Near Infrared spectroscopic indices for unresolved stellar populations.
  I. Template galaxy spectra
  A new generation of spectral synthesis models has been developed in the
recent years, but there is no matching -- in terms of quality and resolution --
set of template galaxy spectra for testing and refining the new models. Our
main goal is to find and calibrate new near-infrared spectral indices along the
Hubble sequence of galaxies which will be used to obtain additional constraints
to the population analysis based on medium resolution integrated spectra of
galaxies. Spectra of previously studied and well understood galaxies with
relatively simple stellar populations (e.g., ellipticals or bulge dominated
galaxies) are needed to provide a baseline data set for spectral synthesis
models. X-Shooter spectra spanning the optical and infrared wavelength
(350-2400\,nm) of bright nearby elliptical galaxies with resolving power $
R\sim$4000-5400 were obtained. Heliocentric systemic velocity, velocity
dispersion and Mg, Fe and \Hb\ line-strength indices are presented. We present
a library of very high quality spectra of galaxies covering a large range of
age, metallicity and morphological type. Such as a dataset of spectra will be
crucial to address important questions of the modern investigation concerning
galaxy formation and evolution.
