  We examine X-ray emission produced from hot gas 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, supernova feedback, and accreting
supermassive black holes. We find that during a merger, the colliding gas in
the disks is shock-heated 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 terms of their stellar kinematics and
structural properties, the merger remnants in our simulations resemble
elliptical galaxies. We find that the X-ray luminosities of the remnants with
B-band luminosities in the range L_B ~ 10^10 - 10^11 Lsun are consistent with
observations, while remnants with smaller or larger masses are underluminous in
X-rays. Moreover, because the majority of the merger remnants are broadly
consistent with the observed scaling relations between temperature, B-band
luminosity and X-ray luminosity we conclude that major mergers are a viable
mechanism for producing the X-ray halos of large, luminous elliptical galaxies.
