D. Eckert

The gas distribution in the outer regions of galaxy clusters

Aims. We present our analysis of a local (z = 0.04-0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters.

The cool-core bias in X-ray galaxy cluster samples - I. Method and application to HIFLUGCS

Aims. When selecting flux-limited cluster samples, the detection efficiency of X-ray instruments is not the same for centrally-peaked and flat objects, which introduces a bias in flux-limited cluster samples. We quantify this effect in the case of a well-known cluster sample, HIFLUGCS. Methods. We simulate a population of X-ray clusters with various surface-brightness profiles, and use the instrumental characteristics of the ROSAT All-Sky Survey (RASS) to select flux-limited samples similar to the HIFLUGCS sample and predict the expected bias. For comparison, we also estimate observationally the bias in the HIFLUGCS sample using XMM-Newton and ROSAT data. Results. We find that the selection of X-ray cluster samples is significantly biased (∼29%) in favor of the peaked, cool-core (CC) objects, with respect to non-cool-core (NCC) systems. Interestingly, we find that the bias affects the low-mass, nearby objects (groups, poor clusters) much more than the more luminous objects (i.e massive clusters). We also note a moderate increase of the bias for the more distant systems. Conclusions. Observationally, we propose to select the objects according to their flux in a well-defined physical range excluding the cores, 0.2r500−r500, to get rid of the bias. From the fluxes in this range, we reject 13 clusters out of the 64 in the HIFLUGCS sample, none of which appears to be NCC. As a result, we estimate that less than half (35–37%) of the galaxy clusters in the local Universe are strong CC. In the paradigm where the CC objects trace relaxed clusters as opposed to unrelaxed, merging objects, this implies that to the present day the majority of the objects are not in a relaxed state. From this result, we estimate a rate of heating events of ∼1/ 3G yr −1 per dark-matter halo.

Constraints on 3.55 keV line emission from stacked observations of dwarf spheroidal galaxies

Several recent works have reported the detection of an unidentified x-ray line at 3.55 keV, which could possibly be attributed to the decay of dark matter (DM) particles in the halos of galaxy clusters and in the M31 galaxy. We analyze all publicly available XMM-Newton satellite data of dwarf spheroidal galaxies to test the possible DM origin of the line. Dwarf spheroidal galaxies have high mass-to-light ratios, and their interstellar medium is not a source of diffuse x-ray emission; thus, they are expected to provide the cleanest DM decay line signal. Our analysis shows no evidence for the presence of the line in the stacked spectra of the dwarf galaxies. It excludes the sterile neutrino DM decay origin of the 3.5 keV line reported by Bulbul et al. (2014) at the level of

The XXL Survey I. Scientific motivations - XMM-Newton observing plan - Follow-up observations and simulation programme

4.1\ensuremath{\sigma}

Hubble Frontier Fields: A High-Precision Strong-Lensing Analysis of Galaxy Cluster MACSJ0416.1-2403 Using 200 Multiple Images

under standard assumptions about the Galactic DM column density in the direction of selected dwarf galaxies and at the level of

The X-ray/SZ view of the virial region - I. Thermodynamic properties

3.2\ensuremath{\sigma}

Hubble Frontier Fields: a high-precision strong-lensing analysis of the massive galaxy cluster Abell 2744 using ∼180 multiple images

assuming minimal Galactic DM column density. Our analysis is still consistent with the estimate of sterile neutrino DM parameters by Boyarsky et al. (2014) because of its larger uncertainty. However, the central value of their estimate of the mixing angle is inconsistent with our dwarf spheroidals data at the

Hubble Frontier Fields: the geometry and dynamics of the massive galaxy cluster merger MACSJ0416.1−2403

3.4\ensuremath{\sigma}

The stripping of a galaxy group diving into the massive cluster A2142

(

Properties of gas clumps and gas clumping factor in the intra-cluster medium

2.5\ensuremath{\sigma}