Ram pressure stripping of halo gas in disk galaxies: Implications on
  galactic star formation in different environments
  We numerically investigate evolution of gaseous halos around disk galaxies in
different environments ranging from small groups to rich clusters in order to
understand galaxy evolution in these environments. Our simulations
self-consistently incorporate effects of ram pressure of intergalactic medium
(IGM) on disk and halo gas of galaxies and hydrodynamical interaction between
disk and halo gas so that mass fractions of halos gas stripped by ram pressure
of IGM (F_strip) can be better estimated. We mainly investigate how F_strip
depends on total masses of their host environments (M_host}), galactic masses
(M_gal), densities and temperature of IGM (T_IGM and rho_IGM, respectively),
relative velocities between IGM and galaxies (V_r), and physical properties of
disks (e.g., gas mass fraction). We find that typically 60-80% of halo gas can
be efficiently stripped from Milky Way-type disk galaxies by ram pressure in
clusters with M_host 10^{14} M_sun We also find that F_strip depends on M_host
such that F_strip is higher for larger M_host. Furthermore it is found that
F_strip can be higher in disk galaxies with smaller M_gal for a given
environment. Our simulations demonstrate that the presence of disk gas can
suppress ram pressure stripping of halo gas owing to hydrodynamical interaction
between halo and disk gas. Ram pressure stripping of halo gas is found to be
efficient (i.e., F_strip>0.5) even in small and/or compact groups, if rho_IGM ~
10^5 M_sun/kpc^3 and V_r ~ 400 km/s. Based on the derived radial distributions
of remaining halo gas after ram pressure stripping, we propose that truncation
of star formation after halo gas stripping can occur outside-in in disk
galaxies.
