Activity in galactic nuclei of cluster and field galaxies in the local
  universe
  We study the environmental effects on the activity in galactic nuclei by
comparing galaxies in clusters and in the field. Using a spectroscopic sample
of galaxies in Abell clusters from the SDSS DR7, we investigate the dependence
of nuclear activity on the physical parameters of clusters as well as the
nearest neighbor galaxy. We also compare galaxy properties between AGN hosts
and non-AGN galaxies. We find that the AGN fraction of early-type galaxies
starts to decrease around one virial radius of clusters (r_{200,cl}) as
decreasing clustercentric radius, while that of late types starts to decrease
close to the cluster center (R~0.1-0.5r_{200,cl}). The AGN fractions of
early-type cluster galaxies on average are found to be lower than those of
early-type field galaxies by a factor ~3. However, the mean AGN fractions of
late-type cluster galaxies are similar to those of late-type field galaxies.
The AGN fraction of early-type BCGs lies between those of other early-type,
cluster and field galaxies with similar luminosities. In the field, the AGN
fraction strongly depends on the morphology of and the distance to the nearest
neighbor galaxy. We find an anti-correlation between the AGN fraction and the
velocity dispersion of clusters for all subsamples divided by morphology and
luminosity of host galaxies. The AGN power indicated by L_[OIII]/M_BH is found
to depend strongly on the mass of host galaxies rather than the clustercentric
radius. The difference in physical parameters such as luminosity, (u-r) colors,
SFRs, and (g-i) color gradients between AGN hosts and non-AGN galaxies is seen
for both early and late types at all clustercentric radii, while the difference
in structure parameters between the two is significant only for late types.
These results support the idea that the nuclear activity is triggered through
galaxy-galaxy interactions and mergers when gas supply for AGN is available.
