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Date and Time of the Query: 2019-06-16 T06:13:43 PDT
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For refcode 1988ApJ...331..102S:
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1988ApJ...331..102S THE X-RAY EMISSION OF NORMAL ELLIPTICAL GALAXIES: STEADY STATE COOLING FLOW MODELS CRAIG L. SARAZIN Department of Astronomy, University of Virginia AND RAYMOND E. WHITE III Institute of Astronomy, Cambridge University Received 1987 October 16; accepted 1988 February 2 ABSTRACT Steady state, spherical, homogeneous cooling flow models are compared to the observed X-ray luminosities, spectra, and surface-brightness profiles of elliptical galaxies. Four elliptical galaxy model types are investigated: (1) galaxies without heavy halos and supernovae (bare), (2) galaxies without heavy halos but with supernovae (SN), (3) galaxies with heavy halos but without supernovae (HH), and (4) galaxies with heavy halos and supernovae (SN-HH). Bare models have temperatures which are too low and X-ray surface- brightness profiles which are too rapidly decreasing with radius to fit the observations. SN-HH models have luminosities which are too large except for the highest luminosity ellipticals. SN models have temperatures which are probably too cool in the outer parts. The favored models are of the HH type, where the gas is heated by the motions of gas-losing stars and by infall and compression in a heavy halo potential. This suggests that elliptical galaxies have heavy halos of optically dark material. However, even these models have some problems: (1) they do not account for the very large range of X-ray luminosity observed for elliptical galaxies of a given optical luminosity; (2) all of the models give X-ray luminosities which are too large for many elliptical galaxies; and (3) the X-ray surface-brightness profiles of the HH models are too centrally peaked. The latter problem is the result of having all of the gas flow into the galaxy center while still quite hot. We argue that thermal instabilities will cause most of the gas to cool below X-ray-emitting temperatures before it flows in very far. This would eliminate the central peak in the model surface-brightness profiles, and would also lower the X-ray luminosities of the models. Subject headings: galaxies: intergalactic medium - galaxies: stellar content - galaxies: structure - galaxies: X-rays
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