Numerical Simulations of Hot Halo Gas in Galaxy Mergers

Galaxy merger simulations have explored the behavior of gas within a galactic disk, yet the dynamics of hot gas within the galaxy halo has been neglected. 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, contributing to the total X-ray background in the Universe. (iv) Approximately 10-20% of the initial gas mass is unbound from the galaxies for equal-mass mergers, while 3-5% of the gas mass is released for the 3:1 and 10:1 mergers. This unbound gas ends up far from the galaxy and can be a feasible mechanism for metal enrichment of the WHIM. We use an analytical halo merger tree to estimate the fraction of gas mass lost over the history of the Universe.