Evidence for Intermediate-Age Stellar Populations in Early-Type Galaxies from K-Band Spectroscopy

Mármol-Queraltó, E.; Cardiel, N.; Sánchez-Blázquez, P.; Trager, S. C.; Peletier, R. F.; Kuntschner, H.; Silva, D. R.; Cenarro, A. J.; Vazdekis, A.; Gorgas, J.
Bibliographical reference

The Astrophysical Journal Letters, Volume 705, Issue 2, pp. L199-L203 (2009).

Advertised on:
11
2009
Number of authors
10
IAC number of authors
3
Citations
28
Refereed citations
24
Description
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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Traces of Galaxy Formation: Stellar populations, Dynamics and Morphology
We are a large, diverse, and very active research group aiming to provide a comprehensive picture for the formation of galaxies in the Universe. Rooted in detailed stellar population analysis, we are constantly exploring and developing new tools and ideas to understand how galaxies came to be what we now observe.
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