger, A.

    2006-01-01

    We present new computations of the final fate of massive AGB-stars. These stars form ONeMg cores after a phase of carbon burning and are called Super AGB stars (SAGB). Detailed stellar evolutionary models until the thermally pulsing AGB were computed using three di erent stellar evolution codes. The

  3. KMOS{sup 3D} Reveals Low-level Star Formation Activity in Massive Quiescent Galaxies at 0.7 < z < 2.7

    Energy Technology Data Exchange (ETDEWEB)

    Belli, Sirio; Genzel, Reinhard; Förster Schreiber, Natascha M.; Wisnioski, Emily; Wilman, David J.; Mendel, J. Trevor; Beifiori, Alessandra; Bender, Ralf; Burkert, Andreas; Chan, Jeffrey; Davies, Rebecca L.; Davies, Ric; Fabricius, Maximilian; Fossati, Matteo; Galametz, Audrey; Lang, Philipp; Lutz, Dieter [Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching (Germany); Wuyts, Stijn [Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY (United Kingdom); Brammer, Gabriel B.; Momcheva, Ivelina G. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

    2017-05-20

    We explore the H α emission in the massive quiescent galaxies observed by the KMOS{sup 3D} survey at 0.7 < z < 2.7. The H α line is robustly detected in 20 out of 120 UVJ -selected quiescent galaxies, and we classify the emission mechanism using the H α line width and the [N ii]/H α line ratio. We find that AGNs are likely to be responsible for the line emission in more than half of the cases. We also find robust evidence for star formation activity in nine quiescent galaxies, which we explore in detail. The H α kinematics reveal rotating disks in five of the nine galaxies. The dust-corrected H α star formation rates are low (0.2–7 M {sub ⊙} yr{sup −1}), and place these systems significantly below the main sequence. The 24 μ m-based, infrared luminosities, instead, overestimate the star formation rates. These galaxies present a lower gas-phase metallicity compared to star-forming objects with similar stellar mass, and many of them have close companions. We therefore conclude that the low-level star formation activity in these nine quiescent galaxies is likely to be fueled by inflowing gas or minor mergers, and could be a sign of rejuvenation events.

  4. Massive stars and X-ray pulsars

    International Nuclear Information System (INIS)

    Henrichs, H.

    1982-01-01

    This thesis is a collection of 7 separate articles entitled: long term changes in ultraviolet lines in γ CAS, UV observations of γ CAS: intermittent mass-loss enhancement, episodic mass loss in γ CAS and in other early-type stars, spin-up and spin-down of accreting neutron stars, an excentric close binary model for the X Persei system, has a 97 minute periodicity in 4U 1700-37/HD 153919 really been discovered, and, mass loss and stellar wind in massive X-ray binaries. (Articles 1, 2, 5, 6 and 7 have been previously published). The first three articles are concerned with the irregular mass loss in massive stars. The fourth critically reviews thoughts since 1972 on the origin of the changes in periodicity shown by X-ray pulsars. The last articles indicate the relation between massive stars and X-ray pulsars. (C.F.)

  5. A full general relativistic neutrino radiation-hydrodynamics simulation of a collapsing very massive star and the formation of a black hole

    Science.gov (United States)

    Kuroda, Takami; Kotake, Kei; Takiwaki, Tomoya; Thielemann, Friedrich-Karl

    2018-06-01

    We study the final fate of a very massive star by performing full general relativistic (GR), three-dimensional (3D) simulation with three-flavour multi-energy neutrino transport. Utilizing a 70 solar mass zero-metallicity progenitor, we self-consistently follow the radiation-hydrodynamics from the onset of gravitational core-collapse until the second collapse of the proto-neutron star (PNS), leading to black hole (BH) formation. Our results show that the BH formation occurs at a post-bounce time of Tpb ˜ 300 ms for the 70 M⊙ star. This is significantly earlier than those in the literature where lower mass progenitors were employed. At a few ˜10 ms before BH formation, we find that the stalled bounce shock is revived by intense neutrino heating from the very hot PNS, which is aided by violent convection behind the shock. In the context of 3D-GR core-collapse modelling with multi-energy neutrino transport, our numerical results present the first evidence to validate a fallback BH formation scenario of the 70 M⊙ star.

  6. A full general relativistic neutrino radiation-hydrodynamics simulation of a collapsing very massive star and the formation of a black hole

    Science.gov (United States)

    Kuroda, Takami; Kotake, Kei; Takiwaki, Tomoya; Thielemann, Friedrich-Karl

    2018-04-01

    We study the final fate of a very massive star by performing full general relativistic (GR), three-dimensional (3D) simulation with three-flavor multi-energy neutrino transport. Utilizing a 70 solar mass zero metallicity progenitor, we self-consistently follow the radiation-hydrodynamics from the onset of gravitational core-collapse until the second collapse of the proto-neutron star (PNS), leading to black hole (BH) formation. Our results show that the BH formation occurs at a post-bounce time of Tpb ˜ 300 ms for the 70 M⊙ star. This is significantly earlier than those in the literature where lower mass progenitors were employed. At a few ˜10 ms before BH formation, we find that the stalled bounce shock is revived by intense neutrino heating from the very hot PNS, which is aided by violent convection behind the shock. In the context of 3D-GR core-collapse modeling with multi-energy neutrino transport, our numerical results present the first evidence to validate a fallback BH formation scenario of the 70M⊙ star.

  7. The formation of galaxies from pregalactic stars

    International Nuclear Information System (INIS)

    Jones, Janet

    1982-01-01

    A knowledge of how and when the first stars formed is vital for our understanding of the formation and early evolution of galaxies. Evidence is given that the first stars were pregalactic: indeed, that at least two generations of stars had formed before galaxies collapsed. A model is presented describing the effects of pregalactic stars on galaxy evolution. The first generation -primordial stars- were massive and few in number. A brief description is given for the formation of such a star. The second generation included stars of all masses and involved widespread star formation. Gas ejected from these stars on timescales of 6 x 10 7 to 6 x 10 8 years induced a qualitative change into the dynamics of collapsing perturbations, leading to a characteristic mass of galaxies of 10 10 - 10 12 M 0 . Variations in the rate of gas ejection were responsible for different morphological structures - elliptical and spirals. A few comments are made on some other implications of the model

  8. The Evolution of Low-Metallicity Massive Stars

    Science.gov (United States)

    Szécsi, Dorottya

    2016-07-01

    Massive star evolution taking place in astrophysical environments consisting almost entirely of hydrogen and helium - in other words, low-metallicity environments - is responsible for some of the most intriguing and energetic cosmic phenomena, including supernovae, gamma-ray bursts and gravitational waves. This thesis aims to investigate the life and death of metal-poor massive stars, using theoretical simulations of the stellar structure and evolution. Evolutionary models of rotating, massive stars (9-600 Msun) with an initial metal composition appropriate for the low-metallicity dwarf galaxy I Zwicky 18 are presented and analyzed. We find that the fast rotating models (300 km/s) become a particular type of objects predicted only at low-metallicity: the so-called Transparent Wind Ultraviolet INtense (TWUIN) stars. TWUIN stars are fast rotating massive stars that are extremely hot (90 kK), very bright and as compact as Wolf-Rayet stars. However, as opposed to Wolf-Rayet stars, their stellar winds are optically thin. As these hot objects emit intense UV radiation, we show that they can explain the unusually high number of ionizing photons of the dwarf galaxy I Zwicky 18, an observational quantity that cannot be understood solely based on the normal stellar population of this galaxy. On the other hand, we find that the most massive, slowly rotating models become another special type of object predicted only at low-metallicity: core-hydrogen-burning cool supergiant stars. Having a slow but strong stellar wind, these supergiants may be important contributors in the chemical evolution of young galactic globular clusters. In particular, we suggest that the low mass stars observed today could form in a dense, massive and cool shell around these, now dead, supergiants. This scenario is shown to explain the anomalous surface abundances observed in these low mass stars, since the shell itself, having been made of the mass ejected by the supergiant’s wind, contains nuclear

  9. Nitrogen chronology of massive main sequence stars

    NARCIS (Netherlands)

    Köhler, K.; Borzyszkowski, M.; Brott, I.; Langer, N.; de Koter, A.

    2012-01-01

    Context. Rotational mixing in massive main sequence stars is predicted to monotonically increase their surface nitrogen abundance with time. Aims. We use this effect to design a method for constraining the age and the inclination angle of massive main sequence stars, given their observed luminosity,

  10. Evolution of massive stars

    International Nuclear Information System (INIS)

    Loore, C. de

    1984-01-01

    The evolution of stars with masses larger than 15 sun masses is reviewed. These stars have large convective cores and lose a substantial fraction of their matter by stellar wind. The treatment of convection and the parameterisation of the stellar wind mass loss are analysed within the context of existing disagreements between theory and observation. The evolution of massive close binaries and the origin of Wolf-Rayet Stars and X-ray binaries is also sketched. (author)

  11. The History and Rate of Star Formation within the G305 Complex

    Science.gov (United States)

    Faimali, Alessandro Daniele

    2013-07-01

    Within this thesis, we present an extended multiwavelength analysis of the rich massive Galactic star-forming complex G305. We have focused our attention on studying the both the embedded massive star-forming population within G305, while also identifying the intermediate-, to lowmass content of the region also. Though massive stars play an important role in the shaping and evolution of their host galaxies, the physics of their formation still remains unclear. We have therefore set out to studying the nature of star formation within this complex, and also identify the impact that such a population has on the evolution of G305. We firstly present a Herschel far-infrared study towards G305, utilising PACS 70, 160 micron and SPIRE 250, 350, and 500 micron observations from the Hi-GAL survey of the Galactic plane. The focus of this study is to identify the embedded massive star-forming population within G305, by combining far-infrared data with radio continuum, H2O maser, methanol maser, MIPS, and Red MSX Source survey data available from previous studies. From this sample we identify some 16 candidate associations are identified as embedded massive star-forming regions, and derive a two-selection colour criterion from this sample of log(F70/F500) >= 1 and log(F160/F350) >= 1.6 to identify an additional 31 embedded massive star candidates with no associated star-formation tracers. Using this result, we are able to derive a star formation rate (SFR) of 0.01 - 0.02 Msun/yr. Comparing this resolved star formation rate, to extragalactic star formation rate tracers (based on the Kennicutt-Schmidt relation), we find the star formation activity is underestimated by a factor of >=2 in comparison to the SFR derived from the YSO population. By next combining data available from 2MASS and VVV, Spitzer GLIMPSE and MIPSGAL, MSX, and Herschel Hi-GAL, we are able to identify the low-, to intermediate-mass YSOs present within the complex. Employing a series of stringent colour

  12. Triggered massive star formation associated with the bubble Hii region Sh2-39 (N5)

    Science.gov (United States)

    Duronea, N. U.; Cappa, C. E.; Bronfman, L.; Borissova, J.; Gromadzki, M.; Kuhn, M. A.

    2017-09-01

    Aims: We perform a multiwavelength analysis of the bubble Hii region Sh2-39 (N5) and its environs with the aim of studying the physical properties of Galactic IR bubbles and exploring their impact in triggering massive star formation. Methods: To analyze the molecular gas, we used CO(3-2) and HCO+(4-3) line data obtained with the on-the-fly technique from the ASTE telescope. To study the distribution and physical characteristics of the dust, we made use of archival data from ATLASGAL, Herschel, and MSX, while the ionized gas was studied making use of an NVSS image. We used public WISE, Spitzer, and MSX point source catalogs to search for infrared candidate young stellar objects (YSOs) in the region. To investigate the stellar cluster [BDS2003]6 we used IR spectroscopic data obtained with the ARCoIRIS spectrograph, mounted on Blanco 4 m Telescope at CTIO, and new available IR Ks band observations from the VVVeXtended ESO Public Survey (VVVX). Results: The new ASTE observations allowed the molecular gas component in the velocity range from 30 km s-1 to 46 km s-1, associated with Sh2-39, to be studied in detail. The morphology of the molecular gas suggests that the ionized gas is expanding against its parental cloud. We identified four molecular clumps, which were likely formed by the expansion of the ionization front, and determined some of their physical and dynamical properties. Clumps with HCO+ and 870 μm counterparts show evidence of gravitational collapse. We identified several candidate YSOs across the molecular component. Their spatial distribution and the fragmentation time derived for the collected layers of the molecular gas suggest that massive star formation might have been triggered by the expansion of the nebula via the collect and collapse mechanism. The spectroscopical distance obtained for the stellar cluster [BDS2003]6, placed over one of the collapsing clumps in the border of the Hii region, reveals that this cluster is physically associated with

  13. Bulk yields of nucleosynthesis from massive stars

    International Nuclear Information System (INIS)

    Arnett, W.D.

    1978-01-01

    Preliminary estimates are made of the absolute yields of abundant nuclei synthesized in observed stars. The compositions of nine helium stars of mass 3 or =10M/sub sun/ is estimated. A variety of choices for the initial mass function (IMF) are used to calculate the yield per stellar generation. For standard choices of the (IMF) the absolute and relative yields of 12 C, 16 O, 20 Ne, 24 Mg, the Si to Ca group, and the iron group agree with solar system values, to the accuracy of the calculations. The relative yields are surprisingly insensitive to the slope of the IMF. In a second approach, using standard estimates (Ostriker, Richstone, and Thuan) for the current rate of stellar death, I find the present rate of nucleosynthesis in the solar neighborhood to be about 10%of the average rate over galactic history. This result is consistent with many standard models of galactic evolution (for example, the Schmidt model in which star formation goes as gas density squared). It appears that if the star formation rate is high enough to produce the stars we see around us, then the nucleosynthesis rate is large enough to produce the processed nuclei (except 4 He) seen in those stars. The typical nucleosynthesis source is massive (Mapprox. =30 M/sub sun/); the death rate of such stars is a small fraction (3-10%) of recent estimates of the total rate of supernovae

  14. THE GALACTIC CENTER CLOUD G0.253+0.016: A MASSIVE DENSE CLOUD WITH LOW STAR FORMATION POTENTIAL

    Energy Technology Data Exchange (ETDEWEB)

    Kauffmann, Jens; Pillai, Thushara [Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Zhang Qizhou, E-mail: jens.kauffmann@astro.caltech.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS78, Cambridge, MA 02138 (United States)

    2013-03-10

    We present the first interferometric molecular line and dust emission maps for the Galactic Center (GC) cloud G0.253+0.016, observed using CARMA and the SMA. This cloud is very dense, and concentrates a mass exceeding the Orion Molecular Cloud Complex (2 Multiplication-Sign 10{sup 5} M{sub Sun }) into a radius of only 3 pc, but it is essentially starless. G0.253+0.016 therefore violates ''star formation laws'' presently used to explain trends in galactic and extragalactic star formation by a factor {approx}45. Our observations show a lack of dense cores of significant mass and density, thus explaining the low star formation activity. Instead, cores with low densities and line widths {approx}< 1 km s{sup -1}-probably the narrowest lines reported for the GC region to date-are found. Evolution over several 10{sup 5} yr is needed before more massive cores, and possibly an Arches-like stellar cluster, could form. Given the disruptive dynamics of the GC region, and the potentially unbound nature of G0.253+0.016, it is not clear that this evolution will happen.

  15. Observations of Bright Massive Stars Using Small Size Telescopes

    Science.gov (United States)

    Beradze, Sopia; Kochiashvili, Nino

    2017-11-01

    The size of a telescope determines goals and objects of observations. During the latest decades it becomes more and more difficult to get photometric data of bright stars because most of telescopes of small sizes do not operate already. But there are rather interesting questions connected to the properties and evolution ties between different types of massive stars. Multi-wavelength photometric data are needed for solution of some of them. We are presenting our observational plans of bright Massive X-ray binaries, WR and LBV stars using a small size telescope. All these stars, which are presented in the poster are observational targets of Sopia Beradze's future PhD thesis. We already have got very interesting results on the reddening and possible future eruption of the massive hypergiant star P Cygni. Therefore, we decided to choose some additional interesting massive stars of different type for future observations. All Massive stars play an important role in the chemical evolution of galaxies because of they have very high mass loss - up to 10-4M⊙/a year. Our targets are on different evolutionary stages and three of them are the members of massive binaries. We plan to do UBVRI photometric observations of these stars using the 48 cm Cassegrain telescope of the Abastumani Astrophisical Observatory.

  16. Insights from simulations of star formation

    International Nuclear Information System (INIS)

    Larson, Richard B

    2007-01-01

    Although the basic physics of star formation is classical, numerical simulations have yielded essential insights into how stars form. They show that star formation is a highly nonuniform runaway process characterized by the emergence of nearly singular peaks in density, followed by the accretional growth of embryo stars that form at these density peaks. Circumstellar discs often form from the gas being accreted by the forming stars, and accretion from these discs may be episodic, driven by gravitational instabilities or by protostellar interactions. Star-forming clouds typically develop filamentary structures, which may, along with the thermal physics, play an important role in the origin of stellar masses because of the sensitivity of filament fragmentation to temperature variations. Simulations of the formation of star clusters show that the most massive stars form by continuing accretion in the dense cluster cores, and this again is a runaway process that couples star formation and cluster formation. Star-forming clouds also tend to develop hierarchical structures, and smaller groups of forming objects tend to merge into progressively larger ones, a generic feature of self-gravitating systems that is common to star formation and galaxy formation. Because of the large range of scales and the complex dynamics involved, analytic models cannot adequately describe many aspects of star formation, and detailed numerical simulations are needed to advance our understanding of the subject. 'The purpose of computing is insight, not numbers.' Richard W Hamming, in Numerical Methods for Scientists and Engineers (1962) 'There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.' William Shakespeare, in Hamlet, Prince of Denmark (1604) (key issues review)

  17. Insights from simulations of star formation

    Energy Technology Data Exchange (ETDEWEB)

    Larson, Richard B [Department of Astronomy, Yale University, Box 208101, New Haven, CT 06520-8101 (United States)

    2007-03-15

    Although the basic physics of star formation is classical, numerical simulations have yielded essential insights into how stars form. They show that star formation is a highly nonuniform runaway process characterized by the emergence of nearly singular peaks in density, followed by the accretional growth of embryo stars that form at these density peaks. Circumstellar discs often form from the gas being accreted by the forming stars, and accretion from these discs may be episodic, driven by gravitational instabilities or by protostellar interactions. Star-forming clouds typically develop filamentary structures, which may, along with the thermal physics, play an important role in the origin of stellar masses because of the sensitivity of filament fragmentation to temperature variations. Simulations of the formation of star clusters show that the most massive stars form by continuing accretion in the dense cluster cores, and this again is a runaway process that couples star formation and cluster formation. Star-forming clouds also tend to develop hierarchical structures, and smaller groups of forming objects tend to merge into progressively larger ones, a generic feature of self-gravitating systems that is common to star formation and galaxy formation. Because of the large range of scales and the complex dynamics involved, analytic models cannot adequately describe many aspects of star formation, and detailed numerical simulations are needed to advance our understanding of the subject. 'The purpose of computing is insight, not numbers.' Richard W Hamming, in Numerical Methods for Scientists and Engineers (1962) 'There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.' William Shakespeare, in Hamlet, Prince of Denmark (1604) (key issues review)

  18. YOUNG STELLAR OBJECTS IN THE MASSIVE STAR-FORMING REGION W49

    Energy Technology Data Exchange (ETDEWEB)

    Saral, G.; Hora, J. L.; Willis, S. E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Koenig, X. P. [Yale University, Department of Astronomy, 208101, New Haven, CT 06520-8101 (United States); Gutermuth, R. A. [University of Massachusetts, Department of Astronomy, Amherst, MA 01003 (United States); Saygac, A. T., E-mail: gsaral@cfa.harvard.edu [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

    2015-11-01

    We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the young stellar objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate objects using color–color and color–magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ≥7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.

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

    Science.gov (United States)

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

    2017-11-01

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

  20. Neutron stars structure in the context of massive gravity

    Energy Technology Data Exchange (ETDEWEB)

    Hendi, S.H.; Bordbar, G.H.; Panah, B. Eslam; Panahiyan, S., E-mail: hendi@shirazu.ac.ir, E-mail: ghbordbar@shirazu.ac.ir, E-mail: behzad.eslampanah@gmail.com, E-mail: sh.panahiyan@gmail.com [Physics Department and Biruni Observatory, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)

    2017-07-01

    Motivated by the recent interests in spin−2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

  1. Neutron stars structure in the context of massive gravity

    Science.gov (United States)

    Hendi, S. H.; Bordbar, G. H.; Eslam Panah, B.; Panahiyan, S.

    2017-07-01

    Motivated by the recent interests in spin-2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

  2. Neutron stars structure in the context of massive gravity

    International Nuclear Information System (INIS)

    Hendi, S.H.; Bordbar, G.H.; Panah, B. Eslam; Panahiyan, S.

    2017-01-01

    Motivated by the recent interests in spin−2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

  3. SALT Spectroscopy of Evolved Massive Stars

    Science.gov (United States)

    Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

    2017-06-01

    Long-slit spectroscopy with the Southern African Large Telescope (SALT) of central stars of mid-infrared nebulae detected with the Spitzer Space Telescope and Wide-Field Infrared Survey Explorer (WISE) led to the discovery of numerous candidate luminous blue variables (cLBVs) and other rare evolved massive stars. With the recent advent of the SALT fiber-fed high-resolution echelle spectrograph (HRS), a new perspective for the study of these interesting objects is appeared. Using the HRS we obtained spectra of a dozen newly identified massive stars. Some results on the recently identified cLBV Hen 3-729 are presented.

  4. Luminous Infrared Galaxies. III. Multiple Merger, Extended Massive Star Formation, Galactic Wind, and Nuclear Inflow in NGC 3256

    Science.gov (United States)

    Lípari, S.; Díaz, R.; Taniguchi, Y.; Terlevich, R.; Dottori, H.; Carranza, G.

    2000-08-01

    We report detailed evidence for multiple merger, extended massive star formation, galactic wind, and circular/noncircular motions in the luminous infrared galaxy NGC 3256, based on observations of high-resolution imaging (Hubble Space Telescope, ESO NTT), and extensive spectroscopic data (more than 1000 spectra, collected at Estación Astrofísica de Bosque Alegre, Complejo Astronómico el Leoncito, Cerro Tololo InterAmerican Observatory, and IUE observatories). We find in a detailed morphological study (resolution ~15 pc) that the extended massive star formation process detected previously in NGC 3256 shows extended triple asymmetrical spiral arms (r~5 kpc), emanating from three different nuclei. The main optical nucleus shows a small spiral disk (r~500 pc), which is a continuation of the external one and reaches the very nucleus. The core shows blue elongated structure (50 pc×25 pc) and harbors a blue stellar cluster candidate (r~8 pc). We discuss this complex morphology in the framework of an extended massive star formation driven by a multiple merger process (models of Hernquist et al. and Taniguchi et al.). We study the kinematics of this system and present a detailed Hα velocity field for the central region (40''×40'' rmax~30''~5 kpc), with a spatial resolution of 1" and errors of +/-15 km s-1. The color and isovelocity maps show mainly (1) a kinematic center of circular motion with ``spider'' shape, located between the main optical nucleus and the close (5") mid-IR nucleus and (2) noncircular motions in the external parts. We obtained three ``sinusoidal rotation curves'' (from the Hα velocity field) around position angle (P.A.) ~55°, ~90°, and ~130°. In the main optical nucleus we found a clear ``outflow component'' associated with galactic winds plus an ``inflow radial motion.'' The outflow component was also detected in the central and external regions (rstandard models of photoionization, shocks, and starbursts). We present four detailed emission

  5. Massive stars in the Sagittarius Dwarf Irregular Galaxy

    Science.gov (United States)

    Garcia, Miriam

    2018-02-01

    Low metallicity massive stars hold the key to interpret numerous processes in the past Universe including re-ionization, starburst galaxies, high-redshift supernovae, and γ-ray bursts. The Sagittarius Dwarf Irregular Galaxy [SagDIG, 12+log(O/H) = 7.37] represents an important landmark in the quest for analogues accessible with 10-m class telescopes. This Letter presents low-resolution spectroscopy executed with the Gran Telescopio Canarias that confirms that SagDIG hosts massive stars. The observations unveiled three OBA-type stars and one red supergiant candidate. Pending confirmation from high-resolution follow-up studies, these could be the most metal-poor massive stars of the Local Group.

  6. GALAXY FORMATION WITH SELF-CONSISTENTLY MODELED STARS AND MASSIVE BLACK HOLES. I. FEEDBACK-REGULATED STAR FORMATION AND BLACK HOLE GROWTH

    International Nuclear Information System (INIS)

    Kim, Ji-hoon; Abel, Tom; Wise, John H.; Alvarez, Marcelo A.

    2011-01-01

    There is mounting evidence for the coevolution of galaxies and their embedded massive black holes (MBHs) in a hierarchical structure formation paradigm. To tackle the nonlinear processes of galaxy-MBH interaction, we describe a self-consistent numerical framework which incorporates both galaxies and MBHs. The high-resolution adaptive mesh refinement (AMR) code Enzo is modified to model the formation and feedback of molecular clouds at their characteristic scale of 15.2 pc and the accretion of gas onto an MBH. Two major channels of MBH feedback, radiative feedback (X-ray photons followed through full three-dimensional adaptive ray tracing) and mechanical feedback (bipolar jets resolved in high-resolution AMR), are employed. We investigate the coevolution of a 9.2 x 10 11 M sun galactic halo and its 10 5 M sun embedded MBH at redshift 3 in a cosmological ΛCDM simulation. The MBH feedback heats the surrounding interstellar medium (ISM) up to 10 6 K through photoionization and Compton heating and locally suppresses star formation in the galactic inner core. The feedback considerably changes the stellar distribution there. This new channel of feedback from a slowly growing MBH is particularly interesting because it is only locally dominant and does not require the heating of gas globally on the disk. The MBH also self-regulates its growth by keeping the surrounding ISM hot for an extended period of time.

  7. Star Formation in Dwarf-Dwarf Mergers: Fueling Hierarchical Assembly

    Science.gov (United States)

    Stierwalt, Sabrina; Johnson, K. E.; Kallivayalil, N.; Patton, D. R.; Putman, M. E.; Besla, G.; Geha, M. C.

    2014-01-01

    We present early results from the first systematic study a sample of isolated interacting dwarf pairs and the mechanisms governing their star formation. Low mass dwarf galaxies are ubiquitous in the local universe, yet the efficiency of gas removal and the enhancement of star formation in dwarfs via pre-processing (i.e. dwarf-dwarf interactions occurring before the accretion by a massive host) are currently unconstrained. Studies of Local Group dwarfs credit stochastic internal processes for their complicated star formation histories, but a few intriguing examples suggest interactions among dwarfs may produce enhanced star formation. We combine archival UV imaging from GALEX with deep optical broad- and narrow-band (Halpha) imaging taken with the pre- One Degree Imager (pODI) on the WIYN 3.5-m telescope and with the 2.3-m Bok telescope at Steward Observatory to confirm the presence of stellar bridges and tidal tails and to determine whether dwarf-dwarf interactions alone can trigger significant levels of star formation. We investigate star formation rates and global galaxy colors as a function of dwarf pair separation (i.e. the dwarf merger sequence) and dwarf-dwarf mass ratio. This project is a precursor to an ongoing effort to obtain high spatial resolution HI imaging to assess the importance of sequential triggering caused by dwarf-dwarf interactions and the subsequent affect on the more massive hosts that later accrete the low mass systems.

  8. Processes and problems in secondary star formation

    International Nuclear Information System (INIS)

    Klein, R.I.; Whitaker, R.W.; Sandford, M.T. II.

    1984-03-01

    Recent developments relating the conditions in molecular clouds to star formation triggered by a prior stellar generation are reviewed. Primary processes are those that lead to the formation of a first stellar generation. The secondary processes that produce stars in response to effects caused by existing stars are compared and evaluated in terms of the observational data presently available. We discuss the role of turbulence to produce clumpy cloud structures and introduce new work on colliding inter-cloud gas flows leading to non-linear inhomogeneous cloud structures in an intially smooth cloud. This clumpy morphology has important consequences for secondary formation. The triggering processes of supernovae, stellar winds, and H II regions are discussed with emphasis on the consequences for radiation driven implosion as a promising secondary star formation mechanism. Detailed two-dimensional, radiation-hydrodynamic calculations of radiation driven implosion are discussed. This mechanism is shown to be highly efficient in synchronizing the formation of new stars in congruent to 1-3 x 10 4 years and could account for the recent evidence for new massive star formation in several UCHII regions. It is concluded that, while no single theory adequately explains the variety of star formation observed, a uniform description of star formation is likely to involve several secondary processes. Advances in the theory of star formation will require multiple dimensional calculations of coupled processes. The important non-linear interactions include hydrodynamics, radiation transport, and magnetic fields

  9. Processes and problems in secondary star formation

    International Nuclear Information System (INIS)

    Klein, R.I.; Whitaker, R.W.; Sandford, M.T. II

    1985-01-01

    Recent developments relating the conditions in molecular clouds to star formation triggered by a prior stellar generation are reviewed. Primary processes are those that lead to the formation of a first stellar generation. The secondary processes that produce stars in response to effects caused by existing stars are compared and evaluated in terms of observational data presently available. We discuss the role of turbulence to produce clumpy cloud structures and introduce new work on colliding intercloud gas flows leading to nonlinear inhomogeneous cloud structures in an initially smooth cloud. This clumpy morphology has important consequences for secondary formation. The triggering processes of supernovae, stellar winds, and H II regions are discussed with emphasis on the consequences for radiation-driven implosion as a promising secondary star formation mechanism. Detailed two-dimensional, radiation-hydrodynamic calculations of radiation-driven implosion are discussed. This mechanism is shown to be highly efficient in synchronizing the formation of new stars in -- 1-3 x 10/sup 4/ yr and could account for the recent evidence for new massive star formation in several ultracompact H II regions. It is concluded that, while no single theory adequately explains the variety of star formation observed, a uniform description of star formation is likely to involve several secondary processes. Advances in the theory of star formation will require multi-dimensional calculations of coupled processes. Important nonlinear interactions include hydrodynamics, radiation transport, and magnetic fields

  10. Highly efficient star formation in NGC 5253 possibly from stream-fed accretion.

    Science.gov (United States)

    Turner, J L; Beck, S C; Benford, D J; Consiglio, S M; Ho, P T P; Kovács, A; Meier, D S; Zhao, J-H

    2015-03-19

    Gas clouds in present-day galaxies are inefficient at forming stars. Low star-formation efficiency is a critical parameter in galaxy evolution: it is why stars are still forming nearly 14 billion years after the Big Bang and why star clusters generally do not survive their births, instead dispersing to form galactic disks or bulges. Yet the existence of ancient massive bound star clusters (globular clusters) in the Milky Way suggests that efficiencies were higher when they formed ten billion years ago. A local dwarf galaxy, NGC 5253, has a young star cluster that provides an example of highly efficient star formation. Here we report the detection of the J = 3→2 rotational transition of CO at the location of the massive cluster. The gas cloud is hot, dense, quiescent and extremely dusty. Its gas-to-dust ratio is lower than the Galactic value, which we attribute to dust enrichment by the embedded star cluster. Its star-formation efficiency exceeds 50 per cent, tenfold that of clouds in the Milky Way. We suggest that high efficiency results from the force-feeding of star formation by a streamer of gas falling into the galaxy.

  11. Tracing early evolutionary stages of high-mass star formation with molecular lines

    NARCIS (Netherlands)

    Marseille, M. G.; van der Tak, F. F. S.; Herpin, F.; Jacq, T.

    2010-01-01

    Context. Despite its major role in the evolution of the interstellar medium, the formation of high-mass stars (M >= 10 M(circle dot)) remains poorly understood. Two types of massive star cluster precursors, the so-called massive dense cores (MDCs), have been observed, which differ in terms of their

  12. Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

    Energy Technology Data Exchange (ETDEWEB)

    Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B. [Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn (Germany); De Mink, S. E. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101 (United States); De Koter, A.; Sana, H. [Astronomical Institute " Anton Pannekoek" , Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands); Gvaramadze, V. V. [Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetskij Pr. 13, Moscow 119992 (Russian Federation); Liermann, A., E-mail: fschneid@astro.uni-bonn.de [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)

    2014-01-10

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M {sub ☉} limit and observations of four stars with initial masses of 165-320 M {sub ☉} in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M {sub ☉} star. Using the stellar population of R136, we revise the upper mass limit to values in the range

  13. Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

    International Nuclear Information System (INIS)

    Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B.; De Mink, S. E.; Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" data-affiliation=" (Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" >De Koter, A.; Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" data-affiliation=" (Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" >Sana, H.; Gvaramadze, V. V.; Liermann, A.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ☉ limit and observations of four stars with initial masses of 165-320 M ☉ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M ☉ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M ☉ .

  14. Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

    Science.gov (United States)

    Schneider, F. R. N.; Izzard, R. G.; de Mink, S. E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V. V.; Hußmann, B.; Liermann, A.; Sana, H.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ⊙ limit and observations of four stars with initial masses of 165-320 M ⊙ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M ⊙ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M ⊙.

  15. Evolution of massive close binary stars

    International Nuclear Information System (INIS)

    Masevich, A.G.; Tutukov, A.V.

    1982-01-01

    Some problems of the evolution of massive close binary stars are discussed. Most of them are nonevolutionized stars with close masses of components. After filling the Roche cavity and exchange of matter between the components the Wolf-Rayet star is formed. As a result of the supernovae explosion a neutron star or a black hole is formed in the system. The system does not disintegrate but obtains high space velocity owing to the loss of the supernovae envelope. The satellite of the neutron star or black hole - the star of the O or B spectral class loses about 10 -6 of the solar mass for a year. Around the neighbouring component a disc of this matter is formed the incidence of which on a compact star leads to X radiation appearance. The neutron star cannot absorb the whole matter of the widening component and the binary system submerges into the common envelope. As a result of the evolution of massive close binary systems single neutron stars can appear which after the lapse of some time become radiopulsars. Radiopulsars with such high space velocities have been found in our Galaxy [ru

  16. Star formation induced by cloud-cloud collisions and galactic giant molecular cloud evolution

    Science.gov (United States)

    Kobayashi, Masato I. N.; Kobayashi, Hiroshi; Inutsuka, Shu-ichiro; Fukui, Yasuo

    2018-05-01

    Recent millimeter/submillimeter observations towards nearby galaxies have started to map the whole disk and to identify giant molecular clouds (GMCs) even in the regions between galactic spiral structures. Observed variations of GMC mass functions in different galactic environments indicates that massive GMCs preferentially reside along galactic spiral structures whereas inter-arm regions have many small GMCs. Based on the phase transition dynamics from magnetized warm neutral medium to molecular clouds, Kobayashi et al. (2017, ApJ, 836, 175) proposes a semi-analytical evolutionary description for GMC mass functions including a cloud-cloud collision (CCC) process. Their results show that CCC is less dominant in shaping the mass function of GMCs than the accretion of dense H I gas driven by the propagation of supersonic shock waves. However, their formulation does not take into account the possible enhancement of star formation by CCC. Millimeter/submillimeter observations within the Milky Way indicate the importance of CCC in the formation of star clusters and massive stars. In this article, we reformulate the time-evolution equation largely modified from Kobayashi et al. (2017, ApJ, 836, 175) so that we additionally compute star formation subsequently taking place in CCC clouds. Our results suggest that, although CCC events between smaller clouds are more frequent than the ones between massive GMCs, CCC-driven star formation is mostly driven by massive GMCs ≳ 10^{5.5} M_{⊙} (where M⊙ is the solar mass). The resultant cumulative CCC-driven star formation may amount to a few 10 percent of the total star formation in the Milky Way and nearby galaxies.

  17. Gas, dust, stars, star formation, and their evolution in M 33 at giant molecular cloud scales

    Science.gov (United States)

    Komugi, Shinya; Miura, Rie E.; Kuno, Nario; Tosaki, Tomoka

    2018-04-01

    We report on a multi-parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M 33. A catalog of GMCs identifed in 12CO(J = 3-2) was used to compile associated 12CO(J = 1-0), dust, stellar mass, and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components, PC1 and PC2, which retain 75% of the information from the original data set. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. Young (activity compared to intermediate-age and older clouds. Comparison of average cloud properties in different evolutionary stages imply that GMCs may be heated or grow denser and more massive via aggregation of diffuse material in their first ˜ 10 Myr. The PCA also objectively identified a set of tight relations between ISM and star formation. The ratio of the two CO lines is nearly constant, but weakly modulated by massive star formation. Dust is more strongly correlated with the star formation rate than the CO lines, supporting recent findings that dust may trace molecular gas better than CO. Stellar mass contributes weakly to the star formation rate, reminiscent of an extended form of the Schmidt-Kennicutt relation with the molecular gas term substituted by dust.

  18. Star formation properties of galaxy cluster A1767

    International Nuclear Information System (INIS)

    Yan, Peng-Fei; Li, Feng; Yuan, Qi-Rong

    2015-01-01

    Abell 1767 is a dynamically relaxed, cD cluster of galaxies with a redshift of 0.0703. Among 250 spectroscopically confirmed member galaxies within a projected radius of 2.5r 200 , 243 galaxies (∼ 97%) are spectroscopically covered by the Sloan Digital Sky Survey. Based on this homogeneous spectral sample, the stellar evolutionary synthesis code STARLIGHT is applied to investigate the stellar populations and star formation histories of galaxies in this cluster. The star formation properties of galaxies, such as mean stellar ages, metallicities, stellar masses, and star formation rates, are presented as functions of local galaxy density. A strong environmental effect is found such that massive galaxies in the high-density core region of the cluster tend to have higher metallicities, older mean stellar ages, and lower specific star formation rates (SSFRs), and their recent star formation activities have been remarkably suppressed. In addition, the correlations of the metallicity and SSFR with stellar mass are confirmed. (paper)

  19. FORMATION OF MASSIVE GALAXIES AT HIGH REDSHIFT: COLD STREAMS, CLUMPY DISKS, AND COMPACT SPHEROIDS

    International Nuclear Information System (INIS)

    Dekel, Avishai; Sari, Re'em; Ceverino, Daniel

    2009-01-01

    We present a simple theoretical framework for massive galaxies at high redshift, where the main assembly and star formation occurred, and report on the first cosmological simulations that reveal clumpy disks consistent with our analysis. The evolution is governed by the interplay between smooth and clumpy cold streams, disk instability, and bulge formation. Intense, relatively smooth streams maintain an unstable dense gas-rich disk. Instability with high turbulence and giant clumps, each a few percent of the disk mass, is self-regulated by gravitational interactions within the disk. The clumps migrate into a bulge in ∼ sun yr -1 , and each clump converts into stars in ∼0.5 Gyr. While the clumps coalesce dissipatively to a compact bulge, the star-forming disk is extended because the incoming streams keep the outer disk dense and susceptible to instability and because of angular momentum transport. Passive spheroid-dominated galaxies form when the streams are more clumpy: the external clumps merge into a massive bulge and stir up disk turbulence that stabilize the disk and suppress in situ clump and star formation. We predict a bimodality in galaxy type by z ∼ 3, involving giant-clump star-forming disks and spheroid-dominated galaxies of suppressed star formation. After z ∼ 1, the disks tend to be stabilized by the dominant stellar disks and bulges. Most of the high-z massive disks are likely to end up as today's early-type galaxies.

  20. How Very Massive Metal Free Stars Start Cosmological Reionization

    International Nuclear Information System (INIS)

    Wise, John H.; Abel, Tom

    2007-01-01

    The initial conditions and relevant physics for the formation of the earliest galaxies are well specified in the concordance cosmology. Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include non-equilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the Case B approximation using adaptively ray traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of ∼10 6 . These first sources of reionization are highly intermittent and anisotropic and first photoionize the small scales voids surrounding the halos they form in, rather than the dense filaments they are embedded in. As the merging objects form larger, dwarf sized galaxies, the escape fraction of UV radiation decreases and the H II regions only break out on some sides of the galaxies making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately 5 ionizing photons are needed per sustained ionization when star formation in 10 6 M · halos are dominant in the calculation. As the halos become larger than ∼10 7 M # circle d ot#, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15--50, in calculations with stellar feedback only. Supernova feedback in these more massive halos creates a more diffuse medium, allowing the stellar radiation to escape more easily and maintaining the ratio of 5 ionizing photons per sustained ionization

  1. Star Formation in Dwarf Galaxies: Life in a Rough Neighborhood

    Energy Technology Data Exchange (ETDEWEB)

    Murray, S

    2003-10-16

    Star formation within dwarf galaxies is governed by several factors. Many of these factors are external, including ram-pressure stripping, tidal stripping, and heating by external UV radiation. The latter, in particular, may prevent star formation in the smallest systems. Internal factors include negative feedback in the form of UV radiation, winds and supernovae from massive stars. These act to reduce the star formation efficiency within dwarf systems, which may, in turn, solve several theoretical and observational problems associated with galaxy formation. In this contribution, we discuss our recent work being done to examine the importance of the many factors in the evolution of dwarf galaxies.

  2. Revealing evolved massive stars with Spitzer

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Fabrika, S.

    2010-06-01

    Massive evolved stars lose a large fraction of their mass via copious stellar wind or instant outbursts. During certain evolutionary phases, they can be identified by the presence of their circumstellar nebulae. In this paper, we present the results of a search for compact nebulae (reminiscent of circumstellar nebulae around evolved massive stars) using archival 24-μm data obtained with the Multiband Imaging Photometer for Spitzer. We have discovered 115 nebulae, most of which bear a striking resemblance to the circumstellar nebulae associated with luminous blue variables (LBVs) and late WN-type (WNL) Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). We interpret this similarity as an indication that the central stars of detected nebulae are either LBVs or related evolved massive stars. Our interpretation is supported by follow-up spectroscopy of two dozen of these central stars, most of which turn out to be either candidate LBVs (cLBVs), blue supergiants or WNL stars. We expect that the forthcoming spectroscopy of the remaining objects from our list, accompanied by the spectrophotometric monitoring of the already discovered cLBVs, will further increase the known population of Galactic LBVs. This, in turn, will have profound consequences for better understanding the LBV phenomenon and its role in the transition between hydrogen-burning O stars and helium-burning WR stars. We also report on the detection of an arc-like structure attached to the cLBV HD 326823 and an arc associated with the LBV R99 (HD 269445) in the LMC. Partially based on observations collected at the German-Spanish Astronomical Centre, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK); fabrika@sao.ru (SF)

  3. THE STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF STAR-FORMING GALAXIES IN THE NEARBY UNIVERSE

    International Nuclear Information System (INIS)

    Torres-Papaqui, J. P.; Coziol, R.; Ortega-Minakata, R. A.; Neri-Larios, D. M.

    2012-01-01

    We have determined the metallicity (O/H) and nitrogen abundance (N/O) of a sample of 122,751 star-forming galaxies (SFGs) from the Data Release 7 of the Sloan Digital Sky Survey. For all these galaxies we have also determined their morphology and obtained a comprehensive picture of their star formation history (SFH) using the spectral synthesis code STARLIGHT. The comparison of the chemical abundance with the SFH allows us to describe the chemical evolution of the SFGs in the nearby universe (z ≤ 0.25) in a manner consistent with the formation of their stellar populations and morphologies. A high fraction (45%) of the SFGs in our sample show an excess abundance of nitrogen relative to their metallicity. We also find this excess to be accompanied by a deficiency of oxygen, which suggests that this could be the result of effective starburst winds. However, we find no difference in the mode of star formation of the nitrogen-rich and nitrogen-poor SFGs. Our analysis suggests that they all form their stars through a succession of bursts of star formation extended over a period of few Gyr. What produces the chemical differences between these galaxies seems therefore to be the intensity of the bursts: the galaxies with an excess of nitrogen are those that are presently experiencing more intense bursts or have experienced more intense bursts in their past. We also find evidence relating the chemical evolution process to the formation of the galaxies: the galaxies with an excess of nitrogen are more massive, and have more massive bulges and earlier morphologies than those showing no excess. Contrary to expectation, we find no evidence that the starburst wind efficiency decreases with the mass of the galaxies. As a possible explanation we propose that the loss of metals consistent with starburst winds took place during the formation of the galaxies, when their potential wells were still building up, and consequently were weaker than today, making starburst winds more

  4. EVIDENCE FOR REDUCED SPECIFIC STAR FORMATION RATES IN THE CENTERS OF MASSIVE GALAXIES AT z  = 4

    Energy Technology Data Exchange (ETDEWEB)

    Jung, Intae; Finkelstein, Steven L. [Department of Astronomy, The University of Texas at Austin, Austin, TX 78712 (United States); Song, Mimi; Straughn, Amber N. [Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Dickinson, Mark [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Dekel, Avishai [Center for Astrophysics and Planetary Science, Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Ferguson, Henry C.; Koekemoer, Anton M.; Ryan, Russell E. Jr.; Salmon, Brett [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Fontana, Adriano [INAF—Osservatorio Astronomico di Roma, via di Frascati 33, I-00040, Monte Porzio Catone (Italy); Lu, Yu [The Observatories, The Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Mobasher, Bahram [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Papovich, Casey, E-mail: itjung@astro.as.utexas.edu [George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States)

    2017-01-01

    We perform the first spatially resolved stellar population study of galaxies in the early universe ( z = 3.5–6.5), utilizing the Hubble Space Telescope Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey imaging data set over the GOODS-S field. We select a sample of 418 bright and extended galaxies at z  = 3.5–6.5 from a parent sample of ∼8000 photometric-redshift-selected galaxies from Finkelstein et al. We first examine galaxies at 3.5 ≲ z ≲ 4.0 using additional deep K -band survey data from the HAWK-I UDS and GOODS Survey which covers the 4000 Å break at these redshifts. We measure the stellar mass, star formation rate, and dust extinction for galaxy inner and outer regions via spatially resolved spectral energy distribution fitting based on a Markov Chain Monte Carlo algorithm. By comparing specific star formation rates (sSFRs) between inner and outer parts of the galaxies we find that the majority of galaxies with high central mass densities show evidence for a preferentially lower sSFR in their centers than in their outer regions, indicative of reduced sSFRs in their central regions. We also study galaxies at z ∼ 5 and 6 (here limited to high spatial resolution in the rest-frame ultraviolet only), finding that they show sSFRs which are generally independent of radial distance from the center of the galaxies. This indicates that stars are formed uniformly at all radii in massive galaxies at z  ∼ 5–6, contrary to massive galaxies at z ≲ 4.

  5. How Massive Single Stars End Their Life

    Science.gov (United States)

    Heger, A.; Fryer, C. L.; Woosley, S. E.; Langer, N.; Hartmann, D. H.

    2003-01-01

    How massive stars die-what sort of explosion and remnant each produces-depends chiefly on the masses of their helium cores and hydrogen envelopes at death. For single stars, stellar winds are the only means of mass loss, and these are a function of the metallicity of the star. We discuss how metallicity, and a simplified prescription for its effect on mass loss, affects the evolution and final fate of massive stars. We map, as a function of mass and metallicity, where black holes and neutron stars are likely to form and where different types of supernovae are produced. Integrating over an initial mass function, we derive the relative populations as a function of metallicity. Provided that single stars rotate rapidly enough at death, we speculate on stellar populations that might produce gamma-ray bursts and jet-driven supernovae.

  6. Galaxy Formation with Self-Consistently Modeled Stars and Massive Black Holes. I: Feedback-Regulated Star Formation and Black Hole Growth

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ji-hoon; Wise, John H.; /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Princeton U., Astrophys. Sci. Dept.; Alvarez, Marcelo A.; /Canadian Inst. Theor. Astrophys.; Abel, Tom; /KIPAC, Menlo Park /Stanford U., Phys. Dept.

    2011-11-04

    There is mounting evidence for the coevolution of galaxies and their embedded massive black holes (MBHs) in a hierarchical structure formation paradigm. To tackle the nonlinear processes of galaxy-MBH interaction, we describe a self-consistent numerical framework which incorporates both galaxies and MBHs. The high-resolution adaptive mesh refinement (AMR) code Enzo is modified to model the formation and feedback of molecular clouds at their characteristic scale of 15.2 pc and the accretion of gas onto an MBH. Two major channels of MBH feedback, radiative feedback (X-ray photons followed through full three-dimensional adaptive ray tracing) and mechanical feedback (bipolar jets resolved in high-resolution AMR), are employed. We investigate the coevolution of a 9.2 x 10{sup 11} M {circle_dot} galactic halo and its 10{sup 5} {circle_dot} M embedded MBH at redshift 3 in a cosmological CDM simulation. The MBH feedback heats the surrounding interstellar medium (ISM) up to 10{sup 6} K through photoionization and Compton heating and locally suppresses star formation in the galactic inner core. The feedback considerably changes the stellar distribution there. This new channel of feedback from a slowly growing MBH is particularly interesting because it is only locally dominant and does not require the heating of gas globally on the disk. The MBH also self-regulates its growth by keeping the surrounding ISM hot for an extended period of time.

  7. CANDELS: CORRELATIONS OF SPECTRAL ENERGY DISTRIBUTIONS AND MORPHOLOGIES WITH STAR FORMATION STATUS FOR MASSIVE GALAXIES AT z ∼ 2

    International Nuclear Information System (INIS)

    Wang Tao; Gu Qiusheng; Huang Jiasheng; Fang Guanwen; Fazio, G. G.; Faber, S. M.; McGrath, Elizabeth J.; Kocevski, Dale; Wuyts, Stijn; Yan Haojing; Dekel, Avishai; Guo Yicheng; Ferguson, Henry C.; Grogin, Norman; Lotz, Jennifer M.; Lucas, Ray A.; Koekemoer, A. M.; Weiner, Benjamin; Hathi, Nimish P.; Kong Xu

    2012-01-01

    We present a study on spectral energy distributions, morphologies, and star formation for an IRAC-selected extremely red object sample in the GOODS Chandra Deep Field-South. This work was enabled by new HST/WFC3 near-IR imaging from the CANDELS survey as well as the deepest available X-ray data from Chandra 4 Ms observations. This sample consists of 133 objects with the 3.6 μm limiting magnitude of [3.6] = 21.5 and is approximately complete for galaxies with M * > 10 11 M ☉ at 1.5 ≤ z ≤ 2.5. We classify this sample into two types, quiescent and star-forming galaxies (SFGs), in the observed infrared color-color ([3.6]–[24] versus K – [3.6]) diagram. The further morphological study of this sample shows a consistent result with the observed color classification. The classified quiescent galaxies are bulge dominated and SFGs in the sample have disk or irregular morphologies. Our observed infrared color classification is also consistent with the rest-frame color (U – V versus V – J) classification. We also found that quiescent and SFGs are well separated in the nonparametric morphology parameter (Gini versus M 20 ) diagram measuring their concentration and clumpiness: quiescent galaxies have a Gini coefficient higher than 0.58 and SFGs have a Gini coefficient lower than 0.58. We argue that the star formation quenching process must lead to or be accompanied by the increasing galaxy concentration. One prominent morphological feature of this sample is that disks are commonly seen in this massive galaxy sample at 1.5 ≤ z ≤ 2.5: 30% of quiescent galaxies and 70% of SFGs with M * > 10 11 M ☉ have disks in their rest-frame optical morphologies. The prevalence of these extended, relatively undisturbed disks challenges the merging scenario as the main mode of massive galaxy formation.

