期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 392, 期 1, 页码 L35-L39出版社
OXFORD UNIV PRESS
DOI: 10.1111/j.1745-3933.2008.00579.x
关键词
galaxies: abundances; galaxies: elliptical and lenticular, cD; galaxies: formation
资金
- Alfred P. Sloan Foundation
- National Science Foundation
- US Department of Energy
- National Aeronautics and Space Administration
- Japanese Monbukagakusho
- Max Planck Society
- Higher Education Funding Council for England
- [ASI-INAF I/016/07/0]
- STFC [ST/G002916/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/G002916/1] Funding Source: researchfish
We define a volume-limited sample of over 14 000 early-type galaxies (ETGs) selected from Data Release 6 of the Sloan Digital Sky Survey. The density of environment of each galaxy is robustly measured. By comparing narrow-band spectral line indices with recent models of simple stellar populations (SSPs), we investigate trends in the star formation history as a function of galaxy mass (velocity dispersion), density of environment and galactic radius. We find that age, metallicity and alpha-enhancement all increase with galaxy mass and that field ETGs are younger than their cluster counterparts by similar to 2 Gyr. We find negative radial metallicity gradients for all masses and environments, and positive radial age gradients for ETGs with velocity dispersion over 180 km s(-1). Our results are qualitatively consistent with a relatively simple picture for ETG evolution in which the low-mass haloes accreted by a protoETG contained not only gas but also a stellar population. This fossil population is preferentially found at large radii in massive ETGs because the stellar accretions were dissipationless. We estimate that the typical, massive ETG should have been assembled at z less than or similar to 3.5. The process is similar in the cluster and field but occurred earlier in dense environments.
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