scholarly journals Understanding the growth of massive galaxies via stellar populations

2012 ◽  
Vol 8 (S295) ◽  
pp. 125-128
Author(s):  
Ignacio Ferreras
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Past History ◽  
Stellar Populations ◽  
Open Problems ◽  
Massive Galaxies ◽  
Spectroscopic Observations ◽  
Formation And Evolution ◽  
Minor Mergers ◽  
Star Formation Histories

AbstractThe formation and evolution of massive galaxies represent one of the most intriguing open problems in astrophysics. Their underlying stellar populations encode valuable information about their past history. Detailed spectroscopic observations allow us to constrain the star formation histories, revealing a complicated mixture of a strong, early formation process, followed by passive evolution in the cores, along with an extended assembly of the outer regions via minor mergers. In this contributed talk, some recent results are presented from the analysis of samples of massive galaxies both at z ~ 0 and moderate redshift.

scholarly journals The evolution of massive galaxies in semi-analytical models of galaxy formation

2012 ◽  
Vol 8 (S295) ◽  
pp. 191-199
Author(s):  
Carlton M. Baugh
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Formation Process ◽  
Hierarchical Models ◽  
Gravitational Instability ◽  
Stellar Populations ◽  
Analytical Models ◽  
Massive Galaxies ◽  
Current State ◽  
The Galaxy

AbstractMassive galaxies with old stellar populations have been put forwards as a challenge to models in which cosmic structures grow hierarchically through gravitational instability. I will explain how the growth of massive galaxies is helped by features of hierarchical models. I give a brief outline of how the galaxy formation process is modelled in hierarchical cosmologies using semi-analytical models, and illustrate how these models can be refined as our understanding of processes such as star formation improves. I then present a brief survey of the current state of play in the modelling of massive galaxies and list some outstanding challenges.

scholarly journals The stellar populations of massive galaxies in the local Universe

2012 ◽  
Vol 8 (S295) ◽  
pp. 290-299
Author(s):  
Richard M. McDermid
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Stellar Population ◽  
Stellar Populations ◽  
Early Type ◽  
Massive Galaxies ◽  
Spatially Resolved ◽  
Low Mass ◽  
Galaxy Environment ◽  
Star Formation Histories

AbstractI present a brief review of the stellar population properties of massive galaxies, focusing on early-type galaxies in particular, with emphasis on recent results from the ATLAS3D Survey. I discuss the occurence of young stellar ages, cold gas, and ongoing star formation in early-type galaxies, the presence of which gives important clues to the evolutionary path of these galaxies. Consideration of empirical star formation histories gives a meaningful picture of galaxy stellar population properties, and allows accurate comparison of mass estimates from populations and dynamics. This has recently provided strong evidence of a non-universal IMF, as supported by other recent evidences. Spatially-resolved studies of stellar populations are also crucial to connect distinct components within galaxies to spatial structures seen in other wavelengths or parameters. Stellar populations in the faint outer envelopes of early-type galaxies are a formidable frontier for observers, but promise to put constraints on the ratio of accreted stellar mass versus that formed ‘in situ’ - a key feature of recent galaxy formation models. Galaxy environment appears to play a key role in controlling the stellar population properties of low mass galaxies. Simulations remind us, however, that current day galaxies are the product of a complex assembly and environment history, which gives rise to the trends we see. This has strong implications for our interpretation of environmental trends.

scholarly journals Evidence for Non-smooth Quenching in Massive Galaxies at z ∼ 1

2019 ◽  
Author(s):  
Timothy Carleton ◽  
Yicheng Guo ◽  
Hooshang Nayyeri ◽  
Michael Cooper ◽  
Gregory Rudnick ◽  
...  
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Broad Band ◽  
Gas Flows ◽  
Massive Galaxies ◽  
Star Forming ◽  
Hα Emission ◽  
Minor Mergers ◽  
Star Formation Histories ◽  
Small Dispersion

Abstract We investigate a large sample of massive galaxies at z ∼ 1 with combined HST broad-band and grism observations to constrain the star-formation histories of these systems as they transition from a star-forming state to quiescence. Among our sample of massive ($M_*>10^{10}~\hbox{${\rm M}_{\odot }$}{}$) galaxies at 0.7 < z < 1.2, dust-corrected Hα and UV star-formation indicators agree with a small dispersion (∼0.2 dex) for galaxies on the main sequence, but diverge and exhibit substantial scatter (∼0.7 dex) once they drop significantly below the star-forming main sequence. Significant Hα emission is present in galaxies with low dust-corrected UV SFR values as well as galaxies classified as quiescent using the UVJ diagram. We compare the observed Hα flux distribution to the expected distribution assuming bursty or smooth star-formation histories, and find that massive galaxies at z ∼ 1 are most consistent with a quick, bursty quenching process. This suggests that mechanisms such as feedback, stochastic gas flows, and minor mergers continue to induce low-level bursty star formation in massive galaxies at moderate redshift, even as they quench.

