X-ray Emission from Rotating Ellipticals

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Session 52 -- Elliptical Galaxies
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[52.22] X-ray Emission from Rotating Ellipticals

Patricia C. Hanlan, Patricia M. Knezek, Joel N. Bregman (U. Michigan)

The stars in elliptical galaxies are not, in general, supported by rotation; neverthless, rotational velocities near 100 km/s are seen in some galaxies, allowing one to probe the internal dynamics of these galaxies. This kinematic information, since it does not control the shape of the galaxy, can contain information about the recent history and the formation of these galaxies. A recent model by Kley and Mathews (1994) predicts how rotation affects the X-ray emitting gas in elliptical galaxies. According to this model, galaxies have soft X-ray isophotes which are flattened along the major axes as compared to their stellar distribution. We will test this model by comparing its predictions to the observed X-ray emission in rotating galaxies.

Franx, Illingworth and Heckman (1989) compiled a sample of 22 early type ellipticals, most of which show evidence of rotation. X-ray observations with the ROSAT PSPC have been obtained for about $1/3$ of this sample; a few have been detected with the HRI, which provides the high spatial resolution necessary for detailed comparisons to the model. We are analyzing ROSAT observations of all known rotating ellipticals, including the galaxies from the Franx {et al.} \rm ~(1989) sample, to compare the observations to the predictions of the Kley and Mathews model. Preliminary results indicate that in NGC 1404 the isophotes are flattened near the center and are round towards the edges of the X-ray emission, as predicted by the model. In at least one case, NGC 1395, the X-ray isophotes are more affected by galaxy-galaxy interactions than the simple rotation that the Kley and Mathews model considered. However, NGC 1395 is a known shell galaxy and so its hot ISM may be dominated by the effects of a recent merger event, rather than rotation. Since some of the galaxies in our sample are not shell galaxies, we will be able to test the rotation {\it{vs.} \rm} merger hypothesis.

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