  8. CANDELS: CORRELATIONS OF SPECTRAL ENERGY DISTRIBUTIONS AND MORPHOLOGIES WITH STAR FORMATION STATUS FOR MASSIVE GALAXIES AT z {approx} 2

    Energy Technology Data Exchange (ETDEWEB)

    Wang Tao; Gu Qiusheng [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Huang Jiasheng; Fang Guanwen; Fazio, G. G. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Faber, S. M.; McGrath, Elizabeth J.; Kocevski, Dale [University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Wuyts, Stijn [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching (Germany); Yan Haojing [Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States); Dekel, Avishai [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Guo Yicheng [Astronomy Department, University of Massachusetts, 710 N. Pleasant Street, Amherst, MA 01003 (United States); Ferguson, Henry C.; Grogin, Norman; Lotz, Jennifer M.; Lucas, Ray A.; Koekemoer, A. M. [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Weiner, Benjamin [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Hathi, Nimish P. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Kong Xu, E-mail: taowang@nju.edu.cn [Center for Astrophysics, University of Science and Technology of China, Hefei 230026 (China)

    2012-06-20

    We present a study on spectral energy distributions, morphologies, and star formation for an IRAC-selected extremely red object sample in the GOODS Chandra Deep Field-South. This work was enabled by new HST/WFC3 near-IR imaging from the CANDELS survey as well as the deepest available X-ray data from Chandra 4 Ms observations. This sample consists of 133 objects with the 3.6 {mu}m limiting magnitude of [3.6] = 21.5 and is approximately complete for galaxies with M{sub *} > 10{sup 11} M{sub Sun} at 1.5 {<=} z {<=} 2.5. We classify this sample into two types, quiescent and star-forming galaxies (SFGs), in the observed infrared color-color ([3.6]-[24] versus K - [3.6]) diagram. The further morphological study of this sample shows a consistent result with the observed color classification. The classified quiescent galaxies are bulge dominated and SFGs in the sample have disk or irregular morphologies. Our observed infrared color classification is also consistent with the rest-frame color (U - V versus V - J) classification. We also found that quiescent and SFGs are well separated in the nonparametric morphology parameter (Gini versus M{sub 20}) diagram measuring their concentration and clumpiness: quiescent galaxies have a Gini coefficient higher than 0.58 and SFGs have a Gini coefficient lower than 0.58. We argue that the star formation quenching process must lead to or be accompanied by the increasing galaxy concentration. One prominent morphological feature of this sample is that disks are commonly seen in this massive galaxy sample at 1.5 {<=} z {<=} 2.5: 30% of quiescent galaxies and 70% of SFGs with M{sub *} > 10{sup 11} M{sub Sun} have disks in their rest-frame optical morphologies. The prevalence of these extended, relatively undisturbed disks challenges the merging scenario as the main mode of massive galaxy formation.

  9. Simulating the Birth of Massive Star Clusters: Is Destruction Inevitable?

    Science.gov (United States)

    Rosen, Anna

    2013-10-01

    Very early in its operation, the Hubble Space Telescope {HST} opened an entirely new frontier: study of the demographics and properties of star clusters far beyond the Milky Way. However, interpretation of HST's observations has proven difficult, and has led to the development of two conflicting models. One view is that most massive star clusters are disrupted during their infancy by feedback from newly formed stars {i.e., "infant mortality"}, independent of cluster mass or environment. The other model is that most star clusters survive their infancy and are disrupted later by mass-dependent dynamical processes. Since observations at present have failed to discriminate between these views, we propose a theoretical investigation to provide new insight. We will perform radiation-hydrodynamic simulations of the formation of massive star clusters, including for the first time a realistic treatment of the most important stellar feedback processes. These simulations will elucidate the physics of stellar feedback, and allow us to determine whether cluster disruption is mass-dependent or -independent. We will also use our simulations to search for observational diagnostics that can distinguish bound from unbound clusters, and to predict how cluster disruption affects the cluster luminosity function in a variety of galactic environments.

  10. A RAPIDLY EVOLVING REGION IN THE GALACTIC CENTER: WHY S-STARS THERMALIZE AND MORE MASSIVE STARS ARE MISSING

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Xian; Amaro-Seoane, Pau, E-mail: Xian.Chen@aei.mpg.de, E-mail: Pau.Amaro-Seoane@aei.mpg.de [Max Planck Institut für Gravitationsphysik (Albert-Einstein-Institut), D-14476 Potsdam (Germany)

    2014-05-10

    The existence of ''S-stars'' within a distance of 1'' from Sgr A* contradicts our understanding of star formation, due to Sgr A* 's forbiddingly violent environment. A suggested possibility is that they form far away and were brought in by some fast dynamical process, since they are young. Nonetheless, all conjectured mechanisms either fail to reproduce their eccentricities—without violating their young age—or cannot explain the problem of {sup i}nverse mass segregation{sup :} the fact that lighter stars (the S-stars) are closer to Sgr A* and more massive ones, Wolf-Rayet (WR) and O-stars, are farther out. In this Letter we propose that the mechanism responsible for both the distribution of the eccentricities and the paucity of massive stars is the Kozai-Lidov-like resonance induced by a sub-parsec disk recently discovered in the Galactic center. Considering that the disk probably extended to a smaller radius in the past, we show that in as short as (a few) 10{sup 6} yr, the stars populating the innermost 1'' region would redistribute in angular-momentum space and recover the observed ''super-thermal'' distribution. Meanwhile, WR and O-stars in the same region intermittently attain ample eccentricities that will lead to their tidal disruptions by the central massive black hole. Our results provide new evidences that Sgr A* was powered several millions years ago by an accretion disk as well as by tidal stellar disruptions.

  11. Magnetic massive stars as progenitors of `heavy' stellar-mass black holes

    Science.gov (United States)

    Petit, V.; Keszthelyi, Z.; MacInnis, R.; Cohen, D. H.; Townsend, R. H. D.; Wade, G. A.; Thomas, S. L.; Owocki, S. P.; Puls, J.; ud-Doula, A.

    2017-04-01

    The groundbreaking detection of gravitational waves produced by the inspiralling and coalescence of the black hole (BH) binary GW150914 confirms the existence of 'heavy' stellar-mass BHs with masses >25 M⊙. Initial characterization of the system by Abbott et al. supposes that the formation of BHs with such large masses from the evolution of single massive stars is only feasible if the wind mass-loss rates of the progenitors were greatly reduced relative to the mass-loss rates of massive stars in the Galaxy, concluding that heavy BHs must form in low-metallicity (Z ≲ 0.25-0.5 Z⊙) environments. However, strong surface magnetic fields also provide a powerful mechanism for modifying mass-loss and rotation of massive stars, independent of environmental metallicity. In this paper, we explore the hypothesis that some heavy BHs, with masses >25 M⊙ such as those inferred to compose GW150914, could be the natural end-point of evolution of magnetic massive stars in a solar-metallicity environment. Using the MESA code, we developed a new grid of single, non-rotating, solar-metallicity evolutionary models for initial zero-age main sequence masses from 40 to 80 M⊙ that include, for the first time, the quenching of the mass-loss due to a realistic dipolar surface magnetic field. The new models predict terminal-age main-sequence (TAMS) masses that are significantly greater than those from equivalent non-magnetic models, reducing the total mass lost by a strongly magnetized 80 M⊙ star during its main-sequence evolution by 20 M⊙. This corresponds approximately to the mass-loss reduction expected from an environment with metallicity Z = 1/30 Z⊙.

  12. Collisions Between Single Stars in Dense Clusters: Runaway Formation of a Massive Object

    NARCIS (Netherlands)

    Freitag, M.; Gürkan, M.A.; Rasio, F.A.

    2007-01-01

    Using Monte Carlo codes, we follow the collisional evolution of clusters in a variety of scenarios. We consider the conditions under which a cluster of main-sequence stars may undergo rapid core collapse due to mass segregation, thus entering a phase of runaway collisions, forming a very massive

  13. How massive the Wolf-Rayet stars are

    International Nuclear Information System (INIS)

    Niemela, V.S.

    1981-01-01

    If the Wolf-Rayet stars are produced by the evolution of massive stars with mass loss (Paczynski 1967, Conti 1976) from O stars to WN stars and thereafter to WC stars, then we may expect to observe a correlation of decreasing mean masses in the same sense as the evolution. Information about the masses of WR stars are obtained from studies of binary systems with WR components. (Auth.)

  14. Characterizing filaments in regions of high-mass star formation: High-resolution submilimeter imaging of the massive star-forming complex NGC 6334 with ArTéMiS

    Science.gov (United States)

    André, Ph.; Revéret, V.; Könyves, V.; Arzoumanian, D.; Tigé, J.; Gallais, P.; Roussel, H.; Le Pennec, J.; Rodriguez, L.; Doumayrou, E.; Dubreuil, D.; Lortholary, M.; Martignac, J.; Talvard, M.; Delisle, C.; Visticot, F.; Dumaye, L.; De Breuck, C.; Shimajiri, Y.; Motte, F.; Bontemps, S.; Hennemann, M.; Zavagno, A.; Russeil, D.; Schneider, N.; Palmeirim, P.; Peretto, N.; Hill, T.; Minier, V.; Roy, A.; Rygl, K. L. J.

    2016-07-01

    Context. Herschel observations of nearby molecular clouds suggest that interstellar filaments and prestellar cores represent two fundamental steps in the star formation process. The observations support a picture of low-mass star formation according to which filaments of ~0.1 pc width form first in the cold interstellar medium, probably as a result of large-scale compression of interstellar matter by supersonic turbulent flows, and then prestellar cores arise from gravitational fragmentation of the densest filaments. Whether this scenario also applies to regions of high-mass star formation is an open question, in part because the resolution of Herschel is insufficient to resolve the inner width of filaments in the nearest regions of massive star formation. Aims: In an effort to characterize the inner width of filaments in high-mass star-forming regions, we imaged the central part of the NGC 6334 complex at a resolution higher by a factor of >3 than Herschel at 350 μm. Methods: We used the large-format bolometer camera ArTéMiS on the APEX telescope and combined the high-resolution ArTéMiS data at 350 μm with Herschel/HOBYS data at 70-500 μm to ensure good sensitivity to a broad range of spatial scales. This allowed us to study the structure of the main narrow filament of the complex with a resolution of 8″ or Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.The final ArTéMiS+SPIRE 350 μm map (Fig. 1b) is available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A54

  15. THE MASSIVE STAR POPULATION IN M101. I. THE IDENTIFICATION AND SPATIAL DISTRIBUTION OF THE VISUALLY LUMINOUS STARS

    International Nuclear Information System (INIS)

    Grammer, Skyler; Humphreys, Roberta M.

    2013-01-01

    An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. But very little is known about the origin of these giant eruptions and their progenitors, many of which are presumably very massive, evolved stars. Motivated by the small number of progenitors positively associated with these giant eruptions, we have begun a survey of the evolved massive star populations in nearby galaxies. The nearby, nearly face-on, giant spiral M101 is an excellent laboratory for studying a large population of very massive stars. In this paper, we present BVI photometry obtained from archival HST/ACS Wide Field Camera images of M101. We have produced a catalog of luminous stars with photometric errors <10% for V < 24.5 and 50% completeness down to V ∼ 26.5 even in regions of high stellar crowding. Using color and luminosity criteria, we have identified candidate luminous OB-type stars and blue supergiants, yellow supergiants, and red supergiants for future observation. We examine their spatial distributions across the face of M101 and find that the ratio of blue to red supergiants decreases by two orders of magnitude over the radial extent of M101 corresponding to 0.5 dex in metallicity. We discuss the resolved stellar content in the giant star-forming complexes NGC 5458, 5453, 5461, 5451, 5462, and 5449 and discuss their color-magnitude diagrams in conjunction with the spatial distribution of the stars to determine their spatio-temporal formation histories

  16. STAR FORMATION IN DENSE CLUSTERS

    International Nuclear Information System (INIS)

    Myers, Philip C.

    2011-01-01

    A model of core-clump accretion with equally likely stopping describes star formation in the dense parts of clusters, where models of isolated collapsing cores may not apply. Each core accretes at a constant rate onto its protostar, while the surrounding clump gas accretes as a power of protostar mass. Short accretion flows resemble Shu accretion and make low-mass stars. Long flows resemble reduced Bondi accretion and make massive stars. Accretion stops due to environmental processes of dynamical ejection, gravitational competition, and gas dispersal by stellar feedback, independent of initial core structure. The model matches the field star initial mass function (IMF) from 0.01 to more than 10 solar masses. The core accretion rate and the mean accretion duration set the peak of the IMF, independent of the local Jeans mass. Massive protostars require the longest accretion durations, up to 0.5 Myr. The maximum protostar luminosity in a cluster indicates the mass and age of its oldest protostar. The distribution of protostar luminosities matches those in active star-forming regions if protostars have a constant birthrate but not if their births are coeval. For constant birthrate, the ratio of young stellar objects to protostars indicates the star-forming age of a cluster, typically ∼1 Myr. The protostar accretion luminosity is typically less than its steady spherical value by a factor of ∼2, consistent with models of episodic disk accretion.

  17. High-mass Star Formation and Its Initial Conditions

    Science.gov (United States)

    Zhang, C. P.

    2017-11-01

    In this thesis, we present four works on the infrared dark clouds, fragmentation and deuteration of compact and cold cores, hyper-compact (HC) HII regions, and infrared dust bubbles, respectively. They are not only the products of early high-mass star formation, but reflect different evolutionary sequences of high-mass star formation. (1) Using the IRAM (Institut de Radioastronomie Millimétrique) 30 m telescope, we obtained HCO^+, HNC, N_2^+, and C^{18}O emission in six IRDCs (infrared dark clouds), and study their dynamics, stability, temperature, and density. (2) Fragmentation at the earliest phases is an important process of massive star formation. Eight massive precluster clumps (G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71) were selected from the SCUBA (submillimetre Common-User Bolometer Array) 850 μm and 450 μm data. The VLA (Very Large Array) at 1.3 cm, PbBI at 3.5 mm and 1.3 mm, APEX (Atacama Pathfinder Experiment telescope) at 870 μm observations were followed up, and archival infrared data at 4.5 μm, 8.0 μm, 24 μm, and 70 μm were combined to study the fragmentation and evolution of these clumps. We explored the habitats of the massive clumps at large scale, cores/condensations at small scale, and the fragmentation process at different wavelengths. Star formation in these eight clumps may have been triggered by the UC (ultra-compact) HII regions nearby. (3) The formation of hyper-compact (HC) HII regions is an important stage in massive star formation. We present high angular resolution observations carried out with the SMA (Submillimeter Array) and the VLA (Very Large Array) toward the HC HII region G35.58-0.03. With the 1.3 mm SMA and 1.3 cm VLA, we detected a total of about 25 transitions of 8 different species and their isotopologues (CO, CH_3CN, SO_2, CH_3CCH, OCS, CS, H30α/38β, and NH_{3}). G35.58-0.03 consists of an HC HII core with electron temperature Te* ≥ 5500 K, emission measure EM ≈ 1.9×10^{9} pc

  18. SOUTHERN MASSIVE STARS AT HIGH ANGULAR RESOLUTION: OBSERVATIONAL CAMPAIGN AND COMPANION DETECTION

    Energy Technology Data Exchange (ETDEWEB)

    Sana, H. [European Space Agency/Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Le Bouquin, J.-B.; Duvert, G.; Zins, G. [Université Grenoble Alpes, IPAG, F-38000 Grenoble (France); Lacour, S.; Gauchet, L.; Pickel, D. [LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, Paris Sciences et Lettres, 5 Place Jules Janssen, F-92195 Meudon (France); Berger, J.-P. [European Southern Observatory, Schwarzschild-Str. 2, D-85748 Garching bei München (Germany); Norris, B. [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia); Olofsson, J. [Max-Planck-Institut für Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Absil, O. [Département d' Astrophysique, Géophysique et Océanographie, Université de Liège, 17 Allée du Six Août, B-4000 Liège (Belgium); De Koter, A. [Astrophysical Institute Anton Pannekoek, Universiteit van Amsterdam, Science Park 904, 1098XH Amsterdam (Netherlands); Kratter, K. [JILA, 440 UCB, University of Colorado, Boulder, CO 80309-0440 (United States); Schnurr, O. [Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany); Zinnecker, H., E-mail: hsana@stsci.edu [Deutsches SOFIA Instituut, SOFIA Science Center, NASA Ames Research Center, Mail Stop N232-12, Moffett Field, CA 94035 (United States)

    2014-11-01

    Multiplicity is one of the most fundamental observable properties of massive O-type stars and offers a promising way to discriminate between massive star formation theories. Nevertheless, companions at separations between 1 and 100 milliarcsec (mas) remain mostly unknown due to intrinsic observational limitations. At a typical distance of 2 kpc, this corresponds to projected physical separations of 2-200 AU. The Southern MAssive Stars at High angular resolution survey (SMaSH+) was designed to fill this gap by providing the first systematic interferometric survey of Galactic massive stars. We observed 117 O-type stars with VLTI/PIONIER and 162 O-type stars with NACO/Sparse Aperture Masking (SAM), probing the separation ranges 1-45 and 30-250 mas and brightness contrasts of ΔH < 4 and ΔH < 5, respectively. Taking advantage of NACO's field of view, we further uniformly searched for visual companions in an 8'' radius down to ΔH = 8. This paper describes observations and data analysis, reports the discovery of almost 200 new companions in the separation range from 1 mas to 8'' and presents a catalog of detections, including the first resolved measurements of over a dozen known long-period spectroscopic binaries. Excluding known runaway stars for which no companions are detected, 96 objects in our main sample (δ < 0°; H < 7.5) were observed both with PIONIER and NACO/SAM. The fraction of these stars with at least one resolved companion within 200 mas is 0.53. Accounting for known but unresolved spectroscopic or eclipsing companions, the multiplicity fraction at separation ρ < 8'' increases to f {sub m} = 0.91 ± 0.03. The fraction of luminosity class V stars that have a bound companion reaches 100% at 30 mas while their average number of physically connected companions within 8'' is f {sub c} = 2.2 ± 0.3. This demonstrates that massive stars form nearly exclusively in multiple systems. The nine non-thermal radio

  19. The Final Stages of Massive Star Evolution and Their Supernovae

    Science.gov (United States)

    Heger, Alexander

    In this chapter I discuss the final stages in the evolution of massive stars - stars that are massive enough to burn nuclear fuel all the way to iron group elements in their core. The core eventually collapses to form a neutron star or a black hole when electron captures and photo-disintegration reduce the pressure support to an extent that it no longer can hold up against gravity. The late burning stages of massive stars are a rich subject by themselves, and in them many of the heavy elements in the universe are first generated. The late evolution of massive stars strongly depends on their mass, and hence can be significantly effected by mass loss due to stellar winds and episodic mass loss events - a critical ingredient that we do not know as well as we would like. If the star loses all the hydrogen envelope, a Type I supernova results, if it does not, a Type II supernova is observed. Whether the star makes neutron star or a black hole, or a neutron star at first and a black hole later, and how fast they spin largely affects the energetics and asymmetry of the observed supernova explosion. Beyond photon-based astronomy, other than the sun, a supernova (SN 1987) has been the only object in the sky we ever observed in neutrinos, and supernovae may also be the first thing we will ever see in gravitational wave detectors like LIGO. I conclude this chapter reviewing the deaths of the most massive stars and of Population III stars.

  20. A parsec-scale optical jet from a massive young star in the Large Magellanic Cloud.

    Science.gov (United States)

    McLeod, Anna F; Reiter, Megan; Kuiper, Rolf; Klaassen, Pamela D; Evans, Christopher J

    2018-02-15

    Highly collimated parsec-scale jets, which are generally linked to the presence of an accretion disk, are commonly observed in low-mass young stellar objects. In the past two decades, a few of these jets have been directly (or indirectly) observed from higher-mass (larger than eight solar masses) young stellar objects, adding to the growing evidence that disk-mediated accretion also occurs in high-mass stars, the formation mechanism of which is still poorly understood. Of the observed jets from massive young stars, none is in the optical regime (massive young stars are typically highly obscured by their natal material), and none is found outside of the Milky Way. Here we report observations of HH 1177, an optical ionized jet that originates from a massive young stellar object located in the Large Magellanic Cloud. The jet is highly collimated over its entire measured length of at least ten parsecs and has a bipolar geometry. The presence of a jet indicates ongoing, disk-mediated accretion and, together with the high degree of collimation, implies that this system is probably formed through a scaled-up version of the formation mechanism of low-mass stars. We conclude that the physics that govern jet launching and collimation is independent of stellar mass.

  1. A parsec-scale optical jet from a massive young star in the Large Magellanic Cloud

    Science.gov (United States)

    McLeod, Anna F.; Reiter, Megan; Kuiper, Rolf; Klaassen, Pamela D.; Evans, Christopher J.

    2018-02-01

    Highly collimated parsec-scale jets, which are generally linked to the presence of an accretion disk, are commonly observed in low-mass young stellar objects. In the past two decades, a few of these jets have been directly (or indirectly) observed from higher-mass (larger than eight solar masses) young stellar objects, adding to the growing evidence that disk-mediated accretion also occurs in high-mass stars, the formation mechanism of which is still poorly understood. Of the observed jets from massive young stars, none is in the optical regime (massive young stars are typically highly obscured by their natal material), and none is found outside of the Milky Way. Here we report observations of HH 1177, an optical ionized jet that originates from a massive young stellar object located in the Large Magellanic Cloud. The jet is highly collimated over its entire measured length of at least ten parsecs and has a bipolar geometry. The presence of a jet indicates ongoing, disk-mediated accretion and, together with the high degree of collimation, implies that this system is probably formed through a scaled-up version of the formation mechanism of low-mass stars. We conclude that the physics that govern jet launching and collimation is independent of stellar mass.

  2. STAR FORMATION IN 30 DORADUS

    International Nuclear Information System (INIS)

    De Marchi, Guido; Spezzi, Loredana; Sirianni, Marco; Andersen, Morten; Paresce, Francesco; Panagia, Nino; Mutchler, Max; Whitmore, Bradley C.; Bond, Howard; Beccari, Giacomo; Balick, Bruce; Dopita, Michael A.; Frogel, Jay A.; Calzetti, Daniela; Marcella Carollo, C.; Disney, Michael J.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.

    2011-01-01

    Using observations obtained with the Wide-Field Camera 3 on board the Hubble Space Telescope, we have studied the properties of the stellar populations in the central regions of 30 Dor in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterize and quantify this effect using young massive main-sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main-sequence (PMS) stars by looking for objects with a strong (>4σ) Hα excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one-third of these objects are younger than ∼4 Myr, compatible with the age of the massive stars in the central ionizing cluster R 136, whereas the rest have ages up to ∼30 Myr, with a median age of ∼12 Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very center of the cluster. We attribute this latter effect to photo-evaporation of the older circumstellar disks caused by the massive ionizing members of R 136.

  3. THE SECOND SURVEY OF THE MOLECULAR CLOUDS IN THE LARGE MAGELLANIC CLOUD BY NANTEN. II. STAR FORMATION

    International Nuclear Information System (INIS)

    Kawamura, Akiko; Mizuno, Yoji; Minamidani, Tetsuhiro; Mizuno, Norikazu; Onishi, Toshikazu; Fukui, Yasuo; Fillipovic, Miroslav D.; Staveley-Smith, Lister; Kim, Sungeun; Mizuno, Akira

    2009-01-01

    We studied star formation activities in the molecular clouds in the Large Magellanic Cloud. We have utilized the second catalog of 272 molecular clouds obtained by NANTEN to compare the cloud distribution with signatures of massive star formation including stellar clusters, and optical and radio H II regions. We find that the molecular clouds are classified into three types according to the activities of massive star formation: Type I shows no signature of massive star formation; Type II is associated with relatively small H II region(s); and Type III with both H II region(s) and young stellar cluster(s). The radio continuum sources were used to confirm that Type I giant molecular clouds (GMCs) do not host optically hidden H II regions. These signatures of massive star formation show a good spatial correlation with the molecular clouds in the sense that they are located within ∼100 pc of the molecular clouds. Among possible ideas to explain the GMC types, we favor that the types indicate an evolutionary sequence; i.e., the youngest phase is Type I, followed by Type II, and the last phase is Type III, where the most active star formation takes place leading to cloud dispersal. The number of the three types of GMCs should be proportional to the timescale of each evolutionary stage if a steady state of massive star and cluster formation is a good approximation. By adopting the timescale of the youngest stellar clusters, 10 Myr, we roughly estimate the timescales of Types I, II, and III to be 6 Myr, 13 Myr, and 7 Myr, respectively, corresponding to a lifetime of 20-30 Myr for the GMCs with a mass above the completeness limit, 5 x 10 4 M sun .

  4. Water in massive star-forming regions with Herschel Space Observatory

    Science.gov (United States)

    Chavarria, L.; Herpin, F.; Bontemps, S.; Jacq, T.; Baudry, A.; Braine, J.; van der Tak, F.; Wyrowski, F.; van Dishoeck, E. F.

    2011-05-01

    High-mass stars formation process is much less understood than the low-mass case: short timescales, high opacities and long distance to the sources challenge the study of young massive stars. The instruments on board the Heschel Space Observatory permit us to investigate molecular species at high spectral resolution in the sub-milimeter wavelengths. Water, one of the most abundant molecules in the Universe, might elucidate key episodes in the process of stellar birth and it may play a major role in the formation of high-mass stars. This contribution presents the first results of the Heschel Space Observatory key-program WISH (Water In Star forming regions with Herschel) concerning high-mass protostars. The program main purpose is to follow the process of star formation during the various stages using the water molecule as a physical diagnostic throughout the evolution. In general, we aim to adress the following questions: How does protostars interact with their environment ? How and where water is formed ? How is it transported from cloud to disk ? When and where water becomes a dominant cooling or heating agent ? We use the HIFI and PACS instruments to obtain maps and spectra of ~20 water lines in ~20 massive protostars spanning a large range in physical parameters, from pre-stellar cores to UCHII regions. I will review the status of the program and focus specifically on the spectroscopic results. I will show how powerful are the HIFI high-resolution spectral observations to resolve different physical source components such as the dense core, the outflows and the extended cold cloud around the high-mass object. We derive water abundances between 10-7 and 10-9 in the outer envelope. The abundance variations derived from our models suggest that different chemical mechanisms are at work on these scales (e.g. evaporation of water-rich icy grain mantles). The detection and derived abundance ratios for rare isotopologues will be discussed. Finally, a comparison in tems

  5. Imprints of fast-rotating massive stars in the Galactic Bulge.

    Science.gov (United States)

    Chiappini, Cristina; Frischknecht, Urs; Meynet, Georges; Hirschi, Raphael; Barbuy, Beatriz; Pignatari, Marco; Decressin, Thibaut; Maeder, André

    2011-04-28

    The first stars that formed after the Big Bang were probably massive, and they provided the Universe with the first elements heavier than helium ('metals'), which were incorporated into low-mass stars that have survived to the present. Eight stars in the oldest globular cluster in the Galaxy, NGC 6522, were found to have surface abundances consistent with the gas from which they formed being enriched by massive stars (that is, with higher α-element/Fe and Eu/Fe ratios than those of the Sun). However, the same stars have anomalously high abundances of Ba and La with respect to Fe, which usually arises through nucleosynthesis in low-mass stars (via the slow-neutron-capture process, or s-process). Recent theory suggests that metal-poor fast-rotating massive stars are able to boost the s-process yields by up to four orders of magnitude, which might provide a solution to this contradiction. Here we report a reanalysis of the earlier spectra, which reveals that Y and Sr are also overabundant with respect to Fe, showing a large scatter similar to that observed in extremely metal-poor stars, whereas C abundances are not enhanced. This pattern is best explained as originating in metal-poor fast-rotating massive stars, which might point to a common property of the first stellar generations and even of the 'first stars'.

  6. Evolution of massive stars in very young clusters and associations

    International Nuclear Information System (INIS)

    Stothers, R.B.

    1985-01-01

    The stellar content of very young galactic clusters and associations with well-determined ages has been analyzed statistically to derive information about stellar evolution at high masses. The adopted approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram, together with the stars' apparent magnitudes. Cluster distance moduli are not used. Only the most basic elements of stellar evolution theory are required as input. For stellar aggregates with main-sequence turnups at spectral types between O9 and B2, the following conclusions have emerged: (1) O-type main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most of the O-type blue stragglers are newly formed massive stars, burning core hydrogen; (3) supergiants lying redward of the turnup, as well as most, or all, of the Wolf-Rayet stars, are burning core helium; (4) Wolf-Rayet stars originally had masses greater than 30--40 M/sub sun/, while known M-type supergiants evolved from star less massive than approx.30 M/sub sun/; (5) phases of evolution following core helium burning are unobservably rapid, presumably on account of copious neutrino emission; and (6) formation of stars of high mass continues vigorously in most young clusters and association for approx.8 x 10 6 yr. The important result concerning the evolutionary status of the supergiants depends only on the total number of these stars and not on how they are distributed between blue and red types; the result, however, may be sensitive to the assumed amount of convective core overshooting. Conclusions in the present work refer chiefly to luminous stars in the mass range 10--40 M/sub sun/, belonging to aggregates in the age range (6--25) x 10 6 yr

  7. Young stellar population and star formation history ofW4 HII region/Cluster Complex

    Science.gov (United States)

    Panwar, Neelam

    2018-04-01

    The HII region/cluster complex has been a subject of numerous investigations to study the feedback effect of massive stars on their surroundings. Massive stars not only alter the morphology of the parental molecular clouds, but also influence star formation, circumstellar disks and the mass function of low-mass stars in their vicinity. However, most of the studies of low-mass stellar content of the HII regions are limited only to the nearby regions. We study the star formation in the W4 HII region using deep optical observations obtained with the archival data from Canada - France - Hawaii Telescope, Two-Micron All Sky Survey, Spitzer, Herschel and Chandra. We investigate the spatial distribution of young stellar objects in the region, their association with the remnant molecular clouds, and search for the clustering to establish the sites of recent star formation. Our analysis suggests that the influence of massive stars on circumstellar disks is significant only to thei! r immediate neighborhood. The spatial correlation of the young stars with the distribution of gas and dust of the complex indicate that the clusters would have formed in a large filamentary cloud. The observing facilities at the 3.6-m Devasthal Optical Telescope (DOT), providing high-resolution spectral and imaging capabilities, will fulfill the major objectives in the study of HII regions.

  8. Young Stellar Objects in the Massive Star-forming Regions W51 and W43

    Energy Technology Data Exchange (ETDEWEB)

    Saral, G.; Audard, M. [Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix (Switzerland); Hora, J. L.; Martínez-Galarza, J. R.; Smith, H. A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Koenig, X. P. [Yale University, Department of Astronomy, 208101, New Haven, CT 06520-8101 (United States); Motte, F. [Institut de Plantologie et d’Astrophysique de Grenoble, Univ. Grenoble Alpes—CNRS-INSU, BP 53, F-38041 Grenoble Cedex 9 (France); Nguyen-Luong, Q. [National Astronomical Observatory of Japan, Chile Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Saygac, A. T. [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

    2017-04-20

    We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color–magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions and, based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH ii regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H ii regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.

  9. The coupling between pulsation and mass loss in massive stars

    OpenAIRE

    Townsend, Rich

    2007-01-01

    To what extent can pulsational instabilities resolve the mass-loss problem of massive stars? How important is pulsation in structuring and modulating the winds of these stars? What role does pulsation play in redistributing angular momentum in massive stars? Although I cannot offer answers to these questions, I hope at the very least to explain how they come to be asked.

  10. Effect of mass loss on the chemical yields from massive stars

    Energy Technology Data Exchange (ETDEWEB)

    Chiosi, C; Caimmi, R [Padua Univ. (Italy). Istituto di Astronomia

    1979-01-01

    Recent results on the calculation of the chemical yields from massive stars, are rediscussed by taking into account the occurrence of mass loss by stellar wind during the core H- and He-burning phases. The new yields are found to be compatible with the observed distribution of chemical abundances in the solar system, except for He. The net enrichment of several elements over the galaxy's lifetime is found to be consistent with the current estimate of the star formation rate, if we adopt a two phase process of galaxy formation (halodisk). The relative He to heavy element enrichment rate ..delta..Y/..delta..Z turns out to agree with the observational value when mass loss by stellar wind is taken into account.

  11. KEY ISSUES REVIEW: Insights from simulations of star formation

    Science.gov (United States)

    Larson, Richard B.

    2007-03-01

    Although the basic physics of star formation is classical, numerical simulations have yielded essential insights into how stars form. They show that star formation is a highly nonuniform runaway process characterized by the emergence of nearly singular peaks in density, followed by the accretional growth of embryo stars that form at these density peaks. Circumstellar discs often form from the gas being accreted by the forming stars, and accretion from these discs may be episodic, driven by gravitational instabilities or by protostellar interactions. Star-forming clouds typically develop filamentary structures, which may, along with the thermal physics, play an important role in the origin of stellar masses because of the sensitivity of filament fragmentation to temperature variations. Simulations of the formation of star clusters show that the most massive stars form by continuing accretion in the dense cluster cores, and this again is a runaway process that couples star formation and cluster formation. Star-forming clouds also tend to develop hierarchical structures, and smaller groups of forming objects tend to merge into progressively larger ones, a generic feature of self-gravitating systems that is common to star formation and galaxy formation. Because of the large range of scales and the complex dynamics involved, analytic models cannot adequately describe many aspects of star formation, and detailed numerical simulations are needed to advance our understanding of the subject. 'The purpose of computing is insight, not numbers.' Richard W Hamming, in Numerical Methods for Scientists and Engineers (1962) 'There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.' William Shakespeare, in Hamlet, Prince of Denmark (1604)

  12. Stellar signatures of AGN-jet-triggered star formation

    International Nuclear Information System (INIS)

    Dugan, Zachary; Silk, Joseph; Bryan, Sarah; Gaibler, Volker; Haas, Marcel

    2014-01-01

    To investigate feedback between relativistic jets emanating from active galactic nuclei and the stellar population of the host galaxy, we analyze the long-term evolution of the orbits of the stars formed in the galaxy-scale simulations by Gaibler et al. of jets in massive, gas-rich galaxies at z ∼ 2-3. We find strong, jet-induced differences in the resulting stellar populations of galaxies that host relativistic jets and galaxies that do not, including correlations in stellar locations, velocities, and ages. Jets are found to generate distributions of increased radial and vertical velocities that persist long enough to effectively augment the stellar structure of the host. The jets cause the formation of bow shocks that move out through the disk, generating rings of star formation within the disk. The bow shock often accelerates pockets of gas in which stars form, yielding populations of stars with significant radial and vertical velocities, some of which have large enough velocities to escape the galaxy. These stellar population signatures can serve to identify past jet activity as well as jet-induced star formation.

  13. How Very Massive Metal-Free Stars Start Cosmological Reionization

    Science.gov (United States)

    Wise, John H.; Abel, Tom

    2008-01-01

    The initial conditions and relevant physics for the formation of the earliest galaxies are well specified in the concordance cosmology. Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include nonequilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the case B approximation using adaptively ray-traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of approx.10(exp 6). These first sources of reionization are highly intermittent and anisotropic and first photoionize the small-scale voids surrounding the halos they form in, rather than the dense filaments they are embedded in. As the merging objects form larger, dwarf-sized galaxies, the escape fraction of UV radiation decreases and the H II regions only break out on some sides of the galaxies, making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately five ionizing photons are needed per sustained ionization when star formation in 10(exp 6) stellar Mass halos is dominant in the calculation. As the halos become larger than approx.10(exp 7) Stellar Mass, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15-50, in calculations with stellar feedback only. Radiative feedback decreases clumping factors by 25% when compared to simulations without star formation and increases the average temperature of ionized gas to values between 3000 and 10,000 K.

  14. Galactic Winds and the Role Played by Massive Stars

    Science.gov (United States)

    Heckman, Timothy M.; Thompson, Todd A.

    Galactic winds from star-forming galaxies play at key role in the evolution of galaxies and the intergalactic medium. They transport metals out of galaxies, chemically enriching the intergalactic medium and modifying the chemical evolution of galaxies. They affect the surrounding interstellar and circumgalactic media, thereby influencing the growth of galaxies though gas accretion and star formation. In this contribution we first summarize the physical mechanisms by which the momentum and energy output from a population of massive stars and associated supernovae can drive galactic winds. We use the prototypical example of M 82 to illustrate the multiphase nature of galactic winds. We then describe how the basic properties of galactic winds are derived from the data, and summarize how the properties of galactic winds vary systematically with the properties of the galaxies that launch them. We conclude with a brief discussion of the broad implications of galactic winds.

  15. Formation of massive seed black holes via collisions and accretion

    Science.gov (United States)

    Boekholt, T. C. N.; Schleicher, D. R. G.; Fellhauer, M.; Klessen, R. S.; Reinoso, B.; Stutz, A. M.; Haemmerlé, L.

    2018-05-01

    Models aiming to explain the formation of massive black hole seeds, and in particular the direct collapse scenario, face substantial difficulties. These are rooted in rather ad hoc and fine-tuned initial conditions, such as the simultaneous requirements of extremely low metallicities and strong radiation backgrounds. Here, we explore a modification of such scenarios where a massive primordial star cluster is initially produced. Subsequent stellar collisions give rise to the formation of massive (104-105 M⊙) objects. Our calculations demonstrate that the interplay among stellar dynamics, gas accretion, and protostellar evolution is particularly relevant. Gas accretion on to the protostars enhances their radii, resulting in an enhanced collisional cross-section. We show that the fraction of collisions can increase from 0.1 to 1 per cent of the initial population to about 10 per cent when compared to gas-free models or models of protostellar clusters in the local Universe. We conclude that very massive objects can form in spite of initial fragmentation, making the first massive protostellar clusters viable candidate birth places for observed supermassive black holes.

  16. Search for molecular outflows associated with peculiar nebulosities and regions of star formation

    Energy Technology Data Exchange (ETDEWEB)

    Torrelles, J M; Rodriguez, L F; Canto, J; Marcaide, J; Gyulbudaghian, A L

    1983-01-01

    We surveyed an extensive list of peculiar nebulosities and regions of star formation searching for conspicuous cases of high-velocity carbon monoxide emission. We detected an apparently isotropic outflow associated with the star-forming region GL 2591. Among the other sources surveyed, the cometary nebula GM 24 is of interest since it is located in a very hot molecular spot where formation of massive stars took place recently.

  17. EXTENDED STAR FORMATION IN THE INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 2209

    International Nuclear Information System (INIS)

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2012-01-01

    We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters.

  18. Massive runaway stars in the Large Magellanic Cloud

    Science.gov (United States)

    Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

    2010-09-01

    The origin of massive field stars in the Large Magellanic Cloud (LMC) has long been an enigma. The recent measurements of large offsets (˜ 100 km s-1) between the heliocentric radial velocities of some very massive (O2-type) field stars and the systemic LMC velocity provides a possible explanation of this enigma and suggests that the field stars are runaway stars ejected from their birthplaces at the very beginning of their parent cluster's dynamical evolution. A straightforward way to prove this explanation is to measure the proper motions of the field stars and to show that they are moving away from one of the nearby star clusters or OB associations. This approach is, however, complicated by the long distance to the LMC, which makes accurate proper motion measurements difficult. We used an alternative approach for solving the problem (first applied for Galactic field stars), based on the search for bow shocks produced by runaway stars. The geometry of detected bow shocks would allow us to infer the direction of stellar motion, thereby determining their possible parent clusters. In this paper we present the results of a search for bow shocks around six massive field stars that have been proposed as candidate runaway stars. Using archival Spitzer Space Telescope data, we found a bow shock associated with one of our programme stars, the O2 V((f*)) star BI 237, which is the first-ever detection of bow shocks in the LMC. Orientation of the bow shock suggests that BI 237 was ejected from the OB association LH 82 (located at ≃ 120 pc in projection from the star). A by-product of our search is the detection of bow shocks generated by four OB stars in the field of the LMC and an arc-like structure attached to the candidate luminous blue variable R81 (HD 269128). The geometry of two of these bow shocks is consistent with the possibility that their associated stars were ejected from the 30 Doradus star-forming complex. We discuss implications of our findings for the

  19. TIDAL TAILS OF MINOR MERGERS. II. COMPARING STAR FORMATION IN THE TIDAL TAILS OF NGC 2782

    Energy Technology Data Exchange (ETDEWEB)

    Knierman, Karen A.; Scowen, Paul; Veach, Todd; Groppi, Christopher [School of Earth and Space Exploration, Arizona State University, 550 E. Tyler Mall, Room PSF-686 (P.O. Box 871404), Tempe, AZ 85287-1404 (United States); Mullan, Brendan; Charlton, Jane [Department of Astronomy and Astrophysics, Penn State University, 525 Davey Lab, University Park, PA (United States); Konstantopoulos, Iraklis [Australian Astronomical Observatory, P.O. Box 915, North Ryde NSW 1670 (Australia); Knezek, Patricia M., E-mail: karen.knierman@asu.edu, E-mail: paul.scowen@asu.edu, E-mail: tveach@asu.edu, E-mail: cgroppi@asu.edu, E-mail: mullan@astro.psu.edu, E-mail: iraklis@aao.gov.au, E-mail: pknezek@noao.edu [WIYN Consortium, Inc., 950 N. Cherry Avenue, Tucson, AZ 85719 (United States)

    2013-09-10

    The peculiar spiral NGC 2782 is the result of a minor merger with a mass ratio {approx}4: 1 occurring {approx}200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun. However, deep UBVR and H{alpha} narrowband images show evidence of recent star formation in the western tail, though it lacks massive star clusters and cluster complexes. Using Herschel PACS spectroscopy, we discover 158 {mu}m [C II] emission at the location of the three most luminous H{alpha} sources in the eastern tail, but not at the location of the even brighter H{alpha} source in the western tail. The western tail is found to have a normal star formation efficiency (SFE), but the eastern tail has a low SFE. The lack of CO and [C II] emission suggests that the western tail H II region may have a low carbon abundance and be undergoing its first star formation. The western tail is more efficient at forming stars, but lacks massive clusters. We propose that the low SFE in the eastern tail may be due to its formation as a splash region where gas heating is important even though it has sufficient molecular and neutral gas to make massive star clusters. The western tail, which has lower gas surface density and does not form high-mass star clusters, is a tidally formed region where gravitational compression likely enhances star formation.

  20. TIDAL TAILS OF MINOR MERGERS. II. COMPARING STAR FORMATION IN THE TIDAL TAILS OF NGC 2782

    International Nuclear Information System (INIS)

    Knierman, Karen A.; Scowen, Paul; Veach, Todd; Groppi, Christopher; Mullan, Brendan; Charlton, Jane; Konstantopoulos, Iraklis; Knezek, Patricia M.

    2013-01-01

    The peculiar spiral NGC 2782 is the result of a minor merger with a mass ratio ∼4: 1 occurring ∼200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun. However, deep UBVR and Hα narrowband images show evidence of recent star formation in the western tail, though it lacks massive star clusters and cluster complexes. Using Herschel PACS spectroscopy, we discover 158 μm [C II] emission at the location of the three most luminous Hα sources in the eastern tail, but not at the location of the even brighter Hα source in the western tail. The western tail is found to have a normal star formation efficiency (SFE), but the eastern tail has a low SFE. The lack of CO and [C II] emission suggests that the western tail H II region may have a low carbon abundance and be undergoing its first star formation. The western tail is more efficient at forming stars, but lacks massive clusters. We propose that the low SFE in the eastern tail may be due to its formation as a splash region where gas heating is important even though it has sufficient molecular and neutral gas to make massive star clusters. The western tail, which has lower gas surface density and does not form high-mass star clusters, is a tidally formed region where gravitational compression likely enhances star formation

  1. Accretion Processes in Star Formation

    DEFF Research Database (Denmark)

    Küffmeier, Michael

    for short-lived radionuclides that enrich the cloud as a result of supernova explosions of the massive stars allows us to analyze the distribution of the short-lived radionuclides around young forming stars. In contradiction to results from highly-idealized models, we find that the discrepancy in 26 Al...... that the accretion process of stars is heterogeneous in space, time and among different protostars. In some cases, disks form a few thousand years after stellar birth, whereas in other cases disk formation is suppressed due to efficient removal of angular momentum. Angular momentum is mainly transported outward...... with potentially observable fluctuations in the luminosity profile that are induced by variations in the accretion rate. Considering that gas inside protoplanetary disks is not fully ionized, I implemented a solver that accounts for nonideal MHD effects into a newly developed code framework called dispatch...

  2. DRIVING TURBULENCE AND TRIGGERING STAR FORMATION BY IONIZING RADIATION

    International Nuclear Information System (INIS)

    Gritschneder, Matthias; Naab, Thorsten; Walch, Stefanie; Burkert, Andreas; Heitsch, Fabian

    2009-01-01

    We present high-resolution simulations on the impact of ionizing radiation of massive O stars on the surrounding turbulent interstellar medium (ISM). The simulations are performed with the newly developed software iVINE which combines ionization with smoothed particle hydrodynamics (SPH) and gravitational forces. We show that radiation from hot stars penetrates the ISM, efficiently heats cold low-density gas and amplifies overdensities seeded by the initial turbulence. The formation of observed pillar-like structures in star-forming regions (e.g. in M16) can be explained by this scenario. At the tip of the pillars gravitational collapse can be induced, eventually leading to the formation of low-mass stars. Detailed analysis of the evolution of the turbulence spectra shows that UV radiation of O stars indeed provides an excellent mechanism to sustain and even drive turbulence in the parental molecular cloud.

  3. The Wolf-Rayet Content of the Andromeda Galaxy: What Do Massive Stars Really Do When the Metallicity is Above Solar?

    Science.gov (United States)

    Massey, Philip

    2000-08-01

    We are proposing to survey M 31 for Wolf-Rayet stars (WRs) and red supergiants (RSGs), providing much needed information about how massive stars evolve at greater-than-solar metallicities. Our understanding of massive star evolution is hampered by the effects of mass-loss on these stars; at higher metallicities mass-loss effects become ever more pronounced. Our previous work on other Local Group galaxies (Massey & Johnson 1998) has shown that the number of RSGs to WRs correlates well with metallicity, changing by a factor of 6 from NGC 6822 (log O/H+12=8.3) to the inner parts of M 33 (8.7). Our study of five small regions in M 31 suggests that above this value the ratio of RSGs to WRs doesn't change: does this mean that no massive star that becomes a WR spends any time as a RSG at above solar metallicities? We fear instead that our sample (selected, afterall, for containing WR stars) was not sufficiently well-mixed in age to provide useful global values; the study we propose here will survey all of M 31. Detection of WRs will provide fundamental data not only on massive star evolution, but also act as tracers of the most massive stars, and improve our knowledge of recent star-formation in the Andromeda Galaxy.

  4. The low-metallicity starburst NGC346: massive-star population and feedback

    Science.gov (United States)

    Oskinova, Lida

    2017-08-01

    The Small Magellanic Cloud (SMC) is ideal to study young, massive stars at low metallicity. The compact cluster NGC346 contains about half of all O-type stars in the entire SMC. The massive-star population of this cluster powers N66, the brightest and largest HII region in the SMC. We propose to use HST-STIS to slice NGC346 with 20 long-slit exposures, in order to obtain the UV spectra of most of the massive early-type stars of this cluster. Archival data of 13 exposures that cover already a minor part of this cluster will be included in our analyses. Our aim is to quantitatively analyze virtually the whole massive-star population of NGC346. We have already secured the optical spectra of all massive stars in the field with the integral-field spectrograph MUSE at the ESO-VLT. However, for the determination of the stellar-wind parameters, i.e. the mass-loss rates and the wind velocities, ultraviolet spectra are indispensable. Our advanced Potsdam Wolf-Rayet (PoWR) code will be used for modeling the stellar and wind spectra in the course of the analysis. Finally, we will obtain:(a) the fundamental stellar and wind parameters of all stars brighter than spectral type B2V in the field, which, e,g,, will constrain the initial mass function in this young low-metallicity starburst;(b) mass-loss rates of many more OB-type stars at SMC metallicity than hitherto known, allowing to better constrain their metallicity dependence;(c) the integrated feedback by ionizing radiation and stellar winds of the whole massive-star population of NGC346, which will be used as input to model the ecology of the giant HII region N66.These HST UV data will be of high legacy value.

  5. Massive Star Burps, Then Explodes

    Science.gov (United States)

    2007-04-01

    Berkeley -- In a galaxy far, far away, a massive star suffered a nasty double whammy. On Oct. 20, 2004, Japanese amateur astronomer Koichi Itagaki saw the star let loose an outburst so bright that it was initially mistaken for a supernova. The star survived, but for only two years. On Oct. 11, 2006, professional and amateur astronomers witnessed the star actually blowing itself to smithereens as Supernova 2006jc. Swift UVOT Image Swift UVOT Image (Credit: NASA / Swift / S.Immler) "We have never observed a stellar outburst and then later seen the star explode," says University of California, Berkeley, astronomer Ryan Foley. His group studied the event with ground-based telescopes, including the 10-meter (32.8-foot) W. M. Keck telescopes in Hawaii. Narrow helium spectral lines showed that the supernova's blast wave ran into a slow-moving shell of material, presumably the progenitor's outer layers ejected just two years earlier. If the spectral lines had been caused by the supernova's fast-moving blast wave, the lines would have been much broader. artistic rendering This artistic rendering depicts two years in the life of a massive blue supergiant star, which burped and spewed a shell of gas, then, two years later, exploded. When the supernova slammed into the shell of gas, X-rays were produced. (Credit: NASA/Sonoma State Univ./A.Simonnet) Another group, led by Stefan Immler of NASA's Goddard Space Flight Center, Greenbelt, Md., monitored SN 2006jc with NASA's Swift satellite and Chandra X-ray Observatory. By observing how the supernova brightened in X-rays, a result of the blast wave slamming into the outburst ejecta, they could measure the amount of gas blown off in the 2004 outburst: about 0.01 solar mass, the equivalent of about 10 Jupiters. "The beautiful aspect of our SN 2006jc observations is that although they were obtained in different parts of the electromagnetic spectrum, in the optical and in X-rays, they lead to the same conclusions," says Immler. "This

  6. Interactions, Starbursts, and Star Formation

    Directory of Open Access Journals (Sweden)

    Johan H. Knapen

    2015-12-01

    Full Text Available We study how interactions between galaxies affect star formation within them by considering a sample of almost 1500 of the nearest galaxies, all within a distance of ∼45 Mpc. We use the far-IR emission to define the massive star formation rate (SFR, and then normalise the SFR by the stellar mass of the galaxy to obtain the specific star formation rate (SSFR. We explore the distribution of (SSFR with morphological type and with stellar mass. We calculate the relative enhancement of SFR and SSFR for each galaxy by normalising them by the median SFR and SSFR values of individual control samples of similar non-interacting galaxies. We find that both the median SFR and SSFR are enhanced in interacting galaxies, and more so as the degree of interaction is higher. The increase is moderate, reaching a maximum of a factor of 1.9 for the highest degree of interaction (mergers. While the SFR and SSFR are enhanced statistically by interactions, in many individual interacting galaxies they are not enhanced at all. Our study is based on a representative sample of nearby galaxies and should be used to place constraints on studies based on samples of galaxies at larger distances.

  7. The fate of NGC602, an intense region of star-formation in the Wing of the SMC

    Science.gov (United States)

    Sabbi, Elena

    2017-08-01

    This is a small 2 orbit proposal designed to measure the internal dynamics of NGC602, a small region of intense star formation in the Wing of the SMC, with a low gas and dust density that has been often considered an unfavorable place for star formation. Small regions of massive star formation are important to study for our understanding of the process of star and cluster formation, the ionization of the interstellar medium, and the injection of energy and momentum into their host galaxy. By combining our new observations with archival ACS/WFC data acquired in July 2004, we will be able to measure the relative proper motions of the NGC602 sub-structures better than 2.3 km/s and investigate the nature of the apparently isolated massive stars found around NGC602. This study will provide unique observational data to characterize the early phase of cluster evolution and test cluster formation theories. It will also address significant open issues in star formation, cluster dynamics and the origin of isolated supernovae and GRBs.

  8. THE VERY MASSIVE STAR CONTENT OF THE NUCLEAR STAR CLUSTERS IN NGC 5253

    Energy Technology Data Exchange (ETDEWEB)

    Smith, L. J. [Space Telescope Science Institute and European Space Agency, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Crowther, P. A. [Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom); Calzetti, D. [Department of Astronomy, University of Massachusetts—Amherst, Amherst, MA 01003 (United States); Sidoli, F., E-mail: lsmith@stsci.edu [London Centre for Nanotechnology, University College London, London WC1E 6BT (United Kingdom)

    2016-05-20

    The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters, separated by a projected distance of 5 pc. One cluster (#5) coincides with the peak of the H α emission and the other (#11) with a massive ultracompact H ii region. A recent analysis of these clusters shows that they have a photometric age of 1 ± 1 Myr, in apparent contradiction with the age of 3–5 Myr inferred from the presence of Wolf-Rayet features in the cluster #5 spectrum. We examine Hubble Space Telescope ultraviolet and Very Large Telescope optical spectroscopy of #5 and show that the stellar features arise from very massive stars (VMSs), with masses greater than 100 M {sub ⊙}, at an age of 1–2 Myr. We further show that the very high ionizing flux from the nuclear clusters can only be explained if VMSs are present. We investigate the origin of the observed nitrogen enrichment in the circumcluster ionized gas and find that the excess N can be produced by massive rotating stars within the first 1 Myr. We find similarities between the NGC 5253 cluster spectrum and those of metal-poor, high-redshift galaxies. We discuss the presence of VMSs in young, star-forming galaxies at high redshift; these should be detected in rest-frame UV spectra to be obtained with the James Webb Space Telescope . We emphasize that population synthesis models with upper mass cutoffs greater than 100 M {sub ⊙} are crucial for future studies of young massive star clusters at all redshifts.

