On the Lack of a Soft X-Ray Excess from Clusters of Galaxies
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2006
- DOI:
- 10.1086/503551
- arXiv:
- arXiv:astro-ph/0602527
- Bibcode:
- 2006ApJ...644..167B
- Keywords:
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- Methods: Data Analysis;
- X-Rays: Galaxies: Clusters;
- Astrophysics
- E-Print:
- 8 pages, 6 figures, accepted for publication in ApJ