XMM-Newton Observations of Three Interacting Luminous Infrared Galaxies

Abstract

We investigate the X-ray properties of three interacting luminous infrared galaxy systems. In one of these systems, IRAS 18329+5950, we resolve two separate sources. A second, IRAS 20550+1656, and third, IRAS 19354+4559, have only a single X-ray source detected. We compare the observed emission to PSF profiles and determine that three are extended in emission. One is compact, which is suggestive of an AGN, although all of our profiles have large uncertainties. We then model the spectra to determine soft (0.5--2 keV) and hard (2--10 keV) luminosities for the resolved sources and then compare these to relationships found in the literature between infrared and X-ray luminosities for starburst galaxies. We obtain luminosities of $\log (L_{\text{soft}}/{\text{L}}_{\odot })=7.32,7.06,7.68$ and $\log (L_{\text{hard}}/{\text{L}}_{\odot })=7.33,7.07,7.88$ for IRAS 18329+5950, IRAS 19354+4559, and IRAS 20550+1656, respectively. These are intermediate to two separate predictions in the literature for star-formation-dominated sources. Our highest quality spectrum of IRAS 20550+1656 suggests super-solar abundance of alpha elements at $2\sigma$ significance, with $\log (\frac{\alpha }{{\alpha }_{\odot }})=[\alpha ]=0.4\pm 0.2$. This is suggestive of recent enrichment with Type II supernovae, consistent with a starburst environment. The X-ray properties of the target galaxies are most likely due to starbursts, but we cannot conclusively rule out AGN.

Updated with substantial changes to match journal version. For a brief video summary of the original version of the paper, see http://www.youtube.com/watch?v=bOD6wLCtkIE

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