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Session 49 - Elliptical Galaxies & Bulges.
Display session, Thursday, January 08
Exhibit Hall,

[49.05] The Environmental Role in Observed X-Ray Emission from Early-Type Galaxies

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

We have obtained an optically flux-limited sample of early-type galaxies observed with the ROSAT PSPC and HRI with the goal of testing the present picture of cooling flow ellipticals. We identify a stellar X-ray component that is prominent in the X-ray fainter galaxies, and when this component is removed, a steep relationship is found between the X-ray and optical luminosities due to the gaseous emission; the slope m = 3.0-3.5 in the L_x \propto L_B^m relationship, with a large dispersion about the correlation. We confirm the previously discovered correlation between the X-ray temperature and velocity dispersion temperature, although with a slightly steeper relationsh ip, T_x \propto T_\sigma ^n, where n = 1.43\pm0.21. These results are inconsistent with predictions of the standard cooling flow model for elliptical galaxies and we suggest a modification of the model that places environment in a central role in determining the X-ray emission properties. In our model, galaxies try to drive galactic winds, which are selectively stifled by the ambient medium in moderate richness environments, leading to hotter and more luminous systems, as observed.

Program listing for Thursday