Decoding the spectra of SDSS early-type galaxies: New indicators of age and recent star formation
arXiv:0709.0300 · doi:10.1111/j.1365-2966.2007.12446.x
Abstract
(Abridged) We apply Principal Component Analysis (PCA) to a sample of early-type galaxies from the Sloan Digital Sky Survey (SDSS) in order to infer differences in their star formation histories. Out of the first few principal components (PC), we study four which give information about stellar populations and velocity dispersion. We construct two parameters (eta and zeta) as linear combinations of PC1 and PC2. We find zeta to be most sensitive to recent episodes of star formation, and eta to be strongly dependent on the average age of the stellar populations. The distribution of the eta component of the composites appear to be indistinguishable between high and low density regions, whereas the distribution of zeta parameters have a significant skew towards lower values for galaxies in low density regions. This result suggests that galaxies in lower density environments are less likely to present weak episodes of recent star formation. In contrast, a significant number of galaxies from our high density subsample -- which includes clusters (both outer regions and centres) and groups -- underwent small but detectable recent star formation at high metallicity, in agreement with recent estimates targeting elliptical galaxies in Hickson Compact Groups and in the field (Ferreras et al.).
19 pages, 12 figures. Accepted for publication in MNRAS
References in corpus (6)
- Molecular Gas and Star Formation in the SAURON Early-type Galaxies
- The star formation history of early-type galaxies as a function of mass and environment
- The NOAO Fundamental Plane Survey - III. Variations in the stellar populations of red-sequence galaxies from the cluster core to the virial radius
- Truncated Star Formation in Compact Groups of Galaxies: A Stellar Population Study
- Young stellar populations in early-type galaxies in the Sloan Digital Sky Survey
- H-delta in the Integrated Light of Galaxies: What Are We Actually Measuring?