  Recent observations have revealed that the time evolution of the S0 number
fraction at intermediate and high redshifts (0.2<z<0.8) is more dramatic in
groups of galaxies than in clusters. In order to understand the origin of S0s
in groups, we investigate numerically the morphological transformation of
spirals into S0s through group-related physical processes. Our chemodynamical
simulations show that spirals in group environments can be strongly influenced
by repetitive slow encounters with group member galaxies so that those with
thin disks and prominent spiral arm structures can be transformed into S0s with
thick disks and without prominent spiral arm structure. Such tidal interactions
can also trigger repetitive starbursts within the bulges of spirals and
consequently increase significantly the masses of their bulges. Owing to rapid
consumption of gas initially in spirals during the bulge growth, the S0s can
become gas-poor. The S0s transformed from spirals in this way have young and
metal-rich stellar populations in the inner regions of their bulges. The
simulated S0s have lower maximum rotational velocities and flatter radial
line-of-sight velocity dispersion profiles in comparison to their progenitor
spirals. The formation processes of S0s due to tidal interactions depend not
only on the masses and orbits of the progenitor spirals, but also on group
mass. A significant fraction (10-30%) of stars and gas can be stripped during
this spiral to S0 morphological transformation so that intragroup stars and gas
can be formed. Based on these results, we discuss structures, kinematics,
chemical properties, and the Tully-Fisher relation of S0s in groups.
