A Spitzer/IRS Study of Local Luminous Infrared Galaxies
  We present the first results of our program to study a sample of local
luminous infrared galaxies (LIRGs, L_IR = 10^11-10^12 L_sun) with the Spitzer
infrared spectrograph (IRS). In these proceedings we investigate the behavior
of the 9.7 um silicate feature in LIRGs. As opposed to the extreme silicate
absorptions observed in ultraluminous infrared galaxies (ULIRGs, L_IR =
10^12-10^13 L_sun), LIRGs exhibit intermediate silicate absorption features,
comparable to those of starburst galaxies. We also find that most of the LIRGs
have the minima of the [NeIII]/[NeII] ratio located at their nuclei. It is
likely that increased densities in the nuclei are responsible for the smaller
nuclear ratios. In the nuclei, it is also possible that the most massive stars
are either absent, or still embedded in ultracompact HII regions. Finally we
discuss the possible contribution of an AGN to the nuclear mid-IR emission of
the galaxy, which in general is low in these local LIRGs.