  9. Stellar Wind Retention and Expulsion in Massive Star Clusters

    Science.gov (United States)

    Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

    2018-05-01

    Mass and energy injection throughout the lifetime of a star cluster contributes to the gas reservoir available for subsequent episodes of star formation and the feedback energy budget responsible for ejecting material from the cluster. In addition, mass processed in stellar interiors and ejected as winds has the potential to augment the abundance ratios of currently forming stars, or stars which form at a later time from a retained gas reservoir. Here we present hydrodynamical simulations that explore a wide range of cluster masses, compactnesses, metallicities and stellar population age combinations in order to determine the range of parameter space conducive to stellar wind retention or wind powered gas expulsion in star clusters. We discuss the effects of the stellar wind prescription on retention and expulsion effectiveness, using MESA stellar evolutionary models as a test bed for exploring how the amounts of wind retention/expulsion depend upon the amount of mixing between the winds from stars of different masses and ages. We conclude by summarizing some implications for gas retention and expulsion in a variety of compact (σv ≳ 20 kms-1) star clusters including young massive star clusters (105 ≲ M/M⊙ ≲ 107, age ≲ 500 Myrs), intermediate age clusters (105 ≲ M/M⊙ ≲ 107, age ≈ 1 - 4 Gyrs), and globular clusters (105 ≲ M/M⊙ ≲ 107, age ≳ 10 Gyrs).

  10. Massive Stars as Progenitors of Supernovae and GRBs

    NARCIS (Netherlands)

    Langer, N.; van Marle, A.J.; Poelarends, A.J.T.; Yoon, S.C.

    2007-01-01

    The evolutionary fate of massive stars in our Milky Way is thought to be reasonably well understood: stars above ˜ 8 M_o produce neutron stars and supernovae, while those above ˜ 20...30 M_o are presumed to form black holes. At metallicities below that of the SMC, however, our knowledge becomes

  11. Star Formation at the Galactic Center

    Science.gov (United States)

    Kohler, Susanna

    2015-08-01

    Could stars be forming in the inhospitable environment near Sagittarius A* in the heart of the Milky Way? A possible signature of low-mass star formation has recently been found just two light-years from the black hole at the center of our galaxy — a region that was previously thought to be too hostile for such activity. Searching for Signatures: Previous observations of the central few light-years of the Milky Way had focused on a population of about 200 massive, young and very bright stars in tight orbits around Sgr A*. These stars are only a few million years old and prompted scientists to wonder: have they somehow managed to form in situ, in spite of their close proximity to the black hole, or did they form further out and then migrate in? Motivated by this mystery, Farhad Yusef-Zadeh of Northwestern University and collaborators looked for evidence of even younger stars close to Sagittarius A*, which would demonstrate that star formation in the area is an ongoing process. Using the Very Large Array (VLA), the collaboration discovered several small sources in one arm of activity near Sgr A*. This 34-GHz image provides a close-up view of two protoplanetary disk candidates (labeled P26 and P8) located near Sgr A*. These objects are outlined on the right side by a bow shock caused by impacting stellar wind that streams from the young, hot stars closer to the Galactic center. The disks are thought to contain recently-formed, low-mass stars. (Credit: Yusef-Zadeh et al., 2015) Heated Disks: The team identified these sources as candidate photoevaporative protoplanetary disks, or “proplyds” — areas of dense, ionized gas and dust surrounding young, newly formed stars. The proplyd candidates are between 10,000 and 100,000 years old, and they lie along the edge of a large molecular cloud. It is likely that this cloud produced the disks by providing a reservoir of gas to feed the star-formation activity. The region surrounding these proplyds is blasted with harsh

  12. Metallicity dependence of envelope inflation in massive stars

    Czech Academy of Sciences Publication Activity Database

    Sanyal, D.; Langer, N.; Szécsi, Dorottya; Yoon, S.-C.; Grassitelli, L.

    2017-01-01

    Roč. 597, January (2017), A71/1-A71/16 E-ISSN 1432-0746 R&D Projects: GA ČR(CZ) GA14-02385S Institutional support: RVO:67985815 Keywords : stars evolution * stars massive * stars interiors Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.014, year: 2016

  13. Spiral Structure and Global Star Formation Processes in M 51

    Science.gov (United States)

    Gruendl, Robert A.

    1994-12-01

    The nearby grand design spiral galaxy, M 51, is an obvious proving ground for studies of spiral structure and large scale star formation processes. New near--infrared observations of M 51 made with COB (Cryogenic Optical Bench) on the Kitt Peak 1.3m allow us to examine the stellar distribution and the young star formation regions as well as probe regions of high extinction such as dust lanes. We also present an analysis of the kinematics of the ionized gas observed with the Maryland--Caltech Imaging Fabry Perot. The color information we derive from the near--infrared bands provides a more accurate tracer of extinction than optical observations. We find that the dust extinction and CO emission in the arms are well correlated. Our kinematic data show unambiguously that these dense gas concentrations are associated with kinematic perturbations. In the inner disk, these perturbations are seen to be consistent with the streaming motions predicted by classical density wave theory. The dust lanes, and presumably the molecular arms, form a narrow ridge that matches these velocity perturbations wherever the viewing angle is appropriate. This interpretation requires that the corotation radius be inward of the outer tidal arms. The outer tidal arms however show streaming velocities of the sign that would be expected interior to the corotation point. This can be reconciled if the outer arms are part of a second spiral pattern, most likely due to the interaction with the companion NGC 5195. The near--infrared observations also show emission from the massive star forming regions. These observations are less affected by extinction than optical observations of H II regions and show clearly that the sites of massive star formation are correlated with but downstream from the concentrations of dense molecular material. This provides clear evidence that the ISM has been organized by the streaming motions which have in turn triggered massive star formation.

  14. OGLE-2008-BLG-355Lb: A massive planet around a late-type star

    Energy Technology Data Exchange (ETDEWEB)

    Koshimoto, N.; Sumi, T.; Fukagawa, M.; Shibai, H. [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Udalski, A. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Bennett, D. P. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Bond, I. A.; Ling, C. H. [Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland (New Zealand); Rattenbury, N.; Botzler, C. S.; Freeman, M. [Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand); Abe, F.; Furusawa, K.; Itow, Y.; Masuda, K.; Matsubara, Y. [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, 464-8601 (Japan); Fukui, A. [Okayama Astrophysical Observatory, National Astronomical Observatory, 3037-5 Honjo, Kamogata, Asakuchi, Okayama 719-0232 (Japan); Muraki, Y. [Department of Physics, Konan University, Nishiokamoto 8-9-1, Kobe 658-8501 (Japan); Ohnishi, K. [Nagano National College of Technology, Nagano 381-8550 (Japan); Saito, To. [Tokyo Metropolitan College of Industrial Technology, Tokyo 116-8523 (Japan); Collaboration: MOA Collaboration; OGLE Collaboration; and others

    2014-06-20

    We report the discovery of a massive planet, OGLE-2008-BLG-355Lb. The light curve analysis indicates a planet:host mass ratio of q = 0.0118 ± 0.0006 at a separation of 0.877 ± 0.010 Einstein radii. We do not measure a significant microlensing parallax signal and do not have high angular resolution images that could detect the planetary host star. Therefore, we do not have a direct measurement of the host star mass. A Bayesian analysis, assuming that all host stars have equal probability to host a planet with the measured mass ratio, implies a host star mass of M{sub h}=0.37{sub −0.17}{sup +0.30} M{sub ⊙} and a companion of mass M{sub P}=4.6{sub −2.2}{sup +3.7}M{sub J}, at a projected separation of r{sub ⊥}=1.70{sub −0.30}{sup +0.29} AU. The implied distance to the planetary system is D {sub L} = 6.8 ± 1.1 kpc. A planetary system with the properties preferred by the Bayesian analysis may be a challenge to the core accretion model of planet formation, as the core accretion model predicts that massive planets are far more likely to form around more massive host stars. This core accretion model prediction is not consistent with our Bayesian prior of an equal probability of host stars of all masses to host a planet with the measured mass ratio. Thus, if the core accretion model prediction is right, we should expect that follow-up high angular resolution observations will detect a host star with a mass in the upper part of the range allowed by the Bayesian analysis. That is, the host would probably be a K or G dwarf.

  15. Asymmetric core collapse of rapidly rotating massive star

    Science.gov (United States)

    Gilkis, Avishai

    2018-02-01

    Non-axisymmetric features are found in the core collapse of a rapidly rotating massive star, which might have important implications for magnetic field amplification and production of a bipolar outflow that can explode the star, as well as for r-process nucleosynthesis and natal kicks. The collapse of an evolved rapidly rotating MZAMS = 54 M⊙ star is followed in three-dimensional hydrodynamic simulations using the FLASH code with neutrino leakage. A rotating proto-neutron star (PNS) forms with a non-zero linear velocity. This can contribute to the natal kick of the remnant compact object. The PNS is surrounded by a turbulent medium, where high shearing is likely to amplify magnetic fields, which in turn can drive a bipolar outflow. Neutron-rich material in the PNS vicinity might induce strong r-process nucleosynthesis. The rapidly rotating PNS possesses a rotational energy of E_rot ≳ 10^{52} erg. Magnetar formation proceeding in a similar fashion will be able to deposit a portion of this energy later on in the supernova ejecta through a spin-down mechanism. These processes can be important for rare supernovae generated by rapidly rotating progenitors, even though a complete explosion is not simulated in the present study.

  16. Chemical evolution, stellar nucleosynthesis and a variable star formation rate

    International Nuclear Information System (INIS)

    Olive, K.A.; Thielemann, F.K.; Truran, J.W.

    1986-04-01

    The effects of a decreasing star formation rate (SFR) on the galactic abundances of elements produced in massive stars (M ≥ 10 Msub solar). On the basis of a straightforward model of galactic evolution, a relation between the upper mass limit of type II supernovae (M/sub SN/) contributing to chemical evolution and the decline of the SFR (tau) is derived, when the oxygen abundance is determined only by massive stars. The additional requirement that all intermediate mass elements (Ne-Ti), which are also predominantly due to nucleosynthesis in massive stars, are produced in solar proportions leads to a unique value of M/sub SN/ and tau. The application of this method with abundance yields from Arnett (1978) and Woosley and Weaver (1986) resuults, however, in contradicting solutions: M/sub SN/ ≅ 45 Msub solar, tau = ∞, and M/sub SN/ ≅ 15 Msub solar, tau = 3 x 10 9 y. Thus, in order that this approach provide an effective probe of the SFR over the history of our galaxy it is essential that converging and more accurate predictions of the consequences of stellar and supernova nucleosynthesis will be forthcoming. 54 refs., 2 figs., 2 tabs

  17. B fields in OB stars (BOB): Low-resolution FORS2 spectropolarimetry of the first sample of 50 massive stars

    NARCIS (Netherlands)

    Fossati, L.; Castro, N.; Schöller, M.; Hubrig, S.; Langer, N.; Morel, T.; Briquet, M.; Herrero, A.; Przybilla, N.; Sana, H.; Schneider, F.R.N.; de Koter, A.

    2015-01-01

    Within the context of the collaboration "B fields in OB stars" (BOB), we used the FORS2 low-resolution spectropolarimeter to search for a magnetic field in 50 massive stars, including two reference magnetic massive stars. Because of the many controversies of magnetic field detections obtained with

  18. Physical characteristics of a dark cloud in an early stage of star formation toward NGC 7538 - An outer Galaxy infrared dark cloud?

    NARCIS (Netherlands)

    Frieswijk, W. W. F.; Spaans, M.; Shipman, R. F.; Teyssier, D.; Hily-Blant, P.

    2007-01-01

    Context. In the inner parts of the Galaxy the Infrared Dark Clouds (IRDCs) are presently believed to be the progenitors of massive stars and star clusters. Many of them are predominantly devoid of active star formation and for now they represent the earliest observed stages of massive star

  19. One of the most massive stars in the Galaxy may have formed in isolation

    OpenAIRE

    Oskinova, L. M.; Steinke, M.; Hamann, W. -R.; Sander, A.; Todt, H.; Liermann, A.

    2013-01-01

    Very massive stars, 100 times heavier than the sun, are rare. It is not yet known whether such stars can form in isolation or only in star clusters. The answer to this question is of fundamental importance. The central region of our Galaxy is ideal for investigating very massive stars and clusters located in the same environment. We used archival infrared images to investigate the surroundings of apparently isolated massive stars presently known in the Galactic Center. We find that two such i...

  20. The Evolution of Massive Stars: a Selection of Facts and Questions

    Science.gov (United States)

    Vanbeveren, D.

    In the present paper we discuss a selection of facts and questions related to observations and evolutionary calculations of massive single stars and massive stars in interacting binaries. We focus on the surface chemical abundances, the role of stellar winds, the early Be-stars, the high mass X-ray binaries and the effects of rotation on stellar evolution. Finally, we present an unconventionally formed object scenario (UFO-scenario) of WR binaries in dense stellar environments.

  1. A model for the origin of bursty star formation in galaxies

    Science.gov (United States)

    Faucher-Giguère, Claude-André

    2018-01-01

    We propose a simple analytic model to understand when star formation is time steady versus bursty in galaxies. Recent models explain the observed Kennicutt-Schmidt relation between star formation rate and gas surface densities in galaxies as resulting from a balance between stellar feedback and gravity. We argue that bursty star formation occurs when such an equilibrium cannot be stably sustained, and identify two regimes in which galaxy-scale star formation should be bursty: (i) at high redshift (z ≳ 1) for galaxies of all masses, and (ii) at low masses (depending on gas fraction) for galaxies at any redshift. At high redshift, characteristic galactic dynamical time-scales become too short for supernova feedback to effectively respond to gravitational collapse in galactic discs (an effect recently identified for galactic nuclei), whereas in dwarf galaxies star formation occurs in too few bright star-forming regions to effectively average out. Burstiness is also enhanced at high redshift owing to elevated gas fractions in the early Universe. Our model can thus explain the bursty star formation rates predicted in these regimes by recent high-resolution galaxy formation simulations, as well as the bursty star formation histories observationally inferred in both local dwarf and high-redshift galaxies. In our model, bursty star formation is associated with particularly strong spatiotemporal clustering of supernovae. Such clustering can promote the formation of galactic winds and our model may thus also explain the much higher wind mass loading factors inferred in high-redshift massive galaxies relative to their z ∼ 0 counterparts.

  2. X-RAY EMISSION FROM MAGNETIC MASSIVE STARS

    International Nuclear Information System (INIS)

    Nazé, Yaël; Petit, Véronique; Rinbrand, Melanie; Owocki, Stan; Cohen, David; Ud-Doula, Asif; Wade, Gregg A.

    2014-01-01

    Magnetically confined winds of early-type stars are expected to be sources of bright and hard X-rays. To clarify the systematics of the observed X-ray properties, we have analyzed a large series of Chandra and XMM-Newton observations, corresponding to all available exposures of known massive magnetic stars (over 100 exposures covering ∼60% of stars compiled in the catalog of Petit et al.). We show that the X-ray luminosity is strongly correlated with the stellar wind mass-loss rate, with a power-law form that is slightly steeper than linear for the majority of the less luminous, lower- M-dot B stars and flattens for the more luminous, higher- M-dot O stars. As the winds are radiatively driven, these scalings can be equivalently written as relations with the bolometric luminosity. The observed X-ray luminosities, and their trend with mass-loss rates, are well reproduced by new MHD models, although a few overluminous stars (mostly rapidly rotating objects) exist. No relation is found between other X-ray properties (plasma temperature, absorption) and stellar or magnetic parameters, contrary to expectations (e.g., higher temperature for stronger mass-loss rate). This suggests that the main driver for the plasma properties is different from the main determinant of the X-ray luminosity. Finally, variations of the X-ray hardnesses and luminosities, in phase with the stellar rotation period, are detected for some objects and they suggest that some temperature stratification exists in massive stars' magnetospheres

  3. The effect of photoionizing feedback on star formation in isolated and colliding clouds

    Science.gov (United States)

    Shima, Kazuhiro; Tasker, Elizabeth J.; Federrath, Christoph; Habe, Asao

    2018-05-01

    We investigate star formation occurring in idealized giant molecular clouds, comparing structures that evolve in isolation versus those undergoing a collision. Two different collision speeds are investigated and the impact of photoionizing radiation from the stars is determined. We find that a colliding system leads to more massive star formation both with and without the addition of feedback, raising overall star formation efficiencies (SFE) by a factor of 10 and steepening the high-mass end of the stellar mass function. This rise in SFE is due to increased turbulent compression during the cloud collision. While feedback can both promote and hinder star formation in an isolated system, it increases the SFE by approximately 1.5 times in the colliding case when the thermal speed of the resulting H II regions matches the shock propagation speed in the collision.

  4. Peering to the Heart of Massive Star Birth

    Science.gov (United States)

    Tan, Jonathan

    2015-10-01

    We propose a small survey of massive/intermediate-mass protostars with WFC3/IR to probe J and H band continuum emission, the Pa-beta and the [FeII] emission. The protostar sample is already the subject of approved SOFIA-FORCAST observations from 10-40 microns. Combined with sophisticated radiative transfer models, these observations are providing the most detailed constraints on the nature of massive protostars, their luminosities, outflow cavity structures and orientations, and distribution of surrounding dense core gas and dust. Recently, we were also awarded ALMA Cycle 3 time to study these sources at up to 0.14 resolution. The proposed HST observations, with very similar resolution, have three main goals: 1) Detect and characterize J and H band continuum emission from the massive/intermediate-mass protostars, which is expected to arise from jet and outflow knot features and from scattered light emerging from the outflow cavities; 2) Detect and characterize Pa-beta and [FeII] line emission tracing ionized and FUV-illuminated regions around the massive protostars, important diagnostics of the protostellar source and its outflow structure; 3) Search for lower-mass protostars that may be clustered around the forming massive protostar. All of these objectives will help test massive star formation theories. The high sensitivity and angular resolution of WFC3/IR enables these observations to be carried out efficiently in a timely fashion. Mid-Cycle observations are critical for near contemporaneous observation with ALMA, since jet/outflow knots may have large proper motions, and to maximize the potential time baseline for a future HST study of jet/outflow proper motions.

  5. MORPHOLOGICAL QUENCHING OF STAR FORMATION: MAKING EARLY-TYPE GALAXIES RED

    International Nuclear Information System (INIS)

    Martig, Marie; Bournaud, Frederic; Teyssier, Romain; Dekel, Avishai

    2009-01-01

    We point out a natural mechanism for quenching of star formation in early-type galaxies (ETGs). It automatically links the color of a galaxy with its morphology and does not require gas consumption, removal or termination of gas supply. Given that star formation takes place in gravitationally unstable gas disks, it can be quenched when a disk becomes stable against fragmentation to bound clumps. This can result from the growth of a stellar spheroid, for instance by mergers. We present the concept of morphological quenching (MQ) using standard disk instability analysis, and demonstrate its natural occurrence in a cosmological simulation using an efficient zoom-in technique. We show that the transition from a stellar disk to a spheroid can be sufficient to stabilize the gas disk, quench star formation, and turn an ETG red and dead while gas accretion continues. The turbulence necessary for disk stability can be stirred up by sheared perturbations within the disk in the absence of bound star-forming clumps. While other quenching mechanisms, such as gas stripping, active galactic nucleus feedback, virial shock heating, and gravitational heating are limited to massive halos, MQ can explain the appearance of red ETGs also in halos less massive than ∼10 12 M sun . The dense gas disks observed in some of today's red ellipticals may be the relics of this mechanism, whereas red galaxies with quenched gas disks could be more frequent at high redshift.

  6. Profiles of the stochastic star formation process in spiral galaxies

    International Nuclear Information System (INIS)

    Comins, N.

    1981-01-01

    The formation of spiral arms in disc galaxies is generally attributed to the effects of spiral density waves. These relatively small (i.e. 5 per cent) non-axisymmetric perturbations of the interstellar medium cause spiral arms highlighted by O and B type stars to be created. In this paper another mechanism for spiral arm formation, the stochastic self-propagating star formation (SSPSF) process is examined. The SSPSF process combines the theory that shock waves from supernovae will compress the interstellar medium to create new stars, some of which will be massive enough to also supernova, with a disc galaxy's differential rotation to create spiral arms. The present work extends this process to the case where the probability of star formation from supernova shocks decreases with galactic radius. Where this work and previous investigations overlap (namely the uniform probability case), the agreement is very good, pretty spirals with various numbers of arms are generated. The decreasing probability cases, taken to vary as rsup(-j), still form spiral arms for 0 1.5 the spiral structure is essentially non-existent. (author)

  7. Massive stars on the verge of exploding: the properties of oxygen sequence Wolf-Rayet stars

    NARCIS (Netherlands)

    Tramper, F.; Straal, S.M.; Sanyal, D.; Sana, H.; de Koter, A.; Gräfener, G.; Langer, N.; Vink, J.S.; de Mink, S.E.; Kaper, L.

    2015-01-01

    Context. Oxygen sequence Wolf-Rayet (WO) stars are a very rare stage in the evolution of massive stars. Their spectra show strong emission lines of helium-burning products, in particular highly ionized carbon and oxygen. The properties of WO stars can be used to provide unique constraints on the

  8. High-precision atmospheric parameter and abundance determination of massive stars, and consequences for stellar and Galactic evolution

    International Nuclear Information System (INIS)

    Nieva, Maria-Fernanda; Przybilla, Norbert; Irrgang, Andreas

    2011-01-01

    The derivation of high precision/accuracy parameters and chemical abundances of massive stars is of utmost importance to the fields of stellar evolution and Galactic chemical evolution. We concentrate on the study of OB-type stars near the main sequence and their evolved progeny, the BA-type supergiants, covering masses of ∼6 to 25 solar masses and a range in effective temperature from ∼8000 to 35 000 K. The minimization of the main sources of systematic errors in the atmospheric model computation, the observed spectra and the quantitative spectral analysis play a critical role in the final results. Our self-consistent spectrum analysis technique employing a robust non-LTE line formation allows precise atmospheric parameters of massive stars to be derived, achieving 1σ-uncertainties as low as 1% in effective temperature and ∼0.05–0.10 dex in surface gravity. Consequences on the behaviour of the chemical elements carbon, nitrogen and oxygen are discussed here in the context of massive star evolution and Galactic chemical evolution, showing tight relations covered in previous work by too large statistical and systematic uncertainties. The spectral analysis of larger star samples, like from the upcoming Gaia-ESO survey, may benefit from these findings.

  9. FAKE STAR FORMATION BURSTS: BLUE HORIZONTAL BRANCH STARS MASQUERADE AS YOUNG MASSIVE STARS IN OPTICAL INTEGRATED LIGHT SPECTROSCOPY

    International Nuclear Information System (INIS)

    Ocvirk, P.

    2010-01-01

    Model color-magnitude diagrams of low-metallicity globular clusters (GCs) usually show a deficit of hot evolved stars with respect to observations. We investigate quantitatively the impact of such modeling inaccuracies on the significance of star formation history reconstructions obtained from optical integrated spectra. To do so, we analyze the sample of spectra of galactic globular clusters of Schiavon et al. with STECKMAP (Ocvirk et al.), and the stellar population models of Vazdekis et al. and Bruzual and Charlot, and focus on the reconstructed stellar age distributions. First, we show that background/foreground contamination correlates with E(B - V), which allows us to define a clean subsample of uncontaminated GCs, on the basis of an E(B - V) filtering. We then identify a 'confusion zone' where fake young bursts of star formation pop up in the star formation history although the observed population is genuinely old. These artifacts appear for 70%-100% of cases depending on the population model used, and contribute up to 12% of the light in the optical. Their correlation with the horizontal branch (HB) ratio indicates that the confusion is driven by HB morphology: red HB clusters are well fitted by old stellar population models while those with a blue HB require an additional hot component. The confusion zone extends over [Fe/H] = [ - 2, - 1.2], although we lack the data to probe extreme high and low metallicity regimes. As a consequence, any young starburst superimposed on an old stellar population in this metallicity range could be regarded as a modeling artifact, if it weighs less than 12% of the optical light, and if no emission lines typical of an H II region are present. This work also provides a practical method for constraining HB morphology from high signal to noise integrated light spectroscopy in the optical. This will allow post-asymptotic giant branch evolution studies in a range of environments and at distances where resolving stellar populations

  10. HOW TO FIND YOUNG MASSIVE CLUSTER PROGENITORS

    Energy Technology Data Exchange (ETDEWEB)

    Bressert, E.; Longmore, S.; Testi, L. [European Southern Observatory, Karl Schwarzschild Str. 2, D-85748 Garching bei Muenchen (Germany); Ginsburg, A.; Bally, J.; Battersby, C. [Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309 (United States)

    2012-10-20

    We propose that bound, young massive stellar clusters form from dense clouds that have escape speeds greater than the sound speed in photo-ionized gas. In these clumps, radiative feedback in the form of gas ionization is bottled up, enabling star formation to proceed to sufficiently high efficiency so that the resulting star cluster remains bound even after gas removal. We estimate the observable properties of the massive proto-clusters (MPCs) for existing Galactic plane surveys and suggest how they may be sought in recent and upcoming extragalactic observations. These surveys will potentially provide a significant sample of MPC candidates that will allow us to better understand extreme star-formation and massive cluster formation in the Local Universe.

  11. Star & Planet Formation Studies and Opportunities with SOFIA

    Science.gov (United States)

    Smith, Kimberly Ennico

    2018-01-01

    Star formation, the most fundamental process in the universe, is linked to planet formation and thus to the origin and evolution of life. We have a general outline of how planets and stars form, yet unraveling the details of the physics and chemistry continues to challenge us. The infrared and submillimeter part of the spectrum hold the most promise for studying the beginnings of star formation. The observational landscape recently shaped by Spitzer, Herschel and ALMA, continues to challenge our current theories. SOFIA, the Stratospheric Observatory for Infrared Astronomy, equipped with state-of-the-art infrared instrumentation to a vantage point at 45,000 feet (13.7 kilometers) flight altitude that is above 99.9 percent of the Earth's water vapor, enables observations in the infrared through terahertz frequencies not possible from the ground. SOFIA is a community observatory, about to start its sixth annual observing cycle. My talk will focus on recent results in advancing star and planet formation processes using SOFIA's imaging and polarimetric capabilities, and the upcoming science enabled by the 3rd generation instrument High-Resolution Mid-Infrared Spectrometer (HIRMES) to be commissioned in 2019. I will show how mid-infrared imaging is used to test massive star formation theories, how far-infrared polarimetry on sub-parsec scales is directly testing the role of magnetic fields in molecular clouds, and how velocity-resolved high-resolution spectroscopy will push forward our understanding of proto-planetary disk science. I will also summarize upcoming opportunities with the SOFIA observatory. For the latest news about your flying observatory, see https://sofia.usra.edu/.

  12. THE FORMATION OF SECONDARY STELLAR GENERATIONS IN MASSIVE YOUNG STAR CLUSTERS FROM RAPIDLY COOLING SHOCKED STELLAR WINDS

    Energy Technology Data Exchange (ETDEWEB)

    Wünsch, R.; Palouš, J.; Ehlerová, S. [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague (Czech Republic); Tenorio-Tagle, G. [Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla, México (Mexico)

    2017-01-20

    We study a model of rapidly cooling shocked stellar winds in young massive clusters and estimate the circumstances under which secondary star formation, out of the reinserted winds from a first stellar generation (1G), is possible. We have used two implementations of the model: a highly idealized, computationally inexpensive, spherically symmetric semi-analytic model, and a complex, three-dimensional radiation-hydrodynamic, simulation; they are in a good mutual agreement. The results confirm our previous findings that, in a cluster with 1G mass 10{sup 7} M {sub ⊙} and half-mass–radius 2.38 pc, the shocked stellar winds become thermally unstable, collapse into dense gaseous structures that partially accumulate inside the cluster, self-shield against ionizing stellar radiation, and form the second generation (2G) of stars. We have used the semi-analytic model to explore a subset of the parameter space covering a wide range of the observationally poorly constrained parameters: the heating efficiency, η {sub he}, and the mass loading, η {sub ml}. The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if η {sub he} ≲ 10%, which is suggested by the observations. Furthermore, for low η {sub he}, the model provides a self-consistent mechanism predicting 2G stars forming only in the central zones of the cluster. Finally, we have calculated the accumulated warm gas emission in the H30 α recombination line, analyzed its velocity profile, and estimated its intensity for super star clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas should be detectable with ALMA.

  13. Massive stars in colliding wind systems: the GLAST perspective

    International Nuclear Information System (INIS)

    Reimer, Anita; Reimer, Olaf

    2007-01-01

    Colliding winds of massive stars in binary systems arc considered as candidate sites of high-energy non-thermal photon emission. They are already among the suggested counterparts for a few individual unidentified EGRET sources, but may constitute a detectable source population for the GLAST observatory.The present work investigates such population study of massive colliding wind systems at high-energy gamma-rays. Based on the recent detailed model (Reimer et al. 2006) for non-thermal photon production in prime candidate systems, we unveil the expected characteristics of this source class in the observables accessible at LAT energies. Combining the broadband emission model with the presently cataloged distribution of such systems and their individual parameters allows us to conclude on the expected maximum number of LAT-detections among massive stars in colliding wind binary systems

  14. How the First Stars Regulated Star Formation. II. Enrichment by Nearby Supernovae

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Ke-Jung [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Tokyo 181-8588 (Japan); Whalen, Daniel J. [Institute of Cosmology and Gravitation, Portsmouth University, Portsmouth (United Kingdom); Wollenberg, Katharina M. J.; Glover, Simon C. O.; Klessen, Ralf S., E-mail: ken.chen@nao.ac.jp [Zentrum für Astronomie, Institut für Theoretische Astrophysik, Universität Heidelberg (Germany)

    2017-08-01

    Metals from Population III (Pop III) supernovae led to the formation of less massive Pop II stars in the early universe, altering the course of evolution of primeval galaxies and cosmological reionization. There are a variety of scenarios in which heavy elements from the first supernovae were taken up into second-generation stars, but cosmological simulations only model them on the largest scales. We present small-scale, high-resolution simulations of the chemical enrichment of a primordial halo by a nearby supernova after partial evaporation by the progenitor star. We find that ejecta from the explosion crash into and mix violently with ablative flows driven off the halo by the star, creating dense, enriched clumps capable of collapsing into Pop II stars. Metals may mix less efficiently with the partially exposed core of the halo, so it might form either Pop III or Pop II stars. Both Pop II and III stars may thus form after the collision if the ejecta do not strip all the gas from the halo. The partial evaporation of the halo prior to the explosion is crucial to its later enrichment by the supernova.

  15. Effects of Combined Stellar Feedback on Star Formation in Stellar Clusters

    Science.gov (United States)

    Wall, Joshua Edward; McMillan, Stephen; Pellegrino, Andrew; Mac Low, Mordecai; Klessen, Ralf; Portegies Zwart, Simon

    2018-01-01

    We present results of hybrid MHD+N-body simulations of star cluster formation and evolution including self consistent feedback from the stars in the form of radiation, winds, and supernovae from all stars more massive than 7 solar masses. The MHD is modeled with the adaptive mesh refinement code FLASH, while the N-body computations are done with a direct algorithm. Radiation is modeled using ray tracing along long characteristics in directions distributed using the HEALPIX algorithm, and causes ionization and momentum deposition, while winds and supernova conserve momentum and energy during injection. Stellar evolution is followed using power-law fits to evolution models in SeBa. We use a gravity bridge within the AMUSE framework to couple the N-body dynamics of the stars to the gas dynamics in FLASH. Feedback from the massive stars alters the structure of young clusters as gas ejection occurs. We diagnose this behavior by distinguishing between fractal distribution and central clustering using a Q parameter computed from the minimum spanning tree of each model cluster. Global effects of feedback in our simulations will also be discussed.

  16. Rates of star formation

    International Nuclear Information System (INIS)

    Larson, R.B.

    1977-01-01

    It is illustrated that a theoretical understanding of the formation and evolution of galaxies depends on an understanding of star formation, and especially of the factors influencing the rate of star formation. Some of the theoretical problems of star formation in galaxies, some approaches that have been considered in models of galaxy evolution, and some possible observational tests that may help to clarify which processes or models are most relevant are reviewed. The material is presented under the following headings: power-law models for star formation, star formation processes (conditions required, ways of achieving these conditions), observational indications and tests, and measures of star formation rates in galaxies. 49 references

  17. STAR FORMATION AT 4 < z < 6 FROM THE SPITZER LARGE AREA SURVEY WITH HYPER-SUPRIME-CAM (SPLASH)

    Energy Technology Data Exchange (ETDEWEB)

    Steinhardt, Charles L.; Capak, Peter; Masters, Dan; Petric, Andreea [Caltech, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Speagle, Josh S.; Silverman, John D. [Kavli IPMU, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi, Chiba 277-8583 (Japan); Carollo, Marcella [ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich (Switzerland); Dunlop, James [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Hashimoto, Yasuhiro [National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Rd., Taipei 11677, Taiwan R.O.C. (China); Hsieh, Bau-Ching; Lin, Lihwai; Lin, Yen-Ting [ASIAA Sinica, AS/NTU. No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan, R.O.C. (China); Ilbert, Olivier; Le Fevre, Olivier [Laboratoire d' Astrophysique de Marseille, 38 rue Frederic Joliot Curie, F-13388 Marseille (France); Le Floc' h, Emeric [Service d' Astrophysique, CEA-Saclay, Orme des Merisiers, Bat. 709, F-91191 Gif-sur-Yvette (France); Lee, Nicholas; Sanders, Dave [Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); McCracken, Henry J. [Institut d' Astrophysique de Paris, 98 bis boulevard Arago, F-75014 Paris (France); Nagao, Tohru [Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan); Salvato, Mara [Max Planck Institute for Extraterrestrial Physics (MPE), Giessenbachstr. 1, D-85748 Garching (Germany); and others

    2014-08-20

    Using the first 50% of data collected for the Spitzer Large Area Survey with Hyper-Suprime-Cam observations on the 1.8 deg{sup 2} Cosmological Evolution Survey we estimate the masses and star formation rates of 3398 M {sub *} > 10{sup 10} M {sub ☉} star-forming galaxies at 4 < z < 6 with a substantial population up to M {sub *} ≳ 10{sup 11.5} M {sub ☉}. We find that the strong correlation between stellar mass and star formation rate seen at lower redshift (the ''main sequence'' of star-forming galaxies) extends to z ∼ 6. The observed relation and scatter is consistent with a continued increase in star formation rate at fixed mass in line with extrapolations from lower-redshift observations. It is difficult to explain this continued correlation, especially for the most massive systems, unless the most massive galaxies are forming stars near their Eddington-limited rate from their first collapse. Furthermore, we find no evidence for moderate quenching at higher masses, indicating quenching either has not occurred prior to z ∼ 6 or else occurs rapidly, so that few galaxies are visible in transition between star-forming and quenched.

  18. Massive Star Clusters in Ongoing Galaxy Interactions: Clues to Cluster Formation

    Science.gov (United States)

    Keel, William C.; Borne, Kirk D.

    2003-09-01

    We present HST WFPC2 observations, supplemented by ground-based Hα data, of the star-cluster populations in two pairs of interacting galaxies selected for being in very different kinds of encounters seen at different stages. Dynamical information and n-body simulations provide the details of encounter geometry, mass ratio, and timing. In NGC 5752/4 we are seeing a weak encounter, well past closest approach, after about 2.5×108 yr. The large spiral NGC 5754 has a normal population of disk clusters, while the fainter companion NGC 5752 exhibits a rich population of luminous clusters with a flatter luminosity function. The strong, ongoing encounter in NGC 6621/2, seen about 1.0×108 yr past closest approach between roughly equal-mass galaxies, has produced an extensive population of luminous clusters, particularly young and luminous in a small region between the two nuclei. This region is dynamically interesting, with such a strong perturbation in the velocity field that the rotation curve reverses sign. From these results, in comparison with other strongly interacting systems discussed in the literature, cluster formation requires a threshold level of perturbation, with stage of the interaction a less important factor. The location of the most active star formation in NGC 6621/2 draws attention to a possible role for the Toomre stability threshold in shaping star formation in interacting galaxies. The rich cluster populations in NGC 5752 and NGC 6621 show that direct contact between gas-rich galaxy disks is not a requirement to form luminous clusters and that they can be triggered by processes happening within a single galaxy disk (albeit triggered by external perturbations). Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  19. Modeling UV Radiation Feedback from Massive Stars. II. Dispersal of Star-forming Giant Molecular Clouds by Photoionization and Radiation Pressure

    Science.gov (United States)

    Kim, Jeong-Gyu; Kim, Woong-Tae; Ostriker, Eve C.

    2018-05-01

    UV radiation feedback from young massive stars plays a key role in the evolution of giant molecular clouds (GMCs) by photoevaporating and ejecting the surrounding gas. We conduct a suite of radiation hydrodynamic simulations of star cluster formation in marginally bound, turbulent GMCs, focusing on the effects of photoionization and radiation pressure on regulating the net star formation efficiency (SFE) and cloud lifetime. We find that the net SFE depends primarily on the initial gas surface density, Σ0, such that the SFE increases from 4% to 51% as Σ0 increases from 13 to 1300 {M}ȯ {pc}}-2. Cloud destruction occurs within 2–10 Myr after the onset of radiation feedback, or within 0.6–4.1 freefall times (increasing with Σ0). Photoevaporation dominates the mass loss in massive, low surface density clouds, but because most photons are absorbed in an ionization-bounded Strömgren volume, the photoevaporated gas fraction is proportional to the square root of the SFE. The measured momentum injection due to thermal and radiation pressure forces is proportional to {{{Σ }}}0-0.74, and the ejection of neutrals substantially contributes to the disruption of low mass and/or high surface density clouds. We present semi-analytic models for cloud dispersal mediated by photoevaporation and by dynamical mass ejection, and show that the predicted net SFE and mass loss efficiencies are consistent with the results of our numerical simulations.

  20. Star-Formation in Free-Floating Evaporating Gaseous Globules

    Science.gov (United States)

    Sahai, Raghvendra

    2017-08-01

    We propose to study the stellar embryos in select members of a newly recognized class of Free-floating Evaporating Gaseous Globules (frEGGS) embedded in HII regions and having head-tail shapes. We discovered two of these in the Cygnus massive star-forming region (MSFR) with HST, including one of the most prominent members of this class (IRAS20324). Subsequent archival searches of Spitzer imaging of MSFRs has allowed us to build a statistical sample of frEGGs. Our molecular-line observations show the presence of dense molecular cores with total gas masses of (0.5-few) Msun in these objects, and our radio continuum images and Halpha images (from the IPHAS survey) reveal bright photo-ionized peripheries around these objects. We hypothesize that frEGGs are density concentrations originating in giant molecular clouds, that, when subject to the sculpting and compression by strong winds and UV radiation from massive stars, become active star-forming cores. For the 4 frEGGs with HST or near-IR AO images showing young stars and bipolar cavities produced by their jets or collimated outflows, the symmetry axis points roughly toward the external ionizing star or star cluster - exciting new evidence for our overpressure-induced star formation hypothesis. We propose to test this hypothesis by imaging 24 frEGGs in two nearby MSFRs that represent different radiation-dominated environments. Using ACS imaging with filters F606W, F814W, & F658N (Ha+[NII]), we will search for jets and outflow-excavated cavities, investigate the stellar nurseries inside frEGGs, and determine whether the globules are generally forming multiple star systems or small clusters, as in IRAS20324.

  1. The E-MOSAICS project: simulating the formation and co-evolution of galaxies and their star cluster populations

    Science.gov (United States)

    Pfeffer, Joel; Kruijssen, J. M. Diederik; Crain, Robert A.; Bastian, Nate

    2018-04-01

    We introduce the MOdelling Star cluster population Assembly In Cosmological Simulations within EAGLE (E-MOSAICS) project. E-MOSAICS incorporates models describing the formation, evolution, and disruption of star clusters into the EAGLE galaxy formation simulations, enabling the examination of the co-evolution of star clusters and their host galaxies in a fully cosmological context. A fraction of the star formation rate of dense gas is assumed to yield a cluster population; this fraction and the population's initial properties are governed by the physical properties of the natal gas. The subsequent evolution and disruption of the entire cluster population are followed accounting for two-body relaxation, stellar evolution, and gravitational shocks induced by the local tidal field. This introductory paper presents a detailed description of the model and initial results from a suite of 10 simulations of ˜L⋆ galaxies with disc-like morphologies at z = 0. The simulations broadly reproduce key observed characteristics of young star clusters and globular clusters (GCs), without invoking separate formation mechanisms for each population. The simulated GCs are the surviving population of massive clusters formed at early epochs (z ≳ 1-2), when the characteristic pressures and surface densities of star-forming gas were significantly higher than observed in local galaxies. We examine the influence of the star formation and assembly histories of galaxies on their cluster populations, finding that (at similar present-day mass) earlier-forming galaxies foster a more massive and disruption-resilient cluster population, while galaxies with late mergers are capable of forming massive clusters even at late cosmic epochs. We find that the phenomenological treatment of interstellar gas in EAGLE precludes the accurate modelling of cluster disruption in low-density environments, but infer that simulations incorporating an explicitly modelled cold interstellar gas phase will overcome

  2. Star Formation in M 33 (HerM33es)

    Science.gov (United States)

    Kramer, C.; Boquien, M.; Braine, J.; Buchbender, C.; Calzetti, D.; Gratier, P.; Mookerjea, B.; Relaño, M.; Verley, S.

    2011-11-01

    Within the key project "Herschel M 33 extended survey" (HerM33es), we are studying the physical and chemical processes driving star formation and galactic evolution in the nearby galaxy M 33, combining the study of local conditions affecting individual star formation with properties only becoming apparent on global scales. Here, we present recent results obtained by the HerM33es team. Combining Spitzer and Herschel data ranging from 3.6 μm to 500μm, along with H i, Hα, and GALEX UV data, we have studied the dust at high spatial resolutions of 150 pc, providing estimators of the total infrared (TIR) brightness and of the star formation rate. While the temperature of the warm dust at high brightness is driven by young massive stars, evolved stellar populations appear to drive the temperature of the cold dust. Plane-parallel models of photon dominated regions (PDRs) fail to reproduce fully the [C ii], [O i], and CO maps obtained in a first spectroscopic study of one 2' × 2' subregion of M 33, located on the inner, northern spiral arm and encompassing the H ii region BCLMP 302.

  3. Massive stars dying alone: Extremely remote environments of SN2009ip and SN2010jp

    Science.gov (United States)

    Smith, Nathan

    2014-10-01

    We propose an imaging study of the astonishingly remote environments of two recent supernovae (SNe): SN2009ip and SN2010jp. Both were unusual Type IIn explosions that crashed into dense circumstellar material (CSM) ejected by the star shortly before explosion. The favored progenitors of these SNe are very massive luminous blue variable (LBV) stars. In fact, SN2009ip presents an extraordinay case where the LBV-like progenitor was actually detected directly in archival HST data, and where we obtained spectra and photometry for numerous pre-SN eruptions. No other SN has this treasure trove of detailed information about the progenitor (not even SN1987A). SN2010jp represents a possible collapsar-powered event, since it showed evidence of a fast bipolar jet in spectra and a low 56Ni mass; this would be an analog of the black-hole forming explosions that cause gamma ray bursts, but where the relativistic jet is damped by a residual H envelope on the star. In both cases, the only viable models for these SNe involve extremely massive (initial masses of 40-100 Msun) progenitor stars. This seems at odds with their extremely remote environments in the far outskirts of their host galaxies, with no detected evidence for an underlying massive star population in ground-based data (nor in the single shallow WFPC2/F606W image of SN2009ip). Here we propose deep UV HST images to search for any mid/late O-type stars nearby, deep red images to detect any red supergiants, and an H-alpha image to search for any evidence of ongoing star formation in the vicinity. These observations will place important and demanding constraints on the initial masses and ages of these progenitors.

  4. Late stages of massive star evolution and nucleosynthesis

    International Nuclear Information System (INIS)

    Nomoto, Ken'ichi; Hashimoto, Masa-aki.

    1986-01-01

    The evolution of massive stars in the mass range of 8 to 25 M solar mass is reviewed. The effect of electron degeneracy on the gravothermal nature of stars is discussed. Depending on the stellar mass, the stars form three types of cores, namely, non-degenerate, semi-degenerate, and strongly degenerate cores. The evolution for these cases is quite distinct from each other and leads to the three different types of final fate. It is suggested that our helium star model, which is equivalent to a 25 M solar mass star, will form a relatively small mass iron core despite the faster 12 C(α,γ) 16 O reaction. 50 refs., 21 figs

  5. Star formation and galactic evolution. I. General expressions and applications to our galaxy

    International Nuclear Information System (INIS)

    Kaufman, M.

    1979-01-01

    The study of galactic evolution involves three mechanisms for triggering star formation in interstellar clouds: (i) star formation triggered by a galactic spiral density wave, (ii) star formation triggered by shock waves from supernovae, and (iii) star formation triggered by an expanding H II region. Useful analytic approximations to the birthrate per unit mass are obtained by treating the efficiencies of these various mechanisms as time independent. In situations where shock waves from high-mass stars (either expanding H II regions or supernova explosions) are the only important star-forming mechanisms, the birthrate is exponential in time. This case is appropriate for the past evolution of an elliptical galaxy, nuclear bulge, or galactic halo. In the disk of a spiral galaxy where all three mechanisms operate, the birthrate consists of an exponential term plus a time-independent term. In both situations, the value of the time constant T in the exponential term is directly related to the efficiency of the shock waves from massive stars in initiating star formation.For our Galaxy, this simplified model is used to compute the radial distributions of young objects and low-mass stars in the disk, and the past and present birthrates in the solar-neighborhood shell

  6. Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

    NARCIS (Netherlands)

    Schneider, F.R.N.; Izzard, R.G.; de Mink, S.E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V.V.; Huβman, B.; Liermann, A.; Sana, H.

    2014-01-01

    Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass

  7. LoCuSS: THE STEADY DECLINE AND SLOW QUENCHING OF STAR FORMATION IN CLUSTER GALAXIES OVER THE LAST FOUR BILLION YEARS

    International Nuclear Information System (INIS)

    Haines, C. P.; Pereira, M. J.; Egami, E.; Rawle, T. D.; Smith, G. P.; Sanderson, A. J. R.; Babul, A.; Finoguenov, A.; Merluzzi, P.; Busarello, G.; Okabe, N.

    2013-01-01

    We present an analysis of the levels and evolution of star formation activity in a representative sample of 30 massive galaxy clusters at 0.15 or approx. 10 10 M ☉ ) star-forming cluster galaxies within r 200 are found to be systematically ∼28% lower than their counterparts in the field at fixed stellar mass and redshift, a difference significant at the 8.7σ level. This is the unambiguous signature of star formation in most (and possibly all) massive star-forming galaxies being slowly quenched upon accretion into massive clusters, their star formation rates (SFRs) declining exponentially on quenching timescales in the range 0.7-2.0 Gyr. We measure the mid-infrared Butcher-Oemler effect over the redshift range 0.0-0.4, finding rapid evolution in the fraction (f SF ) of massive (M K 200 with SFRs > 3 M ☉ yr –1 , of the form f SF ∝(1 + z) 7.6±1.1 . We dissect the origins of the Butcher-Oemler effect, revealing it to be due to the combination of a ∼3 × decline in the mean specific SFRs of star-forming cluster galaxies since z ∼ 0.3 with a ∼1.5 × decrease in number density. Two-thirds of this reduction in the specific SFRs of star-forming cluster galaxies is due to the steady cosmic decline in the specific SFRs among those field galaxies accreted into the clusters. The remaining one-third reflects an accelerated decline in the star formation activity of galaxies within clusters. The slow quenching of star formation in cluster galaxies is consistent with a gradual shut down of star formation in infalling spiral galaxies as they interact with the intracluster medium via ram-pressure stripping or starvation mechanisms. The observed sharp decline in star formation activity among cluster galaxies since z ∼ 0.4 likely reflects the increased susceptibility of low-redshift spiral galaxies to gas removal mechanisms as their gas surface densities decrease with time. We find no evidence for the build-up of cluster S0 bulges via major nuclear starburst

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

    Science.gov (United States)

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

    1991-01-01

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

  9. X-ray sources in regions of star formation. II. The pre-main-sequence G star HDE 283572

    International Nuclear Information System (INIS)

    Walter, F.M.; Brown, A.; Linsky, J.L.; Rydgren, A.E.; Vrba, F.; Joint Institute for Laboratory Astrophysics, Boulder, CO; Computer Sciences Corp., El Segundo, CA; Naval Observatory, Flagstaff, AZ)

    1987-01-01

    This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a naked T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars. 49 references

  10. Gravitational waves from remnant massive neutron stars of binary neutron star merger: Viscous hydrodynamics effects

    Science.gov (United States)

    Shibata, Masaru; Kiuchi, Kenta

    2017-06-01

    Employing a simplified version of the Israel-Stewart formalism of general-relativistic shear-viscous hydrodynamics, we explore the evolution of a remnant massive neutron star of binary neutron star merger and pay special attention to the resulting gravitational waveforms. We find that for the plausible values of the so-called viscous alpha parameter of the order 10-2 the degree of the differential rotation in the remnant massive neutron star is significantly reduced in the viscous time scale, ≲5 ms . Associated with this, the degree of nonaxisymmetric deformation is also reduced quickly, and as a consequence, the amplitude of quasiperiodic gravitational waves emitted also decays in the viscous time scale. Our results indicate that for modeling the evolution of the merger remnants of binary neutron stars we would have to take into account magnetohydrodynamics effects, which in nature could provide the viscous effects.

  11. The role of turbulence in star formation laws and thresholds

    Energy Technology Data Exchange (ETDEWEB)

    Kraljic, Katarina; Renaud, Florent; Bournaud, Frédéric [CEA, IRFU, SAp, F-91191 Gif-sur-Yvette Cedex (France); Combes, Françoise [Observatoire de Paris, LERMA et CNRS, 61 Av de l' Observatoire, F-75014 Paris (France); Elmegreen, Bruce [IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States); Emsellem, Eric [European Southern Observatory, D-85748 Garching bei Muenchen (Germany); Teyssier, Romain [Institute for Theoretical Physics, University of Zürich, CH-8057 Zürich (Switzerland)

    2014-04-01

    The Schmidt-Kennicutt relation links the surface densities of gas to the star formation rate in galaxies. The physical origin of this relation, and in particular its break, i.e., the transition between an inefficient regime at low gas surface densities and a main regime at higher densities, remains debated. Here, we study the physical origin of the star formation relations and breaks in several low-redshift galaxies, from dwarf irregulars to massive spirals. We use numerical simulations representative of the Milky Way and the Large and Small Magellanic Clouds with parsec up to subparsec resolution, and which reproduce the observed star formation relations and the relative variations of the star formation thresholds. We analyze the role of interstellar turbulence, gas cooling, and geometry in drawing these relations at 100 pc scale. We suggest in particular that the existence of a break in the Schmidt-Kennicutt relation could be linked to the transition from subsonic to supersonic turbulence and is independent of self-shielding effects. With this transition being connected to the gas thermal properties and thus to the metallicity, the break is shifted toward high surface densities in metal-poor galaxies, as observed in dwarf galaxies. Our results suggest that together with the collapse of clouds under self-gravity, turbulence (injected at galactic scale) can induce the compression of gas and regulate star formation.