scholarly journals Star formation histories of resolved galaxies

2008 ◽  
Vol 4 (S258) ◽  
pp. 61-72
Author(s):  
Monica Tosi
Keyword(s):  
Star Formation ◽  
Observational Data ◽  
Stellar Populations ◽  
Morphological Type ◽  
The Other ◽  
Early Type ◽  
Significant Rate ◽  
Star Formation Histories

AbstractThe colour-magnitude diagrams of resolved stellar populations are the best tool to study the star formation histories of the host galactic regions. In this review the method to derive star formation histories by means of synthetic colour-magnitude diagrams is briefly outlined, and the results of its application to resolved galaxies of various morphological types are summarized. It is shown that all the galaxies studied so far were already forming stars at the lookback time reached by the observational data, independently of morphological type and metallicity. Early-type galaxies have formed stars predominantly, but in several cases not exclusively, at the earliest epochs. All the other galaxies appear to have experienced rather continuous star formation activities throughout their lifetimes, although with significant rate variations and, sometimes, short quiescent phases.

scholarly journals The size and mass evolution of the massive galaxies over cosmic time

2012 ◽  
Vol 8 (S295) ◽  
pp. 27-36
Author(s):  
Ignacio Trujillo
Keyword(s):  
Structural Evolution ◽  
Cosmic Time ◽  
Stellar Populations ◽  
Massive Galaxies ◽  
Active Line ◽  
Satellite Galaxies ◽  
Compact Galaxies ◽  
Minor Mergers ◽  
Stellar Properties

AbstractOnce understood as the paradigm of passively evolving objects, the discovery that massive galaxies experienced an enormous structural evolution in the last ten billion years has opened an active line of research. The most significant pending question in this field is the following: which mechanism has made galaxies to grow largely in size without altering their stellar populations properties dramatically? The most viable explanation is that massive galaxies have undergone a significant number of minor mergers which have deposited most of their material in the outer regions of the massive galaxies. This scenario, although appealing, is still far from be observationally proved since the number of satellite galaxies surrounding the massive objects appears insufficient at all redshifts. The presence also of a population of nearby massive compact galaxies with mixture stellar properties is another piece of the puzzle that still does not nicely fit within a comprehensive scheme. I will review these and other intriguing properties of the massive galaxies in this contribution.

scholarly journals The connection between prestellar cores and filaments in the Aquila molecular cloud complex

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Vera Könyves ◽  
Philippe André
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Strong Correlation ◽  
Molecular Clouds ◽  
Spatial Distributions ◽  
Complete Sample ◽  
Physical Mechanisms ◽  
Prestellar Cores ◽  
Formation And Evolution ◽  
Cloud Complex

AbstractOne of the main scientific goals of the Herschel Gould Belt survey is to elucidate the physical mechanisms responsible for the formation and evolution of prestellar cores in molecular clouds. In the ~11 deg2 field of Aquila imaged with Herschel/PACS-SPIRE at 70–500 μm, we have identified a complete sample of 651 starless cores, 446 of them are gravitationally-bound candidate prestellar cores. Our Herschel observations also provide an unprecedented census of filaments in the Aquila cloud and suggest an intimate connection between these filaments and the formation process of prestellar cores. Indeed, a strong correlation is found between their spatial distributions. These Herschel findings support a filamentary paradigm for the early stages of star formation, where the cores result from the gravitational fragmentation of the densest filaments.

scholarly journals Stellar populations across galaxy bars in the MUSE TIMER project

2020 ◽  
Vol 637 ◽  
pp. A56 ◽  
Author(s):  
Justus Neumann ◽  
Francesca Fragkoudi ◽  
Isabel Pérez ◽  
Dimitri A. Gadotti ◽  
Jesús Falcón-Barroso ◽  
...  
Keyword(s):  
Star Formation ◽  
Major Axis ◽  
Stellar Populations ◽  
Barred Galaxies ◽  
Chemical Enrichment ◽  
Spatially Resolved ◽  
Stellar Ages ◽  
Hydrodynamical Simulations ◽  
Inner Region ◽  
Star Formation Histories

