The matter distribution in z ~ 0.5 redshift clusters of galaxies. II : The link between dark and visible matter

We present an optical analysis of a sample of 11 clusters built from the EXCPRES sample of X-ray selected clusters at intermediate redshift (z ~ 0.5). With a careful selection of the background galaxies we provide the mass maps reconstructed from the weak lensing by the clusters. We compare them with the light distribution traced by the early-type galaxies selected along the red sequence for each cluster. The strong correlations between dark matter and galaxy distributions are confirmed, although some discrepancies arise, mostly for merging or perturbed clusters. The average M/L ratio of the clusters is found to be: M/L_r = 160 +/- 60 in solar units (with no evolutionary correction), in excellent agreement with similar previous studies. No strong evolutionary effects are identified even if the small sample size reduces the significance of the result. We also provide a individual analysis of each cluster in the sample with a comparison between the dark matter, the galaxies and the gas distributions. Some of the clusters are studied for the first time in the optical.Comment: 25 pages, 9 figues + 11 figures in Annex, 4 tables. Accepted for publication in A&A. 1 reference correcte

Investigating the turbulent hot gas in X-COP galaxy clusters

Turbulent processes at work in the intracluster medium perturb this environment, displacing gas, and creating local density fluctuations that can be quantified via X-ray surface brightness fluctuation analyses. Improved knowledge of these phenomena would allow for a better determination of the mass of galaxy clusters, as well as a better understanding of their dynamic assembly. In this work, we aim to set constraints on the structure of turbulence using X-ray surface brightness fluctuations. We seek to consider the stochastic nature of this observable and to constrain the structure of the underlying power spectrum. We propose a new Bayesian approach, relying on simulation-based inference to account for the whole error budget. We used the X-COP cluster sample to individually constrain the power spectrum in four regions and within $R_{500}$. We spread the analysis on the 12 systems to alleviate the sample variance. We then interpreted the density fluctuations as the result of either gas clumping or turbulence. For each cluster considered individually, the normalisation of density fluctuations correlates positively with the Zernike moment and centroid shift, but negatively with the concentration and the Gini coefficient. The spectral index within $R_{500}$ and evaluated over all clusters is consistent with a Kolmogorov cascade. The normalisation of density fluctuations, when interpreted in terms of clumping, is consistent within $0.5 R_{500}$ with the literature results and numerical simulations; however, it is higher between 0.5 and $1 R_{500}$. Conversely, when interpreted on the basis of turbulence, we deduce a non-thermal pressure profile that is lower than the predictions of the simulations within 0.5 $R_{500}$, but still in agreement in the outer regions. We explain these results by the presence of central structural residues that are remnants of the dynamic assembly of the clusters.Comment: Accepted for publication in A&A. Abstract slightly abridged for arXi

Outskirts of Galaxy Clusters

Until recently, only about 10% of the total intracluster gas volume had been studied with high accuracy, leaving a vast region essentially unexplored. This is now changing and a wide area of hot gas physics and chemistry awaits discovery in galaxy cluster outskirts. Also, robust large-scale total mass profiles and maps are within reach. First observational and theoretical results in this emerging field have been achieved in recent years with sometimes surprising findings. Here, we summarize and illustrate the relevant underlying physical and chemical processes and review the recent progress in X-ray, Sunyaev--Zel'dovich, and weak gravitational lensing observations of cluster outskirts, including also brief discussions of technical challenges and possible future improvements.Comment: 52 pages. Review paper. Accepted for publication in Space Science Reviews (eds: S. Ettori, M. Meneghetti). This is a product of the work done by an international team at the International Space Science Institute (ISSI) in Bern on "Astrophysics and Cosmology with Galaxy Clusters: the X-ray and Lensing View

Simulating the impact of dust cooling on the statistical properties of the intracluster medium

From the first stages of star and galaxy formation, non-gravitational processes such as ram pressure stripping, SNs, galactic winds, AGNs, galaxy-galaxy mergers, etc... lead to the enrichment of the IGM in stars, metals as well as dust, via the ejection of galactic material into the IGM. We know now that these processes shape, side by side with gravitation, the formation and the evolution of structures. We present here hydrodynamic simulations of structure formation implementing the effect of the cooling by dust on large scale structure formation. We focus on the scale of galaxy clusters and study the statistical properties of clusters. Here we present our results on the $T_X-M$ and the $L_X-M$ scaling relations which exhibit changes on both the slope and normalization when adding cooling by dust to the standard radiative cooling model. For example, the normalization of the $T_X-M$ relation changes only by a maximum of 2% at $M=10^{14}$ M$_\odot$ whereas the normalization of the $L_X-T_X$ changes by as much as 10% at $T_X=1$ keV for models that including dust cooling. Our study shows that the dust is an added non-gravitational process that contributes shaping the thermodynamical state of the hot ICM gas.Comment: 11 pages, 4 figures, ASR in pres

New constraints on MOND from galaxy clusters

We revisit the application of Modified Newtonian Dynamics (MOND) to galaxy clusters. We confront the high quality X-ray data for eight clusters of galaxies observed by the \xmm satellite with the predictions of MOND. We obtain a ratio of the MOND dynamical mass to the baryonic mass of $M_m/M_b=4.94\pm 0.50$ in the outer parts (i.e $r\sim 0.5$ ~ R$_{vir}$), in the concordance cosmological model where the predicted asymptotic ratio, if any baryons are present, is $7.7^{+1.4}_{-1.1}$ (at $r\geq 0.3$ ~ R$_{vir}$). We confirm that the MOND paradigm lowers the discrepancy between the binding mass and the baryonic mass in clusters by a factor of $\sim 1.6$ at about half the virial radius. However, at this radius about 80% of the mass is still missing, and as pointed out by \citet{sanders03}, this necessitates a component of dark baryons or neutrinos in the cluster core. Concerning the neutrino hypothesis, application of the new data requires a minimum neutrino mass of $m_\nu>1.74\pm 0.34$ eV to fill this gap. The corresponding 2$\sigma$ lower limit of $m_\nu>1.06$ eV is marginally inconsistent with the current constraints from the cluster number counts, and from the CMB and large scale structure data. MOND must invoke neutrinos to represent the main component that account for the missing mass problem in clusters.Comment: 5 pages, 1 figure, accepted for publication in MNRAS. A section on the neutrino mass in the MOND framework was added to the discussio