期刊
ASTROPHYSICAL JOURNAL LETTERS
卷 705, 期 2, 页码 L199-L203出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/705/2/L199
关键词
galaxies: clusters: general; galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: formation; galaxies: stellar content
资金
- SMES [AYA2007-67752-C0301]
- Marie Curie European Reintegration Grant
- [AYA2006-15698-C02-02]
The study of stellar populations in early-type galaxies in different environments is a powerful tool for constraining their star formation histories. This study has been traditionally restricted to the optical range, where dwarfs around the turn-off and stars at the base of the red giant branch dominate the integrated light at all ages. The near-infrared spectral range is especially interesting since in the presence of an intermediate-age population, asymptotic giant branch stars are the main contributors. In this Letter, we measure the near-infrared indices Na I and D-CO for a sample of 12 early-type galaxies in low-density environments and compare them with the Fornax galaxy sample presented by Silva et al.. The analysis of these indices in combination with Lick/IDS indices in the optical range reveals that (1) the Na I index is a metallicity indicator as good as C4668 in the optical range, and (2) D-CO is a tracer of intermediate-age stellar populations. We find that low-mass galaxies in low-density environments show higher Na I and D-CO than those located in the Fornax cluster, which points toward a late stage of star formation for the galaxies in less dense environments, in agreement with results from other studies using independent methods.
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