Near-Infrared spectral diagnostics for unresolved stellar population galaxies

TL;DR

This study develops and tests near-infrared spectral diagnostics for unresolved stellar populations in galaxies, finding specific features that trace chemical abundance and are unaffected by age.

Contribution

It introduces a semi-empirical NIR population model and evaluates its correlation with optical indices in galaxy spectra.

Findings

CaI, NaI, and CO trace alpha-enhancement

NIR features are not influenced by galaxy age

No significant correlation between NIR features and optical Mg2

Abstract

We want to develop spectral diagnostics of stellar populations in the near-infrared (NIR), for unresolved stellar populations. We created a semi-empirical population model and we compare the model output with the observed spectra of a sample of elliptical and bulge-dominated galaxies that have reliable Lick-indices from literature to test if the correlation between Mg2 and CO 1.62 micron remains valid in galaxies and to calibrate it as an abundance indicator. We find that (i) there are no significant correlations between any NIR feature and the optical Mg2; (ii) the CaI, NaI and CO trace the alpha-enhancement; and (iii) the NIR absorption features are not influenced by the galaxy's age.