X-ray emission from the extended discs of spiral galaxies

We present a study of the X-ray properties of a sample of six nearby late-type spiral galaxies based oil XMM-Newton observations. Since our primary focus is oil 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 (0.3-2 keV) X-ray luminosity to star formation rate (SFR) ratio varies from 1-5 x 10(39) erg s(-1) (M-circle dot yr(-1))(-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 similar to 0.2 and similar to 0.65 keV, in line With published results for other normal and star-forming galaxies. The hot component Contributes I higher fraction of the soft luminosity in the galaxies with highest X-ray/SFR ratio. suggesting I 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 remnants.