Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...393..134k&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 393, no. 1, July 1, 1992, p. 134-148. Research supported by Smithsonian Ins
Astronomy and Astrophysics
Astrophysics
131
Astronomical Spectroscopy, Elliptical Galaxies, Interstellar Matter, Spiral Galaxies, X Ray Spectra, Color-Color Diagram, Emission Spectra, Galactic Clusters, Rosat Mission
Scientific paper
The 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.
Fabbiano Giuseppina
Kim Dae Wook
Trinchieri Ginevra
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