scholarly journals Stellar Population and Elemental Abundance Gradients of Early-type Galaxies*

2021 ◽  
Vol 923 (1) ◽  
pp. 65
Author(s):  
A. Feldmeier-Krause ◽  
I. Lonoce ◽  
W. L. Freedman
Keyword(s):  
Stellar Population ◽  
Stellar Populations ◽  
Initial Mass Function ◽  
Elemental Abundance ◽  
Early Type ◽  
Elemental Abundances ◽  
Global Correlation ◽  
Wide Range ◽  
Local Correlations ◽  
The Imf

Abstract The evolution of galaxies is imprinted on their stellar populations. Several stellar population properties in massive early-type galaxies have been shown to correlate with intrinsic galaxy properties such as the galaxy’s central velocity dispersion, suggesting that stars formed in an initial collapse of gas (z ∼ 2). However, stellar populations change as a function of galaxy radius, and it is not clear how local gradients of individual galaxies are influenced by global galaxy properties and galaxy environment. In this paper, we study the stellar populations of eight early-type galaxies as a function of radius. We use optical spectroscopy (∼4000–8600 Å) and full spectral fitting to measure stellar population age, metallicity, slope of the initial mass function (IMF), and nine elemental abundances (O, Mg, Si, Ca, Ti, C, N, Na, and Fe) out to 1 R e for each galaxy individually. We find a wide range of properties, with ages ranging from 3–13 Gyr. Some galaxies have a radially constant, Salpeter-like IMF, and other galaxies have a super-Salpeter IMF in the center, decreasing to a sub-Salpeter IMF at ∼0.5 R e . We find a global correlation of the central [Z/H] with the central IMF and the radial gradient of the IMF for the eight galaxies, but local correlations of the IMF slope with other stellar population parameters hold only for subsets of the galaxies in our sample. Some elemental abundances also correlate locally with each other within a galaxy, suggesting a common production channel. These local correlations appear only in subsets of our galaxies, indicating variations of the stellar content among different galaxies.

The IMF-SFH connection in massive early-type galaxies

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
I. Ferreras ◽  
C. Weidner ◽  
A. Vazdekis ◽  
F. La Barbera
Keyword(s):  
Age Distribution ◽  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
Population Synthesis ◽  
Early Type ◽  
Massive Galaxies ◽  
Stellar Initial Mass Function ◽  
The Many ◽  
The Imf

The stellar initial mass function (IMF) is one of the fundamental pillars in studies of stellar populations. It is the mass distribution of stars at birth, and it is traditionally assumed to be universal, adopting generic functions constrained by resolved (i.e. nearby) stellar populations (e.g., Salpeter 1955; Kroupa 2001; Chabrier 2003). However, for the vast majority of cases, stars are not resolved in galaxies. Therefore, the interpretation of the photo-spectroscopic observables is complicated by the many degeneracies present between the properties of the unresolved stellar populations, including IMF, age distribution, and chemical composition. The overall good match of the photometric and spectroscopic observations of galaxies with population synthesis models, adopting standard IMF choices, made this issue a relatively unimportant one for a number of years. However, improved models and observations have opened the door to constraints on the IMF in unresolved stellar populations via gravity-sensitive spectral features. At present, there is significant evidence of a non-universal IMF in early-type galaxies (ETGs), with a trend towards a dwarf-enriched distribution in the most massive systems (see, e.g., van Dokkum & Conroy 2010; Ferreras et al. 2013; La Barbera et al. 2013). Dynamical and strong-lensing constraints of the stellar M/L in similar systems give similar results, with heavier M/L in the most massive ETGs (see, e.g., Cappellari et al. 2012; Posacki et al. 2015). Although the interpretation of the results is still open to discussion (e.g., Smith 2014; La Barbera 2015), one should consider the consequences of such a bottom-heavy IMF in massive galaxies.

