  We analyze the stellar absorption features in high signal-to-noise ratio
near-infrared (NIR) spectra of the nuclear region of 12 nearby galaxies, mostly
spirals. The features detected in some or all of the galaxies in this sample
are the TiO (0.843 $\mu$m\ and 0.886 $\mu$m), VO (1.048 $\mu$m), CN (1.1
$\mu$m\ and 1.4 $\mu$m), H$\rm _2$O (1.4 $\mu$m\ and 1.9 $\mu$m) and CO (1.6
$\mu$m\ and 2.3 $\mu$m) bands. The C$\rm _2$ (1.17 $\mu$m\ and 1.76 $\mu$m)
bands are generally weak or absent, although C$\rm _2$ (1.76 $\mu$m) may be
weakly present in the mean galaxy spectrum. A deep feature near 0.93 $\mu$m,
likely caused by CN, TiO and/or ZrO, is also detected in all objects. Fitting a
combination of stellar spectra to the mean spectrum shows that the absorption
features are produced by evolved stars: cool giants and supergiant stars in the
early- or thermally-pulsing asymptotic giant branch (E-AGB or TP-AGB) phases.
The high luminosity of TP-AGB stars, and the appearance of VO and ZrO features
in the data, suggest that TP-AGB stars dominate these spectral features.
However, a contribution from other evolved stars is also likely. Comparison
with evolutionary population synthesis models shows that models based on
empirical libraries that predict relatively strong NIR features provide a more
accurate description of the data. However, none of the models tested accurately
reproduces all of the features observed in the spectra. To do so, the models
will need to not only improve the treatment of TP-AGB stars, but also include
good quality spectra of red giant and E-AGB stars. The uninterrupted wavelength
coverage, high S/N, and quantity of features we present here will provide a
benchmark for the next generation of models aiming to explain and predict the
NIR properties of galaxies.
