Abstract
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 disks, 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, comprised of 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(/Msun/yr), 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 keV and ~0.65 keV, 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 disks are consistent with a clumpy thin-disk distribution, presumably composed of diffuse structures such as superbubbles together with the integrated emission of unresolved discrete sources including young supernova remnants.
Highlights
The first detailed studies of the X-ray emission from nearby latetype galaxies were carried out with the Einstein observatory, and revealed both individual luminous X-ray sources, as well as an extended, often complex, underlying structure (Fabbiano 1989)
In a previous paper (Warwick et al 2007, hereafter W07), we reported the results of an XMM–Newton study of one of these galaxies, namely M101, and here we apply a similar methodology to extend the sample, thereby allowing the intercomparison of the galaxy X-ray characteristics based on XMM– Newton observations
Since our goal is to study the latter rather than the former, we have limited our galaxy sample to nearby face-on systems of Hubble-type Sbc–Sd with major-axis D25 extent greater than 7 arcmin, thereby ameliorating the source confusion problem. [We have excluded M33 from our study since this galaxy has a D25 diameter of 70 arcmin, and extends well beyond the European Photon Imaging Camera (EPIC) field of view; M33 is the subject of a specific XMM–Newton programme utilizing multiple pointings (Pietsch et al 2004; Misanovic et al 2006).]
Summary
The first detailed studies of the X-ray emission from nearby latetype galaxies were carried out with the Einstein observatory, and revealed both individual luminous X-ray sources, as well as an extended, often complex, underlying structure (Fabbiano 1989). The superior spatial resolution and enhanced soft X-ray response of ROSAT greatly extended this work, leading to the detection of substantial numbers of discrete sources as well as establishing a much clearer picture of the diffuse emission components The advent of XMM–Newton and Chandra has extended our knowledge of the discrete X-ray source populations and the ultrahot interstellar medium (ISM) in nearby galaxies to unprecedented luminosity and surface brightness thresholds
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
