A Spitzer Study of Pseudobulges in S0 Galaxies : Secular Evolution of
  Disks
  In this Letter, we present a systematic study of lenticular (S0) galaxies
based on mid-infrared imaging data on 185 objects taken using the Spitzer Infra
Red Array Camera. We identify the S0s hosting pseudobulges based on the
position of the bulge on the Kormendy diagram and the S\'{e}rsic index of the
bulge. We find that pseudobulges preferentially occur in the fainter luminosity
class (defined as having total K-band absolute magnitude M_K fainter than
-22.66 in the AB system). We present relations between bulge and disk
parameters obtained as a function of the bulge type. The disks in the
pseudobulge hosting galaxies are found to have distinct trends on the r_e-r_d
and \mu_d (0) - r_d correlations compared to those in galaxies with classical
bulges. We show that the disks of pseudobulge hosts possess on average a
smaller scale length and have a fainter central surface brightness than their
counterparts occurring in classical bulge hosting galaxies. The differences
found for discs in pseudobulge and classical bulge hosting galaxies may be a
consequence of the different processes creating the central mass
concentrations.