  12. The role of turbulence in star formation laws and thresholds

    International Nuclear Information System (INIS)

    Kraljic, Katarina; Renaud, Florent; Bournaud, Frédéric; Combes, Françoise; Elmegreen, Bruce; Emsellem, Eric; Teyssier, Romain

    2014-01-01

    The Schmidt-Kennicutt relation links the surface densities of gas to the star formation rate in galaxies. The physical origin of this relation, and in particular its break, i.e., the transition between an inefficient regime at low gas surface densities and a main regime at higher densities, remains debated. Here, we study the physical origin of the star formation relations and breaks in several low-redshift galaxies, from dwarf irregulars to massive spirals. We use numerical simulations representative of the Milky Way and the Large and Small Magellanic Clouds with parsec up to subparsec resolution, and which reproduce the observed star formation relations and the relative variations of the star formation thresholds. We analyze the role of interstellar turbulence, gas cooling, and geometry in drawing these relations at 100 pc scale. We suggest in particular that the existence of a break in the Schmidt-Kennicutt relation could be linked to the transition from subsonic to supersonic turbulence and is independent of self-shielding effects. With this transition being connected to the gas thermal properties and thus to the metallicity, the break is shifted toward high surface densities in metal-poor galaxies, as observed in dwarf galaxies. Our results suggest that together with the collapse of clouds under self-gravity, turbulence (injected at galactic scale) can induce the compression of gas and regulate star formation.

  13. A CATALOG OF NEW SPECTROSCOPICALLY CONFIRMED MASSIVE OB STARS IN CARINA

    Energy Technology Data Exchange (ETDEWEB)

    Alexander, Michael J.; Hanes, Richard J.; McSwain, M. Virginia [Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, PA 18015 (United States); Povich, Matthew S., E-mail: alexamic@lafayette.edu, E-mail: rjh314@lehigh.edu, E-mail: mcswain@lehigh.edu, E-mail: mspovich@cpp.edu [Department of Physics and Astronomy, California State Polytechnic University, Pomona, CA 91768 (United States)

    2016-12-01

    The Carina star-forming region is one of the largest in the Galaxy, and its massive star population is still being unveiled. The large number of stars combined with high, and highly variable, interstellar extinction makes it inherently difficult to find OB stars in this type of young region. We present the results of a spectroscopic campaign to study the massive star population of the Carina Nebula, with the primary goal to confirm or reject previously identified Carina OB star candidates. A total of 141 known O- and B-type stars and 94 candidates were observed, of which 73 candidates had high enough signal-to-noise ratio to classify. We find 23 new OB stars within the Carina Nebula, a 32% confirmation rate. One of the new OB stars has blended spectra and is suspected to be a double-lined spectroscopic binary (SB2). We also reclassify the spectral types of the known OB stars and discover nine new SB2s among this population. Finally, we discuss the spatial distribution of these new OB stars relative to known structures in the Carina Nebula.

  14. Supersonic gas streams enhance the formation of massive black holes in the early universe.

    Science.gov (United States)

    Hirano, Shingo; Hosokawa, Takashi; Yoshida, Naoki; Kuiper, Rolf

    2017-09-29

    The origin of super-massive black holes in the early universe remains poorly understood. Gravitational collapse of a massive primordial gas cloud is a promising initial process, but theoretical studies have difficulty growing the black hole fast enough. We report numerical simulations of early black hole formation starting from realistic cosmological conditions. Supersonic gas motions left over from the Big Bang prevent early gas cloud formation until rapid gas condensation is triggered in a protogalactic halo. A protostar is formed in the dense, turbulent gas cloud, and it grows by sporadic mass accretion until it acquires 34,000 solar masses. The massive star ends its life with a catastrophic collapse to leave a black hole-a promising seed for the formation of a monstrous black hole. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  15. Hot stars in young massive clusters: Mapping the current Galactic metallicity

    Science.gov (United States)

    de la Fuente, Diego; Najarro, Francisco; Davies, Ben; Trombley, Christine; Figer, Donald F.; Herrero, Artemio

    2013-06-01

    Young Massive Clusters (YMCs) with ages guarantee that these objects present the same chemical composition than the surrounding environment where they are recently born. Finally, the YMCs host very massive stars whose extreme luminosities allow to accomplish detailed spectroscopic analyses even in the most distant regions of the Milky Way. Our group has carried out ISAAC/VLT spectroscopic observations of hot massive stars belonging to several YMCs in different locations around the Galactic disk. As a result, high signal-to-noise, near-infrared spectra of dozens of blue massive stars (including many OB supergiants, Wolf-Rayet stars and a B hypergiant) have been obtained. These data are fully reduced, and NLTE spherical atmosphere modeling is in process. Several line diagnostics will be combined in order to calculate metal abundances accurately for each cluster. The diverse locations of the clusters will allow us to draw a two-dimensional chemical map of the Galactic disk for the first time. The study of the radial and azimuthal variations of elemental abundances will be crucial for understanding the chemical evolution of the Milky Way. Particularly, the ratio between Fe-peak and alpha elements will constitute a powerful tool to investigate the past stellar populations that originated the current Galactic chemistry.

  16. Asymmetric Star Formation Efficiency Due to Ram Pressure Stripping

    Directory of Open Access Journals (Sweden)

    Paulina Troncoso Iribarren

    2016-12-01

    Full Text Available Previous works have shown that a dense cluster environment affects satellite galaxy properties and accelerates or truncates their evolutionary processes. In this work, we use the EAGLE simulation to study this effect, dissecting the galaxies in two halves: the one that is falling directly to the cluster (leading half and the one behind (trailing half. Considering all galaxies within the virial radius of the most massive groups and clusters of the simulation ( M h a l o > 10 13 . 8 [ M ⊙ ] , we find that on average the leading half presents an enhancement of the star formation rate with respect to the trailing half. We conclude that galaxies falling into the intra-cluster medium experience a boost in star-formation in their leading half due to ram pressure. Sparse observations of jellyfish galaxies have revealed visually the enhancement of the star formation in the leading half. In order to confirm this effect statistically using observations, different cases must be investigated using the simulation as a test dataset.

  17. Big Fish in Small Ponds: massive stars in the low-mass clusters of M83

    Energy Technology Data Exchange (ETDEWEB)

    Andrews, J. E.; Calzetti, D.; McElwee, Sean [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Chandar, R. [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States); Elmegreen, B. G. [IBM T. J. Watson Research Center, Yorktown Heights, NY 10598 (United States); Kennicutt, R. C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Kim, Hwihyun [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404 (United States); Krumholz, Mark R. [Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Lee, J. C.; Whitmore, B. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); O' Connell, R. W., E-mail: jandrews@astro.umass.edu, E-mail: callzetti@astro.umass.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)

    2014-09-20

    We have used multi-wavelength Hubble Space Telescope WFC3 data of the starbursting spiral galaxy M83 in order to measure variations in the upper end of the stellar initial mass function (uIMF) using the production rate of ionizing photons in unresolved clusters with ages ≤ 8 Myr. As in earlier papers on M51 and NGC 4214, the uIMF in M83 is consistent with a universal IMF, and stochastic sampling of the stellar populations in the ∼<10{sup 3} M {sub ☉} clusters are responsible for any deviations in this universality. The ensemble cluster population, as well as individual clusters, also imply that the most massive star in a cluster does not depend on the cluster mass. In fact, we have found that these small clusters seem to have an over-abundance of ionizing photons when compared to an expected universal or truncated IMF. This also suggests that the presence of massive stars in these clusters does not affect the star formation in a destructive way.

  18. The role of rotation in the evolution of massive stars losing mass

    International Nuclear Information System (INIS)

    Sreenivasan, S.R.; Wilson, W.J.F.

    1979-01-01

    The role of differential and solid body rotation in the evolution of massive stars undergoing mass loss is discussed. The implications for Of, WR, β Cephei stars and shell stars are brought out. (Auth.)

  19. Exploring the Dust Content, Metallicity, Star Formation and AGN Activity in Distant Dusty, Star-Forming Galaxies Using Cosmic Telescope

    Science.gov (United States)

    Walth, Gregory; Egami, Eiichi; Clément, Benjamin; Rujopakarn, Wiphu; Rawle, Tim; Richard, Johan; Dessauges, Miroslava; Perez-Gonzalez, Pablo; Ebeling, Harald; Vayner, Andrey; Wright, Shelley; Cosens, Maren; Herschel Lensing Survey

    2018-01-01

    We present our recent ALMA observations of Herschel-detected gravitationally lensed dusty, star-forming galaxies (DSFGs) and how they compliment our near-infrared spectroscopic observations of their rest-frame optical nebular emission. This provides the complete picture of star formation; from the molecular gas that fuels star formation, to the dust emission which are the sites of star formation, and the nebular emission which is the gas excited by the young stars. DSFGs undergo the largest starbursts in the Universe, contributing to the bulk of the cosmic star formation rate density between redshifts z = 1 - 4. Internal processes within high-redshift DSFGs remains largely unexplored; such as feedback from star formation, the role of turbulence, gas surface density of molecular gas, AGN activity, and the rates of metal production. Much that is known about DSFGs star formation properties comes from their CO and dust emission. In order to fully understand the star formation history of DSFGs, it is necessary to observe their optical nebular emission. Unfortunately, UV/optical emission is severely attenuated by dust, making it challenging to detect. With the Herschel Lensing Survey, a survey of the cores of almost 600 massive galaxy clusters, we are able to probe faint dust-attenuated nebular emission. We are currently conducting a new survey using Keck/OSIRIS to resolve a sample of gravitationally lensed DSFGs from the Herschel Lensing Survey (>100 mJy, with SFRs >100 Msun/yr) at redshifts z=1-4 with magnifications >10x all with previously detected nebular emission lines. We present the physical and resolved properties of gravitationally lensed DSFGs at unprecedented spatial scales; such as ionization, metallicity, AGN activity, and dust attenuation.

  20. FORMATION EPOCHS, STAR FORMATION HISTORIES, AND SIZES OF MASSIVE EARLY-TYPE GALAXIES IN CLUSTER AND FIELD ENVIRONMENTS AT z = 1.2: INSIGHTS FROM THE REST-FRAME ULTRAVIOLET

    International Nuclear Information System (INIS)

    Rettura, Alessandro; Demarco, R.; Ford, H. C.; Rosati, P.; Gobat, R.; Nonino, M.; Fosbury, R. A. E.; Menci, N.; Strazzullo, V.; Mei, S.

    2010-01-01

    We derive stellar masses, ages, and star formation histories (SFHs) of massive early-type galaxies in the z = 1.237 RDCS1252.9-2927 cluster and compare them with those measured in a similarly mass-selected sample of field contemporaries drawn from the Great Observatories Origin Deep Survey South Field. Robust estimates of these parameters are obtained by comparing a large grid of composite stellar population models with 8-9 band photometry in the rest-frame near-ultraviolet, optical, and IR, thus sampling the entire relevant domain of emission of the different stellar populations. Additionally, we present new, deep U-band photometry of both fields, giving access to the critical far-ultraviolet rest frame, in order to empirically constrain the dependence of the most recent star formation processes on the environment. We also analyze the morphological properties of both samples to examine the dependence of their scaling relations on their mass and environment. We find that early-type galaxies, both in the cluster and in the field, show analogous optical morphologies, follow comparable mass versus size relation, have congruent average surface stellar mass densities, and lie on the same Kormendy relation. We also show that a fraction of early-type galaxies in the field employ longer timescales, τ, to assemble their mass than their cluster contemporaries. Hence, we conclude that while the formation epoch of early-type galaxies only depends on their mass, the environment does regulate the timescales of their SFHs. Our deep U-band imaging strongly supports this conclusion. We show that cluster galaxies are at least 0.5 mag fainter than their field contemporaries of similar mass and optical-to-infrared colors, implying that the last episode of star formation must have happened more recently in the field than in the cluster.

  1. An Observational Study of Blended Young Stellar Clusters in the Galactic Plane - Do Massive Stars form First?

    Science.gov (United States)

    Martínez-Galarza, Rafael; Protopapas, Pavlos; Smith, Howard A.; Morales, Esteban

    2018-01-01

    From an observational point of view, the early life of massive stars is difficult to understand partly because star formation occurs in crowded clusters where individual stars often appear blended together in the beams of infrared telescopes. This renders the characterization of the physical properties of young embedded clusters via spectral energy distribution (SED) fitting a challenging task. Of particular relevance for the testing of star formation models is the question of whether the claimed universality of the IMF (references) is reflected in an equally universal integrated galactic initial mass function (IGIMF) of stars. In other words, is the set of all stellar masses in the galaxy sampled from a single universal IMF, or does the distribution of masses depend on the environment, making the IGIMF different from the canonical IMF? If the latter is true, how different are the two? We present a infrared SED analysis of ~70 Spitzer-selected, low mass ($facilities.

  2. ORIGIN OF THE GALAXY MASS-METALLICITY-STAR FORMATION RELATION

    International Nuclear Information System (INIS)

    Harwit, Martin; Brisbin, Drew

    2015-01-01

    We describe an equilibrium model that links the metallicity of low-redshift galaxies to stellar evolution models. It enables the testing of different stellar initial mass functions and metal yields against observed galaxy metallicities. We show that the metallicities of more than 80,000 Sloan Digital Sky Survey galaxies in the low-redshift range 0.07 ≤ z ≤ 0.3 considerably constrain stellar evolution models that simultaneously relate galaxy stellar mass, metallicity, and star formation rates to the infall rate of low-metallicity extragalactic gas and outflow of enriched matter. A feature of our model is that it encompasses both the active star forming phases of a galaxy and epochs during which the same galaxy may lie fallow. We show that the galaxy mass-metallicity-star formation relation can be traced to infall of extragalactic gas mixing with native gas from host galaxies to form stars of observed metallicities, the most massive of which eject oxygen into extragalactic space. Most consequential among our findings is that, on average, extragalactic infall accounts for one half of the gas required for star formation, a ratio that is remarkably constant across galaxies with stellar masses ranging at least from M* = 2 × 10 9 to 6 × 10 10 M ☉ . This leads us to propose that star formation is initiated when extragalactic infall roughly doubles the mass of marginally stable interstellar clouds. The processes described may also account quantitatively for the metallicity of extragalactic space, though to check this the fraction of extragalactic baryons will need to be more firmly established

  3. ORIGIN OF THE GALAXY MASS-METALLICITY-STAR FORMATION RELATION

    Energy Technology Data Exchange (ETDEWEB)

    Harwit, Martin; Brisbin, Drew, E-mail: harwit@verizon.net [Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853 (United States)

    2015-02-20

    We describe an equilibrium model that links the metallicity of low-redshift galaxies to stellar evolution models. It enables the testing of different stellar initial mass functions and metal yields against observed galaxy metallicities. We show that the metallicities of more than 80,000 Sloan Digital Sky Survey galaxies in the low-redshift range 0.07 ≤ z ≤ 0.3 considerably constrain stellar evolution models that simultaneously relate galaxy stellar mass, metallicity, and star formation rates to the infall rate of low-metallicity extragalactic gas and outflow of enriched matter. A feature of our model is that it encompasses both the active star forming phases of a galaxy and epochs during which the same galaxy may lie fallow. We show that the galaxy mass-metallicity-star formation relation can be traced to infall of extragalactic gas mixing with native gas from host galaxies to form stars of observed metallicities, the most massive of which eject oxygen into extragalactic space. Most consequential among our findings is that, on average, extragalactic infall accounts for one half of the gas required for star formation, a ratio that is remarkably constant across galaxies with stellar masses ranging at least from M* = 2 × 10{sup 9} to 6 × 10{sup 10} M {sub ☉}. This leads us to propose that star formation is initiated when extragalactic infall roughly doubles the mass of marginally stable interstellar clouds. The processes described may also account quantitatively for the metallicity of extragalactic space, though to check this the fraction of extragalactic baryons will need to be more firmly established.

  4. Age gradients in the stellar populations of massive star forming regions based on a new stellar chronometer

    Energy Technology Data Exchange (ETDEWEB)

    Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.; Broos, Patrick S.; Townsley, Leisa K.; Luhman, Kevin L. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Naylor, Tim [School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Povich, Matthew S. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States); Garmire, Gordon P. [Huntingdon Institute for X-ray Astronomy, LLC, 10677 Franks Road, Huntingdon, PA 16652 (United States)

    2014-06-01

    A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, Age {sub JX} . Stellar masses are derived from X-ray luminosities using the L{sub X} -M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. Age {sub JX} is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The Age {sub JX} method has been applied to 5525 out of 31,784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The Age {sub JX} ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J – H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters.

  5. Effects of a new 3-alpha reaction on the s-process in massive stars

    International Nuclear Information System (INIS)

    Kikuch, Yukihiro; Ono, Masaomi; Matsuo, Yasuhide; Hashimoto, Masa-aki; Fujimoto, Shin-ichiro

    2012-01-01

    Effect of a new 3-alpha reaction rate on the s-process during the evolution of a massive star of 25 solar mass is investigated for the first time, because the s-process in massive stars have been believed to be established with only minor change. We find that the s-process with use of the new rate during the core helium burning is very inefficient compared to the case with the previous 3-alpha rate. However, the difference of the overproduction is found to be largely compensated by the subsequent carbon burning. Since the s-process in massive stars has been attributed so far to the neutron irradiation during core helium burning, our finding reveals for the first time the importance of the carbon burning for the s-process during the evolution of massive stars.

  6. Star formation and mass assembly in high redshift galaxies

    Science.gov (United States)

    Santini, P.; Fontana, A.; Grazian, A.; Salimbeni, S.; Fiore, F.; Fontanot, F.; Boutsia, K.; Castellano, M.; Cristiani, S.; de Santis, C.; Gallozzi, S.; Giallongo, E.; Menci, N.; Nonino, M.; Paris, D.; Pentericci, L.; Vanzella, E.

    2009-09-01

    Aims: The goal of this work is to infer the star formation properties and the mass assembly process of high redshift (0.3 ≤ z MUSIC catalog, which has multiwavelength coverage from 0.3 to 24 μm and either spectroscopic or accurate photometric redshifts. We describe how the catalog has been extended by the addition of mid-IR fluxes derived from the MIPS 24 μm image. We compared two different estimators of the star formation rate (SFR hereafter). One is the total infrared emission derived from 24 μm, estimated using both synthetic and empirical IR templates. The other one is a multiwavelength fit to the full galaxy SED, which automatically accounts for dust reddening and age-star formation activity degeneracies. For both estimates, we computed the SFR density and the specific SFR. Results: We show that the two SFR indicators are roughly consistent, once the uncertainties involved are taken into account. However, they show a systematic trend, IR-based estimates exceeding the fit-based ones as the star formation rate increases. With this new catalog, we show that: a) at z>0.3, the star formation rate is correlated well with stellar mass, and this relationship seems to steepen with redshift if one relies on IR-based estimates of the SFR; b) the contribution to the global SFRD by massive galaxies increases with redshift up to ≃ 2.5, more rapidly than for galaxies of lower mass, but appears to flatten at higher z; c) despite this increase, the most important contributors to the SFRD at any z are galaxies of about, or immediately lower than, the characteristic stellar mass; d) at z≃ 2, massive galaxies are actively star-forming, with a median {SFR} ≃ 300 M_⊙ yr-1. During this epoch, our targeted galaxies assemble a substantial part of their final stellar mass; e) the specific SFR (SSFR) shows a clear bimodal distribution. Conclusions: The analysis of the SFR density and the SSFR seems to support the downsizing scenario, according to which high mass galaxies

  7. A ram-pressure threshold for star formation

    Science.gov (United States)

    Whitworth, A. P.

    2016-05-01

    In turbulent fragmentation, star formation occurs in condensations created by converging flows. The condensations must be sufficiently massive, dense and cool to be gravitationally unstable, so that they start to contract; and they must then radiate away thermal energy fast enough for self-gravity to remain dominant, so that they continue to contract. For the metallicities and temperatures in local star-forming clouds, this second requirement is only met robustly when the gas couples thermally to the dust, because this delivers the capacity to radiate across the full bandwidth of the continuum, rather than just in a few discrete spectral lines. This translates into a threshold for vigorous star formation, which can be written as a minimum ram pressure PCRIT ˜ 4 × 10-11 dyne. PCRIT is independent of temperature, and corresponds to flows with molecular hydrogen number density n_{{H_2.FLOW}} and velocity vFLOW satisfying n_{{H_2.FLOW}} v_{FLOW}^2≳ 800 cm^{-3} (km s^{-1})^2. This in turn corresponds to a minimum molecular hydrogen column density for vigorous star formation, N_{{H_2.CRIT}} ˜ 4 × 10^{21} cm^{-2} (ΣCRIT ˜ 100 M⊙ pc-2), and a minimum visual extinction AV, CRIT ˜ 9 mag. The characteristic diameter and line density for a star-forming filament when this threshold is just exceeded - a sweet spot for local star formation regions - are 2RFIL ˜ 0.1 pc and μFIL ˜ 13 M⊙ pc-2. The characteristic diameter and mass for a prestellar core condensing out of such a filament are 2RCORE ˜ 0.1 pc and MCORE ˜ 1 M⊙. We also show that fragmentation of a shock-compressed layer is likely to commence while the convergent flows creating the layer are still ongoing, and we stress that, under this circumstance, the phenomenology and characteristic scales for fragmentation of the layer are fundamentally different from those derived traditionally for pre-existing layers.

  8. Massive stars, successes and challenges

    OpenAIRE

    Meynet, Georges; Maeder, André; Georgy, Cyril; Ekström, Sylvia; Eggenberger, Patrick; Barblan, Fabio; Song, Han Feng

    2017-01-01

    We give a brief overview of where we stand with respect to some old and new questions bearing on how massive stars evolve and end their lifetime. We focus on the following key points that are further discussed by other contributions during this conference: convection, mass losses, rotation, magnetic field and multiplicity. For purpose of clarity, each of these processes are discussed on its own but we have to keep in mind that they are all interacting between them offering a large variety of ...

  9. The distribution of satellites around massive galaxies at 1 < z < 3 in ZFOURGE/CANDELS: Dependence on star formation activity

    Energy Technology Data Exchange (ETDEWEB)

    Kawinwanichakij, Lalitwadee; Papovich, Casey; Quadri, Ryan F.; Tran, Kim-Vy H.; Mehrtens, Nicola [George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); Spitler, Lee R.; Cowley, Michael [Department of Physics and Astronomy, Faculty of Sciences, Macquarie University, Sydney, NSW 2109 (Australia); Kacprzak, Glenn G.; Glazebrook, Karl; Nanayakkara, Themiya [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia); Labbé, Ivo; Straatman, Caroline M. S. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Allen, Rebecca [Australian Astronomical Observatories, P.O. Box 915, North Ryde, NSW 1670 (Australia); Davé, Romeel [University of the Western Cape, Bellville, Cape Town 7535 (South Africa); Dekel, Avishai [Center for Astrophysics and Planetary Science, Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Ferguson, Henry C.; Koekemoer, Anton M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Hartley, W. G. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Koo, David C. [University of California Observatories/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Lu, Yu, E-mail: kawinwanichakij@physics.tamu.edu [Kavli Institute for Particle Astrophysics and Cosmology, 452 Lomita Mall, Stanford, CA 94305 (United States); and others

    2014-09-10

    We study the statistical distribution of satellites around star-forming and quiescent central galaxies at 1 < z < 3 using imaging from the FourStar Galaxy Evolution Survey and the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey. The deep near-IR data select satellites down to log (M/M {sub ☉}) > 9 at z < 3. The radial satellite distribution around centrals is consistent with a projected Navarro-Frenk-White profile. Massive quiescent centrals, log (M/M {sub ☉}) > 10.78, have ∼2 times the number of satellites compared to star-forming centrals with a significance of 2.7σ even after accounting for differences in the centrals' stellar-mass distributions. We find no statistical difference in the satellite distributions of intermediate-mass quiescent and star-forming centrals, 10.48 < log (M/M {sub ☉}) < 10.78. Compared to the Guo et al. semi-analytic model, the excess number of satellites indicates that quiescent centrals have halo masses 0.3 dex larger than star-forming centrals, even when the stellar-mass distributions are fixed. We use a simple toy model that relates halo mass and quenching, which roughly reproduces the observed quenched fractions and the differences in halo mass between star-forming and quenched galaxies only if galaxies have a quenching probability that increases with halo mass from ∼0 for log (M{sub h} /M {sub ☉}) ∼ 11 to ∼1 for log (M{sub h} /M {sub ☉}) ∼ 13.5. A single halo-mass quenching threshold is unable to reproduce the quiescent fraction and satellite distribution of centrals. Therefore, while halo quenching may be an important mechanism, it is unlikely to be the only factor driving quenching. It remains unclear why a high fraction of centrals remain star-forming even in relatively massive halos.

  10. A BUTTERFLY-SHAPED 'PAPILLON' NEBULA YIELDS SECRETS OF MASSIVE STAR BIRTH

    Science.gov (United States)

    2002-01-01

    A NASA Hubble Space Telescope view of a turbulent cauldron of starbirth, called N159, taking place 170,000 light-years away in our satellite galaxy, the Large Magellanic Cloud (LMC). Torrential stellar winds from hot newborn massive stars within the nebula sculpt ridges, arcs, and filaments in the vast cloud, which is over 150 light-years across. A rare type of compact ionized 'blob' is resolved for the first time to be a butterfly-shaped or 'Papillon' (French for 'butterfly') nebula, buried in the center of the maelstrom of glowing gases and dark dust. The unprecedented details of the structure of the Papillon, itself less than 2 light-years in size (about 2 arcseconds in the sky), are seen in the inset. A possible explanation of this bipolar shape is the outflow of gas from massive stars (over 10 times the mass of our sun) hidden in the central absorption zone. Such stars are so hot that their radiation pressure halts the infall of gas and directs it away from the stars in two opposite directions. Presumably, a dense equatorial disk formed by matter still trying to fall in onto the stars focuses the outstreaming matter into the bipolar directions. This observation is part of a search for young massive stars in the LMC. Rare are the cases where we can see massive stars so early after their birth. The red in this true-color image is from the emission of hydrogen and the yellow from high excitation ionized oxygen. The picture was taken on September 5, 1998 with the Wide Field Planetary Camera 2. The Hubble observations of the Papillon nebula were conducted by the European astronomers Mohammad Heydari-Malayeri (Paris Observatory, France) and co-investigators Michael Rosa (Space Telescope-European Coordinating Facility, European Southern Observatory, Germany), Vassilis Charmandaris (Paris Observatory), Lise Deharveng (Marseille Observatory, France), and Hans Zinnecker (Astrophysical Institute, Potsdam, Germany). Their work is submitted for publication in the European

  11. SEQUENTIAL STAR FORMATION IN RCW 34: A SPECTROSCOPIC CENSUS OF THE STELLAR CONTENT OF HIGH-MASS STAR-FORMING REGIONS

    International Nuclear Information System (INIS)

    Bik, A.; Henning, Th.; Vasyunina, T.; Beuther, H.; Linz, H.; Puga, E.; Waters, L.B.F.M.; Waelkens, Ch.; Horrobin, M.; Kaper, L.; De Koter, A.; Van den Ancker, M.; Comeron, F.; Lenorzer, A.; Churchwell, E.; Kurtz, S.; Kouwenhoven, M. B. N.; Stolte, A.; Thi, W. F.

    2010-01-01

    In this paper, we present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected in the IRAC images in which a cluster of intermediate- and low-mass class II objects is found. At the northern edge of this bubble, an H II region is located, ionized by 3 OB stars, of which the most massive star has spectral type O8.5V. Intermediate-mass stars (2-3 M sun ) are detected of G- and K-spectral type. These stars are still in the pre-main-sequence (PMS) phase. North of the H II region, a photon-dominated region is present, marking the edge of a dense molecular cloud traced by H 2 emission. Several class 0/I objects are associated with this cloud, indicating that star formation is still taking place. The distance to RCW 34 is revised to 2.5 ± 0.2 kpc and an age estimate of 2 ± 1 Myr is derived from the properties of the PMS stars inside the H II region. Between the class II sources in the bubble and the PMS stars in the H II region, no age difference could be detected with the present data. The presence of the class 0/I sources in the molecular cloud, however, suggests that the objects inside the molecular cloud are significantly younger. The most likely scenario for the formation of the three regions is that star formation propagated from south to north. First the bubble is formed, produced by intermediate- and low-mass stars only, after that, the H II region is formed from a dense core at the edge of the molecular cloud, resulting in the expansion similar to a champagne flow. More recently, star formation occurred in the rest of the molecular cloud. Two different formation scenarios are possible. (1) The bubble with the cluster of low- and intermediate-mass stars triggered the formation of the O star at the edge of the molecular cloud, which in its turn induces the current star formation in the molecular cloud. (2) An external triggering is

  12. Constraining the Final Fates of Massive Stars by Oxygen and Iron Enrichment History in the Galaxy

    Science.gov (United States)

    Suzuki, Akihiro; Maeda, Keiichi

    2018-01-01

    Recent observational studies of core-collapse supernovae suggest that only stars with zero-age main-sequence masses smaller than 16–18 {M}ȯ explode when they are red supergiants, producing Type IIP supernovae. This may imply that more massive stars produce other types of supernovae or they simply collapse to black holes without giving rise to bright supernovae. This failed supernova hypothesis can lead to significantly inefficient oxygen production because oxygen abundantly produced in inner layers of massive stars with zero-age main-sequence masses around 20–30 {M}ȯ might not be ejected into the surrounding interstellar space. We first assume an unspecified population of oxygen injection events related to massive stars and obtain a model-independent constraint on how much oxygen should be released in a single event and how frequently such events should happen. We further carry out one-box galactic chemical enrichment calculations with different mass ranges of massive stars exploding as core-collapse supernovae. Our results suggest that the model assuming that all massive stars with 9–100 {M}ȯ explode as core-collapse supernovae is still most appropriate in explaining the solar abundances of oxygen and iron and their enrichment history in the Galaxy. The oxygen mass in the Galaxy is not explained when assuming that only massive stars with zero-age main-sequence masses in the range of 9–17 {M}ȯ contribute to the galactic oxygen enrichment. This finding implies that a good fraction of stars more massive than 17 {M}ȯ should eject their oxygen layers in either supernova explosions or some other mass-loss processes.

  13. STAR FORMATION AND DUST OBSCURATION AT z ∼ 2: GALAXIES AT THE DAWN OF DOWNSIZING

    International Nuclear Information System (INIS)

    Pannella, M.; Carilli, C. L.; Owen, F. N.; Strazzullo, V.; Daddi, E.; Aussel, H.; McCracken, H. J.; Mellier, Y.; Renzini, A.; Civano, F.; Koekemoer, A. M.; Schinnerer, E.; Scoville, N.; Smolcic, V.; Salvato, M.; Taniguchi, Y.; Kneib, J. P.; Ilbert, O.; Thompson, D.; Willott, C. J.

    2009-01-01

    We present first results of a study aimed to constrain the star formation rate (SFR) and dust content of galaxies at z ∼ 2. We use a sample of BzK-selected star-forming galaxies, drawn from the Cosmic Evolution Survey, to perform a stacking analysis of their 1.4 GHz radio continuum as a function of different stellar population properties, after cleaning the sample from contamination by active galactic nuclei. Dust unbiased SFRs are derived from radio fluxes assuming the local radio-IR correlation. The main results of this work are: (1) specific star formation rate (SSFR)s are constant over about 1 dex in stellar mass and up to the highest stellar mass probed, (2) the dust attenuation is a strong function of galaxy stellar mass with more massive galaxies being more obscured than lower mass objects, (3) a single value of the UV extinction applied to all galaxies would lead to a gross underestimate of the SFR in massive galaxies, (4) correcting the observed UV luminosities for dust attenuation based on the Calzetti recipe provides results in very good agreement with the radio derived ones, (5) the mean SSFR of our sample steadily decreases by a factor of ∼4 with decreasing redshift from z = 2.3 to 1.4 and a factor of ∼40 down the local universe. These empirical SFRs would cause galaxies to dramatically overgrow in mass if maintained all the way to low redshifts; we suggest that this does not happen because star formation is progressively quenched, likely starting from the most massive galaxies.

  14. Connecting the Cosmic Star Formation Rate with the Local Star Formation

    Science.gov (United States)

    Gribel, Carolina; Miranda, Oswaldo D.; Williams Vilas-Boas, José

    2017-11-01

    We present a model that unifies the cosmic star formation rate (CSFR), obtained through the hierarchical structure formation scenario, with the (Galactic) local star formation rate (SFR). It is possible to use the SFR to generate a CSFR mapping through the density probability distribution functions commonly used to study the role of turbulence in the star-forming regions of the Galaxy. We obtain a consistent mapping from redshift z˜ 20 up to the present (z = 0). Our results show that the turbulence exhibits a dual character, providing high values for the star formation efficiency ( ˜ 0.32) in the redshift interval z˜ 3.5{--}20 and reducing its value to =0.021 at z = 0. The value of the Mach number ({{ M }}{crit}), from which rapidly decreases, is dependent on both the polytropic index (Γ) and the minimum density contrast of the gas. We also derive Larson’s first law associated with the velocity dispersion ( ) in the local star formation regions. Our model shows good agreement with Larson’s law in the ˜ 10{--}50 {pc} range, providing typical temperatures {T}0˜ 10{--}80 {{K}} for the gas associated with star formation. As a consequence, dark matter halos of great mass could contain a number of halos of much smaller mass, and be able to form structures similar to globular clusters. Thus, Larson’s law emerges as a result of the very formation of large-scale structures, which in turn would allow the formation of galactic systems, including our Galaxy.

  15. Confronting Models of Massive Star Evolution and Explosions with Remnant Mass Measurements

    Science.gov (United States)

    Raithel, Carolyn A.; Sukhbold, Tuguldur; Özel, Feryal

    2018-03-01

    The mass distribution of compact objects provides a fossil record that can be studied to uncover information on the late stages of massive star evolution, the supernova explosion mechanism, and the dense matter equation of state. Observations of neutron star masses indicate a bimodal Gaussian distribution, while the observed black hole mass distribution decays exponentially for stellar-mass black holes. We use these observed distributions to directly confront the predictions of stellar evolution models and the neutrino-driven supernova simulations of Sukhbold et al. We find strong agreement between the black hole and low-mass neutron star distributions created by these simulations and the observations. We show that a large fraction of the stellar envelope must be ejected, either during the formation of stellar-mass black holes or prior to the implosion through tidal stripping due to a binary companion, in order to reproduce the observed black hole mass distribution. We also determine the origins of the bimodal peaks of the neutron star mass distribution, finding that the low-mass peak (centered at ∼1.4 M ⊙) originates from progenitors with M ZAMS ≈ 9–18 M ⊙. The simulations fail to reproduce the observed peak of high-mass neutron stars (centered at ∼1.8 M ⊙) and we explore several possible explanations. We argue that the close agreement between the observed and predicted black hole and low-mass neutron star mass distributions provides new, promising evidence that these stellar evolution and explosion models capture the majority of relevant stellar, nuclear, and explosion physics involved in the formation of compact objects.

  16. Massive stars, successes and challenges

    Science.gov (United States)

    Meynet, Georges; Maeder, André; Georgy, Cyril; Ekström, Sylvia; Eggenberger, Patrick; Barblan, Fabio; Song, Han Feng

    2017-11-01

    We give a brief overview of where we stand with respect to some old and new questions bearing on how massive stars evolve and end their lifetime. We focus on the following key points that are further discussed by other contributions during this conference: convection, mass losses, rotation, magnetic field and multiplicity. For purpose of clarity, each of these processes are discussed on its own but we have to keep in mind that they are all interacting between them offering a large variety of outputs, some of them still to be discovered.

  17. GMC Collisions as Triggers of Star Formation. III. Density and Magnetically Regulated Star Formation

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Benjamin [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Tan, Jonathan C. [Department of Physics, University of Florida, Gainesville, FL 32611 (United States); Christie, Duncan [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Nakamura, Fumitaka [National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Van Loo, Sven [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Collins, David, E-mail: ben.wu@nao.ac.jp [Department of Physics, Florida State University, Tallahassee, FL 32306-4350 (United States)

    2017-06-01

    We study giant molecular cloud (GMC) collisions and their ability to trigger star cluster formation. We further develop our three-dimensional magnetized, turbulent, colliding GMC simulations by implementing star formation subgrid models. Two such models are explored: (1) “Density-Regulated,” i.e., fixed efficiency per free-fall time above a set density threshold and (2) “Magnetically Regulated,” i.e., fixed efficiency per free-fall time in regions that are magnetically supercritical. Variations of parameters associated with these models are also explored. In the non-colliding simulations, the overall level of star formation is sensitive to model parameter choices that relate to effective density thresholds. In the GMC collision simulations, the final star formation rates and efficiencies are relatively independent of these parameters. Between the non-colliding and colliding cases, we compare the morphologies of the resulting star clusters, properties of star-forming gas, time evolution of the star formation rate (SFR), spatial clustering of the stars, and resulting kinematics of the stars in comparison to the natal gas. We find that typical collisions, by creating larger amounts of dense gas, trigger earlier and enhanced star formation, resulting in 10 times higher SFRs and efficiencies. The star clusters formed from GMC collisions show greater spatial substructure and more disturbed kinematics.

  18. The Insignificance of Major Mergers in Driving Star Formation at z approximately equal to 2

    Science.gov (United States)

    Kaviraj, S.; Cohen, S.; Windhorst, R. A.; Silk, J.; O'Connell, R. W.; Dopita, M. A.; Dekel, A.; Hathi, N. P.; Straughn, A.; Rutkowski, M.

    2012-01-01

    We study the significance of major mergers in driving star formation in the early Universe, by quantifying the contribution of this process to the total star formation budget in 80 massive (M(*) > 10(exp 10) Solar M) galaxies at z approx = 2. Employing visually-classified morphologies from rest-frame V-band HST imaging, we find that 55(exp +/-14)% of the star formation budget is hosted by non-interacting late-types, with 27(exp +/-18% in major mergers and 18(exp +/- 6)% in spheroids. Given that a system undergoing a major merger continues to experience star formation driven by other processes at this epoch (e.g. cold accretion, minor mergers), approx 27% is a likely upper limit for the major-merger contribution to star formation activity at this epoch. The ratio of the average specific star formation rate in major mergers to that in the non-interacting late-types is approx 2.2:1, suggesting that the typical enhancement of star formation due to major merging is modest and that just under half the star formation in systems experiencing major mergers is unrelated to the merger itself. Taking this into account, we estimate that the actual major-merger contribution to the star formation budget may be as low as approx 15%. While our study does not preclude a major-merger-dominated. era in the very early Universe, if the major-merger contribution to star formation does not evolve significantly into larger look-back times, then this process has a relatively insignificant role in driving stellar mass assembly over cosmic time.

  19. Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

    Energy Technology Data Exchange (ETDEWEB)

    Jabran Zahid, H. [Smithsonian Astrophysical Observatory, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kudritzki, Rolf-Peter; Ho, I-Ting [University of Hawaii at Manoa, Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Conroy, Charlie [Department of Astronomy, Harvard University, Cambridge, MA, 02138 (United States); Andrews, Brett, E-mail: zahid@cfa.harvard.edu [PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260 (United States)

    2017-09-20

    We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.

  20. Stellar Absorption Line Analysis of Local Star-forming Galaxies: The Relation between Stellar Mass, Metallicity, Dust Attenuation, and Star Formation Rate

    International Nuclear Information System (INIS)

    Jabran Zahid, H.; Kudritzki, Rolf-Peter; Ho, I-Ting; Conroy, Charlie; Andrews, Brett

    2017-01-01

    We analyze the optical continuum of star-forming galaxies in the Sloan Digital Sky Survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. We fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass–star formation rate and the stellar mass–gas-phase metallicity relations, respectively. We also fit linear combinations of single-burst models with a range of metallicities and ages. Star formation and chemical evolution histories are unconstrained for these models. The stellar mass–stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. These relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. We measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. However, stellar continuum attenuation is smaller than nebular emission line attenuation. The continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. Our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies.

  1. Resolved star formation on sub-galactic scales in a merger at z = 1.7

    International Nuclear Information System (INIS)

    Whitaker, Katherine E.; Rigby, Jane R.; Teng, Stacy H.; Brammer, Gabriel B.; Gladders, Michael D.; Sharon, Keren; Wuyts, Eva

    2014-01-01

    We present a detailed analysis of Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G141 grism spectroscopy for seven star-forming regions of the highly magnified lensed starburst galaxy RCSGA 032727-132609 at z = 1.704. We measure the spatial variations of the extinction in RCS0327 through the observed Hγ/Hβ emission line ratios, finding a constant average extinction of E(B – V) gas = 0.40 ± 0.07. We infer that the star formation is enhanced as a result of an ongoing interaction, with measured star formation rates derived from demagnified, extinction-corrected Hβ line fluxes for the individual star-forming clumps falling >1-2 dex above the star formation sequence. When combining the HST/WFC3 [O III] λ5007/Hβ emission line ratio measurements with [N II]/Hα line ratios from Wuyts et al., we find that the majority of the individual star-forming regions fall along the local 'normal' abundance sequence. With the first detections of the He I λ5876 and He II λ4686 recombination lines in a distant galaxy, we probe the massive-star content of the star-forming regions in RCS0327. The majority of the star-forming regions have a He I λ5876 to Hβ ratio consistent with the saturated maximum value, which is only possible if they still contain hot O-stars. Two regions have lower ratios, implying that their last burst of new star formation ended ∼5 Myr ago. Together, the He I λ5876 and He II λ4686 to Hβ line ratios provide indirect evidence for the order in which star formation is stopping in individual star-forming knots of this high-redshift merger. We place the spatial variations of the extinction, star formation rate and ionization conditions in the context of the star formation history of RCS0327.

  2. Do All O Stars Form in Star Clusters?

    Science.gov (United States)

    Weidner, C.; Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

    The question whether or not massive stars can form in isolation or only in star clusters is of great importance for the theory of (massive) star formation as well as for the stellar initial mass function of whole galaxies (IGIMF-theory). While a seemingly easy question it is rather difficult to answer. Several physical processes (e.g. star-loss due to stellar dynamics or gas expulsion) and observational limitations (e.g. dust obscuration of young clusters, resolution) pose severe challenges to answer this question. In this contribution we will present the current arguments in favour and against the idea that all O stars form in clusters.

  3. Multidimensional Simulations of Colliding Outbursts from very Massive Stars

    Science.gov (United States)

    Chen, Ke-Jung; Woosley, Stan

    2015-08-01

    Massive stars that end their lives with helium cores in the range of 35 to 65 solar masses are known to produce repeated thermonuclear outbursts due to a recurring pair-instability. In some of these events, solar masses of material are ejected in repeated outbursts of several times 1050 erg each. Such models can be used to explain the strong mass loss rates at the last moment before the massive stars die. Collisions between these shells can sometimes produce very luminous transients. Previous 1D studies of these events produce thin,high-density shells as one ejection plows into another. We present the first multidimensional simulations of these collisions, we show that the development of a Rayleigh-Taylor instability truncates the growth of the high density spike and drives mixing between the shells.

  4. Winds of Massive Magnetic Stars: Interacting Fields and Flow

    Science.gov (United States)

    Daley-Yates, S.; Stevens, I. R.

    2018-01-01

    We present results of 3D numerical simulations of magnetically confined, radiatively driven stellar winds of massive stars, conducted using the astrophysical MHD code Pluto, with a focus on understanding the rotational variability of radio and sub-mm emission. Radiative driving is implemented according to the Castor, Abbott and Klein theory of radiatively driven winds. Many magnetic massive stars posses a magnetic axis which is inclined with respect to the rotational axis. This misalignment leads to a complex wind structure as magnetic confinement, centrifugal acceleration and radiative driving act to channel the circumstellar plasma into a warped disk whose observable properties should be apparent in multiple wavelengths. This structure is analysed to calculate free-free thermal radio emission and determine the characteristic intensity maps and radio light curves.

  5. The Formation of Massive Primordial Stars in the Presence of Moderate UV Backgrounds

    NARCIS (Netherlands)

    Latif, M. A.; Schleicher, D. R. G.; Bovino, S.; Grassi, T.; Spaans, M.

    Radiative feedback produced by stellar populations played a vital role in early structure formation. In particular, photons below the Lyman limit can escape the star-forming regions and produce a background ultraviolet (UV) flux, which consequently may influence the pristine halos far away from the

  6. STAR FORMATION EFFICIENCY IN THE COOL CORES OF GALAXY CLUSTERS

    International Nuclear Information System (INIS)

    McDonald, Michael; Veilleux, Sylvain; Mushotzky, Richard; Reynolds, Christopher; Rupke, David S. N.

    2011-01-01

    We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel) and Hα (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed view of the thin, extended filaments in the cores of these clusters. Based on the ratio of the far-UV to Hα luminosity, the UV spectral energy distribution, and the far-UV and Hα morphology, we conclude that the warm, ionized gas in the cluster cores is photoionized by massive, young stars in all but a few (A1991, A2052, A2580) systems. We show that the extended filaments, when considered separately, appear to be star forming in the majority of cases, while the nuclei tend to have slightly lower far-UV luminosity for a given Hα luminosity, suggesting a harder ionization source or higher extinction. We observe a slight offset in the UV/Hα ratio from the expected value for continuous star formation which can be modeled by assuming intrinsic extinction by modest amounts of dust (E(B - V) ∼ 0.2) or a top-heavy initial mass function in the extended filaments. The measured star formation rates vary from ∼0.05 M sun yr -1 in the nuclei of non-cooling systems, consistent with passive, red ellipticals, to ∼5 M sun yr -1 in systems with complex, extended, optical filaments. Comparing the estimates of the star formation rate based on UV, Hα, and infrared luminosities to the spectroscopically determined X-ray cooling rate suggests a star formation efficiency of 14 +18 -8 %. This value represents the time-averaged fraction, by mass, of gas cooling out of the intracluster medium, which turns into stars and agrees well with the global fraction of baryons in stars required by simulations to reproduce the stellar mass function for galaxies. This result provides a new constraint on the efficiency of star formation in accreting systems.

  7. Star Formation in the Orion Nebula Cluster

    Science.gov (United States)

    Palla, Francesco; Stahler, Steven W.

    1999-11-01

    We study the record of star formation activity within the dense cluster associated with the Orion Nebula. The bolometric luminosity function of 900 visible members is well matched by a simplified theoretical model for cluster formation. This model assumes that stars are produced at a constant rate and distributed according to the field-star initial mass function. Our best-fit age for the system, within this framework, is 2×106 yr. To undertake a more detailed analysis, we present a new set of theoretical pre-main-sequence tracks. These cover all masses from 0.1 to 6.0 Msolar, and start from a realistic stellar birthline. The tracks end along a zero-age main-sequence that is in excellent agreement with the empirical one. As a further aid to cluster studies, we offer an heuristic procedure for the correction of pre-main-sequence luminosities and ages to account for the effects of unresolved binary companions. The Orion Nebula stars fall neatly between our birthline and zero-age main-sequence in the H-R diagram. All those more massive than about 8 Msolar lie close to the main sequence, as also predicted by theory. After accounting for the finite sensitivity of the underlying observations, we confirm that the population between 0.4 and 6.0 Msolar roughly follows a standard initial mass function. We see no evidence for a turnover at lower masses. We next use our tracks to compile stellar ages, also between 0.4 and 6.0 Msolar. Our age histogram reveals that star formation began at a low level some 107 yr ago and has gradually accelerated to the present epoch. The period of most active formation is indeed confined to a few×106 yr, and has recently ended with gas dispersal from the Trapezium. We argue that the acceleration in stellar births, which extends over a wide range in mass, reflects the gravitational contraction of the parent cloud spawning this cluster.

  8. ALMA Reveals Sequential High-mass Star Formation in the G9.62+0.19 Complex

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Tie; Kim, Kee-Tae [Korea Astronomy and Space Science Institute 776, Daedeokdae-ro, Yuseong-gu, Daejeon, Korea 34055 (Korea, Republic of); Lacy, John [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Li, Pak Shing [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Wang, Ke [European Southern Observatory, Karl-Schwarzschild-Str.2, D-85748 Garching bei München (Germany); Qin, Sheng-Li [Department of Astronomy, Yunnan University, and Key Laboratory of Astroparticle Physics of Yunnan Province, Kunming, 650091 (China); Zhang, Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Garay, Guido; Mardones, Diego [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Wu, Yuefang [Department of Astronomy, Peking University, Beijing 100871 (China); Zhu, Qingfeng [Astronomy Department, University of Science and Technology, Chinese Academy of Sciences, Hefei 210008 (China); Tatematsu, Ken’ichi; Hirota, Tomoya [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Ren, Zhiyuan; Li, Di [National Astronomical Observatories, Chinese Academy of Science, A20 Datun Road, Chaoyang District, Beijing 100012 (China); Liu, Sheng-Yuan; Chen, Huei-Ru; Su, Yu-Nung, E-mail: liutiepku@gmail.com [Academia Sinica, Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan (China)

    2017-11-01

    Stellar feedback from high-mass stars (e.g., H ii regions) can strongly influence the surrounding interstellar medium and regulate star formation. Our new ALMA observations reveal sequential high-mass star formation taking place within one subvirial filamentary clump (the G9.62 clump) in the G9.62+0.19 complex. The 12 dense cores (MM1–MM12) detected by ALMA are at very different evolutionary stages, from the starless core phase to the UC H ii region phase. Three dense cores (MM6, MM7/G, MM8/F) are associated with outflows. The mass–velocity diagrams of the outflows associated with MM7/G and MM8/F can be well-fit by broken power laws. The mass–velocity diagram of the SiO outflow associated with MM8/F breaks much earlier than other outflow tracers (e.g., CO, SO, CS, HCN), suggesting that SiO traces newly shocked gas, while the other molecular lines (e.g., CO, SO, CS, HCN) mainly trace the ambient gas continuously entrained by outflow jets. Five cores (MM1, MM3, MM5, MM9, MM10) are massive starless core candidates whose masses are estimated to be larger than 25 M {sub ☉}, assuming a dust temperature of ≤20 K. The shocks from the expanding H ii regions (“B” and “C”) to the west may have a great impact on the G9.62 clump by compressing it into a filament and inducing core collapse successively, leading to sequential star formation. Our findings suggest that stellar feedback from H ii regions may enhance the star formation efficiency and suppress low-mass star formation in adjacent pre-existing massive clumps.

  9. A SPITZER CENSUS OF STAR FORMATION ACTIVITY IN THE PIPE NEBULA

    International Nuclear Information System (INIS)

    Forbrich, Jan; Lada, Charles J.; Muench, August A.; Alves, Joao; Lombardi, Marco

    2009-01-01

    The Pipe Nebula, a large nearby molecular cloud, lacks obvious signposts of star formation in all but one of more than 130 dust extinction cores that have been identified within it. In order to quantitatively determine the current level of star formation activity in the Pipe Nebula, we analyzed 13 deg 2 of sensitive mid-infrared maps of the entire cloud, obtained with the Multiband Imaging Photometer for Spitzer at wavelengths of 24 μm and 70 μm, to search for candidate young stellar objects (YSOs) in the high-extinction regions. We argue that our search is complete for class I and typical class II YSOs with luminosities of L bol ∼ 0.2 L sun and greater. We find only 18 candidate YSOs in the high-extinction regions of the entire Pipe cloud. Twelve of these sources are previously known members of a small cluster associated with Barnard 59, the largest and most massive dense core in the cloud. With only six candidate class I and class II YSOs detected toward extinction cores outside of this cluster, our findings emphatically confirm the notion of an extremely low level of star formation activity in the Pipe Nebula. The resulting star formation efficiency for the entire cloud mass is only ∼0.06%.

  10. The Star Formation History of read and dead galaxies at z=[1.0--1.5

    Science.gov (United States)

    Domínguez Sánchez, H.; Pérez González, P.; Esquej, P.; Eliche Moral, C.; Alcalde Pampliega, B.; SHARDS Team

    2015-05-01

    We analyse the star formation histories (SFH) of M > 10^{10} M_⊙ read and dead galaxies at intermediate redshift (z=1.0-1.5). Current hierarchical models of galaxy formation predict many less massive high-z systems than observed. By combining SHARDS deep spectro-photometric optical data (25 contiguous OSIRIS/GTC medium band filters with R ˜ 50 at 4500-900 nm) with HST-WFC3 grism in the NIR (G141, 1.1-1.6 μm) and broad-band photometry (from FUV to FIR) we construct well-sampled optical SEDs with up to 150 photometric points and sufficient spectral resolution to obtain reliable stellar population parameters such as ages, star formation timescales, dust extinctions and metallicities. We define a complete and uncontaminated sample of red & dead galaxies by combining the color-color UVJ selection with a cut in sSFR (SFR/Mass). We check the robustness of the results depending on different stellar population models (Bruzual & Charlot 2003, Maraston 2005), SED fitting-codes (synthesizer, FAST) or star formation histories (exp{-t/τ}, t exp{-t/τ}). Finally, the dependence of the SFH with the galaxy stellar mass will be studied, to actually measure if more massive galaxies are formed earlier and more rapidly as downsizing suggests.

