Diffuse X-ray-emitting Gas in Major Mergers
  Using archived data from the Chandra X-ray telescope, we have extracted the
diffuse X-ray emission from 49 equal-mass interacting/merging galaxy pairs in a
merger sequence, from widely separated pairs to merger remnants. After removal
of contributions from unresolved point sources, we compared the diffuse thermal
X-ray luminosity from hot gas (L(X)(gas)) with the global star formation rate
(SFR). After correction for absorption within the target galaxy, we do not see
strong trend of L(X)(gas)/SFR with SFR or merger stage for galaxies with SFR >
1 M(sun) yr^-1. For these galaxies, the median L(X)(gas)/SFR is 5.5 X 10^39
((erg s^-1)/M(sun) yr^-1)), similar to that of normal spiral galaxies. These
results suggest that stellar feedback in star forming galaxies reaches an
approximately steady state condition, in which a relatively constant fraction
of about 2% of the total energy output from supernovae and stellar winds is
converted into X-ray flux. Three late-stage merger remnants with low SFRs and
high K band luminosities (L(K)) have enhanced L(X)(gas)/SFR; their
UV/IR/optical colors suggest that they are post-starburst galaxies, perhaps in
the process of becoming ellipticals. Systems with L(K) < 10^10 L(sun) have
lower L(X)(gas)/SFR ratios than the other galaxies in our sample, perhaps due
to lower gravitational fields or lower metallicities. We see no relation
between L(X)(gas)/SFR and Seyfert activity in this sample, suggesting that
feedback from active galactic nuclei is not a major contributor to the hot gas
in our sample galaxies.
