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Session 37 - Clusters of Galaxies - X-Rays.
Display session, Tuesday, January 14
Metropolitan Ballroom,
A ROSAT High Resolution Imager (HRI) observation, and archival Einstein HRI abd ROSAT PSPC observations are used to study the distribution of hot, X-ray emitting gas in the elliptical galaxy NGC 4636. This galaxy is apparently located on the outskirts of the Virgo cluster. On large scales, the X-ray image is asymmetrical, which may indicate that the hot interstellar gas in NGC 4636 is interacting with ambient gas. This ambient gas may be an outer extension of the Virgo cluster, or more local gas due to a smaller group of galaxies. The distribution of the hot gas mass and total gravitating mass are determined assuming hydrostatic equilibrium, but the asymmetry makes this assumption questionable at large radii. At smaller radii, the ROSAT HRI image shows evidence for a central bar-like structure, which was originally identified with the Einstein HRI. We fit elliptical isophotes to the X-ray image, and determine the statistical significance of non-elliptical structures, including the central bar. The central bar is roughly perpendicular to the long axis of the nuclear radio source in this galaxy. We consider a variety of mechanisms for the origin of the central bar, including interaction of the radio plasma with the hot, X-ray emitting interstellar gas. We also consider the possiblity that the bar is a rotating disk of gas seen edge-on, and that this bar feeds an accretion disk around the active nucleus of the galaxy. In this case, the axis of the disk may determine the direction of propagation of the radio jets.
