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