  11. On the formation of runaway stars BN and x in the Orion Nebula Cluster

    Science.gov (United States)

    Farias, J. P.; Tan, J. C.

    2018-05-01

    We explore scenarios for the dynamical ejection of stars BN and x from source I in the Kleinmann-Low nebula of the Orion Nebula Cluster (ONC), which is important because it is the closest region of massive star formation. This ejection would cause source I to become a close binary or a merger product of two stars. We thus consider binary-binary encounters as the mechanism to produce this event. By running a large suite of N-body simulations, we find that it is nearly impossible to match the observations when using the commonly adopted masses for the participants, especially a source I mass of 7 M⊙. The only way to recreate the event is if source I is more massive, that is, 20 M⊙. However, even in this case, the likelihood of reproducing the observed system is low. We discuss the implications of these results for understanding this important star-forming region.

  12. Spontaneous scalarization with an extremely massive field and heavy neutron stars

    Science.gov (United States)

    Morisaki, Soichiro; Suyama, Teruaki

    2017-10-01

    We investigate the internal structure and the mass-radius relation of neutron stars in a recently proposed scalar-tensor theory dubbed asymmetron in which a massive scalar field undergoes spontaneous scalarization inside neutron stars. We focus on the case where the Compton wavelength is shorter than 10 km, which has not been investigated in the literature. By solving the modified Einstein equations, either purely numerically or by partially using a semianalytic method, we find that not only the weakening of gravity by spontaneous scalarization but also the scalar force affect the internal structure significantly in the massive case. We also find that the maximum mass of neutron stars is larger for certain parameter sets than that in general relativity and reaches 2 M⊙ even if the effect of strange hadrons is taken into account. There is even a range of parameters where the maximum mass of neutron stars largely exceeds the threshold that violates the causality bound in general relativity.

  13. What Determines Star Formation Rates?

    Science.gov (United States)

    Evans, Neal John

    2017-06-01

    The relations between star formation and gas have received renewed attention. We combine studies on scales ranging from local (within 0.5 kpc) to distant galaxies to assess what factors contribute to star formation. These include studies of star forming regions in the Milky Way, the LMC, nearby galaxies with spatially resolved star formation, and integrated galaxy studies. We test whether total molecular gas or dense gas provides the best predictor of star formation rate. The star formation ``efficiency," defined as star formation rate divided by mass, spreads over a large range when the mass refers to molecular gas; the standard deviation of the log of the efficiency decreases by a factor of three when the mass of relatively dense molecular gas is used rather than the mass of all the molecular gas. We suggest ways to further develop the concept of "dense gas" to incorporate other factors, such as turbulence.

  14. Star Formation and Young Population of the H II Complex Sh2-294

    Science.gov (United States)

    Samal, M. R.; Pandey, A. K.; Ojha, D. K.; Chauhan, N.; Jose, J.; Pandey, B.

    2012-08-01

    The Sh2-294 H II region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in this region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 H II region at 3.6, 4.5, 5.8, and 8.0 μm observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H2 (2.12 μm) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Class I, Class II, and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the H II region and associated with enhanced H2 emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass (<4 M ⊙) YSOs; however, we also detected a massive YSO (~9 M ⊙) of Class I nature, embedded in a cloud of visual extinction of ~24 mag. Present analysis suggests that the Class I sources are indeed a younger population of the region relative to Class II sources (age ~ 4.5 × 106 yr). We suggest that the majority of the Class I sources, including the massive YSOs, are second-generation stars of the region whose formation is possibly induced by the expansion of the H II region powered by a ~4 × 106 yr B0 main-sequence star.

  15. STAR FORMATION AND YOUNG POPULATION OF THE H II COMPLEX Sh2-294

    International Nuclear Information System (INIS)

    Samal, M. R.; Pandey, A. K.; Chauhan, N.; Jose, J.; Ojha, D. K.; Pandey, B.

    2012-01-01

    The Sh2-294 H II region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in this region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 H II region at 3.6, 4.5, 5.8, and 8.0 μm observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H 2 (2.12 μm) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Class I, Class II, and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the H II region and associated with enhanced H 2 emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass ( ☉ ) YSOs; however, we also detected a massive YSO (∼9 M ☉ ) of Class I nature, embedded in a cloud of visual extinction of ∼24 mag. Present analysis suggests that the Class I sources are indeed a younger population of the region relative to Class II sources (age ∼ 4.5 × 10 6 yr). We suggest that the majority of the Class I sources, including the massive YSOs, are second-generation stars of the region whose formation is possibly induced by the expansion of the H II region powered by a ∼4 × 10 6 yr B0 main-sequence star.

  16. Cloud fluid models of gas dynamics and star formation in galaxies

    Science.gov (United States)

    Struck-Marcell, Curtis; Scalo, John M.; Appleton, P. N.

    1987-01-01

    The large dynamic range of star formation in galaxies, and the apparently complex environmental influences involved in triggering or suppressing star formation, challenges the understanding. The key to this understanding may be the detailed study of simple physical models for the dominant nonlinear interactions in interstellar cloud systems. One such model is described, a generalized Oort model cloud fluid, and two simple applications of it are explored. The first of these is the relaxation of an isolated volume of cloud fluid following a disturbance. Though very idealized, this closed box study suggests a physical mechanism for starbursts, which is based on the approximate commensurability of massive cloud lifetimes and cloud collisional growth times. The second application is to the modeling of colliding ring galaxies. In this case, the driving processes operating on a dynamical timescale interact with the local cloud processes operating on the above timescale. The results is a variety of interesting nonequilibrium behaviors, including spatial variations of star formation that do not depend monotonically on gas density.

  17. A SPECTROSCOPIC SURVEY OF MASSIVE STARS IN M31 AND M33

    Energy Technology Data Exchange (ETDEWEB)

    Massey, Philip; Neugent, Kathryn F.; Smart, Brianna M., E-mail: phil.massey@lowell.edu, E-mail: kneugent@lowell.edu, E-mail: bsmart@astro.wisc.edu [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States)

    2016-09-01

    We describe our spectroscopic follow-up to the Local Group Galaxy Survey (LGGS) photometry of M31 and M33. We have obtained new spectroscopy of 1895 stars, allowing us to classify 1496 of them for the first time. Our study has identified many foreground stars, and established membership for hundreds of early- and mid-type supergiants. We have also found nine new candidate luminous blue variables and a previously unrecognized Wolf–Rayet star. We republish the LGGS M31 and M33 catalogs with improved coordinates, and including spectroscopy from the literature and our new results. The spectroscopy in this paper is responsible for the vast majority of the stellar classifications in these two nearby spiral neighbors. The most luminous (and hence massive) of the stars in our sample are early-type B supergiants, as expected; the more massive O stars are more rare and fainter visually, and thus mostly remain unobserved so far. The majority of the unevolved stars in our sample are in the 20–40 M {sub ⊙} range.

  18. Kinetic temperature of massive star forming molecular clumps measured with formaldehyde

    Science.gov (United States)

    Tang, X. D.; Henkel, C.; Menten, K. M.; Zheng, X. W.; Esimbek, J.; Zhou, J. J.; Yeh, C. C.; König, C.; Yuan, Y.; He, Y. X.; Li, D. L.

    2017-02-01

    Context. For a general understanding of the physics involved in the star formation process, measurements of physical parameters such as temperature and density are indispensable. The chemical and physical properties of dense clumps of molecular clouds are strongly affected by the kinetic temperature. Therefore, this parameter is essential for a better understanding of the interstellar medium. Formaldehyde, a molecule which traces the entire dense molecular gas, appears to be the most reliable tracer to directly measure the gas kinetic temperature. Aims: We aim to determine the kinetic temperature with spectral lines from formaldehyde and to compare the results with those obtained from ammonia lines for a large number of massive clumps. Methods: Three 218 GHz transitions (JKAKC = 303-202, 322-221, and 321-220) of para-H2CO were observed with the 15 m James Clerk Maxwell Telescope (JCMT) toward 30 massive clumps of the Galactic disk at various stages of high-mass star formation. Using the RADEX non-LTE model, we derive the gas kinetic temperature modeling the measured para-H2CO 322-221/303-202 and 321-220/303-202 ratios. Results: The gas kinetic temperatures derived from the para-H2CO (321-220/303-202) line ratios range from 30 to 61 K with an average of 46 ± 9 K. A comparison of kinetic temperature derived from para-H2CO, NH3, and the dust emission indicates that in many cases para-H2CO traces a similar kinetic temperature to the NH3 (2, 2)/(1, 1) transitions and the dust associated with the HII regions. Distinctly higher temperatures are probed by para-H2CO in the clumps associated with outflows/shocks. Kinetic temperatures obtained from para-H2CO trace turbulence to a higher degree than NH3 (2, 2)/(1, 1) in the massive clumps. The non-thermal velocity dispersions of para-H2CO lines are positively correlated with the gas kinetic temperature. The massive clumps are significantly influenced by supersonic non-thermal motions. The reduced spectra (FITS files) are only

  19. SUBMILLIMETER ARRAY OBSERVATIONS TOWARD THE MASSIVE STAR-FORMING CORE MM1 OF W75N

    International Nuclear Information System (INIS)

    Minh, Y. C.; Su, Y.-N.; Liu, S.-Y.; Yan, C.-H.; Chen, H.-R.; Kim, S.-J.

    2010-01-01

    The massive star-forming core MM1 of W75N was observed using the Submillimeter Array with ∼1'' and 2'' spatial resolutions at 217 and 347 GHz, respectively. From the 217 GHz continuum we found that the MM1 core consists of two sources, separated by about 1'': MM1a (∼0.6 M sun ) and MM1b (∼1.4 M sun ), located near the radio continuum sources VLA 2/VLA 3 and VLA 1, respectively. Within MM1b, two gas clumps were found to be expanding away from VLA 1 at about ±3 km s -1 , as a result of the most recent star formation activity in the region. Observed molecular lines show emission peaks at two positions, MM1a and MM1b: sulfur-bearing species have emission peaks toward MM1a, but methanol and saturated species at MM1b. We identified high-temperature (∼200 K) gas toward MM1a and the hot core in MM1b. This segregation may result from the evolution of the massive star-forming core. In the very early phase of star formation, the hot core is seen through the evaporation of dust ice-mantle species. As the mantle species are consumed via evaporation the high-temperature gas species (such as the sulfur-bearing molecules) become bright. The SiO molecule is unique in having an emission peak exactly at the VLA 2 position, probably tracing a shock powered by VLA 2. The observed sulfur-bearing species show similar abundances both in MM1a and MM1b, whereas the methanol and saturated species show significant abundance enhancement toward MM1b, by about an order of magnitude, compared to MM1a.

  20. Formation of massive clouds and dwarf galaxies during tidal encounters

    Science.gov (United States)

    Kaufman, Michele; Elmegreen, Bruce G.; Thomasson, Magnus; Elmegreen, Debra M.

    1993-01-01

    Gerola et al. (1983) propose that isolated dwarf galaxies can form during galaxy interactions. As evidence of this process, Mirabel et al. (1991) find 10(exp 9) solar mass clouds and star formation complexes at the outer ends of the tidal arms in the Antennae and Superantennae galaxies. We describe observations of HI clouds with mass greater than 10(exp 8) solar mass in the interacting galaxy pair IC 2163/NGC 2207. This pair is important because we believe it represents an early stage in the formation of giant clouds during an encounter. We use a gravitational instability model to explain why the observed clouds are so massive and discuss a two-dimensional N-body simulation of an encounter that produces giant clouds.

  1. Stacked Star Formation Rate Profiles of Bursty Galaxies Exhibit “Coherent” Star Formation

    Science.gov (United States)

    Orr, Matthew E.; Hayward, Christopher C.; Nelson, Erica J.; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Kereš, Dušan; Chan, T. K.; Schmitz, Denise M.; Miller, Tim B.

    2017-11-01

    In a recent work based on 3200 stacked Hα maps of galaxies at z˜ 1, Nelson et al. find evidence for “coherent star formation”: the stacked star formation rate (SFR) profiles of galaxies above (below) the “star formation main sequence” (MS) are above (below) that of galaxies on the MS at all radii. One might interpret this result as inconsistent with highly bursty star formation and evidence that galaxies evolve smoothly along the MS rather than crossing it many times. We analyze six simulated galaxies at z˜ 1 from the Feedback in Realistic Environments (FIRE) project in a manner analogous to the observations to test whether the above interpretations are correct. The trends in stacked SFR profiles are qualitatively consistent with those observed. However, SFR profiles of individual galaxies are much more complex than the stacked profiles: the former can be flat or even peak at large radii because of the highly clustered nature of star formation in the simulations. Moreover, the SFR profiles of individual galaxies above (below) the MS are not systematically above (below) those of MS galaxies at all radii. We conclude that the time-averaged coherent star formation evident stacks of observed galaxies is consistent with highly bursty, clumpy star formation of individual galaxies and is not evidence that galaxies evolve smoothly along the MS.

  2. On the evolution of the star formation rate function of massive galaxies: constraints at 0.4 MUSIC catalogue

    Science.gov (United States)

    Fontanot, Fabio; Cristiani, Stefano; Santini, Paola; Fontana, Adriano; Grazian, Andrea; Somerville, Rachel S.

    2012-03-01

    We study the evolution of the star formation rate function (SFRF) of massive (M★ > 1010 M⊙) galaxies over the 0.4 MUSIC) catalogue, which provides a suitable coverage of the spectral region from 0.3 to 24 ?m and either spectroscopic or photometric redshifts for each object. Individual SFRs have been obtained by combining ultraviolet and 24-?m observations, when the latter were available. For all other sources a 'spectral energy distribution (SED) fitting' SFR estimate has been considered. We then define a stellar mass limited sample, complete in the M★ > 1010 M⊙ range and determine the SFRF using the 1/Vmax algorithm. We thus define simulated galaxy catalogues based on the predictions of three different state-of-the-art semi-analytical models (SAMs) of galaxy formation and evolution, and compare them with the observed SFRF. We show that the theoretical SFRFs are well described by a double power law functional form and its redshift evolution is approximated with high accuracy by a pure evolution of the typical SFR (SFR★). We find good agreement between model predictions and the high-SFR end of the SFRF, when the observational errors on the SFR are taken into account. However, the observational SFRF is characterized by a double-peaked structure, which is absent in its theoretical counterparts. At z > 1.0 the observed SFRF shows a relevant density evolution, which is not reproduced by SAMs, due to the well-known overprediction of intermediate-mass galaxies at z˜ 2. SAMs are thus able to reproduce the most intense SFR events observed in the GOODS-MUSIC sample and their redshift distribution. At the same time, the agreement at the low-SFR end is poor: all models overpredict the space density of SFR ˜ 1 M⊙ yr-1 and no model reproduces the double-peaked shape of the observational SFRF. If confirmed by deeper infrared observations, this discrepancy will provide a key constraint on theoretical modelling of star formation and stellar feedback.

  3. ORIGIN AND GROWTH OF NUCLEAR STAR CLUSTERS AROUND MASSIVE BLACK HOLES

    International Nuclear Information System (INIS)

    Antonini, Fabio

    2013-01-01

    The centers of stellar spheroids less luminous than ∼10 10 L ☉ are often marked by the presence of nucleated central regions, called 'nuclear star clusters' (NSCs). The origin of NSCs is still unclear. Here we investigate the possibility that NSCs originate from the migration and merger of stellar clusters at the center of galaxies where a massive black hole (MBH) may sit. We show that the observed scaling relation between NSC masses and the velocity dispersion of their host spheroids cannot be reconciled with a purely 'in situ' dissipative formation scenario. On the other hand, the observed relation appears to be in agreement with the predictions of the cluster merger model. A dissipationless formation model also reproduces the observed relation between the size of NSCs and their total luminosity, R∝√(L NSC ). When an MBH is included at the center of the galaxy, such dependence becomes substantially weaker than the observed correlation, since the size of the NSC is mainly determined by the fixed tidal field of the MBH. We evolve through dynamical friction a population of stellar clusters in a model of a galactic bulge taking into account dynamical dissolution due to two-body relaxation, starting from a power-law cluster initial mass function and adopting an initial total mass in stellar clusters consistent with the present-day cluster formation efficiency of the Milky Way (MW). The most massive clusters reach the center of the galaxy and merge to form a compact nucleus; after 10 10 years, the resulting NSC has properties that are consistent with the observed distribution of stars in the MW NSC. When an MBH is included at the center of a galaxy, globular clusters are tidally disrupted during inspiral, resulting in NSCs with lower densities than those of NSCs forming in galaxies with no MBHs. We suggest this as a possible explanation for the lack of NSCs in galaxies containing MBHs more massive than ∼10 8 M ☉ . Finally, we investigate the orbital

  4. ORIGIN AND GROWTH OF NUCLEAR STAR CLUSTERS AROUND MASSIVE BLACK HOLES

    Energy Technology Data Exchange (ETDEWEB)

    Antonini, Fabio, E-mail: antonini@cita.utoronto.ca [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, Ontario M5S 3H8 (Canada)

    2013-01-20

    The centers of stellar spheroids less luminous than {approx}10{sup 10} L {sub Sun} are often marked by the presence of nucleated central regions, called 'nuclear star clusters' (NSCs). The origin of NSCs is still unclear. Here we investigate the possibility that NSCs originate from the migration and merger of stellar clusters at the center of galaxies where a massive black hole (MBH) may sit. We show that the observed scaling relation between NSC masses and the velocity dispersion of their host spheroids cannot be reconciled with a purely 'in situ' dissipative formation scenario. On the other hand, the observed relation appears to be in agreement with the predictions of the cluster merger model. A dissipationless formation model also reproduces the observed relation between the size of NSCs and their total luminosity, R{proportional_to}{radical}(L{sub NSC}). When an MBH is included at the center of the galaxy, such dependence becomes substantially weaker than the observed correlation, since the size of the NSC is mainly determined by the fixed tidal field of the MBH. We evolve through dynamical friction a population of stellar clusters in a model of a galactic bulge taking into account dynamical dissolution due to two-body relaxation, starting from a power-law cluster initial mass function and adopting an initial total mass in stellar clusters consistent with the present-day cluster formation efficiency of the Milky Way (MW). The most massive clusters reach the center of the galaxy and merge to form a compact nucleus; after 10{sup 10} years, the resulting NSC has properties that are consistent with the observed distribution of stars in the MW NSC. When an MBH is included at the center of a galaxy, globular clusters are tidally disrupted during inspiral, resulting in NSCs with lower densities than those of NSCs forming in galaxies with no MBHs. We suggest this as a possible explanation for the lack of NSCs in galaxies containing MBHs more massive

  5. A Massive-born Neutron Star with a Massive White Dwarf Companion

    Energy Technology Data Exchange (ETDEWEB)

    Cognard, Ismaël; Guillemot, Lucas; Theureau, Gilles [Laboratoire de Physique et Chimie de l’Environnement et de l’Espace, Université d’Orléans/CNRS, F-45071 Orléans Cedex 02 (France); Freire, Paulo C. C. [Station de radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, F-18330 Nançay (France); Tauris, Thomas M.; Wex, Norbert; Graikou, Eleni; Kramer, Michael; Desvignes, Gregory; Lazarus, Patrick [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Stappers, Benjamin; Lyne, Andrew G. [Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, The University of Manchester, M13 9PL (United Kingdom); Bassa, Cees [ASTRON, The Netherlands Institute for Radioastronomy, Postbus 2, 7900 AA, Dwingeloo (Netherlands)

    2017-08-01

    We report on the results of a 4 year timing campaign of PSR J2222−0137, a 2.44 day binary pulsar with a massive white dwarf (WD) companion, with the Nançay, Effelsberg, and Lovell radio telescopes. Using the Shapiro delay for this system, we find a pulsar mass m {sub p} = 1.76 ± 0.06 M {sub ⊙} and a WD mass m {sub c} = 1.293 ± 0.025 M {sub ⊙}. We also measure the rate of advance of periastron for this system, which is marginally consistent with the general relativity prediction for these masses. The short lifetime of the massive WD progenitor star led to a rapid X-ray binary phase with little (< 10{sup −2} M {sub ⊙}) mass accretion onto the neutron star; hence, the current pulsar mass is, within uncertainties, its birth mass, which is the largest measured to date. We discuss the discrepancy with previous mass measurements for this system; we conclude that the measurements presented here are likely to be more accurate. Finally, we highlight the usefulness of this system for testing alternative theories of gravity by tightly constraining the presence of dipolar radiation. This is of particular importance for certain aspects of strong-field gravity, like spontaneous scalarization, since the mass of PSR J2222−0137 puts that system into a poorly tested parameter range.

  6. Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

    NARCIS (Netherlands)

    Meyer, D.M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V.V.; Mignone, A.; Izzard, R.G.; Kaper, L.

    2014-01-01

    At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional

  7. Star-disc interaction in galactic nuclei: formation of a central stellar disc

    Science.gov (United States)

    Panamarev, Taras; Shukirgaliyev, Bekdaulet; Meiron, Yohai; Berczik, Peter; Just, Andreas; Spurzem, Rainer; Omarov, Chingis; Vilkoviskij, Emmanuil

    2018-05-01

    We perform high-resolution direct N-body simulations to study the effect of an accretion disc on stellar dynamics in an active galactic nucleus (AGN). We show that the interaction of the nuclear stellar cluster (NSC) with the gaseous accretion disc (AD) leads to formation of a stellar disc in the central part of the NSC. The accretion of stars from the stellar disc on to the super-massive black hole is balanced by the capture of stars from the NSC into the stellar disc, yielding a stationary density profile. We derive the migration time through the AD to be 3 per cent of the half-mass relaxation time of the NSC. The mass and size of the stellar disc are 0.7 per cent of the mass and 5 per cent of the influence radius of the super-massive black hole. An AD lifetime shorter than the migration time would result in a less massive nuclear stellar disc. The detection of such a stellar disc could point to past activity of the hosting galactic nucleus.

  8. THE AVERAGE STAR FORMATION HISTORIES OF GALAXIES IN DARK MATTER HALOS FROM z = 0-8

    International Nuclear Information System (INIS)

    Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

    2013-01-01

    We present a robust method to constrain average galaxy star formation rates (SFRs), star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates (SSFRs), and cosmic star formation rates (CSFRs) from z = 0 to z = 8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, SFRs, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z = 8. We also provide new compilations of CSFRs and SSFRs; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 10 12 M ☉ are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z ∼ 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z ∼ 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for SFHs that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the SFH of galaxies into a self-consistent framework based on the modern understanding of structure formation in ΛCDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

  9. The Average Star Formation Histories of Galaxies in Dark Matter Halos from z = 0-8

    Science.gov (United States)

    Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

    2013-06-01

    We present a robust method to constrain average galaxy star formation rates (SFRs), star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates (SSFRs), and cosmic star formation rates (CSFRs) from z = 0 to z = 8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, SFRs, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z = 8. We also provide new compilations of CSFRs and SSFRs; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 1012 M ⊙ are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z ~ 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z ~ 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for SFHs that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the SFH of galaxies into a self-consistent framework based on the modern understanding of structure formation in ΛCDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

  10. A Massive Galaxy in Its Core Formation Phase Three Billion Years After the Big Bang

    Science.gov (United States)

    Nelson, Erica; van Dokkum, Pieter; Franx, Marijn; Brammer, Gabriel; Momcheva, Ivelina; Schreiber, Natascha M. Forster; da Cunha, Elisabete; Tacconi, Linda; Bezanson, Rachel; Kirkpatrick, Allison; hide

    2014-01-01

    Most massive galaxies are thought to have formed their dense stellar cores at early cosmic epochs. However, cores in their formation phase have not yet been observed. Previous studies have found galaxies with high gas velocity dispersions or small apparent sizes but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we present a candidate core in formation 11 billion years ago, at z = 2.3. GOODS-N-774 has a stellar mass of 1.0 × 10 (exp 11) solar mass, a half-light radius of 1.0 kpc, and a star formation rate of 90 (sup +45 / sub -20) solar mass/yr. The star forming gas has a velocity dispersion 317 plus or minus 30 km/s, amongst the highest ever measured. It is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, compact quiescent galaxies at z is approximately equal to 2 (exp 8-11) and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 appear to be rare; however, from the star formation rate and size of the galaxy we infer that many star forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.

  11. CHARACTERIZING THE STAR FORMATION OF THE LOW-MASS SHIELD GALAXIES FROM HUBBLE SPACE TELESCOPE IMAGING

    Energy Technology Data Exchange (ETDEWEB)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Simones, Jacob E. [Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 116 Church Street, S.E., Minneapolis, MN 55455 (United States); Cannon, John M. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Haynes, Martha P.; Giovanelli, Riccardo [Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States); Salzer, John J. [Department of Astronomy, Indiana University, 727 East 3rd Street, Bloomington, IN 47405 (United States); Adams, Elizabeth A. K. [Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7900 AA Dwingeloo (Netherlands); Elson, Ed C. [Astrophysics, Cosmology and Gravity Centre (ACGC), Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa); Ott, Jürgen, E-mail: kmcquinn@astro.umn.edu [National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States)

    2015-03-20

    The Survey of Hi in Extremely Low-mass Dwarfs is an on-going multi-wavelength program to characterize the gas, star formation, and evolution in gas-rich, very low-mass galaxies that populate the faint end of the galaxy luminosity function. The galaxies were selected from the first ∼10% of the Hi Arecibo Legacy Fast ALFA survey based on their low Hi mass and low baryonic mass. Here, we measure the star formation properties from optically resolved stellar populations for 12 galaxies using a color–magnitude diagram fitting technique. We derive lifetime average star formation rates (SFRs), recent SFRs, stellar masses, and gas fractions. Overall, the recent SFRs are comparable to the lifetime SFRs with mean birthrate parameter of 1.4, with a surprisingly narrow standard deviation of 0.7. Two galaxies are classified as dwarf transition galaxies (dTrans). These dTrans systems have star formation and gas properties consistent with the rest of the sample, in agreement with previous results that some dTrans galaxies may simply be low-luminosity dwarf irregulars. We do not find a correlation between the recent star formation activity and the distance to the nearest neighboring galaxy, suggesting that the star formation process is not driven by gravitational interactions, but regulated internally. Further, we find a broadening in the star formation and gas properties (i.e., specific SFRs, stellar masses, and gas fractions) compared to the generally tight correlation found in more massive galaxies. Overall, the star formation and gas properties indicate these very low-mass galaxies host a fluctuating, non-deterministic, and inefficient star formation process.

  12. Radiative Feedback from Massive Stars as Traced by Multiband Imaging and Spectroscopic Mosaics

    Science.gov (United States)

    Tielens, Alexander; "PDRs4ever" team

    2018-06-01

    Massive stars disrupt their natal molecular cloud material by dissociating molecules, ionizing atoms and molecules, and heating the gas and dust. These processes drive the evolution of interstellar matter in our Galaxy and throughout the Universe from the era of vigorous star formation at redshifts of 1-3, to the present day. Much of this interaction occurs in Photo-Dissociation Regions (PDRs) where far-ultraviolet photons of these stars create a largely neutral, but warm region of gas and dust. PDR emission dominates the IR spectra of star-forming galaxies and also provides a unique tool to study in detail the physical and chemical processes that are relevant for inter- and circumstellar media including diffuse clouds, molecular cloud and protoplanetary disk surfaces, globules, planetary nebulae, and starburst galaxies.We propose to provide template datasets designed to identify key PDR characteristics in the full 1-28 μm JWST spectra in order to guide the preparation of Cycle 2 proposals on star-forming regions in our Galaxy and beyond. We plan to obtain the first spatially resolved, high spectral resolution IR observations of a PDR using NIRCam, NIRSpec and MIRI. We will observe a nearby PDR with well-defined UV illumination in a typical massive star-forming region. JWST observations will, for the first time, spatially resolve and perform a tomography of the PDR, revealing the individual IR spectral signatures from the key zones and sub-regions within the ionized gas, the PDR and the molecular cloud. These data will test widely used theoretical models and extend them into the JWST era. We will assist the community interested in JWST observations of PDRs through several science-enabling products (maps of spectral features, template spectra, calibration of narrow/broad band filters in gas lines and PAH bands, data-interpretation tools e.g. to infer gas physical conditions or PAH and dust characteristics). This project is supported by a large international team of

  13. The progenitors of local ultra-massive galaxies across cosmic time: from dusty star-bursting to quiescent stellar populations

    Energy Technology Data Exchange (ETDEWEB)

    Marchesini, Danilo; Marsan, Cemile Z. [Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States); Muzzin, Adam; Franx, Marijn [Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden (Netherlands); Stefanon, Mauro [Physics and Astronomy Department, University of Missouri, Columbia, MO 65211 (United States); Brammer, Gabriel G. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Vulcani, Benedetta [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa 277-8582 (Japan); Fynbo, J. P. U.; Milvang-Jensen, Bo [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Dunlop, James S.; Buitrago, Fernando [SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ (United Kingdom)

    2014-10-10

    Using the UltraVISTA catalogs, we investigate the evolution in the 11.4 Gyr since z = 3 of the progenitors of local ultra-massive galaxies (log (M {sub star}/M {sub ☉}) ≈ 11.8; UMGs), providing a complete and consistent picture of how the most massive galaxies at z = 0 have assembled. By selecting the progenitors with a semi-empirical approach using abundance matching, we infer a growth in stellar mass of 0.56{sub −0.25}{sup +0.35} dex, 0.45{sub −0.20}{sup +0.16} dex, and 0.27{sub −0.12}{sup +0.08} dex from z = 3, z = 2, and z = 1, respectively, to z = 0. At z < 1, the progenitors of UMGs constitute a homogeneous population of only quiescent galaxies with old stellar populations. At z > 1, the contribution from star-forming galaxies progressively increases, with the progenitors at 2 < z < 3 being dominated by massive (M {sub star} ≈ 2 × 10{sup 11} M {sub ☉}), dusty (A {sub V} ∼ 1-2.2 mag), star-forming (SFR ∼ 100-400 M {sub ☉} yr{sup –1}) galaxies with a large range in stellar ages. At z = 2.75, ∼15% of the progenitors are quiescent, with properties typical of post-starburst galaxies with little dust extinction and strong Balmer break, and showing a large scatter in color. Our findings indicate that at least half of the stellar content of local UMGs was assembled at z > 1, whereas the remaining was assembled via merging from z ∼ 1 to the present. Most of the quenching of the star-forming progenitors happened between z = 2.75 and z = 1.25, in good agreement with the typical formation redshift and scatter in age of z = 0 UMGs as derived from their fossil records. The progenitors of local UMGs, including the star-forming ones, never lived on the blue cloud since z = 3. We propose an alternative path for the formation of local UMGs that refines previously proposed pictures and that is fully consistent with our findings.

  14. Evolution towards and beyond accretion-induced collapse of massive white dwarfs and formation of millisecond pulsars

    OpenAIRE

    Tauris, Thomas M.; Sanyal, Debashis; Yoon, Sung-Chul; Langer, Norbert

    2013-01-01

    Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs), formed via type Ib/c core-collapse supernovae (SNe), which have been spun up to high rotation rates via accretion from a companion star in a low-mass X-ray binary (LMXB). In an alternative formation channel, NSs are produced via the accretion-induced collapse (AIC) of a massive white dwarf (WD) in a close binary. Here we investigate binary evolution leading to AIC and examine if NSs formed in this way can subsequ...

  15. Massive stars and the energy balance of the ISM: I. The imapct of an isolated 60 M star

    Science.gov (United States)

    Yorke, H. W.; Freyer, T.; Hensler, G.

    2002-01-01

    We present results of numerical simulations carried out with a 2D radiation hydrodynamics code in order to study the impact of massive stars on their surrounding interstellar medium. This first paper deals with the evolution of the circumstellar gas around an isolated 60 M star.

  16. The environment and star formation of H II region Sh2-163: a multi-wavelength study

    Science.gov (United States)

    Yu, Naiping; Wang, Jun-Jie; Li, Nan

    2014-12-01

    To investigate the environment of H II region Sh2-163 and search for evidence of triggered star formation in this region, we performed a multi-wavelength study of this H II region. Most of our data were taken from large-scale surveys: 2MASS, CGPS, MSX and SCUBA. We also made CO molecular line observations, using the 13.7-m telescope. The ionized region of Sh2-163 is detected by both the optical and radio continuum observations. Sh2-163 is partially bordered by an arc-like photodissociation region (PDR), which is coincident with the strongest optical and radio emissions, indicating interactions between the H II region and the surrounding interstellar medium. Two molecular clouds were discovered on the border of the PDR. The morphology of these two clouds suggests they are compressed by the expansion of Sh2-163. In cloud A, we found two molecular clumps. And it seems star formation in clump A2 is much more active than in clump A1. In cloud B, we found new outflow activities and massive star(s) are forming inside. Using 2MASS photometry, we tried to search for embedded young stellar object (YSO) candidates in this region. The very good agreement between CO emission, infrared shell and YSOs suggest that it is probably a star formation region triggered by the expansion of Sh2-163. We also found the most likely massive protostar related to IRAS 23314+6033.

  17. PHIBSS: MOLECULAR GAS, EXTINCTION, STAR FORMATION, AND KINEMATICS IN THE z = 1.5 STAR-FORMING GALAXY EGS13011166

    Energy Technology Data Exchange (ETDEWEB)

    Genzel, R.; Tacconi, L. J.; Kurk, J.; Wuyts, S.; Foerster Schreiber, N. M.; Gracia-Carpio, J. [Max-Planck-Institut fuer extraterrestrische Physik (MPE), Giessenbachstr., D-85748 Garching (Germany); Combes, F.; Freundlich, J. [Observatoire de Paris, LERMA, CNRS, 61 Av. de l' Observatoire, F-75014 Paris (France); Bolatto, A. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Cooper, M. C. [Department of Physics and Astronomy, Frederick Reines Hall, University of California, Irvine, CA 92697 (United States); Neri, R. [IRAM, 300 Rue de la Piscine, F-38406 St. Martin d' Heres, Grenoble (France); Nordon, R. [Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978 (Israel); Bournaud, F. [Service d' Astrophysique, DAPNIA, CEA/Saclay, F-91191 Gif-sur-Yvette Cedex (France); Burkert, A. [Universitaetssternwarte der Ludwig-Maximiliansuniversitaet, Scheinerstr. 1, D-81679 Muenchen (Germany); Comerford, J. [Department of Astronomy and McDonald Observatory, 1 University Station, C1402 Austin, TX 78712-0259 (United States); Cox, P. [Department of Physics, Le Conte Hall, University of California, 94720 Berkeley, CA (United States); Davis, M. [Department of Astronomy, Campbell Hall, University of California, Berkeley, CA 94720 (United States); Garcia-Burillo, S. [Observatorio Astronomico Nacional-OAN, Observatorio de Madrid, Alfonso XII, 3, E-28014 Madrid (Spain); Naab, T. [Max-Planck Institut fuer Astrophysik, Karl Schwarzschildstrasse 1, D-85748 Garching (Germany); Lutz, D., E-mail: genzel@mpe.mpg.de, E-mail: linda@mpe.mpg.de; and others

    2013-08-10

    We report matched resolution imaging spectroscopy of the CO 3-2 line (with the IRAM Plateau de Bure millimeter interferometer) and of the H{alpha} line (with LUCI at the Large Binocular Telescope) in the massive z = 1.53 main-sequence galaxy EGS 13011166, as part of the ''Plateau de Bure high-z, blue-sequence survey'' (PHIBSS: Tacconi et al.). We combine these data with Hubble Space Telescope V-I-J-H-band maps to derive spatially resolved distributions of stellar surface density, star formation rate, molecular gas surface density, optical extinction, and gas kinematics. The spatial distribution and kinematics of the ionized and molecular gas are remarkably similar and are well modeled by a turbulent, globally Toomre unstable, rotating disk. The stellar surface density distribution is smoother than the clumpy rest-frame UV/optical light distribution and peaks in an obscured, star-forming massive bulge near the dynamical center. The molecular gas surface density and the effective optical screen extinction track each other and are well modeled by a ''mixed'' extinction model. The inferred slope of the spatially resolved molecular gas to star formation rate relation, N = dlog{Sigma}{sub starform}/dlog{Sigma}{sub molgas}, depends strongly on the adopted extinction model, and can vary from 0.8 to 1.7. For the preferred mixed dust-gas model, we find N = 1.14 {+-} 0.1.

  18. Small Galactic H II regions. II. The molecular clouds and star formation

    International Nuclear Information System (INIS)

    Hunter, D.A.; Thronson, H.A. Jr.; Wilton, C.

    1990-01-01

    CO maps of molecular clouds associated with 11 small Galactic H II regions are presented and compared with IR images obtained by IRAS. The molecular masses of the clouds are computed and compared with the masses of the stellar content. The mapped clouds have masses of 1000-60,000 solar and are typical of the more numerous, smaller Galactic molecular clouds. All of the clouds have recently made massive OB stars, and many have complex spatial and kinematic structures. The coincidence of IRAS sources and CO peaks suggests that many of the clouds have sites of star formation other than the optically visible H II region. Star-formation efficiencies are uncertain, with values for the clouds ranging from 0.02 to 0.6 with an average value of 0.2. There is no trend of the upper stellar mass limit with Galactic radius and with molecular cloud mass. 53 refs

  19. Constraining the low-mass Slope of the star formation sequence at 0.5 < z < 2.5

    International Nuclear Information System (INIS)

    Whitaker, Katherine E.; Henry, Alaina; Rigby, Jane R.; Franx, Marijn; Fumagalli, Mattia; Labbé, Ivo; Leja, Joel; Van Dokkum, Pieter G.; Momcheva, Ivelina G.; Nelson, Erica J.; Skelton, Rosalind E.; Brammer, Gabriel B.

    2014-01-01

    We constrain the slope of the star formation rate (SFR; log Ψ) to stellar mass (log M * ) relation down to log (M * /M ☉ ) = 8.4 (log (M * /M ☉ ) = 9.2) at z = 0.5 (z = 2.5) with a mass-complete sample of 39,106 star-forming galaxies selected from the 3D-HST photometric catalogs, using deep photometry in the CANDELS fields. For the first time, we find that the slope is dependent on stellar mass, such that it is steeper at low masses (log Ψ∝log M * ) than at high masses (log Ψ∝(0.3-0.6)log M * ). These steeper low-mass slopes are found for three different star formation indicators: the combination of the ultraviolet (UV) and infrared (IR), calibrated from a stacking analysis of Spitzer/MIPS 24 μm imaging; β-corrected UV SFRs; and Hα SFRs. The normalization of the sequence evolves differently in distinct mass regimes as well: for galaxies less massive than log (M * /M ☉ ) < 10 the specific SFR (Ψ/M * ) is observed to be roughly self-similar with Ψ/M * ∝(1 + z) 1.9 , whereas more massive galaxies show a stronger evolution with Ψ/M * ∝(1 + z) 2.2-3.5 for log (M * /M ☉ ) = 10.2-11.2. The fact that we find a steep slope of the star formation sequence for the lower mass galaxies will help reconcile theoretical galaxy formation models with the observations.

  20. Low-metallicity massive single stars with rotation. Evolutionary models applicable to I Zwicky 18

    NARCIS (Netherlands)

    Szécsi, D.; Langer, N.; Yoon, S.C.; Sanyal, D.; de Mink, S.; Evans, C.J.; Dermine, T.

    2015-01-01

    Context. Low-metallicity environments such as the early Universe and compact star-forming dwarf galaxies contain many massive stars. These stars influence their surroundings through intense UV radiation, strong winds and explosive deaths. A good understanding of low-metallicity environments requires

  1. THE 100 Myr STAR FORMATION HISTORY OF NGC 5471 FROM CLUSTER AND RESOLVED STELLAR PHOTOMETRY

    International Nuclear Information System (INIS)

    Garcia-Benito, Ruben; Perez, Enrique; Maiz Apellaniz, Jesus; Cervino, Miguel; Diaz, Angeles I.

    2011-01-01

    We show that star formation in the giant H II region NGC 5471 has been ongoing during the past 100 Myr. Using Hubble Space Telescope/Wide-Field Planetary Camera 2 F547M and F675W, ground-based JHK s , and GALEX FUV and NUV images, we have conducted a photometric study of the star formation history (SFH) in the massive giant extragalactic H II region NGC 5471 in M101. We perform a photometric study of the color-magnitude diagram (CMD) of the resolved stars and an integrated analysis of the main individual star-forming clusters and of NGC 5471 as a whole. The integrated UV-optical-NIR photometry for the whole region provides two different reference ages, 8 Myr and 60 Myr, revealing a complex SFH, clearly confirmed by the CMD-resolved stellar photometry analysis. The spatial distribution of the stars shows that the star formation in NGC 5471 has proceeded along the whole region during, at least, the last 100 Myr. The current ionizing clusters are enclosed within a large bubble, which is likely to have been produced by the stars that formed in a major event ∼20 Myr ago.

  2. TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

    Energy Technology Data Exchange (ETDEWEB)

    Liu Tie; Wu Yuefang; Zhang Huawei [Department of Astronomy, Peking University, 100871 Beijing (China); Qin Shengli, E-mail: liutiepku@gmail.com [I. Physikalisches Institut, Universitaet zu Koeln, Zuelpicher Str. 77, 50937 Koeln (Germany)

    2012-05-20

    The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10{sup 3} cm{sup -3} and kinematic temperature {approx}20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

  3. TRIGGERED STAR FORMATION SURROUNDING WOLF-RAYET STAR HD 211853

    International Nuclear Information System (INIS)

    Liu Tie; Wu Yuefang; Zhang Huawei; Qin Shengli

    2012-01-01

    The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 10 3 cm –3 and kinematic temperature ∼20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core 'A', which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the 'collect and collapse' process functions in this region. The star-forming activities in core 'A' seem to be affected by the 'radiation-driven implosion' process.

  4. SUPPRESSION OF STAR FORMATION IN NGC 1266

    Energy Technology Data Exchange (ETDEWEB)

    Alatalo, Katherine; Lanz, Lauranne; Bitsakis, Theodoros; Appleton, Philip N.; Ogle, Patrick M. [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Lacy, Mark; Lonsdale, Carol J. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Nyland, Kristina; Meier, David S. [Physics Department, New Mexico Tech, Socorro, NM 87801 (United States); Cales, Sabrina L. [Department of Astronomy, Faculty of Physical and Mathematical Sciences, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Chang, Philip [Department of Physics, University of Wisconsin—Milwaukee, Milwaukee, WI 53201 (United States); Davis, Timothy A.; De Zeeuw, P. T. [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany); Martín, Sergio, E-mail: kalatalo@ipac.caltech.edu [Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, Domaine Universitaire, F-38406 Saint Martin d' Hères (France)

    2015-01-01

    NGC 1266 is a nearby lenticular galaxy that harbors a massive outflow of molecular gas powered by the mechanical energy of an active galactic nucleus (AGN). It has been speculated that such outflows hinder star formation (SF) in their host galaxies, providing a form of feedback to the process of galaxy formation. Previous studies, however, indicated that only jets from extremely rare, high-power quasars or radio galaxies could impart significant feedback on their hosts. Here we present detailed observations of the gas and dust continuum of NGC 1266 at millimeter wavelengths. Our observations show that molecular gas is being driven out of the nuclear region at M-dot {sub out}≈110 M{sub ⊙} yr{sup –1}, of which the vast majority cannot escape the nucleus. Only 2 M {sub ☉} yr{sup –1} is actually capable of escaping the galaxy. Most of the molecular gas that remains is very inefficient at forming stars. The far-infrared emission is dominated by an ultra-compact (≲ 50 pc) source that could either be powered by an AGN or by an ultra-compact starburst. The ratio of the SF surface density (Σ{sub SFR}) to the gas surface density (Σ{sub H{sub 2}}) indicates that SF is suppressed by a factor of ≈50 compared to normal star-forming galaxies if all gas is forming stars, and ≈150 for the outskirt (98%) dense molecular gas if the central region is powered by an ultra-compact starburst. The AGN-driven bulk outflow could account for this extreme suppression by hindering the fragmentation and gravitational collapse necessary to form stars through a process of turbulent injection. This result suggests that even relatively common, low-power AGNs are able to alter the evolution of their host galaxies as their black holes grow onto the M-σ relation.

  5. THE NATURE OF HYPERVELOCITY STARS AND THE TIME BETWEEN THEIR FORMATION AND EJECTION

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Cohen, Judith G., E-mail: wbrown@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu, E-mail: jlc@astro.caltech.edu [Palomar Observatory, Mail Stop 249-17, California Institute of Technology, Pasadena, CA 91125 (United States)

    2012-07-20

    We obtain Keck HIRES spectroscopy of HVS5, one of the fastest unbound stars in the Milky Way halo. We show that HVS5 is a 3.62 {+-} 0.11 M{sub Sun} main-sequence B star at a distance of 50 {+-} 5 kpc. The difference between its age and its flight time from the Galactic center is 105 {+-} 18 (stat) {+-}30 (sys) Myr; flight times from locations elsewhere in the Galactic disk are similar. This 10{sup 8} yr 'arrival time' between formation and ejection is difficult to reconcile with any ejection scenario involving massive stars that live for only 10{sup 7} yr. For comparison, we derive arrival times of 10{sup 7} yr for two unbound runaway B stars, consistent with their disk origin where ejection results from a supernova in a binary system or dynamical interactions between massive stars in a dense star cluster. For HVS5, ejection during the first 10{sup 7} yr of its lifetime is ruled out at the 3{sigma} level. Together with the 10{sup 8} yr arrival times inferred for three other well-studied hypervelocity stars (HVSs), these results are consistent with a Galactic center origin for the HVSs. If the HVSs were indeed ejected by the central black hole, then the Galactic center was forming stars {approx_equal}200 Myr ago, and the progenitors of the HVSs took {approx_equal}100 Myr to enter the black hole's loss cone.

  6. THE NATURE OF HYPERVELOCITY STARS AND THE TIME BETWEEN THEIR FORMATION AND EJECTION

    International Nuclear Information System (INIS)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Cohen, Judith G.

    2012-01-01

    We obtain Keck HIRES spectroscopy of HVS5, one of the fastest unbound stars in the Milky Way halo. We show that HVS5 is a 3.62 ± 0.11 M ☉ main-sequence B star at a distance of 50 ± 5 kpc. The difference between its age and its flight time from the Galactic center is 105 ± 18 (stat) ±30 (sys) Myr; flight times from locations elsewhere in the Galactic disk are similar. This 10 8 yr 'arrival time' between formation and ejection is difficult to reconcile with any ejection scenario involving massive stars that live for only 10 7 yr. For comparison, we derive arrival times of 10 7 yr for two unbound runaway B stars, consistent with their disk origin where ejection results from a supernova in a binary system or dynamical interactions between massive stars in a dense star cluster. For HVS5, ejection during the first 10 7 yr of its lifetime is ruled out at the 3σ level. Together with the 10 8 yr arrival times inferred for three other well-studied hypervelocity stars (HVSs), these results are consistent with a Galactic center origin for the HVSs. If the HVSs were indeed ejected by the central black hole, then the Galactic center was forming stars ≅200 Myr ago, and the progenitors of the HVSs took ≅100 Myr to enter the black hole's loss cone.

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

    Science.gov (United States)

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

    2014-01-01

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

  8. The spatial extent and distribution of star formation in 3D-HST mergers at z ˜ 1.5

    Science.gov (United States)

    Schmidt, Kasper B.; Rix, Hans-Walter; da Cunha, Elisabete; Brammer, Gabriel B.; Cox, Thomas J.; van Dokkum, Pieter; Förster Schreiber, Natascha M.; Franx, Marijn; Fumagalli, Mattia; Jonsson, Patrik; Lundgren, Britt; Maseda, Michael V.; Momcheva, Ivelina; Nelson, Erica J.; Skelton, Rosalind E.; van der Wel, Arjen; Whitaker, Katherine E.

    2013-06-01

    We present an analysis of the spatial distribution of star formation in a sample of 60 visually identified galaxy merger candidates at z > 1. Our sample, drawn from the 3D-HST survey, is flux limited and was selected to have high star formation rates based on fits of their broad-band, low spatial resolution spectral energy distributions. It includes plausible pre-merger (close pairs) and post-merger (single objects with tidal features) systems, with total stellar masses and star formation rates derived from multiwavelength photometry. Here we use near-infrared slitless spectra from 3D-HST which produce Hα or [O III] emission line maps as proxies for star formation maps. This provides a first comprehensive high-resolution, empirical picture of where star formation occurred in galaxy mergers at the epoch of peak cosmic star formation rate. We find that detectable star formation can occur in one or both galaxy centres, or in tidal tails. The most common case (58 per cent) is that star formation is largely concentrated in a single, compact region, coincident with the centre of (one of) the merger components. No correlations between star formation morphology and redshift, total stellar mass or star formation rate are found. A restricted set of hydrodynamical merger simulations between similarly massive and gas-rich objects implies that star formation should be detectable in both merger components, when the gas fractions of the individual components are the same. This suggests that z ˜ 1.5 mergers typically occur between galaxies whose gas fractions, masses and/or star formation rates are distinctly different from one another.

  9. Neutron star formation and the weak interaction

    International Nuclear Information System (INIS)

    Burrows, A.

    1986-01-01

    The only known direct diagnostic of the central event is its neutrino emission. The imprint of the entire internal evolution is stamped on the spectrum, mix of flavors, luminosities, and features of the accompanying neutrino burst. Detection and scrutiny of this neutrino signal will test theories concerning stellar collapse, type II supernovae, and the formation of neutron stars in ways impossible by other means. Despite the fact that an incredible 3x10 53 ergs may be emitted in neutrinos after the initiation of collapse, the very weakness of the neutrino/matter interaction that allows them to penetrate the stellar envelope and escape makes their detection at the Earth very difficult. Though neutrino astronomy is not yet a mature discipline, the physical theories of collapse have progressed to a sufficient degree that specific and detailed predictions can be made about the neutrino emissions that with future detector technology might be tested. The time seems propitious to summarize and review what is known and suspected about the neutrino signature of collapse, the potential for its detection, and how it can be used to test our ideas about the death of massive stars and the birth of neutrino stars. (orig./BBOE)

  10. Stellar and wind parameters of massive stars from spectral analysis

    Science.gov (United States)

    Araya, Ignacio; Curé, Michel

    2017-11-01

    The only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line-force parameters α, k and δ (from the line-driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line-force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line-force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind-Momentum Luminosity Relationship (WLR).

  11. FORMATION RATES OF POPULATION III STARS AND CHEMICAL ENRICHMENT OF HALOS DURING THE REIONIZATION ERA

    International Nuclear Information System (INIS)

    Trenti, Michele; Stiavelli, Massimo

    2009-01-01

    The first stars in the universe formed out of pristine primordial gas clouds that were radiatively cooled to a few hundreds of degrees kelvin either via molecular or atomic (Lyman-α) hydrogen lines. This primordial mode of star formation was eventually quenched once radiative and/or chemical (metal enrichment) feedbacks marked the transition to Population II stars. In this paper, we present a model for the formation rate of Population III stars based on Press-Schechter modeling coupled with analytical recipes for gas cooling and radiative feedback. Our model also includes a novel treatment for metal pollution based on self-enrichment due to a previous episode of Population III star formation in progenitor halos. With this model, we derive the star formation history of Population III stars, their contribution to the reionization of the universe and the time of the transition from Population III star formation in minihalos (M ∼ 10 6 M sun , cooled via molecular hydrogen) to that in more massive halos (M ∼> 2 x 10 7 M sun , where atomic hydrogen cooling is also possible). We consider a grid of models highlighting the impact of varying the values for the free parameters used, such as star formation and feedback efficiency. The most critical factor is the assumption that only one Population III star is formed in a halo. In this scenario, metal-free stars contribute only to a minor fraction of the total number of photons required to reionize the universe. In addition, metal-free star formation is primarily located in minihalos, and chemically enriched halos become the dominant locus of star formation very early in the life of the universe-at redshift z ∼ 25-even assuming a modest fraction (0.5%) of enriched gas converted in stars. If instead multiple metal-free stars are allowed to form out of a single halo, then there is an overall boost of Population III star formation, with a consequent significant contribution to the reionizing radiation budget. In addition

  12. Uncertainties in s-process nucleosynthesis in massive stars determined by Monte Carlo variations

    Science.gov (United States)

    Nishimura, N.; Hirschi, R.; Rauscher, T.; St. J. Murphy, A.; Cescutti, G.

