STELLAR POPULATIONS OF ELLIPTICAL GALAXIES IN THE LOCAL UNIVERSE
- Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States)
- Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0424 (United States)
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, {sigma}, 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 ({approx}>L*), and that the highest-{sigma} ellipticals favor high-density environments. We construct average, high signal-to-noise spectra in bins of {sigma} and environment and find the following: (1) lower-{sigma} galaxies have a bluer optical continuum and stronger (but still weak) emission lines; (2) at fixed {sigma}, field ellipticals have a slightly bluer stellar continuum, especially at wavelengths {approx}<4000 A, and have stronger (but still weak) emission lines compared with their group counterparts, although this environmental dependence is strongest for low-{sigma} ellipticals and the highest-{sigma} ellipticals are much less affected. Based on Lick indices measured from both the individual and average spectra, we find that (1) at a given {sigma}, elliptical galaxies in groups have systematically weaker Balmer absorption than their field counterparts, although this environmental dependence is most pronounced at low {sigma}; (2) there is no clear environmental dependence of (Fe), while the {alpha}-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 {alpha}-enhanced. We also find that (1) the SSP-equivalent ages of galaxies in rich groups are, on average, {approx}1 Gyr older than in the field, although once again this effect is strongest at low {sigma}; (2) galaxies in rich groups have slightly lower [Fe/H] and are marginally more strongly {alpha}-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 {sigma}, 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.
- OSTI ID:
- 21464698
- Journal Information:
- Astrophysical Journal, Vol. 722, Issue 1; Other Information: DOI: 10.1088/0004-637X/722/1/491; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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