2009MNRAS.394.1741O

We present a study of the X-ray properties of a sample of six nearby late-type spiral galaxies based on XMM-Newton observations. Since our primary focus is on the linkage between X-ray emission and star formation in extended, extranuclear Galactic discs, we have selected galaxies with near face-on aspect and sufficient angular extent so as to be readily amenable to investigation with the moderate spatial resolution afforded by XMM-Newton. After excluding regions in each galaxy dominated by bright point sources, we study both the morphology and spectral properties of the residual X-ray emission, comprising both diffuse emission and the integrated signal of the fainter discrete source populations. The soft X-ray morphology generally traces the inner spiral arms and shows a strong correlation with the distribution of UV light, indicative of a close connection between the X-ray emission and recent star formation. The soft (0.3-2keV) X-ray luminosity to star formation rate (SFR) ratio varies from 1-5x10³⁹erg/s (M_☉/yr)^–1, with an indication that the lower range of this ratio relates to regions of lower SFR density. The X-ray spectra are well matched by a two-temperature thermal model with derived temperatures of typically ∼0.2 and ∼0.65keV, in line with published results for other normal and star-forming galaxies. The hot component contributes a higher fraction of the soft luminosity in the galaxies with highest X-ray/SFR ratio, suggesting a link between plasma temperature and X-ray production efficiency. The physical properties of the gas present in the galactic discs are consistent with a clumpy thin-disc distribution, presumably composed of diffuse structures such as superbubbles together with the integrated emission of unresolved discrete sources including young supernova remnants.