Diffuse X-Ray-emitting Gas in the Central Region of Star-forming Galaxies

The interstellar medium of galaxies, with temperatures reaching several million degrees, provides a pivotal perspective for understanding the physical and chemical properties of star formation, galactic evolution, and their associated feedback mechanisms. We use archival data from Chandra observations to extract the diffuse X-ray emission from 23 nearby star-forming galaxies and study its correlation with star formation activity in the central region of these galaxies. The surface brightness profile of each galaxy presents a sharp decrease in the central region of ∼0.3−2 kpc and then varies slowly outside this range. Compared to the global relation between the diffuse thermal X-ray luminosity from hot gas ( L0.5−2keVgas ) and the star formation rate (SFR), we found a superlinear relation of log(Lgas0.5−2keV/ergs−1) = 1.34log(SFR/M⊙yr−1)+40.15 for the center of these sample galaxies. This result suggests that more intense stellar feedback is associated with stronger star formation activity in the central region of star-forming galaxies, where more energy output from supernovae and stellar winds is converted into X-ray flux. Furthermore, the slope of the L0.5−2keVgas –SFR relation anticorrelates with spatial scale in the galactic central region. This indicates that the characteristics of central hot gas emission are gradually averaged over larger areas. The diffuse X-ray luminosity also shows a good correlation with molecular gas, stellar mass, and midplane pressure traced by the baryonic mass, although these relations show relatively large scatter.