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.

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 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 Ages and metallicities of early-type galaxies

2009 ◽  
Vol 5 (S262) ◽  
pp. 400-401
Author(s):  
Ricardo Ogando ◽  
Marcio Maia ◽  
Paulo Pellegrini ◽  
Luiz da Costa
Keyword(s):  
Star Formation ◽  
Hierarchical Clustering ◽  
Galaxy Formation ◽  
Velocity Dispersion ◽  
Stellar Populations ◽  
Theoretical Framework ◽  
High Density ◽  
Early Type ◽  
Massive Galaxies ◽  
Low Mass

AbstractThe study of stellar populations in early-type galaxies give us clues on how they form and evolve. We calculate age, [Z/H], and [α/Fe] ratio for 162 early-type galaxies using the SSP models from Thomas, Maraston, & Bender (2003) applied to Lick indices measurements, such as Hβ, Mgb, Fe5270 and Fe5335. Those were obtained from longslit spectra observed in the ESO 1.52m telescope as described in Ogando et al. (2008). We study the relations between the SSP parameters and velocity dispersion, as well as the influence of environment on these relations. We find that age, [Z/H], and [α/Fe] correlate well with velocity dispersion, so that more massive galaxies, have on average, higher metallicities, ages and abundance ratios than that of the low-mass ones. Galaxies in high density regions are older and more metal-rich than those in regions with low number of neighbors. These results are not consistent with standard predictions of hierarchical clustering. In the last decade, this “anti-hierarchical” behavior has also been generally tagged as downsizing and has challenged the current theoretical framework of galaxy formation, calling for new ways of star formation regulation in early-type galaxies.

scholarly journals The Role of Quasars in Galaxy Formation

2009 ◽  
Vol 5 (S267) ◽  
pp. 17-25 ◽  
Author(s):  
D. Elbaz
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Positive Feedback ◽  
Local Environment ◽  
Active Role ◽  
Molecular Gas ◽  
Massive Galaxies ◽  
Radio Jets ◽  
The Galaxy

AbstractWe discuss evidence that quasars, and more generally radio jets, may have played an active role in the formation stage of galaxies by inducing star formation, i.e., through positive feedback. This mechanism first proposed in the 1970s has been considered as anecdotal until now, contrary to the opposite effect that is generally put forward, i.e., the quenching of star formation in massive galaxies to explain the galaxy bimodality, downsizing, and the universal black hole mass over bulge stellar mass ratio. This suggestion is based on the recent discovery of an ultra-luminous infrared galaxy, i.e., an extreme starburst, that appears to be triggered by a radio jet from the QSO HE 0450-2958 at z = 0.2863, together with the finding in several systems of a positional offset between molecular gas and quasars, which may be explained by the positive feedback effect of radio jets on their local environment.

scholarly journals Quenching by gas compression and consumption

2019 ◽  
Vol 624 ◽  
pp. A81 ◽  
Author(s):  
Allison W. S. Man ◽  
Matthew D. Lehnert ◽  
Joël D. R. Vernet ◽  
Carlos De Breuck ◽  
Theresa Falkendal
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Relative Strength ◽  
Star Formation History ◽  
Molecular Gas ◽  
Host Galaxies ◽  
Massive Galaxies ◽  
Star Forming ◽  
Gas Compression ◽  
Formation History

The objective of this work is to study how active galactic nuclei (AGN) influence star formation in host galaxies. We present a detailed investigation of the star-formation history and conditions of a z = 2.57 massive radio galaxy based on VLT/X-shooter and ALMA observations. The deep rest-frame ultraviolet spectrum contains photospheric absorption lines and wind features indicating the presence of OB-type stars. The most significantly detected photospheric features are used to characterize the recent star formation: neither instantaneous nor continuous star-formation history is consistent with the relative strength of the Si IIλ1485 and S Vλ1502 absorption. Rather, at least two bursts of star formation took place in the recent past, at 6+1-2 Myr and ≳20 Myr ago, respectively. We deduce a molecular H2 gas mass of (3.9 ± 1.0) × 1010 M⊙ based on ALMA observations of the [C I] 3P2−3P1 emission. The molecular gas mass is only 13% of its stellar mass. Combined with its high star-formation rate of (1020-170+190 M⊙ yr-1, this implies a high star-formation efficiency of (26 ± 8) Gyr−1 and a short depletion time of (38 ± 12) Myr. We attribute the efficient star formation to compressive gas motions in order to explain the modest velocity dispersions (⩽55 km s−1) of the photospheric lines and of the star-forming gas traced by [C I]. Because of the likely very young age of the radio source, our findings suggest that vigorous star formation consumes much of the gas and works in concert with the AGN to remove any residual molecular gas, and eventually quenching star formation in massive galaxies.