    2017-08-01

    The s-process in massive stars produces the weak component of the s-process (nuclei up to A ˜ 90), in amounts that match solar abundances. For heavier isotopes, such as barium, production through neutron capture is significantly enhanced in very metal-poor stars with fast rotation. However, detailed theoretical predictions for the resulting final s-process abundances have important uncertainties caused both by the underlying uncertainties in the nuclear physics (principally neutron-capture reaction and β-decay rates) as well as by the stellar evolution modelling. In this work, we investigated the impact of nuclear-physics uncertainties relevant to the s-process in massive stars. Using a Monte Carlo based approach, we performed extensive nuclear reaction network calculations that include newly evaluated upper and lower limits for the individual temperature-dependent reaction rates. We found that most of the uncertainty in the final abundances is caused by uncertainties in the neutron-capture rates, while β-decay rate uncertainties affect only a few nuclei near s-process branchings. The s-process in rotating metal-poor stars shows quantitatively different uncertainties and key reactions, although the qualitative characteristics are similar. We confirmed that our results do not significantly change at different metallicities for fast rotating massive stars in the very low metallicity regime. We highlight which of the identified key reactions are realistic candidates for improved measurement by future experiments.

  13. Formation of stars and star clusters in colliding galaxies

    International Nuclear Information System (INIS)

    Belles, Pierre-Emmanuel

    2012-01-01

    Mergers are known to be essential in the formation of large-scale structures and to have a significant role in the history of galaxy formation and evolution. Besides a morphological transformation, mergers induce important bursts of star formation. These starburst are characterised by high Star Formation Efficiencies (SFEs) and Specific Star Formation Rates, i.e., high Star Formation Rates (SFR) per unit of gas mass and high SFR per unit of stellar mass, respectively, compared to spiral galaxies. At all redshifts, starburst galaxies are outliers of the sequence of star-forming galaxies defined by spiral galaxies. We have investigated the origin of the starburst-mode of star formation, in three local interacting systems: Arp 245, Arp 105 and NGC 7252. We combined high-resolution JVLA observations of the 21-cm line, tracing the HI diffuse gas, with UV GALEX observations, tracing the young star-forming regions. We probe the local physical conditions of the Inter-Stellar Medium (ISM) for independent star-forming regions and explore the atomic-to-dense gas transformation in different environments. The SFR/HI ratio is found to be much higher in central regions, compared to outer regions, showing a higher dense gas fraction (or lower HI gas fraction) in these regions. In the outer regions of the systems, i.e., the tidal tails, where the gas phase is mostly atomic, we find SFR/HI ratios higher than in standard HI-dominated environments, i.e., outer discs of spiral galaxies and dwarf galaxies. Thus, our analysis reveals that the outer regions of mergers are characterised by high SFEs, compared to the standard mode of star formation. The observation of high dense gas fractions in interacting systems is consistent with the predictions of numerical simulations; it results from the increase of the gas turbulence during a merger. The merger is likely to affect the star-forming properties of the system at all spatial scales, from large scales, with a globally enhanced turbulence

  14. Super massive black hole in galactic nuclei with tidal disruption of stars

    International Nuclear Information System (INIS)

    Zhong, Shiyan; Berczik, Peter; Spurzem, Rainer

    2014-01-01

    Tidal disruption of stars by super massive central black holes from dense star clusters is modeled by high-accuracy direct N-body simulation. The time evolution of the stellar tidal disruption rate, the effect of tidal disruption on the stellar density profile, and, for the first time, the detailed origin of tidally disrupted stars are carefully examined and compared with classic papers in the field. Up to 128k particles are used in simulation to model the star cluster around a super massive black hole, and we use the particle number and the tidal radius of the black hole as free parameters for a scaling analysis. The transition from full to empty loss-cone is analyzed in our data, and the tidal disruption rate scales with the particle number, N, in the expected way for both cases. For the first time in numerical simulations (under certain conditions) we can support the concept of a critical radius of Frank and Rees, which claims that most stars are tidally accreted on highly eccentric orbits originating from regions far outside the tidal radius. Due to the consumption of stars moving on radial orbits, a velocity anisotropy is found inside the cluster. Finally we estimate the real galactic center based on our simulation results and the scaling analysis.

  15. Super Massive Black Hole in Galactic Nuclei with Tidal Disruption of Stars

    Science.gov (United States)

    Zhong, Shiyan; Berczik, Peter; Spurzem, Rainer

    2014-09-01

    Tidal disruption of stars by super massive central black holes from dense star clusters is modeled by high-accuracy direct N-body simulation. The time evolution of the stellar tidal disruption rate, the effect of tidal disruption on the stellar density profile, and, for the first time, the detailed origin of tidally disrupted stars are carefully examined and compared with classic papers in the field. Up to 128k particles are used in simulation to model the star cluster around a super massive black hole, and we use the particle number and the tidal radius of the black hole as free parameters for a scaling analysis. The transition from full to empty loss-cone is analyzed in our data, and the tidal disruption rate scales with the particle number, N, in the expected way for both cases. For the first time in numerical simulations (under certain conditions) we can support the concept of a critical radius of Frank & Rees, which claims that most stars are tidally accreted on highly eccentric orbits originating from regions far outside the tidal radius. Due to the consumption of stars moving on radial orbits, a velocity anisotropy is found inside the cluster. Finally we estimate the real galactic center based on our simulation results and the scaling analysis.

  16. FIRST INVESTIGATION OF THE COMBINED IMPACT OF IONIZING RADIATION AND MOMENTUM WINDS FROM A MASSIVE STAR ON A SELF-GRAVITATING CORE

    International Nuclear Information System (INIS)

    Ngoumou, Judith; Hubber, David; Dale, James E.; Burkert, Andreas

    2015-01-01

    Massive stars shape the surrounding interstellar matter (ISM) by emitting ionizing photons and ejecting material through stellar winds. To study the impact of the momentum from the wind of a massive star on the surrounding neutral or ionized material, we implemented a new HEALPix-based momentum-conserving wind scheme in the smoothed particle hydrodynamics (SPH) code SEREN. A qualitative study of the impact of the feedback from an O7.5-like star on a self-gravitating sphere shows that on its own, the transfer of momentum from a wind onto cold surrounding gas has both a compressing and dispersing effect. It mostly affects gas at low and intermediate densities. When combined with a stellar source's ionizing ultraviolet (UV) radiation, we find the momentum-driven wind to have little direct effect on the gas. We conclude that during a massive star's main sequence, the UV ionizing radiation is the main feedback mechanism shaping and compressing the cold gas. Overall, the wind's effects on the dense gas dynamics and on the triggering of star formation are very modest. The structures formed in the ionization-only simulation and in the combined feedback simulation are remarkably similar. However, in the combined feedback case, different SPH particles end up being compressed. This indicates that the microphysics of gas mixing differ between the two feedback simulations and that the winds can contribute to the localized redistribution and reshuffling of gas

  17. Thermal generation of the magnetic field in the surface layers of massive stars

    Science.gov (United States)

    Urpin, V.

    2017-11-01

    A new magnetic field-generation mechanism based on the Nernst effect is considered in hot massive stars. This mechanism can operate in the upper atmospheres of O and B stars where departures from the LTE form a region with the inverse temperature gradient.

  18. Two massive stars possibly ejected from NGC 3603 via a three-body encounter

    Science.gov (United States)

    Gvaramadze, V. V.; Kniazev, A. Y.; Chené, A.-N.; Schnurr, O.

    2013-03-01

    We report the discovery of a bow-shock-producing star in the vicinity of the young massive star cluster NGC 3603 using archival data of the Spitzer Space Telescope. Follow-up optical spectroscopy of this star with Gemini-South led to its classification as O6 V. The orientation of the bow shock and the distance to the star (based on its spectral type) suggest that the star was expelled from the cluster, while the young age of the cluster (˜2 Myr) implies that the ejection was caused by a dynamical few-body encounter in the cluster's core. The relative position on the sky of the O6 V star and a recently discovered O2 If*/WN6 star (located on the opposite side of NGC 3603) allows us to propose that both objects were ejected from the cluster via the same dynamical event - a three-body encounter between a single (O6 V) star and a massive binary (now the O2 If*/WN6 star). If our proposal is correct, then one can `weigh' the O2 If*/WN6 star using the conservation of the linear momentum. Given a mass of the O6 V star of ≈30 M⊙, we found that at the moment of ejection the mass of the O2 If*/WN6 star was ≈175 M⊙. Moreover, the observed X-ray luminosity of the O2 If*/WN6 star (typical of a single star) suggests that the components of this originally binary system have merged (e.g., because of encounter hardening).

  19. Ionization impact on molecular clouds and star formation: Numerical simulations and observations

    International Nuclear Information System (INIS)

    Tremblin, Pascal

    2012-01-01

    At all the scales of Astrophysics, the impact of the ionization from massive stars is a crucial issue. At the galactic scale, the ionization can regulate star formation by supporting molecular clouds against gravitational collapse and at the stellar scale, indications point toward a possible birth place of the Solar System close to massive stars. At the molecular cloud scale, it is clear that the hot ionized gas compresses the surrounding cold gas, leading to the formation of pillars, globules, and shells of dense gas in which some young stellar objects are observed. What are the formation mechanisms of these structures? Are the formation of these young stellar objects triggered or would have they formed anyway? Do massive stars have an impact on the distribution of the surrounding gas? Do they have an impact on the mass distribution of stars (the initial mass function, IMF)? This thesis aims at shedding some light on these questions, by focusing especially on the formation of the structures between the cold and the ionized gas. We present the state of the art of the theoretical and observational works on ionized regions (H II regions) and we introduce the numerical tools that have been developed to model the ionization in the hydrodynamic simulations with turbulence performed with the HERACLES code. Thanks to the simulations, we present a new model for the formation of pillars based on the curvature and collapse of the dense shell on itself and a new model for the formations of cometary globules based on the turbulence of the cold gas. Several diagnostics have been developed to test these new models in the observations. If pillars are formed by the collapse of the dense shell on itself, the velocity spectrum of a nascent pillar presents a large spectra with a red-shifted and a blue-shifted components that are caused by the foreground and background parts of the shell that collapse along the line of sight. If cometary globules emerge because of the turbulence of

  20. Star Formation in low mass galaxies

    Science.gov (United States)

    Mehta, Vihang

    2018-01-01

    Our current hierarchical view of the universe asserts that the large galaxies we see today grew via mergers of numerous smaller galaxies. As evidenced by recent literature, the collective impact of these low mass galaxies on the universe is more substantial than previously thought. Studying the growth and evolution of these low mass galaxies is critical to our understanding of the universe as a whole. Star formation is one of the most important ongoing processes in galaxies. Forming stars is fundamental to the growth of a galaxy. One of the main goals of my thesis is to analyze the star formation in these low mass galaxies at different redshifts.Using the Hubble UltraViolet Ultra Deep Field (UVUDF), I investigate the star formation in galaxies at the peak of the cosmic star formation history using the ultraviolet (UV) light as a star formation indicator. Particularly, I measure the UV luminosity function (LF) to probe the volume-averaged star formation properties of galaxies at these redshifts. The depth of the UVUDF is ideal for a direct measurement of the faint end slope of the UV LF. This redshift range also provides a unique opportunity to directly compare UV to the "gold standard" of star formation indicators, namely the Hα nebular emission line. A joint analysis of the UV and Hα LFs suggests that, on average, the star formation histories in low mass galaxies (~109 M⊙) are more bursty compared to their higher mass counterparts at these redshifts.Complementary to the analysis of the average star formation properties of the bulk galaxy population, I investigate the details of star formation in some very bursty galaxies at lower redshifts selected from Spitzer Large Area Survey with Hyper-Suprime Cam (SPLASH). Using a broadband color-excess selection technique, I identify a sample of low redshift galaxies with bright nebular emission lines in the Subaru-XMM Deep Field (SXDF) from the SPLASH-SXDF catalog. These galaxies are highly star forming and have

  1. Star-forming galaxy models: Blending star formation into TREESPH

    Science.gov (United States)

    Mihos, J. Christopher; Hernquist, Lars

    1994-01-01

    We have incorporated star-formation algorithms into a hybrid N-body/smoothed particle hydrodynamics code (TREESPH) in order to describe the star forming properties of disk galaxies over timescales of a few billion years. The models employ a Schmidt law of index n approximately 1.5 to calculate star-formation rates, and explicitly include the energy and metallicity feedback into the Interstellar Medium (ISM). Modeling the newly formed stellar population is achieved through the use of hybrid SPH/young star particles which gradually convert from gaseous to collisionless particles, avoiding the computational difficulties involved in creating new particles. The models are shown to reproduce well the star-forming properties of disk galaxies, such as the morphology, rate of star formation, and evolution of the global star-formation rate and disk gas content. As an example of the technique, we model an encounter between a disk galaxy and a small companion which gives rise to a ring galaxy reminiscent of the Cartwheel (AM 0035-35). The primary galaxy in this encounter experiences two phases of star forming activity: an initial period during the expansion of the ring, and a delayed phase as shocked material in the ring falls back into the central regions.

  2. Polarization and infrared imaging of regions of star formation

    International Nuclear Information System (INIS)

    Moneti, A.

    1985-01-01

    Observational studies of two regions of star formation, the Taurus cloud and the BN-KL region of Orion, are presented. The magnetic field structure in the Taurus cloud was studied in order to investigate its possible role in the evolution of the cloud. It was found that the magnetic field is generally perpendicular to the elongated structures that make up the cloud, and it is deduced that the observed structure could be due to the effects of the magnetic field during the early stages of collapse. In addition, it was found that the magnetic field may have prevented the formation of massive stars by inhibiting the collapse of large cores, while not affecting the collapse of the small ones. Using a new near-infrared array camera, high resolution (1'') images of several young stars embedded in the cloud were obtained. Most of these sources have extended, spatially resolved circumstellar shells. High resolution images of the BN-KL region of Orion at four wavelengths between 1.65 and 4.7 μm were also obtained. At 1.65 μm a large trough is seen in the overall nebulosity; it is suggested that the observed trough is due to the doughnut of material around IRc2 as it obscures the background nebulosity

  3. The Properties of the Massive Star-forming Galaxies with an Outside-in Assembly Mode

    Science.gov (United States)

    Wang, Enci; Kong, Xu; Wang, Huiyuan; Wang, Lixin; Lin, Lin; Gao, Yulong; Liu, Qing

    2017-08-01

    Previous findings show that massive ({M}* > {10}10 {M}⊙ ) star-forming (SF) galaxies usually have an “inside-out” stellar mass assembly mode. In this paper, we have for the first time selected a sample of 77 massive SF galaxies with an “outside-in” assembly mode (called the “targeted sample”) from the Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey. For comparison, two control samples are constructed from the MaNGA sample matched in stellar mass: a sample of 154 normal SF galaxies and a sample of 62 quiescent galaxies. In contrast to normal SF galaxies, the targeted galaxies appear to be smoother and more bulge-dominated and have a smaller size and higher concentration, star formation rate, and gas-phase metallicity as a whole. However, they have a larger size and lower concentration than quiescent galaxies. Unlike the normal SF sample, the targeted sample exhibits a slightly positive gradient of the 4000 Å break and a pronounced negative gradient of Hα equivalent width. Furthermore, the median surface mass density profile is between those of the normal SF and quiescent samples, indicating that the gas accretion of quiescent galaxies is not likely to be the main approach for the outside-in assembly mode. Our results suggest that the targeted galaxies are likely in the transitional phase from normal SF galaxies to quiescent galaxies, with rapid ongoing central stellar mass assembly (or bulge growth). We discuss several possible formation mechanisms for the outside-in mass assembly mode.

  4. The Spatial Extent and Distribution of Star Formation in 3D-HST Mergers at z is approximately 1.5

    Science.gov (United States)

    Schmidt, Kasper B.; Rix, Hans-Walter; da Cunha, Elisabete; Brammer, Gabriel B.; Cox, Thomas J.; Van Dokkum, Pieter; Foerster Schreiber, Natascha M.; Franx, Marijn; Fumagalli, Mattia; Jonsson, Patrik; hide

    2013-01-01

    We present an analysis of the spatial distribution of star formation in a sample of 60 visually identified galaxy merger candidates at z greater than 1. Our sample, drawn from the 3D-HST survey, is flux-limited and was selected to have high star formation rates based on fits of their broad-band, low spatial resolution spectral energy distributions. It includes plausible pre-merger (close pairs) and post-merger (single objects with tidal features) systems,with total stellar masses and star formation rates derived from multi-wavelength photometry. Here we use near-infrared slitless spectra from 3D-HST which produce H or [OIII] emission line maps as proxies for star-formation maps. This provides a first comprehensive high-resolution, empirical picture of where star formation occurred in galaxy mergers at the epoch of peak cosmic star formation rate. We find that detectable star formation can occur in one or both galaxy centres, or in tidal tails. The most common case (58%) is that star formation is largely concentrated in a single, compact region, coincident with the centre of (one of) the merger components. No correlations between star formation morphology and redshift, total stellar mass, or star formation rate are found. A restricted set of hydrodynamical merger simulationsbetween similarly massive and gas-rich objects implies that star formation should be detectable in both merger components, when the gas fractions of the individual components are the same. This suggests that z is approximately 1.5 mergers typically occur between galaxies whose gas fractions, masses, andor star formation rates are distinctly different from one another.

  5. Stellar Population and Star Formation History of the Distant Galactic H II Regions NGC 2282 and Sh2-149

    Science.gov (United States)

    Dutta, S.; Mondal, S.; Jose, J.; Das, R. K.

    2017-06-01

    We present here the recent results on two distant Galactic H II regions, namely NGC 2282 and Sh2-149, obtained with multiwavelength observations. Our optical spectroscopic analysis of the bright sources have been used to identify the massive members, and to derive the fundamental parameters such as age and distance of these regions. Using IR color-color criteria and Hα-emission properties, we have identified and classified the candidate young stellar objects (YSOs) in these regions. The 12CO(1-0) continuum maps along with the K-band extinction maps, and spatial distribution of YSOs are used to investigate the structure and morphology of the molecular cloud associated with these H II regions. Overall analysis of these regions suggests that the star formation occurs at the locations of the denser gas, and we also find possible evidences of the induced star formation due to the feedback from massive stars to its surrounding molecular medium.

  6. Early-type galaxies at intermediate redshift observed with Hubble space telescope WFC3: perspectives on recent star formation

    Energy Technology Data Exchange (ETDEWEB)

    Rutkowski, Michael J. [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Jeong, Hyunjin; Yi, Sukyoung K. [Department of Astronomy, Yonsei University 134, Shinchon-dong, Sudaemun-gu, Seoul 120-179 (Korea, Republic of); Cohen, Seth H.; Windhorst, Rogier A. [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404 (United States); Kaviraj, Sugata [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom); Ryan, Russell E. Jr.; Koekemoer, Anton [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Hathi, Nimish P. [Aix Marseille Université, CNRS, LAM, UMR 7326, F-13388, Marseille (France); Dopita, Michael A. [Research School of Physics and Astronomy, The Australian National University, Canberra, ACT 2611 (Australia)

    2014-12-01

    We present an analysis of the stellar populations of 102 visually selected early-type galaxies (ETGs) with spectroscopic redshifts (0.35 ≲ z ≲ 1.5) from observations in the Early Release Science program with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We fit one- and two-component synthetic stellar models to the ETGs UV-optical-near-IR spectral energy distributions and find that a large fraction (∼40%) are likely to have experienced a minor (f{sub YC} ≲ 10% of stellar mass) burst of recent (t{sub YC} ≲ 1 Gyr) star formation. The measured age and mass fraction of the young stellar populations do not strongly trend with measurements of galaxy morphology. We note that massive (M > 10{sup 10.5} M {sub ☉}) recent star-forming ETGs appear to have larger sizes. Furthermore, high-mass, quiescent ETGs identified with likely companions populate a distinct region in the size-mass parameter space, in comparison with the distribution of massive ETGs with evidence of recent star formation (RSF). We conclude that both mechanisms of quenching star formation in disk-like ETGs and (gas-rich, minor) merger activity contribute to the formation of young stars and the size-mass evolution of intermediate redshift ETGs. The number of ETGs for which we have both HST WFC3 panchromatic (especially UV) imaging and spectroscopically confirmed redshifts is relatively small, therefore, a conclusion about the relative roles of both of these mechanisms remains an open question.

  7. Infra-red data of extended sources as a measure of the star formation rate

    International Nuclear Information System (INIS)

    Puget, J.-L.

    1985-01-01

    Molecular cloud complexes are gravitationally bound systems which contain molecular clouds, HII regions and possibly OB associations after they evaporated their parent cloud. A large fraction of the energy (50%) radiated by the O and B stars is converted into infra-red. Less massive stars still embedded in molecular clouds or still in their vicinity will also see most of their radiation absorbed by dust and reemitted in the infra-red. The two quantities the author deduces directly from the data are: the ratio of the far-infra-red luminosity due to recently formed stars to the mass of gas, as a measure of the star formation rate; and the infra-red excess (IRE): the ratio of the far-infra-red luminosity to the luminosity of HII regions in the Lyman α line, which gives information on the initial mass function. Finally he discusses the possible links between star formation and some of the relevant physical conditions in the molecular clouds: amount and temperature distribution of dust. (Auth.)

  8. Black Hole Growth Is Mainly Linked to Host-galaxy Stellar Mass Rather Than Star Formation Rate

    Science.gov (United States)

    Yang, G.; Chen, C.-T. J.; Vito, F.; Brandt, W. N.; Alexander, D. M.; Luo, B.; Sun, M. Y.; Xue, Y. Q.; Bauer, F. E.; Koekemoer, A. M.; Lehmer, B. D.; Liu, T.; Schneider, D. P.; Shemmer, O.; Trump, J. R.; Vignali, C.; Wang, J.-X.

    2017-06-01

    We investigate the dependence of black hole accretion rate (BHAR) on host-galaxy star formation rate (SFR) and stellar mass (M *) in the CANDELS/GOODS-South field in the redshift range of 0.5≤slant zteam through spectral energy distribution fitting. The average BHAR is correlated positively with both SFR and M *, and the BHAR-SFR and BHAR-M * relations can both be described acceptably by linear models with a slope of unity. However, BHAR appears to be correlated more strongly with M * than SFR. This result indicates that M * is the primary host-galaxy property related to supermassive black hole (SMBH) growth, and the apparent BHAR-SFR relation is largely a secondary effect due to the star-forming main sequence. Among our sources, massive galaxies ({M}* ≳ {10}10{M}⊙ ) have significantly higher BHAR/SFR ratios than less massive galaxies, indicating that the former have higher SMBH fueling efficiency and/or higher SMBH occupation fraction than the latter. Our results can naturally explain the observed proportionality between {M}{BH} and M * for local giant ellipticals and suggest that their {M}{BH}/{M}* is higher than that of local star-forming galaxies. Among local star-forming galaxies, massive systems might have higher {M}{BH}/{M}* compared to dwarfs.

  9. A rare encounter with very massive stars in NGC 3125-A1

    Energy Technology Data Exchange (ETDEWEB)

    Wofford, Aida [UPMC-CNRS, UMR7095, Institut d' Astrophysique de Paris, F-75014 Paris (France); Leitherer, Claus [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Chandar, Rupali [University of Toledo, Department of Physics and Astronomy, Toledo, OH 43606 (United States); Bouret, Jean-Claude, E-mail: wofford@iap.edu [Aix Marseille Universite, CNRS, LAM (Laboratoire d' Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France)

    2014-02-01

    Super star cluster A1 in the nearby starburst galaxy NGC 3125 is characterized by broad He II λ1640 emission (FWHM ∼ 1200 km s{sup –1}) of unprecedented strength (equivalent width, EW = 7.1 ± 0.4 Å). Previous attempts to characterize the massive star content in NGC 3125-A1 were hampered by the low resolution of the UV spectrum and the lack of co-spatial panchromatic data. We obtained far-UV to near-IR spectroscopy of the two principal emitting regions in the galaxy with the Space Telescope Imaging Spectrograph and the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We use these data to study three clusters in the galaxy, A1, B1, and B2. We derive cluster ages of 3-4 Myr, intrinsic reddenings of E(B – V) = 0.13, 0.15, and 0.13, and cluster masses of 1.7 × 10{sup 5}, 1.4 × 10{sup 5}, and 1.1 × 10{sup 5} M {sub ☉}, respectively. A1 and B2 show O V λ1371 absorption from massive stars, which is rarely seen in star-forming galaxies, and have Wolf-Rayet (WR) to O star ratios of N(WN5-6)/N(O) = 0.23 and 0.10, respectively. The high N(WN5-6)/N(O) ratio of A1 cannot be reproduced by models that use a normal initial mass function (IMF) and generic WR star line luminosities. We rule out that the extraordinary He II λ1640 emission and O V λ1371 absorption of A1 are due to an extremely flat upper IMF exponent, and suggest that they originate in the winds of very massive (>120 M {sub ☉}) stars. In order to reproduce the properties of peculiar clusters such as A1, the present grid of stellar evolution tracks implemented in Starburst99 needs to be extended to masses >120 M {sub ☉}.

  10. Evolution of a massive binary in a star field

    International Nuclear Information System (INIS)

    Baranov, A.S.

    1984-01-01

    The orbital evolution of a massive binary system interacting with a background field of single stars whose phase density is homogeneous in configuration space is considered. The velocity distribution is assumed isotropic up to some limiting value, and a typical field star is regarded as having a velocity much higher than the orbital speed of the pair components. An expression is derived for the transfer of energy from the binary to the field stars. The time evolution of the orbit parameters a, e is established, and the evolution rate is estimated for Kardashev's (1983) model galactic nucleus containing a central black-hole binary. On the above assumptions the components should become twice as close together within only a few tens of millennia, although the picture may change fundamentally if the nucleus is rotating. 13 references

  11. THE FRAGMENTATION OF MAGNETIZED, MASSIVE STAR-FORMING CORES WITH RADIATIVE FEEDBACK

    Energy Technology Data Exchange (ETDEWEB)

    Myers, Andrew T.; McKee, Christopher F. [Department of Physics, University of California, Berkeley, Berkeley, CA 94720 (United States); Cunningham, Andrew J. [Lawrence Livermore National Laboratory, P.O. Box 808, L-23, Livermore, CA 94550 (United States); Klein, Richard I. [Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720 (United States); Krumholz, Mark R., E-mail: atmyers@berkeley.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2013-04-01

    We present a set of three-dimensional, radiation-magnetohydrodynamic calculations of the gravitational collapse of massive (300 M{sub Sun }), star-forming molecular cloud cores. We show that the combined effects of magnetic fields and radiative feedback strongly suppress core fragmentation, leading to the production of single-star systems rather than small clusters. We find that the two processes are efficient at suppressing fragmentation in different regimes, with the feedback most effective in the dense, central region and the magnetic field most effective in more diffuse, outer regions. Thus, the combination of the two is much more effective at suppressing fragmentation than either one considered in isolation. Our work suggests that typical massive cores, which have mass-to-flux ratios of about 2 relative to critical, likely form a single-star system, but that cores with weaker fields may form a small star cluster. This result helps us understand why the observed relationship between the core mass function and the stellar initial mass function holds even for {approx}100 M{sub Sun} cores with many thermal Jeans masses of material. We also demonstrate that a {approx}40 AU Keplerian disk is able to form in our simulations, despite the braking effect caused by the strong magnetic field.

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

    Science.gov (United States)

    Grebel, E. K.

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

  13. REVERSAL OF FORTUNE: INCREASED STAR FORMATION EFFICIENCIES IN THE EARLY HISTORIES OF DWARF GALAXIES?

    International Nuclear Information System (INIS)

    Madau, Piero; Weisz, Daniel R.; Conroy, Charlie

    2014-01-01

    On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe

  14. Reversal of Fortune: Increased Star Formation Efficiencies in the Early Histories of Dwarf Galaxies?

    Science.gov (United States)

    Madau, Piero; Weisz, Daniel R.; Conroy, Charlie

    2014-08-01

    On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe.

  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. Bursting star formation and the overabundance of Wolf-Rayet stars

    International Nuclear Information System (INIS)

    Bodigfee, G.; Deloore, C.

    1985-01-01

    The ratio of the number of WR-stars to their OB progenitors appears to be significantly higher in some extragalactic systems than in our Galaxy. This overabundance of Wolf-Rayet-stars can be explained as a consequence of a recent burst of star formation. It is suggested that this burst is the manifestation of a long period nonlinear oscillation in the star formation process, produced by positive feedback effects between young stars and the interstellar medium. Star burst galaxies with large numbers of WR-stars must generate gamma fluxes but due to the distance, all of them are beyond the reach of present-day detectors, except probably 30 Dor

  17. WHEELS OF FIRE. IV. STAR FORMATION AND THE NEUTRAL INTERSTELLAR MEDIUM IN THE RING GALAXY AM0644-741

    International Nuclear Information System (INIS)

    Higdon, James L.; Higdon, Sarah J. U.; Rand, Richard J.

    2011-01-01

    We combine data from the Australia Telescope National Facility and Swedish ESO Submillimeter Telescope to investigate the neutral interstellar medium (ISM) in AM0644-741, a large and robustly star-forming ring galaxy. The galaxy's ISM is concentrated in the 42 kpc diameter starburst ring, but appears dominated by atomic gas, with a global molecular fraction (f mol ) of only 0.062 ± 0.005. Apart from the starburst peak, the gas ring appears stable against the growth of gravitational instabilities (Q gas = 3-11). Including the stellar component lowers Q overall, but not enough to make Q 2 content. AM0644-741's star formation law is highly peculiar: H I obeys a Schmidt law while H 2 is uncorrelated with star formation rate density. Photodissociation models yield low volume densities in the ring, especially in the starburst quadrant (n ∼ 2 cm -3 ), implying a warm neutral medium dominated ISM. At the same time, the ring's pressure and ambient far-ultraviolet radiation field lead to the expectation of a predominantly molecular ISM. We argue that the ring's high SFE, low f mol and n, and peculiar star formation law follow from the ISM's ∼> 100 Myr confinement time in the starburst ring, which amplifies the destructive effects of embedded massive stars and supernovae. As a result, the ring's molecular ISM becomes dominated by small clouds, causing M H 2 to be significantly underestimated by 12 CO line fluxes: in effect, X CO >> X Gal despite the ring's ≥solar metallicity. The observed H I is primarily a low-density photodissociation product, i.e., a tracer rather than a precursor of massive star formation. Such an 'over-cooked' ISM may be a general characteristic of evolved starburst ring galaxies.

  18. Star formations rates in the Galaxy

    International Nuclear Information System (INIS)

    Smith, L.F.; Mezger, P.G.; Biermann, P.

    1978-01-01

    Data relevant to giant HII regions in the Galaxy are collected. The production rate for Lyman continuum photons by O stars in giant HII regions is 4.7 10 52 s -1 in the whole Galaxy. The corresponding present rate of star formation is M (sun)/yr, of which 74% occurs in main spiral arms, 13% in the interarm region and 13% in the galactic center. The star formation rates, the observed heavy element and deuterium abundances in the solar neighbourhood are compared to model predictions based on star formation proportional to a power (k) of the gas surface density. The mass function is terminated at Msub(u)=100 M (sun) above and M 1 below. Msub(u)=50 M (sun) is also considered. Comparing with data derived from observations a) the star formation rate, b) metal abundances, c) deuterium abundances, and d) colors of the stellar population, we find that models of k=1/2 to 1, and M 1 1 M (sun) are formed together with O and B stars, but under rather special conditions of the interstellar gas, while lower mass stars form wherever dense molecular clouds exist. The high rate of star formation in the galactic center may represent a burst. (orig.) [de

  19. PHIBSS: MOLECULAR GAS CONTENT AND SCALING RELATIONS IN z ∼ 1-3 MASSIVE, MAIN-SEQUENCE STAR-FORMING GALAXIES

    International Nuclear Information System (INIS)

    Tacconi, L. J.; Genzel, R.; Wuyts, S.; Förster Schreiber, N. M.; Gracia-Carpio, J.; Lutz, D.; Saintonge, A.; Neri, R.; Cox, P.; Combes, F.; Bolatto, A.; Cooper, M. C.; Bournaud, F.; Burkert, A.; Comerford, J.; Davis, M.; Newman, S.; García-Burillo, S.; Naab, T.; Omont, A.

    2013-01-01

    We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z ∼ 1.2 and 2.2, with log(M * (M ☉ )) ≥ 10.4 and log(SFR(M ☉ /yr)) ≥ 1.5. Including a correction for the incomplete coverage of the M * -SFR plane, and adopting a ''Galactic'' value for the CO-H 2 conversion factor, we infer average gas fractions of ∼0.33 at z ∼ 1.2 and ∼0.47 at z ∼ 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z ∼ 1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z = 1-3 SFGs is near-linear, with a ∼0.7 Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z ∼ 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M * , gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z ∼ 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.

  20. MASSIVE STAR FORMATION IN THE LMC. I. N159 AND N160 COMPLEXES

    Energy Technology Data Exchange (ETDEWEB)

    Gordon, Michael S.; Jones, Terry J.; Gehrz, Robert D. [Minnesota Institute for Astrophysics, School of Physics and Astronomy 116 Church St SE, University of Minnesota, Minneapolis, MN 55455 (United States); Helton, L. Andrew [USRA–SOFIA Science Center, NASA Ames Research Center, Moffett Field, CA 94035 (United States)

    2017-01-10

    We present images and spectral energy distributions (SEDs) of massive young stellar objects (YSOs) in three star-forming H ii regions of the Large Magellanic Cloud: N159A, N159 Papillon, and N160. We use photometry from SOFIA/FORCAST at 25.3–37.1 μ m to constrain model fits to the SEDs and determine luminosities, ages, and dust content of the embedded YSOs and their local environments. By placing these sources on mid-infrared color–magnitude and color–color diagrams, we analyze their dust properties and consider their evolutionary status. Since each object in the FORCAST images has an obvious bright near-infrared counterpart in Spitzer Space Telescope images, we do not find any evidence for new, very cool, previously undiscovered Class 0 YSOs. Additionally, based on its mid-infrared colors and model parameters, N159A is younger than N160 and the Papillon. The nature of the first extragalactic protostars in N159, P1, and P2, is also discussed.

  1. Supernova SN1961v - an explosion of a very massive star

    International Nuclear Information System (INIS)

    Utrobin, V.P.

    1983-01-01

    An investigation of the outburst of the unique supernova SN1961v in the galaxy NGC 1058 is carried out. An analysis of hydrodynamical models of supernoVa outbursts and a comparison with a considerable body of observational data on SN1961v clearly show that the SN1961v phenomenon is an explosion of a very massive star-with the mass of 2000 M and radiUs of about 100 R that results in expelling the envelope with the kinetic energy of 1.8x10 52 erg. The light curve of SN1961v furnishes direct evidence for a heterogeneity of the presupernova interior. The chemical composition produced during the evolution of the very massive star and in the final eXplosion must have a number of the essential features. In particular, hydrogen has to be underabundant relative to the solar content and distributed in the specific manner through the star. At late stages from February 1963 to February 1967, the light curve of SN1961v may be accoUnted for as interaction of the expelled envelope with the stellar wind of presupernova

  2. THE AVERAGE PHYSICAL PROPERTIES AND STAR FORMATION HISTORIES OF THE UV-BRIGHTEST STAR-FORMING GALAXIES AT z ∼ 3.7

    International Nuclear Information System (INIS)

    Lee, Kyoung-Soo; Glikman, Eilat; Dey, Arjun; Reddy, Naveen; Jannuzi, Buell T.; Brown, Michael J. I.; Gonzalez, Anthony H.; Cooper, Michael C.; Fan Xiaohui; Bian Fuyan; Stern, Daniel; Brodwin, Mark; Cooray, Asantha

    2011-01-01

    We investigate the average physical properties and star formation histories (SFHs) of the most UV-luminous star-forming galaxies at z ∼ 3.7. Our results are based on the average spectral energy distributions (SEDs), constructed from stacked optical-to-infrared photometry, of a sample of the 1913 most UV-luminous star-forming galaxies found in 5.3 deg 2 of the NOAO Deep Wide-Field Survey. We find that the shape of the average SED in the rest optical and infrared is fairly constant with UV luminosity, i.e., more UV-luminous galaxies are, on average, also more luminous at longer wavelengths. In the rest UV, however, the spectral slope β (≡ dlogF λ /dlogλ; measured at 0.13 μm rest UV and thus star formation rates (SFRs) scale closely with stellar mass such that more UV-luminous galaxies are also more massive, (2) the median ages indicate that the stellar populations are relatively young (200-400 Myr) and show little correlation with UV luminosity, and (3) more UV-luminous galaxies are dustier than their less-luminous counterparts, such that L ∼ 4-5L* galaxies are extincted up to A(1600) = 2 mag while L ∼ L* galaxies have A(1600) = 0.7-1.5 mag. We argue that the average SFHs of UV-luminous galaxies are better described by models in which SFR increases with time in order to simultaneously reproduce the tight correlation between the UV-derived SFR and stellar mass and their universally young ages. We demonstrate the potential of measurements of the SFR-M * relation at multiple redshifts to discriminate between simple models of SFHs. Finally, we discuss the fate of these UV-brightest galaxies in the next 1-2 Gyr and their possible connection to the most massive galaxies at z ∼ 2.

  3. Self-regulating star formation and disk structure

    International Nuclear Information System (INIS)

    Dopita, M.A.

    1987-01-01

    Star formation processes determine the disk structure of galaxies. Stars heavier than about 1 solar mass determine the chemical evolution of the system and are produced at a rate which maintains (by the momentum input of the stars) the phase structure, pressure, and vertical velocity dispersion of the gas. Low mass stars are produced quiescently within molecular clouds, and their associated T-Tauri winds maintain the support of molecular clouds and regulate the star formation rate. Inefficient cooling suppresses this mode of star formation at low metallicity. Applied to the solar neighborhood, such a model can account for age/metallicity relationships, the increase in the O/Fe ratio at low metallicity, the paucity of metal-poor G and K dwarf stars, the missing mass in the disk and, possibly, the existence of a metal-poor thick disk. For other galaxies, it accounts for constant w-velocity dispersion of the gas, the relationship between gas content and specific rates of star formation, the surface brightness/metallicity relationship and for the shallow radial gradients in both star formation rates and HI content. 71 references

  4. Chemical Compositions of Stars in the Globular Cluster NGC 3201: Tracers of Multi-Epoch Star Formation

    Science.gov (United States)

    Simmerer, Jennifer A.; Ivans, I. I.; Filler, D.

    2012-01-01

    The retrograde halo globular cluster NGC 3201 contains stars of substantially different iron abundance ([Fe/H]), a property that puts it at odds with the vast majority of the Galactic cluster system. Though its unusual orbit prompted speculation that NGC 3201 was the remnant of a captured object, much like the multi-metallicity globular cluster Omega Centauri, NGC 3201 is much less massive than Omega Centauri and all of the other halo globular clusters that have internal metallicity variations. We present the abundances of 21 elements in 24 red giant branch stars in NGC 3201 based on high-resolution (R 40,000), high signal-to-noise (S/N 70) spectra. We find that the detailed abundance pattern of NGC 3201 is unique amongst multi-metallicity halo clusters. Unlike M22, Omega Centauri, and NGC 1851, neither metal-poor nor metal-rich stars show any evidence of s-process enrichment (a product of the advanced evolution of low- and intermediate-mass stars). We find that while Na, O, and Al vary from star to star as is typical in globular clusters, there is no systematic difference between the abundance pattern in the metal-poor cluster stars and that of the metal-rich cluster stars. Furthermore, we find that the metallicity variations in NGC 3201 are independent of the well-known Na-O anticorrelation, which separates it from every other multi-metallicity cluster. In the context of a multi-episode star formation model, this implies that NGC 3201 began life with the [Fe/H] variations we measure now.

  5. A study of the region of massive star formation L379IRS1 in radio lines of methanol and other molecules

    Science.gov (United States)

    Kalenskii, S. V.; Shchurov, M. A.

    2016-04-01

    The results of spectral observations of the region of massive star formation L379IRS1 (IRAS18265-1517) are presented. The observations were carried out with the 30-m Pico Veleta radio telescope (Spain) at seven frequencies in the 1-mm, 2-mm, and 3-mm wavelength bands. Lines of 24 molecules were detected, from simple diatomic or triatomic species to complex eight- or nine-atom compounds such as CH3OCHO or CH3OCH3. Rotation diagrams constructed from methanol andmethyl cyanide lines were used to determine the temperature of the quiescent gas in this region, which is about 40-50 K. In addition to this warm gas, there is a hot component that is revealed through high-energy lines of methanol and methyl cyanide, molecular lines arising in hot regions, and the presence of H2O masers and Class II methanol masers at 6.7 GHz, which are also related to hot gas. One of the hot regions is probably a compact hot core, which is located near the southern submillimeter peak and is related to a group of methanol masers at 6.7 GHz. High-excitation lines at other positions may be associated with other hot cores or hot post-shock gas in the lobes of bipolar outflows. The rotation diagrams can be use to determine the column densities and abundances of methanol (10-9) and methyl cyanide (about 10-11) in the quiescent gas. The column densities of A- and E-methanol in L379IRS1 are essentually the same. The column densities of other observedmolecules were calculated assuming that the ratios of the molecular level abundances correspond to a temperature of 40 K. The molecular composition of the quiescent gas is close to that in another region of massive star formation, DR21(OH). The only appreciable difference is that the column density of SO2 in L379IRS1 is at least a factor of 20 lower than the value in DR21(OH). The SO2/CS and SO2/OCS abundance ratios, which can be used as chemical clocks, are lower in L379IRS1 than in DR21(OH), suggesting that L379IRS1 is probably younger than DR21(OH).

  6. Galaxy formation

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  7. VLA AND ALMA IMAGING OF INTENSE GALAXY-WIDE STAR FORMATION IN z ∼ 2 GALAXIES

    International Nuclear Information System (INIS)

    Rujopakarn, W.; Silverman, J. D.; Dunlop, J. S.; Ivison, R. J.; McLure, R. J.; Michałowski, M. J.; Rieke, G. H.; Cibinel, A.; Nyland, K.; Jagannathan, P.; Bhatnagar, S.; Alexander, D. M.; Biggs, A. D.; Ballantyne, D. R.; Dickinson, M.; Elbaz, D.; Geach, J. E.; Hayward, C. C.; Kirkpatrick, A.

    2016-01-01

    We present ≃0.″4 resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at z  = 1.3–3.0. These galaxies are selected from sensitive blank-field surveys of the 2′ × 2′ Hubble Ultra-Deep Field at λ  = 5 cm and 1.3 mm using the Karl G. Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. They have star formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at z  ∼ 2. Morphological classification performed on spatially resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGNs), thereby representing a diversity of z  ∼ 2 SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of 4.2 ± 1.8 kpc. This provides direct evidence of galaxy-wide star formation in distant blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5 M ⊙ yr −1 kpc −2 , sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGNs, which are found to be cospatial with star formation. The median extinction-independent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies, whose SFRs are 3–8 times larger, providing a constraint on the characteristic SFR (∼300 M ⊙ yr −1 ) above which a significant population of more compact SFGs appears to emerge.

  8. Star formation in active galaxies and quasars

    International Nuclear Information System (INIS)

    Heckman, T.M.

    1987-01-01

    I review the observational evidence for a causal or statistical link between star formation and active galactic nuclei. The chief difficulty is in quantitatively ascertaining the star formation rate in active galaxies: most of the readily observable manifestations of star formation superficially resemble those of an active nucleus. Careful multi-wavelength spatially-resolved observations demonstrate that many Seyfert galaxies are undergoing star formation. Our survey of CO emission from Seyferts (interpreted in conjunction IRAS data) suggests that type 2 Seyferts have unusually high rates of star formation, but type 1 Seyferts do not. Recent work also suggests that many powerful radio galaxies may be actively forming stars: radio galaxies with strong emission-lines often have blue colors and strong far-infrared emission. Determining the star formation rate in the host galaxies of quasars is especially difficult. Multi-color imaging and long-slit spectroscopy suggests that many of the host galaxies of radio-loud quasars are blue and a cold interstellar medium has been detected in some quasar hosts

  9. Astrochemical evolution along star formation: Overview of the IRAM Large Program ASAI

    Science.gov (United States)

    Lefloch, Bertrand; Bachiller, R.; Ceccarelli, C.; Cernicharo, J.; Codella, C.; Fuente, A.; Kahane, C.; López-Sepulcre, A.; Tafalla, M.; Vastel, C.; Caux, E.; González-García, M.; Bianchi, E.; Gómez-Ruiz, A.; Holdship, J.; Mendoza, E.; Ospina-Zamudio, J.; Podio, L.; Quénard, D.; Roueff, E.; Sakai, N.; Viti, S.; Yamamoto, S.; Yoshida, K.; Favre, C.; Monfredini, T.; Quitián-Lara, H. M.; Marcelino, N.; Roberty, H. Boechat; Cabrit, S.

    2018-04-01

    Evidence is mounting that the small bodies of our Solar System, such as comets and asteroids, have at least partially inherited their chemical composition from the first phases of the Solar System formation. It then appears that the molecular complexity of these small bodies is most likely related to the earliest stages of star formation. It is therefore important to characterize and to understand how the chemical evolution changes with solar-type protostellar evolution. We present here the Large Program "Astrochemical Surveys At IRAM" (ASAI). Its goal is to carry out unbiased millimeter line surveys between 80 and 272 GHz of a sample of ten template sources, which fully cover the first stages of the formation process of solar-type stars, from prestellar cores to the late protostellar phase. In this article, we present an overview of the surveys and results obtained from the analysis of the 3 mm band observations. The number of detected main isotopic species barely varies with the evolutionary stage and is found to be very similar to that of massive star-forming regions. The molecular content in O- and C- bearing species allows us to define two chemical classes of envelopes, whose composition is dominated by either a) a rich content in O-rich complex organic molecules, associated with hot corino sources, or b) a rich content in hydrocarbons, typical of Warm Carbon Chain Chemistry sources. Overall, a high chemical richness is found to be present already in the initial phases of solar-type star formation.

  10. SPITZER SAGE INFRARED PHOTOMETRY OF MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Bonanos, A. Z.; Massa, D. L.; Sewilo, M.

    2009-01-01

    We present a catalog of 1750 massive stars in the Large Magellanic Cloud (LMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 1268 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3 to 24 μm in the UBVIJHK s +IRAC+MIPS24 bands. The resulting infrared color-magnitude diagrams illustrate that the supergiant B[e], red supergiant, and luminous blue variable (LBV) stars are among the brightest infrared point sources in the LMC, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to free-free emission among ∼900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant B[e] stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of B[e] supergiants (log L/L sun ≥ 4) and the rare, dusty progenitors of the new class of optical transients (e.g., SN 2008S and NGC 300 OT), plus the fact that dust is present in both types of objects, suggests a common origin for them. We find the infrared colors for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict. The results of this study provide the first comprehensive roadmap for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.

  11. New method for determination of star formation history

    OpenAIRE

    Čeponis, Marius

    2017-01-01

    A New Method for Determination of Star Formation History Without stars there would not be any life and us. Almost all elements in our bodies are made in stars. Yet we still don‘t fully understand all the processes governing formation and evolution of stellar systems. Their star formation histories really help in trying to understand these processes. In this work a new Bayesian method for determination of star formation history is proposed. This method uses photometric data of resolved stars a...

  12. Simulations of Fractal Star Cluster Formation. I. New Insights for Measuring Mass Segregation of Star Clusters with Substructure

    International Nuclear Information System (INIS)

    Yu, Jincheng; Puzia, Thomas H.; Lin, Congping; Zhang, Yiwei

    2017-01-01

    We compare the existent methods, including the minimum spanning tree based method and the local stellar density based method, in measuring mass segregation of star clusters. We find that the minimum spanning tree method reflects more the compactness, which represents the global spatial distribution of massive stars, while the local stellar density method reflects more the crowdedness, which provides the local gravitational potential information. It is suggested to measure the local and the global mass segregation simultaneously. We also develop a hybrid method that takes both aspects into account. This hybrid method balances the local and the global mass segregation in the sense that the predominant one is either caused by dynamical evolution or purely accidental, especially when such information is unknown a priori. In addition, we test our prescriptions with numerical models and show the impact of binaries in estimating the mass segregation value. As an application, we use these methods on the Orion Nebula Cluster (ONC) observations and the Taurus cluster. We find that the ONC is significantly mass segregated down to the 20th most massive stars. In contrast, the massive stars of the Taurus cluster are sparsely distributed in many different subclusters, showing a low degree of compactness. The massive stars of Taurus are also found to be distributed in the high-density region of the subclusters, showing significant mass segregation at subcluster scales. Meanwhile, we also apply these methods to discuss the possible mechanisms of the dynamical evolution of the simulated substructured star clusters.

  13. Simulations of Fractal Star Cluster Formation. I. New Insights for Measuring Mass Segregation of Star Clusters with Substructure

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Jincheng; Puzia, Thomas H. [Institute of Astrophysics, Pontificia Universidad Católica, Av. Vicuña Mackenna 4860, Casilla 306, Santiago 22 (Chile); Lin, Congping; Zhang, Yiwei, E-mail: yujc.astro@gmail.com, E-mail: tpuzia@gmail.com, E-mail: congpinglin@gmail.com, E-mail: yiweizhang831129@gmail.com [Center for Mathematical Science, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 4370074 (China)

    2017-05-10

    We compare the existent methods, including the minimum spanning tree based method and the local stellar density based method, in measuring mass segregation of star clusters. We find that the minimum spanning tree method reflects more the compactness, which represents the global spatial distribution of massive stars, while the local stellar density method reflects more the crowdedness, which provides the local gravitational potential information. It is suggested to measure the local and the global mass segregation simultaneously. We also develop a hybrid method that takes both aspects into account. This hybrid method balances the local and the global mass segregation in the sense that the predominant one is either caused by dynamical evolution or purely accidental, especially when such information is unknown a priori. In addition, we test our prescriptions with numerical models and show the impact of binaries in estimating the mass segregation value. As an application, we use these methods on the Orion Nebula Cluster (ONC) observations and the Taurus cluster. We find that the ONC is significantly mass segregated down to the 20th most massive stars. In contrast, the massive stars of the Taurus cluster are sparsely distributed in many different subclusters, showing a low degree of compactness. The massive stars of Taurus are also found to be distributed in the high-density region of the subclusters, showing significant mass segregation at subcluster scales. Meanwhile, we also apply these methods to discuss the possible mechanisms of the dynamical evolution of the simulated substructured star clusters.

  14. Chemical evolution with rotating massive star yields - I. The solar neighbourhood and the s-process elements

    Science.gov (United States)

    Prantzos, N.; Abia, C.; Limongi, M.; Chieffi, A.; Cristallo, S.

    2018-05-01

    We present a comprehensive study of the abundance evolution of the elements from H to U in the Milky Way halo and local disc. We use a consistent chemical evolution model, metallicity-dependent isotopic yields from low and intermediate mass stars and yields from massive stars which include, for the first time, the combined effect of metallicity, mass loss, and rotation for a large grid of stellar masses and for all stages of stellar evolution. The yields of massive stars are weighted by a metallicity-dependent function of the rotational velocities, constrained by observations as to obtain a primary-like 14N behaviour at low metallicity and to avoid overproduction of s-elements at intermediate metallicities. We show that the Solar system isotopic composition can be reproduced to better than a factor of 2 for isotopes up to the Fe-peak, and at the 10 per cent level for most pure s-isotopes, both light ones (resulting from the weak s-process in rotating massive stars) and the heavy ones (resulting from the main s-process in low and intermediate mass stars). We conclude that the light element primary process (LEPP), invoked to explain the apparent abundance deficiency of the s-elements with A values of ^{12}C/^{13}C in halo red giants, which is rather due to internal processes in those stars.