Stellar populations in barred galaxies save an imprint of the influence of the bar on the host galaxy’s evolution. We present a detailed analysis of star formation histories (SFHs) and chemical enrichment of stellar populations in nine nearby barred galaxies from the TIMER project. We used integral field observations with the MUSE instrument to derive unprecedented spatially resolved maps of stellar ages, metallicities, [Mg/Fe] abundances, and SFHs, as well as Hα as a tracer of ongoing star formation. We find a characteristic V-shaped signature in the SFH that is perpendicular to the bar major axis, which supports the scenario where intermediate-age stars (∼2 − 6 Gyr) are trapped on more elongated orbits shaping a thinner part of the bar, while older stars (> 8 Gyr) are trapped on less elongated orbits shaping a rounder and thicker part of the bar. We compare our data to state-of-the-art cosmological magneto-hydrodynamical simulations of barred galaxies and show that such V-shaped SFHs arise naturally due to the dynamical influence of the bar on stellar populations with different ages and kinematic properties. Additionally, we find an excess of very young stars (< 2 Gyr) on the edges of the bars, predominantly on the leading side, thus confirming typical star formation patterns in bars. Furthermore, mass-weighted age and metallicity gradients are slightly shallower along the bar than in the disc, which is likely due to orbital mixing in the bar. Finally, we find that bars are mostly more metal-rich and less [Mg/Fe]-enhanced than the surrounding discs. We interpret this as a signature that the bar quenches star formation in the inner region of discs, usually referred to as star formation deserts. We discuss these results and their implications on two different scenarios of bar formation and evolution.

Local Group Dwarf Galaxies

2018 ◽  
Vol 14 (S344) ◽  
pp. 29-37
Author(s):  
Andrew A. Cole
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Cosmic Time ◽  
Star Formation History ◽  
Gas Content ◽  
Cosmological Context ◽  
Low Mass ◽  
Formation And Evolution ◽  
Star Formation Histories

AbstractLocal Group dwarf galaxies are a unique astrophysical laboratory because they are the only objects in which we can reliably and precisely characterize the star formation histories of low-mass galaxies going back to the epoch of reionization. There are of order 100 known galaxies less massive than the Small Magellanic Cloud within ~1 Megaparsec of the Milky Way, with a vide variety of star formation history, gas content, and mass to light ratios. In this overview the current understanding of the formation and evolution of low-mass galaxies across cosmic time will be presented, and the possibility of drawing links between the properties of individual systems and the broader Local Group and cosmological context will be discussed. Local Group dwarfs will remain a uniquely powerful testbed to constrain the properties of dark matter and to evaluate the performance of simulations for the foreseeable future.

scholarly journals Stellar population gradients in GASS

2012 ◽  
Vol 8 (S295) ◽  
pp. 304-307
Author(s):  
Jonas Johansson ◽  
Guinevere Kauffmann ◽  
Sean Moran
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Stellar Population ◽  
Neutral Hydrogen ◽  
Stellar Populations ◽  
Element Abundance ◽  
Molecular Gas ◽  
Massive Galaxies ◽  
Additional Formation ◽  
Inside Out

AbstractWe study relationships between the stellar populations and interstellar medium in massive galaxies using the Galex Arecibo SDSS Survey (GASS). The sample consists of HI-observations (~1000 galaxies) and complementary H2-observations (330 galaxies) and long-slit spectroscopy (230 galaxies). Luminosity-weighted stellar population ages, metallicitites and element abundance ratios, are derived by fitting stellar population models of absorption line indices. We find that the ages correlate more strongly with molecular gas fraction (MH2/M*) than with neutral Hydrogen fraction (MHI/M*). This result strengthens the theory that H2 is a better tracer of star-formation than HI. The sample is dominated by negative metallicity-gradients and flat Mg/Fe-gradients. Galaxies with high MH2/M*-ratios show in general flat or weakly negative age-gradients. For low MH2/M*-ratios the age-gradients are overall negative. These results are in agreement with the inside-out galaxy formation scenario. For galaxies with high r90/r50-ratios, a sub-population show positive age-gradients indicating additional formation channels. Furthermore, for galaxies with high MH2/M*-ratios more massive systems have older stellar populations in their centers, suggesting downsizing within the inside-out formation scenario.

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