scholarly journals Galaxy properties as revealed by MaNGA – III. Kinematic profiles and stellar population gradients in S0s

2020 ◽  
Vol 495 (3) ◽  
pp. 2894-2908 ◽  
Author(s):  
H Domínguez Sánchez ◽  
M Bernardi ◽  
F Nikakhtar ◽  
B Margalef-Bentabol ◽  
R K Sheth
Keyword(s):  
Stellar Population ◽  
Velocity Dispersion ◽  
Signal To Noise Ratio ◽  
Elliptical Galaxies ◽  
Element Abundance ◽  
High Signal ◽  
Galactocentric Distance ◽  
Massive Galaxies ◽  
Nearby Galaxies ◽  
Mass Functions

ABSTRACT This is the third paper of a series where we study the stellar population gradients (SP; ages, metallicities, α-element abundance ratios, and stellar initial mass functions) of early-type galaxies (ETGs) at $z$ ≤ 0.08 from the Mapping Nearby Galaxies at APO Data Release 15 (MaNGA-DR15) survey. In this work, we focus on the S0 population and quantify how the SP varies across the population as well as with galactocentric distance. We do this by measuring Lick indices and comparing them to SP synthesis models. This requires spectra with high signal-to-noise ratio which we achieve by stacking in bins of luminosity (Lr) and central velocity dispersion (σ0). We find that: (1) there is a bimodality in the S0 population: S0s more massive than $3\times 10^{10}\, \mathrm{M}_\odot$ show stronger velocity dispersion and age gradients (age and σr decrease outwards) but little or no metallicity gradient, while the less massive ones present relatively flat age and velocity dispersion profiles, but a significant metallicity gradient (i.e. [M/H] decreases outwards). Above $2\times 10^{11}\, \mathrm{M}_\odot$, the number of S0s drops sharply. These two mass scales are also where global scaling relations of ETGs change slope. (2) S0s have steeper velocity dispersion profiles than fast-rotating elliptical galaxies (E-FRs) of the same luminosity and velocity dispersion. The kinematic profiles and SP gradients of E-FRs are both more similar to those of slow-rotating ellipticals (E-SRs) than to S0s, suggesting that E-FRs are not simply S0s viewed face-on. (3) At fixed σ0, more luminous S0s and E-FRs are younger, more metal rich and less α-enhanced. Evidently for these galaxies, the usual statement that ‘massive galaxies are older’ is not true if σ0 is held fixed.

scholarly journals Shaping Disk Galaxy Stellar Populations via Internal and External Processes

2012 ◽  
Vol 10 (H16) ◽  
pp. 372-372
Author(s):  
Rok Roškar
Keyword(s):  
Galaxy Formation ◽  
Stellar Population ◽  
Milky Way ◽  
Stellar Populations ◽  
Radial Migration ◽  
Disk Formation ◽  
Process Understanding ◽  
History Of ◽  
Nearby Galaxies ◽  
Gas Accretion

AbstractIn recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

scholarly journals Satellites and central galaxies in SDSS: the influence of interactions on their properties

2020 ◽  
Vol 501 (1) ◽  
pp. 1046-1058
Author(s):  
Valeria Mesa ◽  
Sol Alonso ◽  
Georgina Coldwell ◽  
Diego García Lambas ◽  
J L Nilo Castellon
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Control Sample ◽  
Stellar Populations ◽  
Control Sets ◽  
Central Galaxy ◽  
Star Formation Activity ◽  
Projected Distance

ABSTRACT We use SDSS-DR14 to construct a sample of galaxy systems consisting of a central object and two satellites. We adopt projected distance and radial velocity difference criteria and impose an isolation criterion to avoid membership in larger structures. We also classify the interaction between the members of each system through a visual inspection of galaxy images, finding ${\sim}80{{\ \rm per\ cent}}$ of the systems lack evidence of interactions whilst the remaining ${\sim}20{{\ \rm per\ cent}}$ involve some kind of interaction, as inferred from their observed distorted morphology. We have considered separately, samples of satellites and central galaxies, and each of these samples were tested against suitable control sets to analyse the results. We find that central galaxies showing signs of interactions present evidence of enhanced star formation activity and younger stellar populations. As a counterpart, satellite samples show these galaxies presenting older stellar populations with a lower star formation rate than the control sample. The observed trends correlate with the stellar mass content of the galaxies and with the projected distance between the members involved in the interaction. The most massive systems are less affected since they show no star formation excess, possibly due to their more evolved stage and less gas available to form new stars. Our results suggest that it is arguably a transfer of material during interactions, with satellites acting as donors to the central galaxy. As a consequence of the interactions, satellite stellar population ages rapidly and new bursts of star formation may frequently occur in the central galaxy.

