A chandra x-ray investigation of the violent interstellar medium:: From dwarf starbursts to ultraluminous infrared galaxies

We have analyzed observations with the Chandra X-Ray Observatory of the diffuse emission by hot gas in seven dwarf starburst galaxies, six edge-on starburst galaxies, and nine ultraluminous infrared galaxies. These systems cover ranges of similar to 10(4) in X-ray luminosity, and several thousand in star formation rate and K-band luminosity (a proxy for stellar mass). Despite this range in fundamental parameters, we find that the properties of the diffuse X-ray emission are very similar in all three classes of starburst galaxies. The spectrum of the diffuse emission is well fitted by thermal emission from gas with kT similar to 0.25-0.8 keV and with several times solar abundance ratios of alpha-elements to Fe. The ratio of the thermal X-ray to far-infrared luminosity is roughly constant, as is the characteristic surface brightness of the diffuse X-ray emission. The size of the diffuse X-ray source increases systematically with both far-infrared and K-band luminosity. All three classes show strong morphological relationships between the regions of hot gas probed by the diffuse X-ray emission and the warm gas probed by optical line emission. These findings suggest that the same physical mechanism is producing the diffuse X-ray emission in the three types of starbursts. These results are consistent with that mechanism being shocks driven by a galactic "superwind,'' which is powered by the kinetic energy collectively supplied by stellar winds and supernovae in the starburst.