X-ray Emission from Disk Galaxies during Major Mergers

We describe a model for the X-ray emission produced during collisions and mergers of disk galaxies. To study this process, we employ simulations that incorporate cosmologically motivated disk-galaxy models and include the effects of radiative cooling, star formation, stellar feedback, and accreting supermassive black holes. We find that during a merger, the colliding gas in the disks is shockheated to X-ray emitting temperatures. The X-ray luminosity is spatially extended, rises during the initial stages of the merger, and peaks when the galactic centers coalesce. When a physical model for accreting black holes is included, the resulting feedback can drive powerful winds that contribute significantly to the amount and metallicity of hot gas, both of which increase the X-ray luminosity. In the particular case we examine here, the merger remnant is a small elliptical galaxy with an Xray luminosity less than those of observed ellipticals of equivalent B-band luminosity. However, the temperature, B-band luminosity and X-ray luminosity are consistent with the scaling relations of Xray luminous elliptical galaxies, indicating that major mergers are a viable mechanism for producing the X-ray halos of large, luminous elliptical galaxies. Subject headings: galaxies:active — evolution — formation — interactions — ISM — methods:N-body simulations