scholarly journals IMF radial gradients in most massive early-type galaxies

2019 ◽  
Vol 489 (3) ◽  
pp. 4090-4110 ◽  
Author(s):  
F La Barbera ◽  
A Vazdekis ◽  
I Ferreras ◽  
A Pasquali ◽  
C Allende Prieto ◽  
...  
Keyword(s):  
Stellar Population ◽  
Velocity Dispersion ◽  
Mass Density ◽  
Initial Mass Function ◽  
Early Type ◽  
Low Mass Stars ◽  
Surface Mass ◽  
Low Mass ◽  
Surface Mass Density ◽  
The Imf

ABSTRACT Using new long-slit spectroscopy obtained with X-Shooter at ESO-VLT, we study, for the first time, radial gradients of optical and near-infrared initial mass function (IMF)-sensitive features in a representative sample of galaxies at the very high mass end of the galaxy population. The sample consists of seven early-type galaxies (ETGs) at z ∼ 0.05, with central velocity dispersion in the range 300 ≲ σ ≲ 350 km s−1. Using state-of-the-art stellar population synthesis models, we fit a number of spectral indices, from different chemical species (including TiO and Na indices), to constrain the IMF slope (i.e. the fraction of low-mass stars), as a function of galactocentric distance, over a radial range out to ∼4 kpc. ETGs in our sample show a significant correlation of IMF slope and surface mass density. The bottom-heavy population (i.e. an excess of low-mass stars in the IMF) is confined to central galaxy regions with surface mass density above $\rm \sim 10^{10}\, M_\odot \, kpc^{-2}$, or, alternatively, within a characteristic radius of ∼2 kpc. Radial distance, in physical units, and surface mass density are the best correlators to IMF variations, with respect to other dynamical (e.g. velocity dispersion) and stellar population (e.g. metallicity) properties. Our results for the most massive galaxies suggest that there is no single parameter that fully explains variations in the stellar IMF, but IMF radial profiles at z ∼ 0 rather result from the complex formation and mass accretion history of galaxy inner and outer regions.

The stellar initial mass function in the early universe revealed from old stellar populations in our neighbourhood

2012 ◽  
Vol 8 (S295) ◽  
pp. 322-322
Author(s):  
Yutaka Komiya ◽  
Shimako Yamada ◽  
Takuma Suda ◽  
Masayuki Y. Fujimoto
Keyword(s):  
Early Universe ◽  
Galactic Halo ◽  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
New Method ◽  
Elemental Abundances ◽  
Stellar Initial Mass Function ◽  
Low Mass ◽  
The Imf

AbstractWe present a new method to investigate the IMF in the early universe from observations of extremely metal-poor (EMP) stars. EMP stars are the low-mass survivors of stars which are formed in the early universe. We can give constraints on the IMF from statistics of the elemental abundances of the EMP stars in the Galactic halo.

scholarly journals Fornax 3D project: a two-dimensional view of the stellar initial mass function in the massive lenticular galaxy FCC 167

2019 ◽  
Vol 626 ◽  
pp. A124 ◽  
Author(s):  
I. Martín-Navarro ◽  
M. Lyubenova ◽  
G. van de Ven ◽  
J. Falcón-Barroso ◽  
L. Coccato ◽  
...  
Keyword(s):  
Stellar Population ◽  
Population Analysis ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Dynamical Structure ◽  
Two Dimensional ◽  
Early Type ◽  
Stellar Initial Mass Function ◽  
The Imf