  15. AN APPARENT PRECESSING HELICAL OUTFLOW FROM A MASSIVE EVOLVED STAR: EVIDENCE FOR BINARY INTERACTION

    Energy Technology Data Exchange (ETDEWEB)

    Lau, R. M.; Hankins, M. J.; Herter, T. L. [Astronomy Department, Cornell University, Ithaca, NY 14853-6801 (United States); Morris, M. R. [Department of Physics and Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095 (United States); Mills, E. A. C. [National Radio Astronomy Observatory, P.O. Box O 1009, Lopezville Drive, Socorro, NM 87801 (United States); Ressler, M. E. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

    2016-02-20

    Massive, evolved stars play a crucial role in the metal enrichment, dust budget, and energetics of the interstellar medium; however, the details of their evolution are uncertain because of their rarity and short lifetimes before exploding as supernovae. Discrepancies between theoretical predictions from single-star evolutionary models and observations of massive stars have evoked a shifting paradigm that implicates the importance of binary interaction. We present mid- to far-infrared observations from the Stratospheric Observatory for Infrared Astronomy of a conical “helix” of warm dust (∼180 K) that appears to extend from the Wolf–Rayet star WR102c. Our interpretation of the helix is a precessing, collimated outflow that emerged from WR102c during a previous evolutionary phase as a rapidly rotating luminous blue variable. We attribute the precession of WR102c to gravitational interactions with an unseen compact binary companion whose orbital period can be constrained to 800 days < P < 1400 days from the inferred precession period, τ{sub p} ∼ 1.4 × 10{sup 4} yr, and limits imposed on the stellar and orbital parameters of the system. Our results concur with the range of orbital periods (P ≲ 1500 days) where spin-up via mass exchange is expected to occur for massive binary systems.

  16. Evidence for feedback and stellar-dynamically regulated bursty star cluster formation: the case of the Orion Nebula Cluster

    Science.gov (United States)

    Kroupa, Pavel; Jeřábková, Tereza; Dinnbier, František; Beccari, Giacomo; Yan, Zhiqiang

    2018-04-01

    A scenario for the formation of multiple co-eval populations separated in age by about 1 Myr in very young clusters (VYCs, ages less than 10 Myr) and with masses in the range 600-20 000 M⊙ is outlined. It rests upon a converging inflow of molecular gas building up a first population of pre-main sequence stars. The associated just-formed O stars ionise the inflow and suppress star formation in the embedded cluster. However, they typically eject each other out of the embedded cluster within 106 yr, that is before the molecular cloud filament can be ionised entirely. The inflow of molecular gas can then resume forming a second population. This sequence of events can be repeated maximally over the life-time of the molecular cloud (about 10 Myr), but is not likely to be possible in VYCs with mass <300 M⊙, because such populations are not likely to contain an O star. Stellar populations heavier than about 2000 M⊙ are likely to have too many O stars for all of these to eject each other from the embedded cluster before they disperse their natal cloud. VYCs with masses in the range 600-2000 M⊙ are likely to have such multi-age populations, while VYCs with masses in the range 2000-20 000 M⊙ can also be composed solely of co-eval, mono-age populations. More massive VYCs are not likely to host sub-populations with age differences of about 1 Myr. This model is applied to the Orion Nebula Cluster (ONC), in which three well-separated pre-main sequences in the colour-magnitude diagram of the cluster have recently been discovered. The mass-inflow history is constrained using this model and the number of OB stars ejected from each population are estimated for verification using Gaia data. As a further consequence of the proposed model, the three runaway O star systems, AE Aur, μ Col and ι Ori, are considered as significant observational evidence for stellar-dynamical ejections of massive stars from the oldest population in the ONC. Evidence for stellar

  17. An infrared view of (candidate accretion) disks around massive young stars

    NARCIS (Netherlands)

    Bik, A.; Lenorzer, A.; Thi, W.F.; Puga Antolín, E.; Waters, L.B.F.M.; Kaper, L.; Martín-Hernández, L.N.

    2008-01-01

    Near-infrared surveys of high-mass star-forming regions start to shed light onto their stellar content. A particular class of objects found in these regions, the so-called massive Young Stellar Objects (YSOs) are surrounded by dense circumstellar material. Several near- and mid-infrared diagnostic

  18. Massive open star clusters using the VVV survey. II. Discovery of six clusters with Wolf-Rayet stars

    Science.gov (United States)

    Chené, A.-N.; Borissova, J.; Bonatto, C.; Majaess, D. J.; Baume, G.; Clarke, J. R. A.; Kurtev, R.; Schnurr, O.; Bouret, J.-C.; Catelan, M.; Emerson, J. P.; Feinstein, C.; Geisler, D.; de Grijs, R.; Hervé, A.; Ivanov, V. D.; Kumar, M. S. N.; Lucas, P.; Mahy, L.; Martins, F.; Mauro, F.; Minniti, D.; Moni Bidin, C.

    2013-01-01

    Context. The ESO Public Survey "VISTA Variables in the Vía Láctea" (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims: This is the second in a series of papers about young, massive open clusters observed using the VVV survey. We present the first study of six recently discovered clusters. These clusters contain at least one newly discovered Wolf-Rayet (WR) star. Methods: Following the methodology presented in the first paper of the series, wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results: We find that the six studied stellar groups are real young (2-7 Myr) and massive (between 0.8 and 2.2 × 103 M⊙) clusters. They are highly obscured (AV ~ 5-24 mag) and compact (1-2 pc). In addition to WR stars, two of the six clusters also contain at least one red supergiant star, and one of these two clusters also contains a blue supergiant. We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission lines which could be classified WR or OIf. Preliminary analysis provides initial masses of ~30-50 M⊙ for the WR stars. Finally, we discuss the spiral structure of the Galaxy using the six new clusters as tracers, together with the previously studied VVV clusters. Based on observations with ISAAC, VLT, ESO (programme 087.D-0341A), New Technology Telescope at ESO's La Silla Observatory (programme 087.D-0490A) and with the Clay telescope at the Las Campanas Observatory (programme CN2011A-086). Also based on data from the VVV survey (programme 172.B-2002).

  19. Variability of Massive Young Stellar Objects in Cygnus-X

    Science.gov (United States)

    Thomas, Nancy H.; Hora, J. L.; Smith, H. A.

    2013-01-01

    Young stellar objects (YSOs) are stars in the process of formation. Several recent investigations have shown a high rate of photometric variability in YSOs at near- and mid-infrared wavelengths. Theoretical models for the formation of massive stars (1-10 solar masses) remain highly idealized, and little is known about the mechanisms that produce the variability. An ongoing Spitzer Space Telescope program is studying massive star formation in the Cygnus-X region. In conjunction with the Spitzer observations, we have conducted a ground-based near-infrared observing program of the Cygnus-X DR21 field using PAIRITEL, the automated infrared telescope at Whipple Observatory. Using the Stetson index for variability, we identified variable objects and a number of variable YSOs in our time-series PAIRITEL data of DR21. We have searched for periodicity among our variable objects using the Lomb-Scargle algorithm, and identified periodic variable objects with an average period of 8.07 days. Characterization of these variable and periodic objects will help constrain models of star formation present. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

  20. CLUSTERED STAR FORMATION AND OUTFLOWS IN AFGL 2591

    International Nuclear Information System (INIS)

    Sanna, A.; Carrasco-González, C.; Menten, K. M.; Brunthaler, A.; Reid, M. J.; Moscadelli, L.; Rygl, K. L. J.

    2012-01-01

    We report on a detailed study of the water maser kinematics and radio continuum emission toward the most massive and young object in the star-forming region AFGL 2591. Our analysis shows at least two spatial scales of multiple star formation, one projected across 0.1 pc on the sky and another one at about 2000 AU from a ZAMS star of about 38 M ☉ . This young stellar object drives a powerful jet- and wind-driven outflow system with the water masers associated to the outflow walls, previously detected as a limb-brightened cavity in the NIR band. At about 1300 AU to the north of this object a younger protostar drives two bow shocks, outlined by arc-like water maser emission, at 200 AU either side of the source. We have traced the velocity profile of the gas that expands along these arc-like maser structures and compared it with the jet-driven outflow model. This analysis suggests that the ambient medium around the northern protostar is swept up by a jet-driven shock (>66 km s –1 ) and perhaps a lower-velocity (∼10 km s –1 ) wind with an opening angle of about 20° from the jet axis.

  1. CLUSTERED STAR FORMATION AND OUTFLOWS IN AFGL 2591

    Energy Technology Data Exchange (ETDEWEB)

    Sanna, A.; Carrasco-Gonzalez, C.; Menten, K. M.; Brunthaler, A. [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany); Reid, M. J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Moscadelli, L. [INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze (Italy); Rygl, K. L. J., E-mail: asanna@mpifr-bonn.mpg.de [IFSI-INAF, Istituto di Fisica dello Spazio Interplanetario, Via del Fosso del Cavaliere 100, 00133 Roma (Italy)

    2012-02-01

    We report on a detailed study of the water maser kinematics and radio continuum emission toward the most massive and young object in the star-forming region AFGL 2591. Our analysis shows at least two spatial scales of multiple star formation, one projected across 0.1 pc on the sky and another one at about 2000 AU from a ZAMS star of about 38 M{sub Sun }. This young stellar object drives a powerful jet- and wind-driven outflow system with the water masers associated to the outflow walls, previously detected as a limb-brightened cavity in the NIR band. At about 1300 AU to the north of this object a younger protostar drives two bow shocks, outlined by arc-like water maser emission, at 200 AU either side of the source. We have traced the velocity profile of the gas that expands along these arc-like maser structures and compared it with the jet-driven outflow model. This analysis suggests that the ambient medium around the northern protostar is swept up by a jet-driven shock (>66 km s{sup -1}) and perhaps a lower-velocity ({approx}10 km s{sup -1}) wind with an opening angle of about 20 Degree-Sign from the jet axis.

  2. The secular tidal disruption of stars by low-mass Super Massive Black Holes secondaries in galactic nuclei

    Science.gov (United States)

    Fragione, Giacomo; Leigh, Nathan

    2018-06-01

    Stars passing too close to a super massive black hole (SMBH) can produce tidal disruption events (TDEs). Since the resulting stellar debris can produce an electromagnetic flare, TDEs are believed to probe the presence of single SMBHs in galactic nuclei, which otherwise remain dark. In this paper, we show how stars orbiting an IMBH secondary are perturbed by an SMBH primary. We find that the evolution of the stellar orbits are severely affected by the primary SMBH due to secular effects and stars orbiting with high inclinations with respect to the SMBH-IMBH orbital plane end their lives as TDEs due to Kozai-Lidov oscillations, hence illuminating the secondary SMBH/IMBH. Above a critical SMBH mass of ≈1.15 × 108 M⊙, no TDE can occur for typical stars in an old stellar population since the Schwarzschild radius exceeds the tidal disruption radius. Consequently, any TDEs due to such massive SMBHs will remain dark. It follows that no TDEs should be observed in galaxies more massive than ≈4.15 × 1010 M⊙, unless a lower-mass secondary SMBH or IMBH is also present. The secular mechanism for producing TDEs considered here therefore offers a useful probe of SMBH-SMBH/IMBH binarity in the most massive galaxies. We further show that the TDE rate can be ≈10-4 - 10-3 yr-1, and that most TDEs occur on ≈0.5 Myr. Finally, we show that stars may be ejected with velocities up to thousands of km s-1, which could contribute to the observed population of Galactic hypervelocity stars.

  3. Stationary bound-state massive scalar field configurations supported by spherically symmetric compact reflecting stars

    Energy Technology Data Exchange (ETDEWEB)

    Hod, Shahar [The Ruppin Academic Center, Emeq Hefer (Israel); The Hadassah Academic College, Jerusalem (Israel)

    2017-12-15

    It has recently been demonstrated that asymptotically flat neutral reflecting stars are characterized by an intriguing no-hair property. In particular, it has been proved that these horizonless compact objects cannot support spatially regular static matter configurations made of scalar (spin-0) fields, vector (spin-1) fields and tensor (spin-2) fields. In the present paper we shall explicitly prove that spherically symmetric compact reflecting stars can support stationary (rather than static) bound-state massive scalar fields in their exterior spacetime regions. To this end, we solve analytically the Klein-Gordon wave equation for a linearized scalar field of mass μ and proper frequency ω in the curved background of a spherically symmetric compact reflecting star of mass M and radius R{sub s}. It is proved that the regime of existence of these stationary composed star-field configurations is characterized by the simple inequalities 1 - 2M/R{sub s} < (ω/μ){sup 2} < 1. Interestingly, in the regime M/R{sub s} << 1 of weakly self-gravitating stars we derive a remarkably compact analytical equation for the discrete spectrum {ω(M,R_s, μ)}{sup n=∞}{sub n=1} of resonant oscillation frequencies which characterize the stationary composed compact-reflecting-star-linearized-massive-scalar-field configurations. Finally, we verify the accuracy of the analytically derived resonance formula of the composed star-field configurations with direct numerical computations. (orig.)

  4. Star formation histories of irregular galaxies

    International Nuclear Information System (INIS)

    Gallagher, J.S. III; Hunter, D.A.; Tutukov, A.V.

    1984-01-01

    We explore the star formation histories of a selection of irregular and spiral galaxies by using three parameters that sample the star formation rate (SFR) at different epochs: (1) the mass of a galaxy in the form of stars measures the SFR integrated over a galaxy's lifetime; (2) the blue luminosity is dominated primarily by stars formed over the past few billion years; and (3) Lyman continuum photon fluxes derived from Hα luminosities give the current ( 8 yr) SFR

  5. Convective shells and the core He-burning phase of massive stars

    Energy Technology Data Exchange (ETDEWEB)

    Chiosi, C [Padua Univ. (Italy). Ist. di Astronomia; Nasi, E [Osservatorio Astronomico, Padova, Italy

    1978-07-01

    In this paper the effect of complete homogenization in the intermediate unstable layers of massive stars is briefly discussed on the effective temperature of the core He-burning models. To this end, a 20 solar masses star of Population I chemical composition (X=0.700, Z=0.020) has been allowed to evolve from the Main Sequence into the core He-exhaustion stage without taking into account semiconvective mixing. The results show that the models are systematically bluer than those computed with the same physical parameters but with the inclusion of semiconvection.

  6. Extinction of gamma-ray burst afterglows as a diagnostic of the location of cosmic star formation

    Science.gov (United States)

    Ramirez-Ruiz, Enrico; Trentham, Neil; Blain, A. W.

    2002-01-01

    The properties of gamma-ray bursts (GRBs) and their afterglows are used to investigate the location of star formation activity through the history of the Universe. This approach is motivated by the following: (i) GRBs are thought to be associated with the deaths of massive stars and so the GRB rate ought to follow the formation rate of massive stars; (ii) GRBs are the last phase of the evolution of these stars, which do not live long enough to travel far from their place of birth, and so GRBs are located where the stars formed; and (iii) GRB afterglows occur over both X-ray and optical wavelengths, and so the differential effects of dust extinction between the two wavebands can reveal whether or not large amounts of dust are present in galaxies hosting GRBs. Recent evidence suggests that a significant fraction of stars in the Universe formed in galaxies that are bright at rest-frame submillimetre (submm) and infrared wavelengths rather than at ultraviolet wavelengths; we estimate about three quarters of the star formation in the Universe occurred in the submm-bright mode. High-redshift submm-selected galaxies are thought to have properties similar to local ultraluminous infrared galaxies (ULIGs) such as Arp 220, based on the concordance between their luminosities and spectral energy distributions. If this is the case, then GRBs in submm-bright galaxies should have their optical afterglows extinguished by internal dust absorption, but only very few should have their 2-10keV X-ray afterglows obscured. The value that we quote of three quarters is marginally consistent with observations of GRBs: 60+/-15 per cent of GRBs have no detected optical afterglow, whereas almost all have an X-ray afterglow. A more definitive statement could be made with observations of soft X-ray afterglows (0.5-2keV), in which extinction should be severe for GRBs located in submm-bright galaxies with gas densities similar to those in local ULIGs. If the X-ray afterglows disappear at soft X

  7. Massive open star clusters using the VVV survey IV. WR 62-2, a new very massive star in the core of the VVV CL041 cluster

    Czech Academy of Sciences Publication Activity Database

    Chene, A.-N.; Alegria, S.R.; Borissova, J.; O'Leary, E.; Martins, F.; Hervé, Anthony; Kuhn, M.; Kurtev, R.; Consuelo Amigo Fuentes, P.; Bonatto, C.; Minniti, D.

    2015-01-01

    Roč. 584, December (2015), A31/1-A31/8 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GA14-02385S Institutional support: RVO:67985815 Keywords : open clusters and associations * VVV CL041 * massive star s Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  8. An Integrated Picture of Star Formation, Metallicity Evolution, and Galactic Stellar Mass Assembly

    Science.gov (United States)

    Cowie, L. L.; Barger, A. J.

    2008-10-01

    We present an integrated study of star formation and galactic stellar mass assembly from z = 0.05 to 1.5 and galactic metallicity evolution from z = 0.05 to 0.9 using a very large and highly spectroscopically complete sample selected by rest-frame NIR bolometric flux in the GOODS-N. We assume a Salpeter IMF and fit Bruzual & Charlot models to compute the galactic stellar masses and extinctions. We determine the expected formed stellar mass density growth rates produced by star formation and compare them with the growth rates measured from the formed stellar mass functions by mass interval. We show that the growth rates match if the IMF is slightly increased from the Salpeter IMF at intermediate masses (~10 M⊙). We investigate the evolution of galaxy color, spectral type, and morphology with mass and redshift and the evolution of mass with environment. We find that applying extinction corrections is critical when analyzing galaxy colors; e.g., nearly all of the galaxies in the green valley are 24 μm sources, but after correcting for extinction, the bulk of the 24 μm sources lie in the blue cloud. We find an evolution of the metallicity-mass relation corresponding to a decrease of 0.21 +/- 0.03 dex between the local value and the value at z = 0.77 in the 1010-1011 M⊙ range. We use the metallicity evolution to estimate the gas mass of the galaxies, which we compare with the galactic stellar mass assembly and star formation histories. Overall, our measurements are consistent with a galaxy evolution process dominated by episodic bursts of star formation and where star formation in the most massive galaxies (gtrsim1011 M⊙) ceases at z Technology, the University of California, and NASA and was made possible by the generous financial support of the W. M. Keck Foundation.

  9. A massive, quiescent galaxy at a redshift of 3.717

    Science.gov (United States)

    Glazebrook, Karl; Schreiber, Corentin; Labbé, Ivo; Nanayakkara, Themiya; Kacprzak, Glenn G.; Oesch, Pascal A.; Papovich, Casey; Spitler, Lee R.; Straatman, Caroline M. S.; Tran, Kim-Vy H.; Yuan, Tiantian

    2017-04-01

    Finding massive galaxies that stopped forming stars in the early Universe presents an observational challenge because their rest-frame ultraviolet emission is negligible and they can only be reliably identified by extremely deep near-infrared surveys. These surveys have revealed the presence of massive, quiescent early-type galaxies appearing as early as redshift z ≈ 2, an epoch three billion years after the Big Bang. Their age and formation processes have now been explained by an improved generation of galaxy-formation models, in which they form rapidly at z ≈ 3-4, consistent with the typical masses and ages derived from their observations. Deeper surveys have reported evidence for populations of massive, quiescent galaxies at even higher redshifts and earlier times, using coarsely sampled photometry. However, these early, massive, quiescent galaxies are not predicted by the latest generation of theoretical models. Here we report the spectroscopic confirmation of one such galaxy at redshift z = 3.717, with a stellar mass of 1.7 × 1011 solar masses. We derive its age to be nearly half the age of the Universe at this redshift and the absorption line spectrum shows no current star formation. These observations demonstrate that the galaxy must have formed the majority of its stars quickly, within the first billion years of cosmic history in a short, extreme starburst. This ancestral starburst appears similar to those being found by submillimetre-wavelength surveys. The early formation of such massive systems implies that our picture of early galaxy assembly requires substantial revision.

  10. A Massive Prestellar Clump Hosting No High-mass Cores

    Energy Technology Data Exchange (ETDEWEB)

    Sanhueza, Patricio; Lu, Xing; Tatematsu, Ken’ichi [National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Jackson, James M. [School of Mathematical and Physical Sciences, University of Newcastle, University Drive, Callaghan, NSW 2308 (Australia); Zhang, Qizhou; Stephens, Ian W. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Guzmán, Andrés E. [Departamento de Astronomía, Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago (Chile); Wang, Ke, E-mail: patricio.sanhueza@nao.ac.jp [European Southern Observatory (ESO) Headquarters, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München (Germany)

    2017-06-01

    The infrared dark cloud (IRDC) G028.23-00.19 hosts a massive (1500 M {sub ⊙}), cold (12 K), and 3.6–70 μ m IR dark clump (MM1) that has the potential to form high-mass stars. We observed this prestellar clump candidate with the Submillimeter Array (∼3.″5 resolution) and Jansky Very Large Array (∼2.″1 resolution) in order to characterize the early stages of high-mass star formation and to constrain theoretical models. Dust emission at 1.3 mm wavelength reveals five cores with masses ≤15 M {sub ⊙}. None of the cores currently have the mass reservoir to form a high-mass star in the prestellar phase. If the MM1 clump will ultimately form high-mass stars, its embedded cores must gather a significant amount of additional mass over time. No molecular outflows are detected in the CO (2-1) and SiO (5-4) transitions, suggesting that the SMA cores are starless. By using the NH{sub 3} (1, 1) line, the velocity dispersion of the gas is determined to be transonic or mildly supersonic (Δ V {sub nt}/Δ V {sub th} ∼ 1.1–1.8). The cores are not highly supersonic as some theories of high-mass star formation predict. The embedded cores are four to seven times more massive than the clump thermal Jeans mass and the most massive core (SMA1) is nine times less massive than the clump turbulent Jeans mass. These values indicate that neither thermal pressure nor turbulent pressure dominates the fragmentation of MM1. The low virial parameters of the cores (0.1–0.5) suggest that they are not in virial equilibrium, unless strong magnetic fields of ∼1–2 mG are present. We discuss high-mass star formation scenarios in a context based on IRDC G028.23-00.19, a study case believed to represent the initial fragmentation of molecular clouds that will form high-mass stars.

  11. The Mass-dependent Star Formation Histories of Disk Galaxies: Infall Model Versus Observations

    Science.gov (United States)

    Chang, R. X.; Hou, J. L.; Shen, S. Y.; Shu, C. G.

    2010-10-01

    We introduce a simple model to explore the star formation histories of disk galaxies. We assume that the disk originate and grows by continuous gas infall. The gas infall rate is parameterized by the Gaussian formula with one free parameter: the infall-peak time tp . The Kennicutt star formation law is adopted to describe how much cold gas turns into stars. The gas outflow process is also considered in our model. We find that, at a given galactic stellar mass M *, the model adopting a late infall-peak time tp results in blue colors, low-metallicity, high specific star formation rate (SFR), and high gas fraction, while the gas outflow rate mainly influences the gas-phase metallicity and star formation efficiency mainly influences the gas fraction. Motivated by the local observed scaling relations, we "construct" a mass-dependent model by assuming that the low-mass galaxy has a later infall-peak time tp and a larger gas outflow rate than massive systems. It is shown that this model can be in agreement with not only the local observations, but also with the observed correlations between specific SFR and galactic stellar mass SFR/M * ~ M * at intermediate redshifts z < 1. Comparison between the Gaussian-infall model and the exponential-infall model is also presented. It shows that the exponential-infall model predicts a higher SFR at early stage and a lower SFR later than that of Gaussian infall. Our results suggest that the Gaussian infall rate may be more reasonable in describing the gas cooling process than the exponential infall rate, especially for low-mass systems.

  12. Polarized bow shocks reveal features of the winds and environments of massive stars

    Science.gov (United States)

    Shrestha, Manisha

    2018-01-01

    Massive stars strongly affect their surroundings through their energetic stellar winds and deaths as supernovae. The bow shock structures created by fast-moving massive stars contain important information about the winds and ultimate fates of these stars as well as their local interstellar medium (ISM). Since bow shocks are aspherical, the light scattered in the dense shock material becomes polarized. Analyzing this polarization reveals details of the bow shock geometry as well as the composition, velocity, density, and albedo of the scattering material. With these quantities, we can constrain the properties of the stellar wind and thus the evolutionary state of the star, as well as the dust composition of the local ISM.In my dissertation research, I use a Monte Carlo radiative transfer code that I optimized to simulate the polarization signatures produced by both resolved and unresolved stellar wind bow shocks (SWBS) illuminated by a central star and by shock emission. I derive bow shock shapes and densities from published analytical calculations and smooth particle hydrodynamic (SPH) models. In the case of the analytical SWBS and electron scattering, I find that higher optical depths produce higher polarization and position angle rotations at specific viewing angles compared to theoretical predictions for low optical depths. This is due to the geometrical properties of the bow shock combined with multiple scattering effects. For dust scattering, the polarization signature is strongly affected by wavelength, dust grain properties, and viewing angle. The behavior of the polarization as a function of wavelength in these cases can distinguish among different dust models for the local ISM. In the case of SPH density structures, I investigate how the polarization changes as a function of the evolutionary phase of the SWBS. My dissertation compares these simulations with polarization data from Betelgeuse and other massive stars with bow shocks. I discuss the

  13. Ionizing feedback from massive stars in massive clusters - III. Disruption of partially unbound clouds

    Science.gov (United States)

    Dale, J. E.; Ercolano, B.; Bonnell, I. A.

    2013-03-01

    We extend our previous smoothed particle hydrodynamics parameter study of the effects of photoionization from O-stars on star-forming clouds to include initially unbound clouds. We generate a set of model clouds in the mass range 104-106 M⊙ with initial virial ratios Ekin/Epot = 2.3, allow them to form stars and study the impact of the photoionizing radiation produced by the massive stars. We find that, on the 3 Myr time-scale before supernovae are expected to begin detonating, the fraction of mass expelled by ionizing feedback is a very strong function of the cloud escape velocities. High-mass clouds are largely unaffected dynamically, while low-mass clouds have large fractions of their gas reserves expelled on this time-scale. However, the fractions of stellar mass unbound are modest and significant portions of the unbound stars are so only because the clouds themselves are initially partially unbound. We find that ionization is much more able to create well-cleared bubbles in the unbound clouds, owing to their intrinsic expansion, but that the presence of such bubbles does not necessarily indicate that a given cloud has been strongly influenced by feedback. We also find, in common with the bound clouds from our earlier work, that many of the systems simulated here are highly porous to photons and supernova ejecta, and that most of them will likely survive their first supernova explosions.

  14. Star formation in the multiverse

    International Nuclear Information System (INIS)

    Bousso, Raphael; Leichenauer, Stefan

    2009-01-01

    We develop a simple semianalytic model of the star formation rate as a function of time. We estimate the star formation rate for a wide range of values of the cosmological constant, spatial curvature, and primordial density contrast. Our model can predict such parameters in the multiverse, if the underlying theory landscape and the cosmological measure are known.

  15. Tidal interaction, star formation and chemical evolution in blue compact dwarf galaxy Mrk 22

    Science.gov (United States)

    Paswan, A.; Omar, A.; Jaiswal, S.

    2018-02-01

    The optical spectroscopic and radio interferometric H I 21 cm-line observations of the blue compact dwarf galaxy Mrk 22 are presented. The Wolf-Rayet (WR) emission-line features corresponding to high ionization lines of He II λ4686 and C IV λ5808 from young massive stars are detected. The ages of two prominent star-forming regions in the galaxy are estimated as ∼10 and ∼ 4 Myr. The galaxy has non-thermal radio deficiency, which also indicates a young starburst and lack of supernovae events from the current star formation activities, consistent with the detection of WR emission-line features. A significant N/O enrichment is seen in the fainter star-forming region. The gas-phase metallicities [12 + log(O/H)] for the bright and faint regions are estimated as 7.98±0.07 and 7.46±0.09, respectively. The galaxy has a large diffuse H I envelop. The H I images reveal disturbed gas kinematics and H I clouds outside the optical extent of the galaxy, indicating recent tidal interaction or merger in the system. The results strongly indicate that Mrk 22 is undergoing a chemical and morphological evolution due to ongoing star formation, most likely triggered by a merger.

  16. StarDOM: From STAR format to XML

    International Nuclear Information System (INIS)

    Linge, Jens P.; Nilges, Michael; Ehrlich, Lutz

    1999-01-01

    StarDOM is a software package for the representation of STAR files as document object models and the conversion of STAR files into XML. This allows interactive navigation by using the Document Object Model representation of the data as well as easy access by XML query languages. As an example application, the entire BioMagResBank has been transformed into XML format. Using an XML query language, statistical queries on the collected NMR data sets can be constructed with very little effort. The BioMagResBank/XML data and the software can be obtained at http://www.nmr.embl-heidelberg.de/nmr/StarDOM/

  17. TIME-VARYING DYNAMICAL STAR FORMATION RATE

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Eve J.; Chang, Philip; Murray, Norman, E-mail: evelee@berkeley.edu [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, University of Toronto, Toronto, ON M5S 3H8 (Canada)

    2015-02-10

    We present numerical evidence of dynamic star formation in which the accreted stellar mass grows superlinearly with time, roughly as t {sup 2}. We perform simulations of star formation in self-gravitating hydrodynamic and magnetohydrodynamic turbulence that is continuously driven. By turning the self-gravity of the gas in the simulations on or off, we demonstrate that self-gravity is the dominant physical effect setting the mass accretion rate at early times before feedback effects take over, contrary to theories of turbulence-regulated star formation. We find that gravitational collapse steepens the density profile around stars, generating the power-law tail on what is otherwise a lognormal density probability distribution function. Furthermore, we find turbulent velocity profiles to flatten inside collapsing regions, altering the size-line width relation. This local flattening reflects enhancements of turbulent velocity on small scales, as verified by changes to the velocity power spectra. Our results indicate that gas self-gravity dynamically alters both density and velocity structures in clouds, giving rise to a time-varying star formation rate. We find that a substantial fraction of the gas that forms stars arrives via low-density flows, as opposed to accreting through high-density filaments.

  18. An evolutionary model for collapsing molecular clouds and their star formation activity. II. Mass dependence of the star formation rate

    Energy Technology Data Exchange (ETDEWEB)

    Zamora-Avilés, Manuel; Vázquez-Semadeni, Enrique [Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apdo. Postal 3-72, Morelia, Michoacán 58089 (Mexico)

    2014-10-01

    We discuss the evolution and dependence on cloud mass of the star formation rate (SFR) and efficiency (SFE) of star-forming molecular clouds (MCs) within the scenario that clouds are undergoing global collapse and that the SFR is controlled by ionization feedback. We find that low-mass clouds (M {sub max} ≲ 10{sup 4} M {sub ☉}) spend most of their evolution at low SFRs, but end their lives with a mini-burst, reaching a peak SFR ∼10{sup 4} M {sub ☉} Myr{sup –1}, although their time-averaged SFR is only (SFR) ∼ 10{sup 2} M {sub ☉} Myr{sup –1}. The corresponding efficiencies are SFE{sub final} ≲ 60% and (SFE) ≲ 1%. For more massive clouds (M {sub max} ≳ 10{sup 5} M {sub ☉}), the SFR first increases and then reaches a plateau because the clouds are influenced by stellar feedback since earlier in their evolution. As a function of cloud mass, (SFR) and (SFE) are well represented by the fits (SFR) ≈ 100(1 + M {sub max}/1.4 × 10{sup 5} M {sub ☉}){sup 1.68} M {sub ☉} Myr{sup –1} and (SFE) ≈ 0.03(M {sub max}/2.5 × 10{sup 5} M {sub ☉}){sup 0.33}, respectively. Moreover, the SFR of our model clouds follows closely the SFR-dense gas mass relation recently found by Lada et al. during the epoch when their instantaneous SFEs are comparable to those of the clouds considered by those authors. Collectively, a Monte Carlo integration of the model-predicted SFR(M) over a Galactic giant molecular cloud mass spectrum yields values for the total Galactic SFR that are within half an order of magnitude of the relation obtained by Gao and Solomon. Our results support the scenario that star-forming MCs may be in global gravitational collapse and that the low observed values of the SFR and SFE are a result of the interruption of each SF episode, caused primarily by the ionizing feedback from massive stars.

  19. SDSS-IV MaNGA: Star Formation Cessation in Low-redshift Galaxies. I. Dependence on Stellar Mass and Structural Properties

    Science.gov (United States)

    Wang, Enci; Li, Cheng; Xiao, Ting; Lin, Lin; Bershady, Matthew; Law, David R.; Merrifield, Michael; Sanchez, Sebastian F.; Riffel, Rogemar A.; Riffel, Rogerio; Yan, Renbin

    2018-04-01

    We investigate radial gradients in the recent star formation history (SFH) of 1917 galaxies with 0.01 < z < 0.14 from the Mapping Nearby Galaxies at Apache Point Observatory project. For each galaxy, we obtain two-dimensional maps and radial profiles for three spectroscopically measured parameters that are sensitive to the recent SFH: D n (4000) (the 4000 Å break), EW(Hδ A ), and EW(Hα) (the equivalent width of the Hδ absorption and the Hα emission line). The majority of the spaxels are consistent with models of a continuously declining star formation rate, indicating that starbursts occur rarely in local galaxies with regular morphologies. We classify the galaxies into three classes: fully star-forming (SF), partly quenched (PQ), and totally quenched (TQ). The galaxies that are less massive than 1010 M ⊙ present at most weak radial gradients in the diagnostic parameters. In contrast, massive galaxies with a stellar mass above 1010 M ⊙ present significant gradients in the three diagnostic parameters if they are classified as SF or PQ but show weak gradients in D n (4000) and EW(Hδ A ) and no gradients in EW(Hα) if they are in the TQ class. This implies the existence of a critical stellar mass (∼1010 M ⊙) above which the star formation in a galaxy is shut down from the inside out. Galaxies tend to evolve synchronously from the inner to the outer regions before their mass reaches the critical value. We have further divided the sample at a fixed mass by both bulge-to-total luminosity ratio and morphological type, finding that our conclusions hold regardless of these factors; it appears that the presence of a central dense object is not a driving parameter but rather a by-product of the star formation cessation process.

  20. WO-Type Wolf-Rayet Stars: the Last Hurrah of the Most Massive Stars?

    Science.gov (United States)

    Massey, Philip

    2014-10-01

    WO-type Wolf-Rayet (WR) stars are considered the final evolutionary stage of the highest mass stars, immediate precursors to Type Ic (He-poor) core-collapse supernovae. These WO stars are rare, and until recently only 6 were known. Our knowledge about their physical properties is mostly based on a single object, Sand 2 in the LMC. It was the only non-binary WO star both bright and unreddened enough that its FUV and NUV spectra could be obtained by FUSE and HST/FOS. A non-LTE analysis showed that Sand 2 is very hot and its (C+O)/He abundance ratio is higher than that found in WC-type WRs, suggesting it is indeed highly evolved. However, the O VI resonance doublet in the FUV required a considerably cooler temperature (120,000 K) model than did the optical O VI lines (170,000 K). Further, the enhanced chemical abundances did not match the predictions of stellar evolutionary models. Another non-LTE study found a 3x higher (C+O)/He abundance ratio and a cooler temperature. We have recently discovered two other bright, single, and lightly reddened WOs in the LMC, allowing us to take a fresh look at these important objects. Our newly found WOs span a range in excitation type, from WO1 (the highest) to WO4 (the lowest). Sand 2 is intermediate (WO3). We propose to use COS to obtain FUV and NUV data of all three stars for as comprehensive a study as is currently possible. These UV data will be combined with our optical Magellan spectra for a detailed analysis with CMFGEN with the latest atomic data. Knowing the degree of chemical evolution of these WO stars is crucial to determining their evolutionary status, and thus in understanding the final stages of the most massive stars.

  1. THE CLUSTERED NATURE OF STAR FORMATION. PRE-MAIN-SEQUENCE CLUSTERS IN THE STAR-FORMING REGION NGC 602/N90 IN THE SMALL MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Gouliermis, Dimitrios A.; Gennaro, Mario; Schmeja, Stefan; Dolphin, Andrew E.; Tognelli, Emanuele; Prada Moroni, Pier Giorgio

    2012-01-01

    Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC 602/N90 is characterized by the H II nebular ring N90 and the young cluster of pre-main-sequence (PMS) and early-type main-sequence stars NGC 602, located in the central area of the ring. We present a thorough cluster analysis of the stellar sample identified with Hubble Space Telescope/Advanced Camera for Surveys in the region. We show that apart from the central cluster low-mass PMS stars are congregated in 13 additional small, compact sub-clusters at the periphery of NGC 602, identified in terms of their higher stellar density with respect to the average background density derived from star counts. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction (∼60%) of the total population being clustered, while the remaining is diffusely distributed in the intercluster area, covering the whole central part of the region. From the corresponding color-magnitude diagrams we disentangle an age difference of ∼2.5 Myr between NGC 602 and the compact sub-clusters, which appear younger, on the basis of comparison of the brighter PMS stars with evolutionary models, which we accurately calculated for the metal abundance of the SMC. The diffuse PMS population appears to host stars as old as those in NGC 602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings, we propose a scenario according to which the region NGC 602/N90 experiences an active clustered star formation for the last ∼5 Myr. The central cluster NGC 602 was formed first

  2. Effects of mass loss on the evolution of massive stars. I. Main-sequence evolution

    International Nuclear Information System (INIS)

    Dearborn, D.S.P.; Blake, J.B.; Hainebach, K.L.; Schramm, D.N.

    1978-01-01

    The effect of mass loss on the evolution and surface composition of massive stars during main-sequence evolution are examined. While some details of the evolutionary track depend on the formula used for the mass loss, the results appear most sensitive to the total mass removed during the main-sequence lifetime. It was found that low mass-loss rates have very little effect on the evolution of a star; the track is slightly subluminous, but the lifetime is almost unaffected. High rates of mass loss lead to a hot, high-luminosity stellar model with a helium core surrounded by a hydrogen-deficient (Xapprox.0.1) envelope. The main-sequence lifetime is extended by a factor of 2--3. These models may be identified with Wolf-Rayet stars. Between these mass-loss extremes are intermediate models which appear as OBN stars on the main sequence. The mass-loss rates required for significant observable effects range from 8 x 10 -7 to 10 -5 M/sub sun/ yr -1 , depending on the initial stellar mass. It is found that observationally consistent mass-loss rates for stars with M> or =30 M/sub sun/ may be sufficiently high that these stars lose mass on a time scale more rapidly than their main-sequence core evolution time. This result implies that the helium cores resulting from the main-sequence evolution of these massive stars may all be very similar to that of a star of Mapprox.30 M/sub sun/ regardless of the zero-age mass

  3. Diffuse remnants of supernova explosions of moving massive stars

    Science.gov (United States)

    Gvaramadze, V. V.

    The modification of the ambient interstellar medium by the wind of massive stars (the progenitors of most of supernovae) results in that the structure and evolution of diffuse supernova remnants (SNRs) significantly deviate from those derived from standard models of SNRs based of the Sedov-Taylor solution. The stellar proper motion and the regular interstellar magnetic field affect the symmetry of the processed medium and cause the SNR to be non-spherically-symmetric. We show that taking into account these effects allows us to explain the diverse morphologies of the known SNRs (the particular attention is paid to the elongated axisymmetric SNRs and the SNRs consisting of two partially overlapping shells) and to infer the ``true" supernova explosion sites in some peculiar SNRs (therefore to search for new neutron stars associated with them).

  4. Delayed star formation in isolated dwarf galaxies: Hubble space telescope star formation history of the Aquarius dwarf irregular

    Energy Technology Data Exchange (ETDEWEB)

    Cole, Andrew A. [School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, Tasmania, 7001 Australia (Australia); Weisz, Daniel R. [Department of Astronomy, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Dolphin, Andrew E. [Raytheon, 1151 East Hermans Road, Tucson, AZ 85706 (United States); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55441 (United States); McConnachie, Alan W. [NRC Herzberg Institute of Astrophysics, Dominion Astrophysical Observatory, Victoria, BC, V9E 2E7 Canada (Canada); Brooks, Alyson M. [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States); Leaman, Ryan, E-mail: andrew.cole@utas.edu.au, E-mail: drw@ucsc.edu, E-mail: adolphin@raytheon.com, E-mail: skillman@astro.umn.edu, E-mail: alan.mcconnachie@nrc-cnrc.gc.ca, E-mail: abrooks@physics.rutgers.edu, E-mail: rleaman@iac.es [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain)

    2014-11-01

    We have obtained deep images of the highly isolated (d = 1 Mpc) Aquarius dwarf irregular galaxy (DDO 210) with the Hubble Space Telescope Advanced Camera for Surveys. The resulting color-magnitude diagram (CMD) reaches more than a magnitude below the oldest main-sequence turnoff, allowing us to derive the star formation history (SFH) over the entire lifetime of the galaxy with a timing precision of ≈10% of the lookback time. Using a maximum likelihood fit to the CMD we find that only ≈10% of all star formation in Aquarius took place more than 10 Gyr ago (lookback time equivalent to redshift z ≈ 2). The star formation rate increased dramatically ≈6-8 Gyr ago (z ≈ 0.7-1.1) and then declined until the present time. The only known galaxy with a more extreme confirmed delay in star formation is Leo A, a galaxy of similar M {sub H} {sub I}/M {sub *}, dynamical mass, mean metallicity, and degree of isolation. The delayed stellar mass growth in these galaxies does not track the mean dark matter accretion rate from CDM simulations. The similarities between Leo A and Aquarius suggest that if gas is not removed from dwarf galaxies by interactions or feedback, it can linger for several gigayears without cooling in sufficient quantity to form stars efficiently. We discuss possible causes for the delay in star formation including suppression by reionization and late-time mergers. We find reasonable agreement between our measured SFHs and select cosmological simulations of isolated dwarfs. Because star formation and merger processes are both stochastic in nature, delayed star formation in various degrees is predicted to be a characteristic (but not a universal) feature of isolated small galaxies.

  5. Star formation is boosted (and quenched) from the inside-out: radial star formation profiles from MaNGA

    Science.gov (United States)

    Ellison, Sara L.; Sánchez, Sebastian F.; Ibarra-Medel, Hector; Antonio, Braulio; Mendel, J. Trevor; Barrera-Ballesteros, Jorge

    2018-02-01

    The tight correlation between total galaxy stellar mass and star formation rate (SFR) has become known as the star-forming main sequence. Using ˜487 000 spaxels from galaxies observed as part of the Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we confirm previous results that a correlation also exists between the surface densities of star formation (ΣSFR) and stellar mass (Σ⋆) on kpc scales, representing a `resolved' main sequence. Using a new metric (ΔΣSFR), which measures the relative enhancement or deficit of star formation on a spaxel-by-spaxel basis relative to the resolved main sequence, we investigate the SFR profiles of 864 galaxies as a function of their position relative to the global star-forming main sequence (ΔSFR). For galaxies above the global main sequence (positive ΔSFR) ΔΣSFR is elevated throughout the galaxy, but the greatest enhancement in star formation occurs at small radii (<3 kpc, or 0.5Re). Moreover, galaxies that are at least a factor of 3 above the main sequence show diluted gas phase metallicities out to 2Re, indicative of metal-poor gas inflows accompanying the starbursts. For quiescent/passive galaxies that lie at least a factor of 10 below the star-forming main sequence, there is an analogous deficit of star formation throughout the galaxy with the lowest values of ΔΣSFR in the central 3 kpc. Our results are in qualitative agreement with the `compaction' scenario in which a central starburst leads to mass growth in the bulge and may ultimately precede galactic quenching from the inside-out.

  6. Effects of stellar evolution and ionizing radiation on the environments of massive stars

    Science.gov (United States)

    Mackey, J.; Langer, N.; Mohamed, S.; Gvaramadze, V. V.; Neilson, H. R.; Meyer, D. M.-A.

    2014-09-01

    We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3-D simulations show that H ii regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

  7. HOW GALACTIC ENVIRONMENT REGULATES STAR FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Meidt, Sharon E. [Max-Planck-Institut für Astronomie/Königstuhl 17 D-69117 Heidelberg (Germany)

    2016-02-10

    In a new simple model I reconcile two contradictory views on the factors that determine the rate at which molecular clouds form stars—internal structure versus external, environmental influences—providing a unified picture for the regulation of star formation in galaxies. In the presence of external pressure, the pressure gradient set up within a self-gravitating turbulent (isothermal) cloud leads to a non-uniform density distribution. Thus the local environment of a cloud influences its internal structure. In the simple equilibrium model, the fraction of gas at high density in the cloud interior is determined simply by the cloud surface density, which is itself inherited from the pressure in the immediate surroundings. This idea is tested using measurements of the properties of local clouds, which are found to show remarkable agreement with the simple equilibrium model. The model also naturally predicts the star formation relation observed on cloud scales and at the same time provides a mapping between this relation and the closer-to-linear molecular star formation relation measured on larger scales in galaxies. The key is that pressure regulates not only the molecular content of the ISM but also the cloud surface density. I provide a straightforward prescription for the pressure regulation of star formation that can be directly implemented in numerical models. Predictions for the dense gas fraction and star formation efficiency measured on large-scales within galaxies are also presented, establishing the basis for a new picture of star formation regulated by galactic environment.

  8. Massive scalar counterpart of gravitational waves in scalarized neutron star binaries

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jing [Sun Yat-sen University, School of Physics and Astronomy, Guangzhou (China)

    2017-09-15

    In analogy with spontaneous magnetization of ferromagnets below the Curie temperature, a neutron star (NS), with a compactness above a certain critical value, may undergo spontaneous scalarization and exhibit an interior nontrivial scalar configuration. Consequently, the exterior spacetime is changed, and an external scalar field appears, which subsequently triggers a scalarization of its companion. The dynamical interplay produces a gravitational scalar counterpart of tensor gravitational waves. In this paper, we resort to scalar-tensor theory and demonstrate that the gravitational scalar counterpart from a double neutron star (DNS) and a neutron star-white dwarf (NS-WD) system become massive. We report that (1) a gravitational scalar background field, arising from convergence of external scalar fields, plays the role of gravitational scalar counterpart in scalarized DNS binary, and the appearance of a mass-dimensional constant in a Higgs-like gravitational scalar potential is responsible for a massive gravitational scalar counterpart with a mass of the order of the Planck scale; (2) a dipolar gravitational scalar radiated field, resulting from differing binding energies of NS and WD, plays the role of a gravitational scalar counterpart in scalarized orbital shrinking NS-WDs, which oscillates around a local and scalar-energy-density-dependent minimum of the gravitational scalar potential and obtains a mass of the order of about 10{sup -21} eV/c{sup 2}. (orig.)

  9. VLA AND ALMA IMAGING OF INTENSE GALAXY-WIDE STAR FORMATION IN z ∼ 2 GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Rujopakarn, W.; Silverman, J. D. [Kavli Institute for the Physics and Mathematics of the universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Dunlop, J. S.; Ivison, R. J.; McLure, R. J.; Michałowski, M. J. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Rieke, G. H. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Cibinel, A. [Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Brighton, BN1 9QH (United Kingdom); Nyland, K. [National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States); Jagannathan, P.; Bhatnagar, S. [National Radio Astronomy Observatory, Socorro, NM 87801 (United States); Alexander, D. M. [Department of Physics, Durham University, Durham DH1 3LE (United Kingdom); Biggs, A. D. [European Southern Observatory, Karl-Schwarzschild-Straße 2, Garching (Germany); Ballantyne, D. R. [Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Dickinson, M. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Elbaz, D. [CEA Saclay, DSM/Irfu/Service d’Astrophysique, Orme des Merisiers, F-91191 Gif-sur-Yvette Cedex (France); Geach, J. E. [Center for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom); Hayward, C. C. [Center for Computational Astrophysics, 160 Fifth Avenue, New York, NY 10010 (United States); Kirkpatrick, A., E-mail: wiphu.rujopakarn@ipmu.jp [Yale Center for Astronomy and Astrophysics, Physics Department, P.O. Box 208120, New Haven, CT 06520 (United States); and others

    2016-12-10

    We present ≃0.″4 resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at z  = 1.3–3.0. These galaxies are selected from sensitive blank-field surveys of the 2′ × 2′ Hubble Ultra-Deep Field at λ  = 5 cm and 1.3 mm using the Karl G. Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. They have star formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at z  ∼ 2. Morphological classification performed on spatially resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGNs), thereby representing a diversity of z  ∼ 2 SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of 4.2 ± 1.8 kpc. This provides direct evidence of galaxy-wide star formation in distant blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5 M {sub ⊙} yr{sup −1} kpc{sup −2}, sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGNs, which are found to be cospatial with star formation. The median extinction-independent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies, whose SFRs are 3–8 times larger, providing a constraint on the characteristic SFR (∼300 M {sub ⊙} yr{sup −1}) above which a significant population of more compact SFGs appears to emerge.

  10. Formation of stars and stellar clusters in galactic environment

    OpenAIRE

    Smilgys, Romas

    2018-01-01

    Star and stellar cluster formation in spiral galaxies is one of the biggest questions of astrophysics. In this thesis, I study how star formation, and the formation of stellar clusters, proceeds using SPH simulations. These simulations model a region of 400 pc and 10⁷ solar masses. Star formation is modelled through the use of sink particles which represent small groups of stars. Star formation occurs in high density regions, created by galactic spiral arm passage. The spiral shock compresses...

  11. A CANDELS-3D-HST synergy: Resolved Star Formation Patterns at 0.7 < z < 1.5

    Science.gov (United States)

    Wuyts, Stijn; Förster Schreiber, Natascha M.; Nelson, Erica J.; van Dokkum, Pieter G.; Brammer, Gabe; Chang, Yu-Yen; Faber, Sandra M.; Ferguson, Henry C.; Franx, Marijn; Fumagalli, Mattia; Genzel, Reinhard; Grogin, Norman A.; Kocevski, Dale D.; Koekemoer, Anton M.; Lundgren, Britt; Lutz, Dieter; McGrath, Elizabeth J.; Momcheva, Ivelina; Rosario, David; Skelton, Rosalind E.; Tacconi, Linda J.; van der Wel, Arjen; Whitaker, Katherine E.

    2013-12-01

    We analyze the resolved stellar populations of 473 massive star-forming galaxies at 0.7 < z < 1.5, with multi-wavelength broadband imaging from CANDELS and Hα surface brightness profiles at the same kiloparsec resolution from 3D-HST. Together, this unique data set sheds light on how the assembled stellar mass is distributed within galaxies, and where new stars are being formed. We find the Hα morphologies to resemble more closely those observed in the ACS I band than in the WFC3 H band, especially for the larger systems. We next derive a novel prescription for Hα dust corrections, which accounts for extra extinction toward H II regions. The prescription leads to consistent star formation rate (SFR) estimates and reproduces the observed relation between the Hα/UV luminosity ratio and visual extinction, on both a pixel-by-pixel and a galaxy-integrated level. We find the surface density of star formation to correlate with the surface density of assembled stellar mass for spatially resolved regions within galaxies, akin to the so-called "main sequence of star formation" established on a galaxy-integrated level. Deviations from this relation toward lower equivalent widths are found in the inner regions of galaxies. Clumps and spiral features, on the other hand, are associated with enhanced Hα equivalent widths, bluer colors, and higher specific SFRs compared to the underlying disk. Their Hα/UV luminosity ratio is lower than that of the underlying disk, suggesting that the ACS clump selection preferentially picks up those regions of elevated star formation activity that are the least obscured by dust. Our analysis emphasizes that monochromatic studies of galaxy structure can be severely limited by mass-to-light ratio variations due to dust and spatially inhomogeneous star formation histories.

  12. The VLT-FLAMES Tarantula Survey. III. A very massive star in apparent isolation from the massive cluster R136

    NARCIS (Netherlands)

    Bestenlehner, J.M.; Vink, J.S.; Gräfener, G.; Najarro, F.; Evans, C.J.; Bastian, N.; Bonanos, A.Z.; Bressert, E.; Crowther, P.A.; Doran, E.; Friedrich, K.; Hénault-Brunet, V.; Herrero, A.; de Koter, A.; Langer, N.; Lennon, D.J.; Maíz Apellániz, J.; Sana, H.; Soszynski, I.; Taylor, W.D.

    2011-01-01

    VFTS 682 is located in an active star-forming region, at a projected distance of 29 pc from the young massive cluster R136 in the Tarantula Nebula of the Large Magellanic Cloud. It was previously reported as a candidate young stellar object, and more recently spectroscopically revealed as a

  13. Probing Minor-merger-driven Star Formation In Early-type Galaxies Using Spatially-resolved Spectro-photometric Studies

    Science.gov (United States)

    Kaviraj, Sugata; Crockett, M.; Silk, J.; O'Connell, R. W.; Whitmore, B.; Windhorst, R.; Cappellari, M.; Bureau, M.; Davies, R.

