  We make use of a catalog of 1600 Pan-STARRS1 groups produced by the
probability friends-of-friends algorithm to explore how the galaxy properties,
i.e. the specific star formation rate (SSFR) and quiescent fraction, depend on
stellar mass and group-centric radius. The work is the extension of Lin et al.
(2014). In this work, powered by a stacking technique plus a background
subtraction for contamination removal, a finer correction and more precise
results are obtained than in our previous work. We find that while the
quiescent fraction increases with decreasing group-centric radius the median
SSFRs of star-forming galaxies in groups at fixed stellar mass drop slightly
from the field toward the group center. This suggests that the major quenching
process in groups is likely a fast mechanism. On the other hand, a reduction in
SSFRs by ~0.2 dex is seen inside clusters as opposed to the field galaxies. If
the reduction is attributed to the slow quenching effect, the slow quenching
process acts dominantly in clusters. In addition, we also examine the
density-color relation, where the density is defined by using a sixth-nearest
neighbor approach. Comparing the quiescent fractions contributed from the
density and radial effect, we find that the density effect dominates over the
massive group or cluster galaxies, and the radial effect becomes more effective
in less massive galaxies. The results support mergers and/or starvation as the
main quenching mechanisms in the group environment, while harassment and/or
starvation dominate in clusters.
