Stellar populations of early-type galaxies in different environments

Abstract

Aims. This paper commences 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. In this paper we describe the details of the galaxy sample, the observations, and the data reduction. Line-strength indices and velocity dispersions (σ) are measured in 98 early-type galaxies drawn from different environments, and the relation of the indices with the velocity dispersion analysed in detail.Results. The present sample indicates that some of the index-σ relations depend on galaxy environment. In particular, the slope of the relation between Balmer lines and σ is steeper for galaxies in the Virgo cluster, small groups, and in the field than for galaxies in the Coma cluster. In several indices there is also a significant offset in the zero point between the relations defined by the different subsamples. The slopes of the index-σ relation for the Virgo and low-density environment galaxies are explained by a variation of both age and metallicity, with velocity dispersion, as previously noted in other studies. For the galaxies in the Coma cluster, however, the relation of the indices with σ only requires a variation of the abundance along the σ sequence. In agreement with other studies, we find that the models that better reproduce the slopes are those in which the α elements vary more than the Fe-peak elements along the σ sequence, while, at a given σ, older galaxies show an higher α/Fe ratio. Conclusions. The results can be explained assuming that galaxies in the Coma cluster have experienced a truncated star formation and chemical enrichment history compared to a more continuous time-extended history for their counterparts in lower density environments.

Chemoarchaeological downsizing in a hierarchical universe: impact of a top-heavy IGIMF

“…15). Hence, older galaxies achieve larger values of [α/Fe] abundance ratios in agreement with observational data (Sánchez-Blázquez et al 2006;Trager et al 2000). This correlation is present for galaxies of different mass, thus explaining the dispersion of the [α/Fe]-stellar mass relation at a given stellar mass.…”

“…Since then, a large amount of work has been done measuring alphaelement abundances to study this trend in all sort of environments (e.g. Worthey et al 1992;Trager et al 2000;Kuntschner 2000;Bernardi et al 2006;Sánchez-Blázquez et al 2006;Spolaor et al 2010; Thomas et al 2010).…”

Evolutionary stellar population synthesis with MILES – II. Scaled-solar and α-enhanced models

“…28 shows three classical index-index diagrams with the predictions of the three models, base, scaled-solar and α-enhanced. Overplotted are the index measurements in the LIS-8.4Å system for the early-type galaxy sample of Sánchez-Blázquez et al (2006a). The model grids obtained when plotting Hβo against Mgb, Fe and [MgFe] indices, which are sensitive to Mg, Fe and total metallicity, respectively, provide similar age/metallicity solutions for the most massive galaxies, i.e.…”

The Stellar Halos of Massive Elliptical Galaxies. Ii. Detailed Abundance Ratios at Large Radius

“…Encouragingly, we recover well-known trends as a function of velocity dispersion. In their centers, higher-dispersion galaxies are older, and have higher [Mg/Fe], [C/Fe] and [N/Fe] ratios (e.g., Trager et al 2000b;Worthey 2004;Thomas et al 2005;Sánchez-Blázquez et al 2006;Graves et al 2007;Smith et al 2009;Price et al 2011;Johansson et al 2012;Worthey et al 2013;Conroy et al 2013).…”