  We investigate the environmental dependence of star formation and the
morphology of galaxies in the local universe based on a volume-limited sample
(0.030<z<0.065 and M_r<M_r^*+2) constructed from the data of the Sloan Digital
Sky Survey. First, we focus on how galaxy properties change with local density.
The star formation and morphology show a 'break' at the critical local density
of log Sigma_crit~0.4 galaxies h_75^2 Mpc^-2, which is in agreement with
previous studies. However, the break can be seen only for faint galaxies
(M^*_r+1 < M_r < M^*_r+2), and bright galaxies (M_r < M^*_r+1) show no break.
Thus, galaxies of different luminosities are found to show different
environmental dependencies. Next, we examine dependencies on richness of galaxy
systems. Star formation activities of galaxies are different from those of
field galaxies even in systems as poor as sigma~100 km/s. This result suggests
that environmental mechanisms that are effective only in rich systems, such as
ram-pressure stripping of cold gas and harassment, have not played a major role
in transforming galaxies into red early-type galaxies. Strangulation and
interactions between galaxies, however, remain candidates of the driver of the
environmental dependence. In the dense environments in the local universe, the
slow transformation of faint galaxies occurs to some extent, but the
transformation of bright galaxies is not clearly visible. We suggest that the
evolution of bright galaxies is not strongly related to galaxy system, such as
groups and clusters, while the evolution of faint galaxies is likely to be
closely connected to galaxy system.
