  Recent models show that TP-AGB stars should dominate the NIR spectra of
populations 0.3 to 2 Gyr old, leaving unique signatures that can be used to
detect young/intermediate stellar population in galaxies. However, no
homogeneous database of star-forming galaxies is available in the NIR to fully
explore these results. With this in mind, we study the NIR spectra of a sample
of 23 HII and starburst galaxies, aimed at characterizing the most prominent
spectral features and continuum shape in the 0.8-2.4 micron region of these
objects. Spectral indices are derived for the relevant absorption lines/bands
and a comparison with optical indices of the same sample available in the
literature is made. We found no correlation between the optical and the NIR
indexes. This is probably due to the differences in aperture between these two
sets of data. That result is further supported by the absence or weakness of
emission lines in the NIR for a subsample galaxies, while in the optical the
emission lines are strong and clear, which means that the ionisation source in
many of these galaxies is not nuclear, but circumnuclear or located in hot
spots. We detected important signatures predicted for a stellar population
dominated by the TP-AGBs, like CN 1.1 micron and CO 2.3 micron. In at least one
galaxy (NGC 4102) the CN band at 1.4 micron was detected for the first time. We
also detect TiO and ZrO bands that have never been reported before in
extragalactic sources. The shape of the continuum emission is found to be
strongly correlated to the presence/lack of emission lines. An observational
template for the star-forming galaxies is derived to be used as a benchmark of
stellar population(s) in starburst galaxies against which to compare near-IR
spectroscopy of different types of galaxies, especially those with AGN activity
and/or those at high-redshift.
