Diffuse X-ray-emitting Gas in Major Mergers

Beverly J. Smith, Kristen Campbell, Curtis Struck, Roberto Soria, Douglas Swartz, Macon Magno, Brianne Dunn, Mark L. Giroux

Published 2017-12-11Version 1

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.