The stellar initial mass function (IMF) regulates the baryonic cycle within galaxies, and is a key ingredient for translating observations into physical quantities. Although it was assumed to be universal for decades, there is now growing observational evidence showing that the center of massive early-type galaxies hosts a larger population of low-mass stars than is expected based on observations from the Milky Way. Moreover, these variations in the IMF have been found to be related to radial metallicity variations in massive galaxies. We present here a two-dimensional stellar population analysis of the massive lenticular galaxy FCC 167 (NGC 1380) as part of the Fornax3D project. Using a newly developed stellar population fitting scheme, we derive a full two-dimensional IMF map of an early-type galaxy. This two-dimensional analysis allows us go further than a radial analysis, showing how the metallicity changes along a disk-like structure while the IMF follows a distinct, less disky distribution. Thus, our findings indicate that metallicity cannot be the sole driver of the observed radial IMF variations. In addition, a comparison with the orbital decomposition shows suggestive evidence of a coupling between stellar population properties and the internal dynamical structure of FCC 167, where metallicity and IMF maps seem to track the distribution of cold and warm orbits, respectively.

scholarly journals What does (not) drive the variation of the low-mass end of the stellar initial mass function of early-type galaxies

2021 ◽  
Vol 645 ◽  
pp. L1
Author(s):  
C. E. Barbosa ◽  
C. Spiniello ◽  
M. Arnaboldi ◽  
L. Coccato ◽  
M. Hilker ◽  
...  
Keyword(s):  
Stellar Population ◽  
Velocity Dispersion ◽  
Mass Function ◽  
Initial Mass Function ◽  
Population Parameters ◽  
Early Type ◽  
Stellar Velocity ◽  
Stellar Initial Mass Function ◽  
Low Mass ◽  
The Imf

Context. The stellar initial mass function (IMF) seems to be variable and not universal, contrary to what has been argued in the literature over the last three decades. Several relations of the low-mass end of the IMF slope with other stellar population, photometrical, and kinematical parameters of massive early-type galaxies (ETGs) have been proposed, but consensus on the factual cause of the observed variations has not yet been reached. Aims. We investigate the relationship between the IMF and other stellar population parameters in NGC 3311, the central galaxy of the Hydra I cluster. NGC 3311 is a unique laboratory, characterized by old and metal-rich stars, that is similar to other massive ETGs for which the IMF slope has been measured to be bottom-heavy (i.e., dwarf-rich); however, it has unusual stellar velocity dispersion and [α/Fe] profiles, both of which increase with radius. Methods. We use the spatially resolved stellar population parameters (age, total metallicity, and [α/Fe]) that were derived in a forthcoming paper (Barbosa et al. 2020) – via the full-spectrum fitting of high signal-to-noise MUSE observations – to compare the IMF slope in the central part of NGC 3311 (R ≲ 16 kpc) against other stellar parameters, with the goal of assessing their relations and dependencies. Results. For NGC 3311, we unambiguously invalidate the previously observed direct correlation between the IMF slope and the local stellar velocity dispersion, confirming some doubts that had been raised in the literature. This relation may simply arise as a spatial coincidence between the region with the largest stellar velocity dispersion and the region where the oldest in situ population is found and dominates the light. We also show robust evidence that the proposed IMF−metallicity relation is contaminated by the degeneracy between these two parameters. We do confirm that the stellar content in the innermost region of NGC 3311 follows a bottom-heavy IMF, in line with other literature results. The tightest correlations we found are those between stellar age and the IMF and between the galactocentric radius and the IMF. Conclusions. The variation of the IMF at its low-mass end is not due to kinematical, dynamical, or global properties in NGC 3311. We speculate instead that the IMF might be dwarf-dominated in the “red nuggets” that formed through a very short and intense star formation episode at high redshifts (z >  2) when the Universe was denser and richer in gas, and which then ended up being the central cores of today’s giant ellipticals.

scholarly journals Extragalactic GCs in the near-infrared: genuinely old in E/S0's?

