Stellar Populations of Elliptical Galaxies in the Local Universe
Abstract
We study the stellar populations of 1923 elliptical galaxies at z < 0.05 selected from the Sloan Digital Sky Survey as a function of velocity dispersion, σ, and environment. Our sample constitutes among the largest high-fidelity samples of elliptical galaxies with uniform imaging and optical spectroscopy assembled to date. Confirming previous studies, we find that elliptical galaxies dominate at high luminosities (gsimL*), and that the highest-σ ellipticals favor high-density environments. We construct average, high signal-to-noise spectra in bins of σ and environment and find the following: (1) lower-σ galaxies have a bluer optical continuum and stronger (but still weak) emission lines; (2) at fixed σ, field ellipticals have a slightly bluer stellar continuum, especially at wavelengths lsim4000 Å, and have stronger (but still weak) emission lines compared with their group counterparts, although this environmental dependence is strongest for low-σ ellipticals and the highest-σ ellipticals are much less affected. Based on Lick indices measured from both the individual and average spectra, we find that (1) at a given σ, elliptical galaxies in groups have systematically weaker Balmer absorption than their field counterparts, although this environmental dependence is most pronounced at low σ (2) there is no clear environmental dependence of langFerang, while the α-element absorption indices such as Mg b are only slightly stronger in galaxies belonging to rich groups. An analysis based on simple stellar populations (SSPs) reveals that more massive elliptical galaxies are older, more metal-rich, and more strongly α-enhanced. We also find that (1) the SSP-equivalent ages of galaxies in rich groups are, on average, ~1 Gyr older than in the field, although once again this effect is strongest at low σ (2) galaxies in rich groups have slightly lower [Fe/H] and are marginally more strongly α-enhanced and (3) there is no significant environmental dependence of total metallicity, [Z/H]. Our results are generally consistent with stronger low-level recent star formation in field ellipticals at low σ, similar to recent results based on ultraviolet and infrared observations. We conclude with a brief discussion of our results in the context of recent theoretical models of elliptical galaxy formation.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2010
- DOI:
- 10.1088/0004-637X/722/1/491
- arXiv:
- arXiv:1006.5055
- Bibcode:
- 2010ApJ...722..491Z
- Keywords:
-
- galaxies: elliptical and lenticular;
- cD;
- galaxies: evolution;
- galaxies: formation;
- galaxies: fundamental parameters;
- galaxies: stellar content;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- Accepted to ApJ, in emulateapj style, 3 tables, 23 figures. Minor changes. Samples are available on http://bias.cosmo.fas.nyu.edu/galevolution/