Jukka Nevalainen

We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the "missing baryon" problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations.

We improve the earlier restrictions on parameters of the dark matter (DM) in the form of a sterile neutrino. The results were obtained from non-observing the DM decay line in the X-ray spectrum of the Milky Way (using the recent XMM-Newton PN blank sky data). We also present a similar constraint coming from the recent XMM-Newton observation of Ursa Minor -- dark, X-ray quiet dwarf spheroidal galaxy. The new Milky way data improve on (by as much as the order of magnitude at masses ~3.5 keV) existing constraints. Although the observation of Ursa Minor has relatively poor statistics, the constraints are comparable to those recently obtained using observations of the Large Magellanic Cloud or M31. This confirms a recent proposal that dwarf satellites of the MW are very interesting candidates for the DM search and dedicated studies should be made to this purpose.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

We analyze XMM-Newton galaxy clusters Abell 1795, Abell S1101, Abell 1835, and MKW 3s in order to test whether their soft X-ray excess emission in the 0.2-0.5 keV band as reported by Kaastra et al. maintains after application of current knowledge of the XMM-Newton background and calibration. In this context, we examine the claim (Bregman & Lloyd-Davies) that the XMM-Newton sub-Galactic H I column density, and the accompanying soft excess continuum emission in the 0.2-0.5 keV band, is an artifact of an incorrect background subtraction. We show that since the cluster regions under scrutiny are within 500 kpc of the bright cluster center, the X-ray background level is negligible compared to the cluster emission level. Thus, at least in the central 500 kpc regions of the studied clusters, the reported soft excess is not a background artifact. We also study the possibility that the incomplete calibration information in the early phase of the XMM-Newton mission resulted in sub-Galactic H I column density, which was interpreted with the presence of a soft excess emitter. Our reanalysis of the four XMM-Newton observations with the MOS instruments yields evidence for the soft excess in all clusters. However, using the PN instrument, the best-fit H I column densities in Abell 1795, Abell 1835, and MKW 3s are at odds with the 2003 analysis of Kaastra et al. and in general agreement with those measured from 21 cm data in the direction of the clusters (Dickey & Lockman). Abell S1101 continues to feature a sub-Galactic NH also with the PN instrument, indicative of soft excess emission in both EPIC detectors. These differences are compatible with the current level of uncertainty in the calibration of both instruments.