The Nuclear Activities of Nearby S0 Galaxies
  We present a study of nuclear activities in nearby S0 galaxies. After
cross-matching the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) with the
Third Reference Catalog of Bright Galaxies (RC3) and visually checking the SDSS
images, we derive a sample of 583 S0 galaxies with the central
spectrophotometric information. In order to separate nebular emission lines
from the underlying stellar contribution, we fit the stellar population model
to the SDSS spectra of these S0 galaxies. According to the BPT diagram, we find
that $8\%$ of S0 galaxies show central star-forming activity, while the
fractions of Seyfert, Composite and LINERs are 2\%, 8\%, and 21.4\%,
respectively. We also find that star-forming S0s have the lowest stellar
masses, over one magnitude lower than the others, and that the active S0s
locate mainly in the sparse environment, while the normal S0s in the dense
environment, which might suggest that the environment plays an important role
in quenching star formation and/or AGN activity in S0 galaxies. By performing
bulge-disk decomposition of 45 star-forming S0s in {\em g}- and {\em r}-bands
with the 2D fitting software \textsc{Galfit}, as well as exploiting the catalog
of 2D photometric decompositions of \citet{Meert2015}, we find that the bulges
of $\sim$ 1/3 star-forming S0 galaxies (16/45) are bluer than their disks,
while for other types of S0s, the bulge and disk components show similar color
distributions. Besides, the S\'{e}rsic index of most star-forming S0s bulges is
less than 2, while for normal S0s, it is between 2 and 6.
