Rosat X-ray colors and emission mechanisms in early-type galaxies

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dc.contributor.authorIrwin, JA
dc.contributor.authorSarazin, CL
dc.contributor.otherUniversity of Virginia
dc.contributor.otherUniversity of Alabama Tuscaloosa
dc.date.accessioned2018-09-17T13:29:03Z
dc.date.available2018-09-17T13:29:03Z
dc.date.issued1998-06-01
dc.description.abstractThe X-ray colors and X-ray-to-optical luminosity ratios (L-X/L-B) of 61 early-type galaxies observed with the ROSAT PSPC are determined. The colors indicate that the X-ray spectral properties of galaxies vary as a function of L-X/L-B. The brightest X-ray galaxies have colors that are consistent with thermal emission from hot gas with roughly the same metallicity of 50% solar. The spatial variation of the colors indicates that the gas temperature in these galaxies increases radially. Galaxies with medium L-X/L-B also have spectral properties consistent with emission from hot gas. If a simple one-component thermal model is assumed to describe the 0.1-2.0 keV X-ray emission in these galaxies, then one possible explanation for the progressive decrease in L-X/L-B among galaxies of this class could be the progressive decrease in metal abundance of the X-ray-emitting gas contained by the galaxies. However, stellar X-ray emission may become a complicating factor for the fainter galaxies in this medium-L-X/L-B class. Galaxies with the lowest L-X/L-B values appear to be lacking a hot interstellar component. Their X-ray colors are consistent with those derived from the bulges of the spiral galaxies M31 and NGC 1291. In M31, the X-ray emission is resolved into discrete sources and is apparently due primarily to low-mass X-ray binaries (LMXBs). We therefore suggest that the bulk of the X-ray emission in the faintest elliptical galaxies is also due to LMXBs. Previously, the X-ray spectra of X-ray-faint galaxies had been found to be described by a hard component, which was attributed to LMXB emission, and a very soft component of unknown origin. We show that the very soft component also likely results from LMXBs, as a very soft component is seen in the X-ray spectra of the nearby LMXB Her X-1 and LMXBs in the bulge of M31. If the X-ray emission in X-ray-faint galaxies is primarily from stellar sources, then a range in L-X/L-B among these galaxies suggests that the stellar X-ray luminosity does not scale with optical luminosity, at least for galaxies of low optical luminosities. This could be the result of a decrease in the proportion of LMXBs with decreasing optical luminosity and/or the effects of fluctuations in the small number of LMXBs expected.en_US
dc.format.mimetypeapplication/pdf
dc.identifier.citationIrwin, J., Sarazin, C. (1998): ROSAT X-Ray Colors and Emission Mechanisms in EarlyType Galaxies. The Astrophysical Journal, 499(2). DOI: 10.1086/305666
dc.identifier.doi10.1086/305666
dc.identifier.urihttp://ir.ua.edu/handle/123456789/3880
dc.languageEnglish
dc.language.isoen_US
dc.publisherIOP Publishing
dc.subjectgalaxies, abundances
dc.subjectgalaxies, elliptical and lenticular, cD
dc.subjectgalaxies, halos
dc.subjectgalaxies, ISM
dc.subjectX-rays, galaxies
dc.subjectX-rays, ISM
dc.subjectELLIPTIC GALAXIES
dc.subjectSPECTRAL PROPERTIES
dc.subjectGLOBULAR-CLUSTERS
dc.subjectPSPC OBSERVATIONS
dc.subjectDARK-MATTER
dc.subjectSKY SURVEY
dc.subjectHOT
dc.subjectSAMPLE
dc.subjectGAS
dc.subjectEVOLUTION
dc.subjectAstronomy & Astrophysics
dc.titleRosat X-ray colors and emission mechanisms in early-type galaxiesen_US
dc.typetext
dc.typeArticle
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