The Effect of Environment on the X-Ray Emission from Early-Type Galaxies
Abstract
In order to help understand the phenomena of X-ray emission from early-type galaxies, we obtained an optically flux-limited sample of 34 early-type galaxies, observed with ROSAT. A previous analysis of this sample suggested that the most X-ray luminous galaxies were in rich environments. Here we investigate environmental influences quantitatively, and find a positive correlation between LB/LX and the local galaxy density. We suggest that this correlation occurs because the X-ray luminosity is enhanced either through accretion of the intergalactic gas or because the ambient medium stifles galactic winds. When the ambient medium is unimportant, partial or global galactic winds can occur, reducing LB/LX. These effects lead to the large observed dispersion in LX at fixed LB. We argue that the transition from global winds to partial winds is one of the principle reasons for the steep relationship between LX and LB. We discuss details of the data reduction not previously presented, and examine the dependence of LX on the choice of outer source radius and background location. Effects of Malmquist bias are shown not to be important for the issues addressed. Finally, we compare the temperature deduced for these galaxies from different analyses of ROSAT and ASCA data.
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