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The X-ray spectra of galaxies. II - Average spectral properties and emission mechanismsThe Imaging Proportional Counter data in the Einstein database is used to study the X-ray spectra of normal galaxies. The X-ray emission temperature of spirals is found to be higher on the average than that of ellipticals. This supports the idea that accreting binaries are a major source of X-rays in spirals, while a hot interstellar medium (ISM) is present in ellipticals. The X-ray spectra of Sa galaxies are intermediate between those of ellipticals and spirals, suggesting that these galaxies contain hot gaseous emission as well as emission from accreting binaries. In E and SO galaxies the emission temperature becomes higher with a decreasing X-ray to optical luminosity ratio, which suggests that the emission of X-ray faint early-type galaxies consists of a large evolved stellar component, while the gaseous emission becomes dominant in X-ray brighter galaxies. The group with the lowest X-ray to optical ratio does not follow this trend; in these galaxies a very soft X-ray component, amounting to about half the total X-ray emission, is found in addition to the hard X-ray component. Possible explanations are integrated emission of M stars and a relatively cool ISM. A very soft component is also found in several spiral galaxies. This may indicate that some spirals contain hot gaseous components similar to those seen in NGC 253 and M82.
Document ID
19920061188
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Kim, D.-W.
(Chungnam National University Taejon, Republic of Korea; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, United States)
Fabbiano, G.
(Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Trinchieri, G.
(Arcetri, Osservatorio Astrofisico, Florence, Italy; Harvard-Smithsonian Center for Astrophysics, Cambridge MA, United States)
Date Acquired
August 15, 2013
Publication Date
July 1, 1992
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 393
Issue: 1 Ju
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
92A43812
Funding Number(s)
CONTRACT_GRANT: NAS8-30751
CONTRACT_GRANT: NAG5-1202
Distribution Limits
Public
Copyright
Other

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