A High Spatial Resolution X‐Ray and Hα Study of Hot Gas in the Halos of Star‐forming Disk Galaxies. II. Quantifying Supernova Feedback

We investigate how the empirical properties of hot X-ray-emitting gas in asample of seven starburst and three normal edge-on spiral galaxies (a samplewhich covers the full range of star-formation intensity found in disk galaxies)correlate with the size, mass, star formation rate and star formation intensityin the host galaxies. Intriguingly, the diffuse X-ray properties of the normalspirals (both in their disks and halos) fall where extrapolation of the trendsfrom the starburst galaxies with superwinds would predict. We demonstrate thatthe luminosity of diffuse X-ray emission in both disk and halo is directlyproportional to the rate of mechanical energy feedback from massive stars.Nevertheless, with only three non-starburst normal spiral galaxies it is hardto exclude an accretion-based origin for extra-planar diffuse X-ray emissionaround normal star-forming galaxies. Larger galaxies have more extendedX-ray-emitting halos, but galaxy mass appears to play no role in determiningthe properties of the disk or extra-planar X-ray emitting plasma. Thecombination of these luminosity and size correlations leads to a correlationbetween the surface brightness of the diffuse X-ray emission and the mean starformation rate per unit area in the disk (L_FIR/D_25^2). We argue that thecrucial spatial region around a galaxy that controls whether gas instarburst-driven superwinds will escape into the IGM is not the outer halo ~100kpc from the host galaxy, but the inner few halo scale heights, within ~20 kpcof the galaxy plane. Given the properties of the gaseous halos we observe,superwind outflows from disk galaxies of mass M ~ 10^10 -- 10^11 Msun shouldstill eject some fraction of their material into the IGM. (abstract abridged)