scholarly journals Fossil group origins

2018 ◽  
Vol 618 ◽  
pp. A172 ◽  
Author(s):  
E. M. Corsini ◽  
L. Morelli ◽  
S. Zarattini ◽  
J. A. L. Aguerri ◽  
L. Costantin ◽  
...  
Keyword(s):  
Stellar Population ◽  
Line Strength ◽  
Abundance Ratio ◽  
Element Abundance ◽  
Population Parameters ◽  
Stellar Kinematics ◽  
Massive Galaxies ◽  
Radial Profiles ◽  
Major Merger ◽  
Satellite Galaxies

Context. Fossil groups (FGs) are galaxy aggregates with an extended and luminous X-ray halo, which are dominated by a very massive early-type galaxy and lack of L∗ objects. FGs are indeed characterized by a large magnitude gap between their central and surrounding galaxies. This is explained by either speculating that FGs are failed groups that formed without bright satellite galaxies and did not suffer any major merger, or by suggesting that FGs are very old systems that had enough time to exhaust their bright satellite galaxies through multiple major mergers. Aims. Since major mergers leave signatures in the stellar populations of the resulting galaxy, we study the stellar population parameters of the brightest central galaxies (BCGs) of FGs as a benchmark against which the formation and evolution scenarios of FGs can be compared. Methods. We present long-slit spectroscopic observations along the major, minor, and diagonal axes of NGC 6482 and NGC 7556, which are the BCGs of two nearby FGs. The measurements include spatially resolved stellar kinematics and radial profiles of line-strength indices, which we converted into stellar population parameters using single stellar-population models. Results. NGC 6482 and NGC 7556 are very massive (M∗ ≃ 1011.5 M⊙) and large (D25 ≃ 50 kpc) galaxies. They host a centrally concentrated stellar population, which is significantly younger and more metal rich than the rest of the galaxy. The age gradients of both galaxies are somewhat larger than those of the other FG BCGs studied so far, whereas their metallicity gradients are similarly negative and shallow. Moreover, they have negligible gradients of α-element abundance ratio. Conclusions. The measured metallicity gradients are less steep than those predicted for massive galaxies that formed monolithically and evolved without experiencing any major merger. We conclude that the observed FGs formed through major mergers rather than being failed groups that lacked bright satellite galaxies from the beginning.

scholarly journals Galaxies hosting an active galactic nucleus: a view from the CALIFA survey

2020 ◽  
Vol 492 (3) ◽  
pp. 3073-3090 ◽  
Author(s):  
Eduardo A D Lacerda ◽  
Sebastián F Sánchez ◽  
R Cid Fernandes ◽  
Carlos López-Cobá ◽  
Carlos Espinosa-Ponce ◽  
...  
Keyword(s):  
Star Formation ◽  
Morphological Type ◽  
Molecular Gas ◽  
Main Role ◽  
Type I ◽  
Massive Galaxies ◽  
Star Forming ◽  
Integral Field Spectroscopy ◽  
Almost All ◽  
Formation Efficiency

ABSTRACT We study the presence of optically-selected active galactic nuclei (AGNs) within a sample of 867 galaxies extracted from the extended Calar-Alto Legacy Integral Field spectroscopy Area (eCALIFA) spanning all morphological classes. We identify 10 Type-I and 24 Type-II AGNs, amounting to ∼4 per cent of our sample, similar to the fraction reported by previous explorations in the same redshift range. We compare the integrated properties of the ionized and molecular gas, and stellar population of AGN hosts and their non-active counterparts, combining them with morphological information. The AGN hosts are found in transitory parts (i.e. green-valley) in almost all analysed properties which present bimodal distributions (i.e. a region where reside star-forming galaxies and another with quiescent/retired ones). Regarding morphology, we find AGN hosts among the most massive galaxies, with enhanced central stellar-mass surface density in comparison to the average population at each morphological type. Moreover, their distribution peaks at the Sab-Sb classes and none are found among very late-type galaxies (>Scd). Finally, we inspect how the AGN could act in their hosts regarding the quenching of star-formation. The main role of the AGN in the quenching process appears to be the removal (or heating) of molecular gas, rather than an additional suppression of the already observed decrease of the star-formation efficiency from late-to-early type galaxies.

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