2012MNRAS.426.1870M

We study the emission from the hot interstellar medium (ISM) in a sample of nearby late-type galaxies defined in Paper I. Our sample covers a broad range of star formation rates (SFRs) from ∼ 0.1 to ∼ 17M_☉/yr and stellar masses from ∼ 3 x 10⁸ to ∼ 6 x 10¹⁰M_☉. We take special care of systematic effects and contamination from bright and faint compact sources. We find that in all galaxies at least one optically thin thermal emission component is present in the unresolved emission, with the average temperature of < kT > = 0.24keV. In about ∼ 1/3 of galaxies, a second, higher temperature component is required, with < kT > = 0.71keV. Although statistically significant variations in temperature between galaxies are present, we do not find any meaningful trends with the stellar mass or SFR of the host galaxy. The apparent luminosity of the diffuse emission in the 0.5–2keV band linearly correlates with the SFR with the scale factor of \mi L\mi X\mo/\mi SFR\mo ≈ \mn 8.3\mo x \mn 10\mn 38erg/s (M_☉/yr)^–1, of which in average ∼ 30–40 percent is likely produced by faint compact sources of various types. We attempt to estimate the bolometric luminosity of the gas and obtain results differing by an order of magnitude, \mo log\mo (\mi L\mi bol\mo/\mi SFR\mo)\mo ∼ \mn 39\mo –\mo –\mn 40, depending on whether intrinsic absorption in star-forming galaxies is allowed or not. Our theoretically most accurate, but in practice the most model-dependent result for the intrinsic bolometric luminosity of the ISM is \mi L\mi bol\mo/\mi SFR\mo ∼ \mn 1.5\mo x \mn 10\mn 40erg/s (M_☉/yr)^–1. Assuming that core-collapse supernovae are the main source of energy, it is implied that epsilon\mi SN\mo ∼ \mn 5\mo x \mn 10\mo –\mn 2\mo (\mi E\mi SN\mo/\mn 10\mn 51\mo)\mo –\mn 1 of mechanical energy of supernovae is converted into thermal energy of the ISM.