Stellar populations of early-type galaxies in different environments

Abstract

Aims. This is the second paper of a series devoted to the study of the stellar content of early-type galaxies. The goal of the series is to set constraints on the evolutionary status of these objects Methods. We use a new set of models that include an improved stellar library (MILES) to derive simple stellar population (SSP)-equivalent parameters in a sample of 98 early-type galaxies. The sample contains galaxies in the field, poor groups, and galaxies in the Virgo and Coma clusters. Results. We find that low-density environment galaxies span a larger range in SSP age and metallicity than their counterparts in high density environments, with a tendency for lower σ galaxies to be younger. Early-type galaxies in low-density environments appear on average ∼1.5 Gyr younger and more metal rich than their counterparts in high density environments. The sample of low-density environment galaxies shows an age-metallicity relation in which younger galaxies are found to be more metal rich, but only when metallicity is measured with a Fe-sensitive index. Conversely, there is no age-metallicity relation when the metallicity is measured with a Mg sensitive index. The mass-metallicity relation is only appreciable for the low-density environment galaxies when the metallicity is measured with a Mg-sensitive index, and not when the metallicity is measured with other indicators. On the contrary, this relation exists for the high-density environment galaxies independent of the indicator used to measure the metallicity.Conclusions. This suggests a dependence of the mass-metallicity relation on the environment of the galaxies. Our data favour a scenario in which galaxies in low density environments have suffered a more extended star formation history than the galaxies in the Coma cluster, which appear to host more homogenous stellar populations.

The accretion histories of brightest cluster galaxies from their stellar population gradients

“…We use the stellar population models of Vazdekis et al (2010), based on the MILES stellar library (Sánchez-Blázquez et al 2006), to estimate the ages and metallicities of galaxies in our sample. The Vazdekis et al (2010) We also considered the stellar population models of PEGASE-HR (Le Borgne et al 2004) coupled to the ELODIE (Prugniel et al 2007) stellar library.…”

An optical/NIR survey of globular clusters in early-type galaxies

“…While this sample is not representative of early-type galaxies as a whole because we do not cover low-mass galaxies (M B > −19), it is quite representative within the SAURON sample, including galaxies with either boxy or disky isophotes, being slow or fast rotators, and having a variety of kinematic properties. The characteristics of these galaxies are listed in Tables 1 and 2 where we also list estimates of ages and metallicities from integrated light studies (Sánchez-Blázquez et al 2006;Yamada et al 2006;Kuntschner et al 2010) and the estimated number of GCs and their specific frequency (S N ) (Peng et al 2008;Kundu & Whitmore 2001).…”

Stellar population study in early-type galaxies: an approach from the K band

“…If less massive galaxies have a younger mean age (i.e., there is a young population component in them) than more massive ones (e.g. Trager et al 2000;Thomas et al 2005;Sánchez-Blázquez et al 2006b), the index could be larger than for the more massive galaxies, even though the latter would have higher metallicities. This does not happen with the Fornax galaxies as this sample is composed of almost coeval objects (Kuntschner 2000).…”

“…The galaxies were selected from the samples of Sánchez-Blázquez et al (2006a) and Kuntschner et al (2002) and chosen to cover a range in σ similar to that spanned by S08's Fornax sample. Previous optical work is available for all galaxies (see SB03, Sánchez-Blázquez et al 2006a, and S08).…”