2009 ◽  
Vol 5 (S262) ◽  
pp. 315-316
Author(s):  
Ana L. Chies-Santos ◽  
Søren S. Larsen
Keyword(s):  
Globular Cluster ◽  
Stellar Population ◽  
Near Infrared ◽  
Local Group ◽  
Stellar Populations ◽  
Age Dating ◽  
Early Type ◽  
Optical Photometry ◽  
Star Forming ◽  
Optical Images

Globular cluster (GC) systems are powerful probes to study the evolutionary histories of galaxies, being tracers of major star fomation episodes (Brodie & Strader 2006). They are found around all major galaxies and are easy to see far beyond the local group. Age dating GCs therefore helps pinpoint epochs of major star forming events. Spectroscopic age dating though (Strader et al. 2005) is extremely time consuming and can only access the few brightest clusters. An alternative is to combine near-infrared (NIR) and optical photometry, and therefore have a better chance in lifting the age metallicity degeneracy than with optical colours alone. This approach relies in testing GC colours against simple stellar population (SSP) models. The first studies following this technique showed the possible existence of a high percentage of intermediate age (2-3 Gyrs) GCs in early-type galaxies known to contain old stellar populations from integrated light studies. Two strong cases can be listed: NGC 4365 (Puzia et al. 2002, Larsen et al. 2005) and NGC 5846 (Hempel et al. 2003). In the present study we combine NIR deep photometry obtained with the WHT/LIRIS instrument and archival HST/ACS optical images to determine g(F475W), z(F840LP) and K(2.2m) magnitudes and colours of GCs in 14 early-type galaxies.

Stellar Population Models of Distant Radio Galaxies

1996 ◽  
Vol 175 ◽  
pp. 588-590
Author(s):  
D. Villani ◽  
S. Di Serego Alighieri
Keyword(s):  
Energy Distribution ◽  
Galaxy Formation ◽  
Stellar Population ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Stellar Populations ◽  
Radio Galaxies ◽  
Initial Mass Function ◽  
Spectral Energy ◽  
The Galaxy

Stellar populations of high redshift radio galaxies (HzRG) (z up to 4.2) are the oldest stellar systems known, that is the ones formed at the earliest cosmological epochs. Therefore they are the best objects for providing us with information about the epoch of galaxy formation. The information on the stellar populations in HzRG are obtained from the study of their Integrated Spectral Energy Distribution (ISED) which are gathered both from spectra and integrated magnitudes. The most common approach for the interpretation of colors and spectral features of the energy distribution of galaxies is the Evolutionary Population Synthesis (EPS), which has been introduced for the first time by Tinsley in 1972. EPS models have often been used in the past to interpret the ISED of HzRG (Chambers & Charlot 1990; Lilly & Longair 1984; di Serego Alighieri et al. 1994) in order to draw conclusions on the age of the stellar populations and therefore on the epoch of galaxy formation. The results are sometimes conflicting and a number of very recent EPS models have become available (Bressan et al. 1995; Bruzual & Charlot 1993; Buzzoni 1989; Guiderdoni & Rocca-Volmerange 1987): we are therefore analysing the differences between the various EPS models with the aim of assessing their suitability to study the stellar population at early epochs. The EPS models assume for stars a given Initial Mass Function(IMF) as well as a Star Formation Rate (SFR). Then one can compute the number of stars with given mass present in the galaxy as a function of time. The position of each star in the HR diagram is determined by means of the isochrones, which are calculated from stellar evolutionary models. The ISED of a galaxy is obtained from the superposition of the spectra of single stars obtained from a stellar spectral library. Thus these models describe the galaxy ISED as a function of the time, giving a complete evolutionary picture.

scholarly journals Dynamical masses of brightest cluster galaxies – II. Constraints on the stellar IMF

2020 ◽  
Vol 500 (3) ◽  
pp. 4153-4165
Author(s):  
S I Loubser ◽  
H Hoekstra ◽  
A Babul ◽  
Y M Bahé ◽  
M Donahue
Keyword(s):  
Gravitational Lensing ◽  
Stellar Population ◽  
Population Analysis ◽  
Stellar Populations ◽  
Stellar Mass ◽  
Initial Mass Function ◽  
Dynamical Mass ◽  
Cluster Galaxies ◽  
Brightest Cluster Galaxies ◽  
Mass Profiles

