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Session 90 - OJ287 and X-Ray Emission from Elliptical Galaxies.
Oral session, Wednesday, January 15
Harbour B,

[90.03] X-Ray Emission in Early-Type Galaxies

B. A. Brown, J. N. Bregman (U. Michigan)

The Einstein Observatory revealed that elliptical galaxies contained 10^7 K gas with masses in the range of 10^7- 10^10M_ødot. These studies did not yield a complete statistical sample, failed to produce accurate temperatures, and produced few good surface brightness distributions. To alleviate these problems, and to address issues of the origin and heating of the hot gas, we have undertaken a study of a complete optically selected sample of 34 early-type galaxies with ROSAT.

First we examine whether there is a contribution to the X-ray emission from stars by comparing the observed X-ray surface brightness distribution to the optical surface brightness distribution. We obtain an upper limit to the stellar contribution of \fracL_x,stellarL_B(\frac10^11L_ødot10^41ergs\:s^-1) \leq 0.21 (to the 90% confidence level), indicating that hot gas is the dominant emission mechanism these galaxies.

Every galaxy in the sample was detected and has good distances and optical properties. The resulting L_x (0.5-2 keV) to L_B slope is 2.1 \pm 0.4, and with a dispersion about the best fit line that is less than in previous works. Also, there is a correlation between the X-ray gas temperature and the stellar velocity dispersion, as expected for gas in hydrostatic equilibrium. Certain galaxies are X-ray overluminous, probably because they sit in the centers of clusters or groups and have accreted cluster gas in addition to that from galactic stellar mass loss. Other galaxies may be X-ray overluminous due to their interaction with their cluster.

Program listing for Wednesday