Generating hot gas in simulations of disk-galaxy major mergers

We report on the merger-induced generation of a shock-heated gas wind and the formation of a remnant gas halo in simulations of colliding disk galaxies. The simulations use cosmologically motivated initial conditions and include the effects of radiative cooling, star formation, stellar feedback, and the nonadiabatic heating of gas. The nonadiabatic heating, i.e., shocks generated in the final merger forces gas out of the central region of the merger remnant and into the dark matter halo. We demonstrate that the amount of heating depends on the size of the progenitor disk galaxy as well as the initial orbit on which the galaxies are placed. On the basis of these dependencies, we motivate a possible recipe for including this effect in semianalytic models of galaxy formation.