ABSTRACT We use stellar and dynamical mass profiles, combined with a stellar population analysis, of 32 brightest cluster galaxies (BCGs) at redshifts of 0.05 ≤$z$ ≤ 0.30, to place constraints on their stellar initial mass function (IMF). We measure the spatially resolved stellar population properties of the BCGs, and use it to derive their stellar mass-to-light ratios ($\Upsilon _{\star \rm POP}$). We find young stellar populations (<200 Myr) in the centres of 22 per cent of the sample, and constant $\Upsilon _{\star \rm POP}$ within 15 kpc for 60 per cent of the sample. We further use the stellar mass-to-light ratio from the dynamical mass profiles of the BCGs ($\Upsilon _{\star \rm DYN}$), modelled using a multi-Gaussian expansion and Jeans Anisotropic Method, with the dark matter contribution explicitly constrained from weak gravitational lensing measurements. We directly compare the stellar mass-to-light ratios derived from the two independent methods, $\Upsilon _{\star \rm POP}$ (assuming some IMF) to $\Upsilon _{\star \rm DYN}$ for the subsample of BCGs with no young stellar populations and constant $\Upsilon _{\star \rm POP}$. We find that for the majority of these BCGs, a Salpeter (or even more bottom-heavy) IMF is needed to reconcile the stellar population and dynamical modelling results although for a small number of BCGs, a Kroupa (or even lighter) IMF is preferred. For those BCGs better fit with a Salpeter IMF, we find that the mass-excess factor against velocity dispersion falls on an extrapolation (towards higher masses) of known literature correlations. We conclude that there is substantial scatter in the IMF amongst the highest mass galaxies.

scholarly journals Variation in the Stellar Initial Mass Function from the Chromospheric Activity of M Dwarfs in Early-type Galaxies

2021 ◽  
Vol 923 (1) ◽  
pp. 43
Author(s):  
Pieter van Dokkum ◽  
Charlie Conroy
Keyword(s):  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Early Type ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Chromospheric Activity ◽  
Stellar Initial Mass Function ◽  
Low Mass ◽  
The Imf

Abstract Mass measurements and absorption-line studies indicate that the stellar initial mass function (IMF) is bottom-heavy in the central regions of many early-type galaxies, with an excess of low-mass stars compared to the IMF of the Milky Way. Here we test this hypothesis using a method that is independent of previous techniques. Low-mass stars have strong chromospheric activity characterized by nonthermal emission at short wavelengths. Approximately half of the UV flux of M dwarfs is contained in the λ1215.7 Lyα line, and we show that the total Lyα emission of an early-type galaxy is a sensitive probe of the IMF with a factor of ∼2 flux variation in response to plausible variations in the number of low-mass stars. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure the Lyα line in the centers of the massive early-type galaxies NGC 1407 and NGC 2695. We detect Lyα emission in both galaxies and demonstrate that it originates in stars. We find that the Lyα to i-band flux ratio is a factor of 2.0 ± 0.4 higher in NGC 1407 than in NGC 2695, in agreement with the difference in their IMFs as previously determined from gravity-sensitive optical absorption lines. Although a larger sample of galaxies is required for definitive answers, these initial results support the hypothesis that the IMF is not universal but varies with environment.

scholarly journals IMF variations in unresolved stellar populations: Challenges

2015 ◽  
Vol 11 (A29B) ◽  
pp. 193-194
Author(s):  
Ignacio Ferreras ◽  
Francesco La Barbera ◽  
Alexandre Vazdekis
Keyword(s):  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Spectral Features ◽  
Early Type ◽  
Stellar Initial Mass Function

AbstractThis talk focuses on the challenges facing the recent discovery of variations of the stellar initial mass function in massive early-type galaxies, with special emphasis on the constraints via gravity-sensitive spectral features.

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