Hot Halo Gas in Galaxy Mergers

We report on the results of high-resolution hydrodynamic simulations of colliding galaxies with hot halo gas. We find that : (i) A strong shock is produced in the galaxy halos before the first passage, increasing the temperature of the gas by almost an order of magnitude to similar to 10(6.3) K. (ii) The X-ray luminosity of the shock is strongly dependent on the gas fraction. It is greater than or similar to 10(39) erg/s for gas fractions larger than 10%. (iii) The hot diffuse gas in the simulation also produces X-ray luminosities as large as 10(42) erg/s. This contributes to the total X-ray background in the Universe. (iv) similar to 10-20% of the initial gas mass is unbound from the galaxies for equal-mass mergers. We use an analytical halo merger tree and estimate that greater than or similar to 10% of the total baryon content of the Universe could have been unbound via mergers over the history of the Universe.