Effects of hot halo gas on the star formation and mass transfer during
  distant galaxy-galaxy encounters
  We use $N$-body/smoothed particle hydrodynamics simulations of encounters
between an early-type galaxy (ETG) and a late-type galaxy (LTG) to study the
effects of hot halo gas on the evolution for a case with the mass ratio of the
ETG to LTG of 2:1 and the closest approach distance of $\sim$100 kpc. We find
that the dynamics of the cold disk gas in the tidal bridge and the amount of
the newly formed stars depend strongly on the existence of a gas halo. In the
run of interacting galaxies not having a hot gas halo, the gas and stars
accreted into the ETG do not include newly formed stars. However, in the run
using the ETG with a gas halo and the LTG without a gas halo, a shock forms
along the disk gas tidal bridge and induces star formation near the closest
approach. The shock front is parallel to a channel along which the cold gas
flows toward the center of the ETG. As a result, the ETG can accrete
star-forming cold gas and newly born stars at and near its center. When both
galaxies have hot gas halos, a shock is formed between the two gas halos
somewhat before the closest approach. The shock hinders the growth of the cold
gas bridge to the ETG and also ionizes it. Only some of the disk stars transfer
through the stellar bridge. We conclude that the hot halo gas can give
significant hydrodynamic effects during distant encounters.
