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2006ApJ...644..167B - Astrophys. J., 644, 167-173 (2006/June-2)

On the lack of a soft X-ray excess from clusters of galaxies.

BREGMAN J.N. and LLOYD-DAVIES E.J.

Abstract (from CDS):

A soft X-ray excess has been claimed to exist in and around a number of galaxy clusters, and this emission has been attributed to the warm-hot intergalactic medium that may constitute most of the baryons in the local universe. We have reexamined a study of the XMM-Newton observations on this topic by Kaastra and coworkers and find that the X-ray excess (or deficit) depends on Galactic latitude and appears to be most closely related to the surface brightness of the 1/4 keV emission, which is largely due to emission from the local hot bubble and the halo of the Milky Way. We suggest that the presence of the soft X-ray excess is due to incorrect subtraction of the soft X-ray background. An analysis is performed for which we choose a 1/4 keV background that is similar to the background near the cluster (and a similar H I column). We find that the soft X-ray excess largely disappears using our background subtraction and conclude that these soft X-ray excesses are not associated with the target clusters. We also show that the detections of redshifted'' O VII lines claimed by Kaastra and coworkers are correlated with solar system charge exchange emission, suggesting that they are not extragalactic either.