Decoding the spectra of SDSS early-type galaxies: New indicators of age and recent star formation

Ben Rogers, Ignacio Ferreras, Ofer Lahav, Mariangela Bernardi, Sugata Kaviraj, Sukyoung Yi

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

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 from their unresolved stellar populations. We select a z < 0.1 volume-limited sample comprising ∼7000 early-type galaxies from SDSS/Data Release 4. Out of the first few principal components (PC), we study four which give information about stellar populations and velocity dispersion. We construct two parameters (η and ζ) as linear combinations of PC1 and PC2. The four components can be presented as 'optimal filters' to explore in detail the properties of the underlying stellar populations. By comparing various photospectroscopic observables - including near-ultraviolet (NUV) photometry from Galaxy Evolution Explorer (GALEX) - we find ζ to be most sensitive to recent episodes of star formation, and η to be strongly dependent on the average age of the stellar populations. Both η and ζ also depend on metallicity. We apply these optimal filters to composite spectra assembled by Bernardi et al. The distribution of the η component of the composites appear to be indistinguishable between high- and low-density regions, whereas the distribution of ζ 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.

Original languageEnglish
Pages (from-to)750-760
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Volume382
Issue number2
DOIs
Publication statusPublished - 2007 Dec 1

Fingerprint

decoding
star formation
galaxies
metallicity
filter
ultraviolet photometry
filters
composite materials
targeting
elliptical galaxies
principal components analysis
principal component analysis
indicator
histories
history
estimates
parameter
distribution

All Science Journal Classification (ASJC) codes

  • Space and Planetary Science

Cite this

Rogers, Ben ; Ferreras, Ignacio ; Lahav, Ofer ; Bernardi, Mariangela ; Kaviraj, Sugata ; Yi, Sukyoung. / Decoding the spectra of SDSS early-type galaxies : New indicators of age and recent star formation. In: Monthly Notices of the Royal Astronomical Society. 2007 ; Vol. 382, No. 2. pp. 750-760.
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Decoding the spectra of SDSS early-type galaxies : New indicators of age and recent star formation. / Rogers, Ben; Ferreras, Ignacio; Lahav, Ofer; Bernardi, Mariangela; Kaviraj, Sugata; Yi, Sukyoung.

In: Monthly Notices of the Royal Astronomical Society, Vol. 382, No. 2, 01.12.2007, p. 750-760.

Research output: Contribution to journalArticle

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T1 - Decoding the spectra of SDSS early-type galaxies

T2 - New indicators of age and recent star formation

AU - Rogers, Ben

AU - Ferreras, Ignacio

AU - Lahav, Ofer

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AU - Kaviraj, Sugata

AU - Yi, Sukyoung

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