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.
Referencia bibliográfica

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

Fecha de publicación:
11
2009
Número de autores
10
Número de autores del IAC
3
Número de citas
28
Número de citas referidas
24
Descripción
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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