    2012-01-01

    Recent studies that leverage the rest-frame ultraviolet (UV) spectrum have revealed widespread recent star formation in early-type galaxies (ETGs), traditionally considered to be old, passively-evolving systems. This recent star formation builds 20% of the ETG stellar mass after z 1, driven by repeated minor mergers between ETGs and small, gas-rich satellites. We demonstrate how spatially-resolved studies, using a combination of high-resolution UV-optical imaging and integral-field spectroscopy (IFS), is a powerful tool to quantify the assembly history of individual ETGs and elucidate the poorly-understood minor-merger process. Using a combination of WFC3 UV-optical (2500-8200 angstroms) imaging and IFS from the SAURON project of the ETG NGC 4150, we show that this galaxy experienced a merger with mass ratio 1:15 around 0.9 Gyr ago, which formed 3% of its stellar mass and a young kinematically-decoupled core. A UV-optical analysis of its globular cluster system shows that the bulk of the stars locked up in these clusters likely formed 6-7 Gyrs in the past. We introduce a new HST-WFC3 programme, approved in Cycle 19, which will leverage similar UV-optical imaging of a representative sample of nearby ETGs from SAURON to study the recent star formation and its drivers in unprecedented detail and put definitive constraints on minor-merger-driven star formation in massive galaxies at late epochs.

  14. Protostar formation in the early universe.

    Science.gov (United States)

    Yoshida, Naoki; Omukai, Kazuyuki; Hernquist, Lars

    2008-08-01

    The nature of the first generation of stars in the universe remains largely unknown. Observations imply the existence of massive primordial stars early in the history of the universe, and the standard theory for the growth of cosmic structure predicts that structures grow hierarchically through gravitational instability. We have developed an ab initio computer simulation of the formation of primordial stars that follows the relevant atomic and molecular processes in a primordial gas in an expanding universe. The results show that primeval density fluctuations left over from the Big Bang can drive the formation of a tiny protostar with a mass 1% that of the Sun. The protostar is a seed for the subsequent formation of a massive primordial star.

  15. Inner Milky Way Raging with Star Formation

    Science.gov (United States)

    2008-01-01

    More than 444,580 frames from NASA's Spitzer Space Telescope were stitched together to create this portrait of the raging star-formation occurring in the inner Milky Way. As inhabitants of a flat galactic disk, Earth and its solar system have an edge-on view of their host galaxy, like looking a glass dish from its edge. From our perspective, most of the galaxy is condensed into a blurry narrow band of light that stretches completely around the sky, also known as the galactic plane. In this mosaic the galactic plane is broken up into five components: the far-left side of the plane (top image); the area just left of the galactic center (second to top); galactic center (middle); the area to the right of galactic center (second to bottom); and the far-right side of the plane (bottom). Together, these panels represent more than 50 percent of our entire Milky Way galaxy. The red haze that permeates the picture comes from organic molecules called polycyclic aromatic hydrocarbons, which are illuminated by light from massive baby stars. On Earth, these molecules are found in automobile exhaust, or charred barbeque grills anywhere carbon molecules are burned incompletely. The patches of black are dense, obscuring dust clouds impenetrable by even Spitzer's super-sensitive infrared eyes. Bright arcs of white throughout the image are massive stellar incubators. The bluish-white haze that hovers heavily in the middle panel is starlight from the older stellar population towards the center of the galaxy. This picture was taken with Spitzer's infrared array camera, as part of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) project. This is a four-color composite where blue is 3.6-micron light, green is 4.5 microns, orange is 5.8 microns and red is 8.0 microns.

  16. CANDELS: THE CORRELATION BETWEEN GALAXY MORPHOLOGY AND STAR FORMATION ACTIVITY AT z ∼ 2

    International Nuclear Information System (INIS)

    Lee, Bomee; Giavalisco, Mauro; Williams, Christina C.; Guo Yicheng; Faber, S. M.; Lotz, Jennifer; Ferguson, Henry C.; Koekemoer, Anton; Grogin, Norman; Van der Wel, Arjen; Kocevski, Dale; Conselice, Christopher J.; Wuyts, Stijn; Dekel, Avishai; Kartaltepe, Jeyhan; Bell, Eric F.

    2013-01-01

    We discuss the state of the assembly of the Hubble sequence in the mix of bright galaxies at redshift 1.4 AB ∼ 26, selected from the HST/ACS and WFC3 images of the GOODS-South field obtained as part of the GOODS and CANDELS observations. We investigate the relationship between the star formation properties and morphology using various parametric diagnostics, such as the Sérsic light profile, Gini (G), M 20 , concentration (C), asymmetry (A), and multiplicity (Ψ) parameters. Our sample clearly separates into massive, red, and passive galaxies versus less massive, blue, and star-forming ones, and this dichotomy correlates very well with the galaxies' morphological properties. Star-forming galaxies show a broad variety of morphological features, including clumpy structures and bulges mixed with faint low surface brightness features, generally characterized by disky-type light profiles. Passively evolving galaxies, on the other hand, very often have compact light distribution and morphology typical of today's spheroidal systems. We also find that artificially redshifted local galaxies have a similar distribution with z ∼ 2 galaxies in a G-M 20 plane. Visual inspection between the rest-frame optical and UV images show that there is a generally weak morphological k-correction for galaxies at z ∼ 2, but the comparison with non-parametric measures show that galaxies in the rest-frame UV are somewhat clumpier than rest-frame optical. Similar general trends are observed in the local universe among massive galaxies, suggesting that the backbone of the Hubble sequence was already in place at z ∼ 2

  17. Massive quiescent galaxies at z > 3 in the Millennium simulation populated by a semi-analytic galaxy formation model

    Science.gov (United States)

    Rong, Yu; Jing, Yingjie; Gao, Liang; Guo, Qi; Wang, Jie; Sun, Shuangpeng; Wang, Lin; Pan, Jun

    2017-10-01

    We take advantage of the statistical power of the large-volume dark-matter-only Millennium simulation (MS), combined with a sophisticated semi-analytic galaxy formation model, to explore whether the recently reported z = 3.7 quiescent galaxy ZF-COSMOS-20115 (ZF) can be accommodated in current galaxy formation models. In our model, a population of quiescent galaxies with stellar masses and star formation rates comparable to those of ZF naturally emerges at redshifts z 3.5 massive QGs are rare (about 2 per cent of the galaxies with the similar stellar masses), the existing AGN feedback model implemented in the semi-analytic galaxy formation model can successfully explain the formation of the high-redshift QGs as it does on their lower redshift counterparts.

  18. SDSS-IV MaNGA - the spatially resolved transition from star formation to quiescence

    Science.gov (United States)

    Belfiore, Francesco; Maiolino, Roberto; Maraston, Claudia; Emsellem, Eric; Bershady, Matthew A.; Masters, Karen L.; Bizyaev, Dmitry; Boquien, Médéric; Brownstein, Joel R.; Bundy, Kevin; Diamond-Stanic, Aleksandar M.; Drory, Niv; Heckman, Timothy M.; Law, David R.; Malanushenko, Olena; Oravetz, Audrey; Pan, Kaike; Roman-Lopes, Alexandre; Thomas, Daniel; Weijmans, Anne-Marie; Westfall, Kyle B.; Yan, Renbin

    2017-04-01

    Using spatially resolved spectroscopy from SDSS-IV MaNGA we have demonstrated that low ionization emission-line regions (LIERs) in local galaxies result from photoionization by hot evolved stars, not active galactic nuclei, hence tracing galactic region hosting old stellar population where, despite the presence of ionized gas, star formation is no longer occurring. LIERs are ubiquitous in both quiescent galaxies and in the central regions of galaxies where star formation takes place at larger radii. We refer to these two classes of galaxies as extended LIER (eLIER) and central LIER (cLIER) galaxies, respectively. cLIERs are late-type galaxies primarily spread across the green valley, in the transition region between the star formation main sequence and quiescent galaxies. These galaxies display regular disc rotation in both stars and gas, although featuring a higher central stellar velocity dispersion than star-forming galaxies of the same mass. cLIERs are consistent with being slowly quenched inside-out; the transformation is associated with massive bulges, pointing towards the importance of bulge growth via secular evolution. eLIERs are morphologically early types and are indistinguishable from passive galaxies devoid of line emission in terms of their stellar populations, morphology and central stellar velocity dispersion. Ionized gas in eLIERs shows both disturbed and disc-like kinematics. When a large-scale flow/rotation is observed in the gas, it is often misaligned relative to the stellar component. These features indicate that eLIERs are passive galaxies harbouring a residual cold gas component, acquired mostly via external accretion. Importantly, quiescent galaxies devoid of line emission reside in denser environments and have significantly higher satellite fraction than eLIERs. Environmental effects thus represent the likely cause for the existence of line-less galaxies on the red sequence.

  19. Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

    Science.gov (United States)

    Meyer, D. M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V. V.; Mignone, A.; Izzard, R. G.; Kaper, L.

    2014-11-01

    At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional axisymmetric hydrodynamical simulations following the evolution of the circumstellar medium of these stars in the Galactic plane from the main sequence to the red supergiant phase. We find that thermal conduction is an important process governing the shape, size and structure of the bow shocks around hot stars, and that they have an optical luminosity mainly produced by forbidden lines, e.g. [O III]. The Hα emission of the bow shocks around hot stars originates from near their contact discontinuity. The Hα emission of bow shocks around cool stars originates from their forward shock, and is too faint to be observed for the bow shocks that we simulate. The emission of optically thin radiation mainly comes from the shocked ISM material. All bow shock models are brighter in the infrared, i.e. the infrared is the most appropriate waveband to search for bow shocks. Our study suggests that the infrared emission comes from near the contact discontinuity for bow shocks of hot stars and from the inner region of shocked wind for bow shocks around cool stars. We predict that, in the Galactic plane, the brightest, i.e. the most easily detectable bow shocks are produced by high-mass stars moving with small space velocities.

  20. The formation of stars

    CERN Document Server

    Stahler, Steven W

    2008-01-01

    This book is a comprehensive treatment of star formation, one of the most active fields of modern astronomy. The reader is guided through the subject in a logically compelling manner. Starting from a general description of stars and interstellar clouds, the authors delineate the earliest phases of stellar evolution. They discuss formation activity not only in the Milky Way, but also in other galaxies, both now and in the remote past. Theory and observation are thoroughly integrated, with the aid of numerous figures and images. In summary, this volume is an invaluable resource, both as a text f

  1. Wolf-Rayet stars

    Energy Technology Data Exchange (ETDEWEB)

    Sahade, J

    1981-12-01

    Aspects of the problems of the Wolf-Rayet stars related to their chemical composition, their evolutionary status, and their apparent dichotomy in two spectral sequences are discussed. Dogmas concerning WR stars are critically discussed, including the belief that WR stars lack hydrogen, that they are helium stars evolved from massive close binaries, and the existence of a second WR stage in which the star is a short-period single-lined binary. The relationship of WR stars with planetary nebulae is addressed, as is the membership of these stars in clusters and associations. The division of WR stars into WN and WC sequences is considered, questioning the reasonability of accounting for WR line formation in terms of abundance differences.

  2. Tracking the Obscured Star Formation Along the Complete Evolutionary Merger Sequence of LIRGs

    Science.gov (United States)

    Diaz-Santos, Tanio

    2014-10-01

    We propose to obtain WFC3 narrow-band Pa-beta imaging of a sample of 24 nearby luminous infrared (IR) galaxies (LIRGs) from the Great Observatories All-sky LIRG survey (GOALS) selected to be in advanced stages of interaction. LIRGs account for half of the obscured star formation of the Universe at z ~ 1-2, and they represent a key population in galaxy formation and evolution. We will use the Pa-beta images to trace the ionized gas in LIRGs and study its spatial distribution from scales of ~ 100 pc to up to several kpc, probing the youngest, massive stars formed in the most buried environments of LIRGs due to the interaction process. This will allow us to measure how the gas in the center of mergers is converted into stars, which eventually leads to the build-up of a nuclear stellar cusp and the "inside-out" growth of bulges. We will also create spatially-resolved Pa-beta equivalent width maps to search for age gradients across the galaxies and correlate the distribution of Pa-beta emission with that of un-obscured star clusters detected in the UV and optical with HST on the same spatial scales. Finally, we will combine our data with previous studies mainly focused on isolated and early-stage interacting LIRG systems to analyze the size and compactness of the starburst along the complete merger sequence of LIRGs. The requested data represent a critical missing piece of information that will allow us to understand both the physics of merger-induced star formation and the applicability of local LIRGs as templates for high-z interacting starburst galaxies.

  3. Star formation rates in isolated galaxies selected from the Two-Micron All-Sky Survey

    Science.gov (United States)

    Melnyk, O.; Karachentseva, V.; Karachentsev, I.

    2015-08-01

    We have considered the star formation properties of 1616 isolated galaxies from the 2MASS XSC (Extended Source Catalog) selected sample (2MIG) with the far-ultraviolet GALEX magnitudes. This sample was then compared with corresponding properties of isolated galaxies from the Local Orphan Galaxies (LOG) catalogue and paired galaxies. We found that different selection algorithms define different populations of isolated galaxies. The population of the LOG catalogue, selected from non-clustered galaxies in the Local Supercluster volume, mostly consists of low-mass spiral and late-type galaxies. The specific star formation rate (SSFR) upper limit in isolated and paired galaxies does not exceed the value of ˜dex(-9.4). This is probably common for galaxies of differing activity and environment (at least at z processes is the galaxy mass. However, the environmental influence is notable: paired massive galaxies with logM* > 11.5 have higher (S)SFR than isolated galaxies. Our results suggest that the environment helps to trigger the star formation in the highest mass galaxies. We found that the fraction of AGN in the paired sample is only a little higher than in our isolated galaxy sample. We assume that AGN phenomenon is probably defined by secular galaxy evolution.

  4. Probing the ejecta of evolved massive stars in transition A VLT/SINFONI K-band survey

    Czech Academy of Sciences Publication Activity Database

    Oksala, Mary E.; Kraus, Michaela; Cidale, L.S.; Muratore, M.F.; Borges Fernandes, M.

    2013-01-01

    Roč. 558, October (2013), A17/1-A17/20 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GAP209/11/1198; GA MŠk 7AMB12AR021 Institutional support: RVO:67985815 Keywords : infrared stars * spectroscopic techniques * massive stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.479, year: 2013

  5. Gravitational instability, evolution of galaxies and star formation

    International Nuclear Information System (INIS)

    Palous, J.

    1979-01-01

    The gravitational collapse is the key to the theories of galaxy and star formation. The observations, showing intrinsic differences between elliptical and spiral galaxies, guide our fundamental conceptions on the formation and evolution of systems in question. Stars in elliptical galaxies and in spherical components of spiral galaxies were formed in a short period of time during early phases of protogalactic collapse, at a time of violent star formation. The disc-like components of spiral galaxies, however, were built gradually in the course of galactic evolution. Star formation in elliptical galaxies is described by the collision model of interstellar clouds, while star formation in discs is characterised by several processes: the expansion of HII regions, the expansion of supernovae remnants and the shock wave related to the presence of the spiral structure. (author)

  6. The many phases of massive galaxies : a near-infrared spectroscopic study of galaxies in the early universe

    NARCIS (Netherlands)

    Kriek, Mariska Therese

    2007-01-01

    A key issue in astronomy today is understanding the star-formation and assembly history of massive galaxies. Stellar population studies show that the bulk of the stars in low-redshift massive galaxies is formed at z~2 or even higher. Furthermore, there are strong indications that about 50% of the

  7. THE LESSER ROLE OF SHEAR IN GALACTIC STAR FORMATION: INSIGHT FROM THE GALACTIC RING SURVEY

    International Nuclear Information System (INIS)

    Dib, Sami; Dariush, Ali; Helou, George; Moore, Toby J. T.; Urquhart, James S.

    2012-01-01

    We analyze the role played by shear in regulating star formation in the Galaxy on the scale of individual molecular clouds. The clouds are selected from the 13 CO J = 1-0 line of the Galactic Ring Survey. For each cloud, we estimate the shear parameter which describes the ability of density perturbations to grow within the cloud. We find that for almost all molecular clouds considered, there is no evidence that shear is playing a significant role in opposing the effects of self-gravity. We also find that the shear parameter of the clouds does not depend on their position in the Galaxy. Furthermore, we find no correlations between the shear parameter of the clouds with several indicators of their star formation activity. No significant correlation is found between the shear parameter and the star formation efficiency of the clouds which is measured using the ratio of the massive young stellar objects luminosities, measured in the Red MSX survey, to the cloud mass. There are also no significant correlations between the shear parameter and the fraction of their mass that is found in denser clumps which is a proxy for their clump formation efficiency, nor with their level of fragmentation expressed in the number of clumps per unit mass. Our results strongly suggest that shear is playing only a minor role in affecting the rates and efficiencies at which molecular clouds convert their gas into dense cores and thereafter into stars.

  8. THE LESSER ROLE OF SHEAR IN GALACTIC STAR FORMATION: INSIGHT FROM THE GALACTIC RING SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Dib, Sami; Dariush, Ali [Astrophysics Group, Blackett Laboratory, Imperial College London, London SW7 2AZ (United Kingdom); Helou, George [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Moore, Toby J. T. [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom); Urquhart, James S., E-mail: s.dib@imperial.ac.uk [Max-Planck Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany)

    2012-10-20

    We analyze the role played by shear in regulating star formation in the Galaxy on the scale of individual molecular clouds. The clouds are selected from the {sup 13}CO J = 1-0 line of the Galactic Ring Survey. For each cloud, we estimate the shear parameter which describes the ability of density perturbations to grow within the cloud. We find that for almost all molecular clouds considered, there is no evidence that shear is playing a significant role in opposing the effects of self-gravity. We also find that the shear parameter of the clouds does not depend on their position in the Galaxy. Furthermore, we find no correlations between the shear parameter of the clouds with several indicators of their star formation activity. No significant correlation is found between the shear parameter and the star formation efficiency of the clouds which is measured using the ratio of the massive young stellar objects luminosities, measured in the Red MSX survey, to the cloud mass. There are also no significant correlations between the shear parameter and the fraction of their mass that is found in denser clumps which is a proxy for their clump formation efficiency, nor with their level of fragmentation expressed in the number of clumps per unit mass. Our results strongly suggest that shear is playing only a minor role in affecting the rates and efficiencies at which molecular clouds convert their gas into dense cores and thereafter into stars.

  9. A TIDALLY DESTRUCTED MASSIVE PLANET AS THE PROGENITOR OF THE TWO LIGHT PLANETS AROUND THE sdB STAR KIC 05807616

    International Nuclear Information System (INIS)

    Bear, Ealeal; Soker, Noam

    2012-01-01

    We propose that the two newly detected Earth-size planets around the hot B subdwarf star KIC 05807616 are remnant of the tidally destructed metallic core of a massive planet. A single massive gas-giant planet was spiralling-in inside the envelope of the red giant branch star progenitor of the extreme horizontal branch (EHB) star KIC 05807616. The released gravitational energy unbound most of the stellar envelope, turning it into an EHB star. The massive planet reached the tidal-destruction radius of ∼1 R ☉ from the core, where the planet's gaseous envelope was tidally removed. In our scenario, the metallic core of the massive planet was tidally destructed into several Earth-like bodies immediately after the gaseous envelope of the planet was removed. Two, and possibly more, Earth-size fragments survived at orbital separations of ∼> 1 R ☉ within the gaseous disk. The bodies interact with the disk and among themselves, and migrated to reach orbits close to a 3:2 resonance. These observed planets can have a planetary magnetic field about 10 times as strong as that of Earth. This strong magnetic field can substantially reduce the evaporation rate from the planets and explain their survivability against the strong UV radiation of the EHB star.

  10. The TESIS Project: Revealing Massive Early-Type Galaxies at z > 1

    Science.gov (United States)

    Saracco, P.; Longhetti, M.; Severgnini, P.; Della Ceca, R.; Braito, V.; Bender, R.; Drory, N.; Feulner, G.; Hopp, U.; Mannucci, F.; Maraston, C.

    How and when present-day massive early-type galaxies built up and what type of evolution has characterized their growth (star formation and/or merging) still remain open issues. The different competing scenarios of galaxy formation predict much different properties of early-type galaxies at z > 1. The "monolithic" collapse predicts that massive spheroids formed at high redshift (z > 2.5-3) and that their comoving density is constant at z 1, their comoving density decreases from z = 0 to z ~ 1.5 and they should experience their last burst of star formation at z 1 can be probed observationally once a well defined sample of massive early-types at z > 1 is available. We are constructing such a sample through a dedicated near-IR very low resolution (λ/Δλ≃50) spectroscopic survey (TNG EROs Spectroscopic Identification Survey, TESIS, [6]) of a complete sample of 30 bright (K < 18.5) Extremely Red Objects (EROs).

  11. Gravitational waves from the collision of tidally disrupted stars with massive black holes

    International Nuclear Information System (INIS)

    East, William E.

    2014-01-01

    We use simulations of hydrodynamics coupled with full general relativity to investigate the gravitational waves produced by a star colliding with a massive black hole when the star's tidal disruption radius lies far outside of the black hole horizon. We consider both main-sequence and white-dwarf compaction stars, and nonspinning black holes, as well as those with near-extremal spin. We study the regime in between where the star can be accurately modeled by a point particle, and where tidal effects completely suppress the gravitational wave signal. We find that nonnegligible gravitational waves can be produced even when the star is strongly affected by tidal forces, as well as when it collides with large angular momentum. We discuss the implications that these results have for the potential observation of gravitational waves from these sources with future detectors.

  12. X-RAY AND RADIO OBSERVATIONS OF THE MASSIVE STAR-FORMING REGION IRAS 20126+4104

    Energy Technology Data Exchange (ETDEWEB)

    Montes, V. A.; Hofner, P.; Anderson, C.; Rosero, V. [Physics Department, New Mexico Tech, 801 Leroy Place, Socorro, NM 87801 (United States)

    2015-08-15

    We present results from Chandra ACIS-I and Karl G. Jansky Very Large Array 6 cm continuum observations of the IRAS 20126+4104 massive star-forming region. We detect 150 X-ray sources within the 17′ × 17′ ACIS-I field, and a total of 13 radio sources within the 9.′2 primary beam at 4.9 GHz. Among these observtions are the first 6 cm detections of the central sources reported by Hofner et al., namely, I20N1, I20S, and I20var. A new variable radio source is also reported. Searching the 2MASS archive, we identified 88 near-infrared (NIR) counterparts to the X-ray sources. Only four of the X-ray sources had 6 cm counterparts. Based on an NIR color–color analysis and on the Besançon simulation of Galactic stellar populations, we estimate that approximately 80 X-ray sources are associated with this massive star-forming region. We detect an increasing surface density of X-ray sources toward the massive protostar and infer the presence of a cluster of at least 43 young stellar objects within a distance of 1.2 pc from the massive protostar.

  13. Star Formation in Merging Galaxies Using FIRE

    Science.gov (United States)

    Perez, Adrianna; Hung, Chao-Ling; Naiman, Jill; Moreno, Jorge; Hopkins, Philip

    2018-01-01

    Galaxy interactions and mergers are efficient mechanisms to birth stars at rates that are significantly higher than found in our Milky Way galaxy. The Kennicut-Schmidt (KS) relation is an empirical relationship between the star-forming rate and gas surface densities of galaxies (Schmidt 1959; Kennicutt 1998). Although most galaxies follow the KS relation, the high levels of star formation in galaxy mergers places them outside of this otherwise tight relationship. The goal of this research is to analyze the gas content and star formation of simulated merging galaxies. Our work utilizes the Feedback In Realistic Environments (FIRE) model (Hopkins et al., 2014). The FIRE project is a high-resolution cosmological simulation that resolves star-forming regions and incorporates stellar feedback in a physically realistic way. In this work, we have noticed a significant increase in the star formation rate at first and second passage, when the two black holes of each galaxy approach one other. Next, we will analyze spatially resolved star-forming regions over the course of the interacting system. Then, we can study when and how the rates that gas converts into stars deviate from the standard KS. These analyses will provide important insights into the physical mechanisms that regulate star formation of normal and merging galaxies and valuable theoretical predictions that can be used to compare with current and future observations from ALMA or the James Webb Space Telescope.

  14. The multiplicity of massive stars: A high angular resolution survey with the HST fine guidance sensor

    International Nuclear Information System (INIS)

    Aldoretta, E. J.; Gies, D. R.; Henry, T. J.; Jao, W.-C.; Norris, R. P.

    2015-01-01

    We present the results of an all-sky survey made with the Fine Guidance Sensor on the Hubble Space Telescope to search for angularly resolved binary systems among massive stars. The sample of 224 stars is comprised mainly of Galactic O- and B-type stars and luminous blue variables, plus a few luminous stars in the Large Magellanic Cloud. The FGS TRANS mode observations are sensitive to the detection of companions with an angular separation between 0.″01 and 1.″0 and brighter than △m=5. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets (43 of these are new detections). These numbers yield a companion detection frequency of 29% for the FGS survey. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample, and we present estimates of the frequency of multiple systems and the companion frequency for subsets of stars residing in clusters and associations, field stars, and runaway stars. These results confirm the high multiplicity fraction, especially among massive stars in clusters and associations. We show that the period distribution is approximately flat in increments of logP. We identify a number of systems of potential interest for long-term orbital determinations, and we note the importance of some of these companions for the interpretation of the radial velocities and light curves of close binaries that have third companions.

  15. Quenching star formation with quasar outflows launched by trapped IR radiation

    Science.gov (United States)

    Costa, Tiago; Rosdahl, Joakim; Sijacki, Debora; Haehnelt, Martin G.

    2018-06-01

    We present cosmological radiation-hydrodynamic simulations, performed with the code RAMSES-RT, of radiatively-driven outflows in a massive quasar host halo at z = 6. Our simulations include both single- and multi-scattered radiation pressure on dust from a quasar and are compared against simulations performed with thermal feedback. For radiation pressure-driving, we show that there is a critical quasar luminosity above which a galactic outflow is launched, set by the equilibrium of gravitational and radiation forces. While this critical luminosity is unrealistically high in the single-scattering limit for plausible black hole masses, it is in line with a ≈ 3 × 10^9 M_⊙ black hole accreting at its Eddington limit, if infrared (IR) multi-scattering radiation pressure is included. The outflows are fast (v ≳ 1000 km s^{-1}) and strongly mass-loaded with peak mass outflow rates ≈ 10^3 - 10^4 M_⊙ yr^{-1}, but short-lived (star formation in the bulge. We hence argue that radiation pressure-driven feedback may be an important ingredient in regulating star formation in compact starbursts, especially during the quasar's `obscured' phase.

  16. Probes of Cosmic Star Formation History

    Indian Academy of Sciences (India)

    I summarize X-ray diagnostic studies of cosmic star formation history in terms of evolutionary schemes for X-ray binary evolution in normal galaxies with evolving star formation. Deep X-ray imaging studies by Chandra and XMM-Newton are now beginning to constrain both the X-ray luminosity evolution of galaxies and the ...

  17. The Formation and Evolution of Star Clusters in Interacting Galaxies

    Science.gov (United States)

    Maji, Moupiya; Zhu, Qirong; Li, Yuexing; Charlton, Jane; Hernquist, Lars; Knebe, Alexander

    2017-08-01

    Observations of globular clusters show that they have universal lognormal mass functions with a characteristic peak at ˜ 2× {10}5 {M}⊙ , but the origin of this peaked distribution is highly debated. Here we investigate the formation and evolution of star clusters (SCs) in interacting galaxies using high-resolution hydrodynamical simulations performed with two different codes in order to mitigate numerical artifacts. We find that massive SCs in the range of ˜ {10}5.5{--}{10}7.5 {M}⊙ form preferentially in the highly shocked regions produced by galaxy interactions. The nascent cluster-forming clouds have high gas pressures in the range of P/k˜ {10}8{--}{10}12 {{K}} {{cm}}-3, which is ˜ {10}4{--}{10}8 times higher than the typical pressure of the interstellar medium but consistent with recent observations of a pre-super-SC cloud in the Antennae Galaxies. Furthermore, these massive SCs have quasi-lognormal initial mass functions with a peak around ˜ {10}6 {M}⊙ . The number of clusters declines with time due to destructive processes, but the shape and the peak of the mass functions do not change significantly during the course of galaxy collisions. Our results suggest that gas-rich galaxy mergers may provide a favorable environment for the formation of massive SCs such as globular clusters, and that the lognormal mass functions and the unique peak may originate from the extreme high-pressure conditions of the birth clouds and may survive the dynamical evolution.

  18. Extended high circular polarization in the Orion massive star forming region: implications for the origin of homochirality in the solar system.

    Science.gov (United States)

    Fukue, Tsubasa; Tamura, Motohide; Kandori, Ryo; Kusakabe, Nobuhiko; Hough, James H; Bailey, Jeremy; Whittet, Douglas C B; Lucas, Philip W; Nakajima, Yasushi; Hashimoto, Jun

    2010-06-01

    We present a wide-field (approximately 6' x 6') and deep near-infrared (K(s) band: 2.14 mum) circular polarization image in the Orion nebula, where massive stars and many low-mass stars are forming. Our results reveal that a high circular polarization region is spatially extended (approximately 0.4 pc) around the massive star-forming region, the BN/KL nebula. However, other regions, including the linearly polarized Orion bar, show no significant circular polarization. Most of the low-mass young stars do not show detectable extended structure in either linear or circular polarization, in contrast to the BN/KL nebula. If our solar system formed in a massive star-forming region and was irradiated by net circularly polarized radiation, then enantiomeric excesses could have been induced, through asymmetric photochemistry, in the parent bodies of the meteorites and subsequently delivered to Earth. These could then have played a role in the development of biological homochirality on Earth.

  19. The interstellar medium and star formation in local galaxies: Variations of the star formation law in simulations

    International Nuclear Information System (INIS)

    Becerra, Fernando; Escala, Andrés

    2014-01-01

    We use the adaptive mesh refinement code Enzo to model the interstellar medium (ISM) in isolated local disk galaxies. The simulation includes a treatment for star formation and stellar feedback. We get a highly supersonic turbulent disk, which is fragmented at multiple scales and characterized by a multi-phase ISM. We show that a Kennicutt-Schmidt relation only holds when averaging over large scales. However, values of star formation rates and gas surface densities lie close in the plot for any averaging size. This suggests an intrinsic relation between stars and gas at cell-size scales, which dominates over the global dynamical evolution. To investigate this effect, we develop a method to simulate the creation of stars based on the density field from the snapshots, without running the code again. We also investigate how the star formation law is affected by the characteristic star formation timescale, the density threshold, and the efficiency considered in the recipe. We find that the slope of the law varies from ∼1.4 for a free-fall timescale, to ∼1.0 for a constant depletion timescale. We further demonstrate that a power law is recovered just by assuming that the mass of the new stars is a fraction of the mass of the cell m * = ερ gas Δx 3 , with no other physical criteria required. We show that both efficiency and density threshold do not affect the slope, but the right combination of them can adjust the normalization of the relation, which in turn could explain a possible bi-modality in the law.

  20. Supernovae from massive stars with extended tenuous envelopes

    Science.gov (United States)

    Dessart, Luc; Yoon, Sung-Chul; Livne, Eli; Waldman, Roni

    2018-04-01

    Massive stars with a core-halo structure are interesting objects for stellar physics and hydrodynamics. Using simulations for stellar evolution, radiation hydrodynamics, and radiative transfer, we study the explosion of stars with an extended and tenuous envelope (i.e. stars in which 95% of the mass is contained within 10% or less of the surface radius). We consider both H-rich supergiant and He-giant progenitors resulting from close-binary evolution and dying with a final mass of 2.8-5 M⊙. An extended envelope causes the supernova (SN) shock to brake and a reverse shock to form, sweeping core material into a dense shell. The shock-deposited energy, which suffers little degradation from expansion, is trapped in ejecta layers of moderate optical depth, thereby enhancing the SN luminosity at early times. With the delayed 56Ni heating, we find that the resulting optical and near-IR light curves all exhibit a double-peak morphology. We show how an extended progenitor can explain the blue and featureless optical spectra of some Type IIb and Ib SNe. The dense shell formed by the reverse shock leads to line profiles with a smaller and near-constant width. This ejecta property can explain the statistically narrower profiles of Type IIb compared to Type Ib SNe, as well as the peculiar Hα profile seen in SN 1993J. At early times, our He-giant star explosion model shows a high luminosity, a blue colour, and featureless spectra reminiscent of the Type Ib SN 2008D, suggesting a low-mass progenitor.

  1. Wolf-Rayet Stars in Starburst Galaxies

    OpenAIRE

    Mas-Hesse, J. Miguel; Kunth, Daniel; Cervino, Miguel

    1999-01-01

    Wolf-Rayet stars have been detected in a large number of galaxies experiencing intense bursts of star formation. All stars initially more massive than a certain, metallicity-dependent, value are believed to experience the Wolf-Rayet phase at the end of their evolution, just before collapsing in supernova explosion. The detection of Wolf-Rayet stars puts therefore important constraints on the evolutionary status of starbursts, the properties of their Initial Mass Functions and their star forma...

  2. Nucleosynthesis and remnants in massive stars of solar metallicity

    International Nuclear Information System (INIS)

    Woosley, S.E.; Heger, A.

    2007-01-01

    Hans Bethe contributed in many ways to our understanding of the supernovae that happen in massive stars, but, to this day, a first principles model of how the explosion is energized is lacking. Nevertheless, a quantitative theory of nucleosynthesis is possible. We present a survey of the nucleosynthesis that occurs in 32 stars of solar metallicity in the mass range 12-120M sun . The most recent set of solar abundances, opacities, mass loss rates, and current estimates of nuclear reaction rates are employed. Restrictions on the mass cut and explosion energy of the supernovae based upon nucleosynthesis, measured neutron star masses, and light curves are discussed and applied. The nucleosynthetic results, when integrated over a Salpeter initial mass function (IMF), agree quite well with what is seen in the sun. We discuss in some detail the production of the long lived radioactivities, 26 Al and 60 Fe, and why recent model-based estimates of the ratio 60 Fe/ 26 Al are overly large compared with what satellites have observed. A major source of the discrepancy is the uncertain nuclear cross sections for the creation and destruction of these unstable isotopes

  3. Hierarchical Star Formation in Turbulent Media: Evidence from Young Star Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Grasha, K.; Calzetti, D. [Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States); Elmegreen, B. G. [IBM Research Division, T.J. Watson Research Center, Yorktown Heights, NY (United States); Adamo, A.; Messa, M. [Department of Astronomy, The Oskar Klein Centre, Stockholm University, Stockholm (Sweden); Aloisi, A.; Bright, S. N.; Lee, J. C.; Ryon, J. E.; Ubeda, L. [Space Telescope Science Institute, Baltimore, MD (United States); Cook, D. O. [California Institute of Technology, 1200 East California Boulevard, Pasadena, CA (United States); Dale, D. A. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY (United States); Fumagalli, M. [Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham (United Kingdom); Gallagher III, J. S. [Department of Astronomy, University of Wisconsin–Madison, Madison, WI (United States); Gouliermis, D. A. [Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Grebel, E. K. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, D-69120, Heidelberg (Germany); Kahre, L. [Department of Astronomy, New Mexico State University, Las Cruces, NM (United States); Kim, H. [Gemini Observatory, La Serena (Chile); Krumholz, M. R., E-mail: kgrasha@astro.umass.edu [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia)

    2017-06-10

    We present an analysis of the positions and ages of young star clusters in eight local galaxies to investigate the connection between the age difference and separation of cluster pairs. We find that star clusters do not form uniformly but instead are distributed so that the age difference increases with the cluster pair separation to the 0.25–0.6 power, and that the maximum size over which star formation is physically correlated ranges from ∼200 pc to ∼1 kpc. The observed trends between age difference and separation suggest that cluster formation is hierarchical both in space and time: clusters that are close to each other are more similar in age than clusters born further apart. The temporal correlations between stellar aggregates have slopes that are consistent with predictions of turbulence acting as the primary driver of star formation. The velocity associated with the maximum size is proportional to the galaxy’s shear, suggesting that the galactic environment influences the maximum size of the star-forming structures.

  4. The ATLAS3D Project - XXX. Star formation histories and stellar population scaling relations of early-type galaxies

    Science.gov (United States)

    McDermid, Richard M.; Alatalo, Katherine; Blitz, Leo; Bournaud, Frédéric; Bureau, Martin; Cappellari, Michele; Crocker, Alison F.; Davies, Roger L.; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Scott, Nicholas; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

    2015-04-01

    We present the stellar population content of early-type galaxies from the ATLAS3D survey. Using spectra integrated within apertures covering up to one effective radius, we apply two methods: one based on measuring line-strength indices and applying single stellar population (SSP) models to derive SSP-equivalent values of stellar age, metallicity, and alpha enhancement; and one based on spectral fitting to derive non-parametric star formation histories, mass-weighted average values of age, metallicity, and half-mass formation time-scales. Using homogeneously derived effective radii and dynamically determined galaxy masses, we present the distribution of stellar population parameters on the Mass Plane (MJAM, σe, R^maj_e), showing that at fixed mass, compact early-type galaxies are on average older, more metal-rich, and more alpha-enhanced than their larger counterparts. From non-parametric star formation histories, we find that the duration of star formation is systematically more extended in lower mass objects. Assuming that our sample represents most of the stellar content of today's local Universe, approximately 50 per cent of all stars formed within the first 2 Gyr following the big bang. Most of these stars reside today in the most massive galaxies (>1010.5 M⊙), which themselves formed 90 per cent of their stars by z ˜ 2. The lower mass objects, in contrast, have formed barely half their stars in this time interval. Stellar population properties are independent of environment over two orders of magnitude in local density, varying only with galaxy mass. In the highest density regions of our volume (dominated by the Virgo cluster), galaxies are older, alpha-enhanced, and have shorter star formation histories with respect to lower density regions.

  5. Supernovae from Wolf-Rayet stars

    International Nuclear Information System (INIS)

    Schaeffer, R.

    1986-01-01

    Wolf-Rayet stars are known to originate from the most massive stars. Under the assumption that these stripped stars explode at the end of their evolution through the same instability mechanism as type II supernovae, we calculate their light curve. The latter is found to be quite similar to the typical SN I light curves but is fainter by about 2 magnitudes. A detailed study of its shape leads to identify the WR supernovae with the SNIp (or SNIb) subclass. The more massive WR stars should explode via the e + e - pair production mechanism, with negligible 56 Ni formation. Their rather dim light curve is predicted to have a ∼ 2 month plateau and afterwards a very sharp decline. A delayed manifestation of such an event might be the Cas A remnant

  6. Inflow of atomic gas fuelling star formation

    DEFF Research Database (Denmark)

    Michałowski, M. J.; Gentile, G.; Hjorth, Jeppe

    2016-01-01

    Gamma-ray burst host galaxies are deficient in molecular gas, and show anomalous metal-poor regions close to GRB positions. Using recent Australia Telescope Compact Array (ATCA) Hi observations we show that they have substantial atomic gas reservoirs. This suggests that star formation in these ga......Gamma-ray burst host galaxies are deficient in molecular gas, and show anomalous metal-poor regions close to GRB positions. Using recent Australia Telescope Compact Array (ATCA) Hi observations we show that they have substantial atomic gas reservoirs. This suggests that star formation...... in these galaxies may be fuelled by recent inflow of metal-poor atomic gas. While this process is debated, it can happen in low-metallicity gas near the onset of star formation because gas cooling (necessary for star formation) is faster than the Hi-to-H2 conversion....

  7. Formation of Globular Clusters with Internal Abundance Spreads in r -Process Elements: Strong Evidence for Prolonged Star Formation

    Energy Technology Data Exchange (ETDEWEB)

    Bekki, Kenji [ICRAR, M468, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, 6009 (Australia); Tsujimoto, Takuji [National Astronomical Observatory of Japan, Mitaka-shi, Tokyo 181-8588 (Japan)

    2017-07-20

    Several globular clusters (GCs) in the Galaxy are observed to show internal abundance spreads in r -process elements (e.g., Eu). We propose a new scenario that explains the origin of these GCs (e.g., M5 and M15). In this scenario, stars with no/little abundance variations first form from a massive molecular cloud (MC). After all of the remaining gas of the MC is expelled by numerous supernovae, gas ejected from asymptotic giant branch stars can be accumulated in the central region of the GC to form a high-density intracluster medium (ICM). Merging of neutron stars then occurs to eject r -process elements, which can be efficiently trapped in and subsequently mixed with the ICM. New stars formed from the ICM can have r -process abundances that are quite different from those of earlier generations of stars within the GC. This scenario can explain both (i) why r -process elements can be trapped within GCs and (ii) why GCs with internal abundance spreads in r -process elements do not show [Fe/H] spreads. Our model shows (i) that a large fraction of Eu-rich stars can be seen in Na-enhanced stellar populations of GCs, as observed in M15, and (ii) why most of the Galactic GCs do not exhibit such internal abundance spreads. Our model demonstrates that the observed internal spreads of r -process elements in GCs provide strong evidence for prolonged star formation (∼10{sup 8} yr).

  8. THERE ARE NO STARLESS MASSIVE PROTO-CLUSTERS IN THE FIRST QUADRANT OF THE GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Ginsburg, A.; Bally, J.; Battersby, C. [Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309 (United States); Bressert, E. [European Southern Observatory, Karl Schwarzschild str. 2, D-85748 Garching bei Muenchen (Germany)

    2012-10-20

    We search the {lambda} = 1.1 mm Bolocam Galactic Plane Survey for clumps containing sufficient mass to form {approx}10{sup 4} M{sub Sun} star clusters. Eighteen candidate massive proto-clusters are identified in the first Galactic quadrant outside of the central kiloparsec. This sample is complete to clumps with mass M{sub clump} > 10{sup 4} M{sub Sun} and radius r {approx}< 2.5 pc. The overall Galactic massive cluster formation rate is CFR(M{sub cluster} > 10{sup 4}) {approx}<5 Myr{sup -1}, which is in agreement with the rates inferred from Galactic open clusters and M31 massive clusters. We find that all massive proto-clusters in the first quadrant are actively forming massive stars and place an upper limit of {tau}{sub starless} < 0.5 Myr on the lifetime of the starless phase of massive cluster formation. If massive clusters go through a starless phase with all of their mass in a single clump, the lifetime of this phase is very short.

  9. THE STAR FORMATION LAWS OF EDDINGTON-LIMITED STAR-FORMING DISKS

    International Nuclear Information System (INIS)

    Ballantyne, D. R.; Armour, J. N.; Indergaard, J.

    2013-01-01

    Two important avenues into understanding the formation and evolution of galaxies are the Kennicutt-Schmidt (K-S) and Elmegreen-Silk (E-S) laws. These relations connect the surface densities of gas and star formation (Σ gas and Σ-dot * , respectively) in a galaxy. To elucidate the K-S and E-S laws for disks where Σ gas ∼> 10 4 M ☉ pc –2 , we compute 132 Eddington-limited star-forming disk models with radii spanning tens to hundreds of parsecs. The theoretically expected slopes (≈1 for the K-S law and ≈0.5 for the E-S relation) are relatively robust to spatial averaging over the disks. However, the star formation laws exhibit a strong dependence on opacity that separates the models by the dust-to-gas ratio that may lead to the appearance of a erroneously large slope. The total infrared luminosity (L TIR ) and multiple carbon monoxide (CO) line intensities were computed for each model. While L TIR can yield an estimate of the average Σ-dot * that is correct to within a factor of two, the velocity-integrated CO line intensity is a poor proxy for the average Σ gas for these warm and dense disks, making the CO conversion factor (α CO ) all but useless. Thus, observationally derived K-S and E-S laws at these values of Σ gas that uses any transition of CO will provide a poor measurement of the underlying star formation relation. Studies of the star formation laws of Eddington-limited disks will require a high-J transition of a high density molecular tracer, as well as a sample of galaxies with known metallicity estimates.

  10. THE STAR FORMATION HISTORY OF THE LARGE MAGELLANIC CLOUD

    International Nuclear Information System (INIS)

    Harris, Jason; Zaritsky, Dennis

    2009-01-01

    We present the first ever global, spatially resolved reconstruction of the star formation history (SFH) of the Large Magellanic Cloud (LMC), based on the application of our StarFISH analysis software to the multiband photometry of 20 million of its stars from the Magellanic Clouds Photometric Survey. The general outlines of our results are consistent with previously published results: following an initial burst of star formation, there was a quiescent epoch from approximately 12 to 5 Gyr ago. Star formation then resumed and has proceeded until the current time at an average rate of roughly 0.2 M sun yr -1 , with temporal variations at the factor of 2 level. The re-ignition of star formation about 5 Gyr ago, in both the LMC and Small Magellanic Cloud (SMC), is suggestive of a dramatic event at that time in the Magellanic system. Among the global variations in the recent star formation rate are peaks at roughly 2 Gyr, 500 Myr, 100 Myr, and 12 Myr. The peaks at 500 Myr and 2 Gyr are nearly coincident with similar peaks in the SFH of the SMC, suggesting a joint history for these galaxies extending back at least several Gyr. The chemical enrichment history recovered from our StarFISH analysis is in broad agreement with that inferred from the LMC's star cluster population, although our constraints on the ancient chemical enrichment history are weak. We conclude from the concordance between the star formation and chemical enrichment histories of the field and cluster populations that the field and cluster star formation modes are tightly coupled.

  11. Formation of Compact Ellipticals in the merging star cluster scenario

    Science.gov (United States)

    Urrutia Zapata, Fernanda Cecilia; Theory and star formation group

    2018-01-01

    In the last years, extended old stellar clusters have been observed. They are like globular clusters (GCs) but with larger sizes(a limit of Re=10 pc is currently seen as reasonable). These extended objects (EOs) cover a huge range of mass. Objects at the low mass end with masses comparable to normal globular clusters are called extended clusters or faint fuzzies Larsen & Brodie (2000) and objects at the high-mass end are called ultra compact dwarf galaxies (UCDs). Ultra compact dwarf galaxies are compact object with luminositys above the brigtest known GCs. UCDs are more compact than typical dwarf galaxies but with comparable luminosities. Usually, a lower mass limit of 2 × 10^6 Solar masses is applied.Fellhauer & Kroupa (2002a,b) demostrated that object like ECs, FFs and UCDs can be the remnants of the merger of star clusters complexes, this scenario is called the Merging Star Cluster Scenario. Amore concise study was performed by Bruens et al. (2009, 2011).Our work tries to explain the formation of compact elliptical(cE). These objects are a comparatively rare class of spheroidal galaxies, possessing very small Re and high central surface brightnesses (Faber 1973). cEs have the same parameters as extended objects but they are slightly larger than 100 pc and the luminosities are in the range of -11 to -12 Mag.The standard formation sceanrio of these systems proposes a galaxy origin. CEs are the result of tidal stripping and truncation of nucleated larger systems. Or they could be a natural extension of the class of elliptical galaxies to lower luminosities and smaller sizes.We want to propose a completely new formation scenario for cEs. In our project we try to model cEs in a similar way that UCDs using the merging star cluster scenario extended to much higher masses and sizes. We think that in the early Universe we might have produced sufficiently strong star bursts to form cluster complexes which merge into cEs. So far it is observationally unknown if cEs are

  12. Shock-induced star formation in a model of the Mice

    OpenAIRE

    Barnes, Joshua E.

    2004-01-01

    Star formation plays an important role in the fate of interacting galaxies. To date, most galactic simulations including star formation have used a density-dependent star formation rule designed to approximate a Schmidt law. Here, I present a new star formation rule which is governed by the local rate of energy dissipation in shocks. The new and old rules are compared using self-consistent simulations of NGC 4676; shock-induced star formation provides a better match to the observations of thi...

  13. Photoionization-regulated star formation and the structure of molecular clouds

    Science.gov (United States)

    Mckee, Christopher F.

    1989-01-01

    A model for the rate of low-mass star formation in Galactic molecular clouds and for the influence of this star formation on the structure and evolution of the clouds is presented. The rate of energy injection by newly formed stars is estimated, and the effect of this energy injection on the size of the cloud is determined. It is shown that the observed rate of star formation appears adequate to support the observed clouds against gravitational collapse. The rate of photoionization-regulated star formation is estimated and it is shown to be in agreement with estimates of the observed rate of star formation if the observed molecular cloud parameters are used. The mean cloud extinction and the Galactic star formation rate per unit mass of molecular gas are predicted theoretically from the condition that photionization-regulated star formation be in equilibrium. A simple model for the evolution of isolated molecular clouds is developed.

  14. Fueling-Controlled the Growth of Massive Black Holes

    Science.gov (United States)

    Escala, A.

    2009-05-01

    We study the relation between nuclear massive black holes and their host spheroid gravitational potential. Using AMR numerical simulations, we analyze how gas is transported into the nuclear (central kpc) regions of galaxies. We study gas fueling onto the inner accretion disk (sub-pc scale) and star formation in a massive nuclear disk like those generally found in proto-spheroids (ULIRGs, SCUBA Galaxies). These sub-pc resolution simulations of gas fueling, which is mainly depleted by star formation, naturally satisfy the `M_BH-M_{virial}' relation, with a scatter considerably less than that observed. We find that a generalized version of the Kennicutt-Schmidt Law for starbursts is satisfied, in which the total gas depletion rate (dot M_gas=dot M_BH + M_SF scales as M_gas/t_orbital. See Escala (2007) for more details about this work.

  15. ON THE STAR FORMATION PROPERTIES OF VOID GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Moorman, Crystal M.; Moreno, Jackeline; White, Amanda; Vogeley, Michael S. [Department of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104 (United States); Hoyle, Fiona [Pontifica Universidad Catolica de Ecuador, 12 de Octubre 1076 y Roca, Quito (Ecuador); Giovanelli, Riccardo; Haynes, Martha P., E-mail: crystal.m.moorman@drexel.edu [Center for Radiophysics and Space Research, Space Sciences Building, Cornell University Ithaca, NY 14853 (United States)

    2016-11-10

    We measure the star formation properties of two large samples of galaxies from the SDSS in large-scale cosmic voids on timescales of 10 and 100 Myr, using H α emission line strengths and GALEX FUV fluxes, respectively. The first sample consists of 109,818 optically selected galaxies. We find that void galaxies in this sample have higher specific star formation rates (SSFRs; star formation rates per unit stellar mass) than similar stellar mass galaxies in denser regions. The second sample is a subset of the optically selected sample containing 8070 galaxies with reliable H i detections from ALFALFA. For the full H i detected sample, SSFRs do not vary systematically with large-scale environment. However, investigating only the H i detected dwarf galaxies reveals a trend toward higher SSFRs in voids. Furthermore, we estimate the star formation rate per unit H i mass (known as the star formation efficiency; SFE) of a galaxy, as a function of environment. For the overall H i detected population, we notice no environmental dependence. Limiting the sample to dwarf galaxies still does not reveal a statistically significant difference between SFEs in voids versus walls. These results suggest that void environments, on average, provide a nurturing environment for dwarf galaxy evolution allowing for higher specific star formation rates while forming stars with similar efficiencies to those in walls.

  16. The stellar content of NGC 346 - A plethora of O stars in the SMC

    International Nuclear Information System (INIS)

    Massey, P.; Parker, J.W.; Garmany, C.D.

    1989-01-01

    The stellar content of NGC 346, the largest and brightest H II region in the SMC, was investigated using the results of CCD UBV photometry and spectroscopy. Spectra of 42 blue stars were classified, showing that 33 are of the O type, of which 11 are of type O6.5 or earlier, which is as many early-type O stars known in the rest of the SMC. The results identify 25-30 NGC 346 stars more massive than 25 solar masses, and six stars more massive than 40 solar masses, indicating that the upper-mass cutoff to the IMF is not lower in the SMC than in the Galaxy or the LMC. The presence of evolved 15 solar-mass stars in the NGC 346 indicates that some massive stars formed 15 million yr ago. The results of spatial distribution suggest that star formation began at the southwest side of the association and has spread to where the central cluster lies now, providing an example of sequential star formation in the SMC. 69 refs

  17. SIMULATING THE FORMATION OF MASSIVE PROTOSTARS. I. RADIATIVE FEEDBACK AND ACCRETION DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Klassen, Mikhail; Pudritz, Ralph E. [Department of Physics and Astronomy, McMaster University, 1280 Main Street W, Hamilton, ON L8S 4M1 (Canada); Kuiper, Rolf [Institute of Astronomy and Astrophysics, Universit