Single stellar populations in the near-infrared II. Synthesis models

TL;DR

This paper introduces near-infrared synthesis models for unresolved stellar populations, based on empirical spectra, enabling better analysis of old galaxies and preparation for future telescope data.

Contribution

The authors develop and validate NIR stellar population models using empirical spectra, extending previous models and facilitating analysis of old and intermediate-age stellar populations.

Findings

Models accurately reproduce observed galaxy colours.

Predicted absorption indices match observed data.

Models are well-suited for unresolved galaxy studies.

Abstract

We present unresolved single stellar population synthesis models in the near-infrared (NIR) range. The extension to the NIR is important for the study of early-type galaxies, since these galaxies are predominantly old and therefore emit most of their light in this wavelength range. The models are based on a library of empirical stellar spectra, the NASA infrared telescope facility (IRTF) spectral library. Integrating these spectra along theoretical isochrones, while assuming an initial mass function (IMF), we have produced model spectra of single age-metallicity stellar populations at a resolution R~2000. These models can be used to fit observed spectral of globular clusters and galaxies, to derive their age distribution, chemical abundances and IMF. The models have been tested by comparing them to observed colours of elliptical galaxies and clusters in the Magellanic Clouds. Predicted absorption line indices have been compared to published indices of other elliptical galaxies. The comparisons show that our models are well suited for studying stellar populations in unresolved galaxies. They are particularly useful for studying the old and intermediate-age stellar populations in galaxies, relatively free from contamination of young stars and extinction by dust. These models will be indispensable for the study of the upcoming data from JWST and extremely large telescopes, such as the E-ELT.