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Register a new userUniversal thermodynamic properties of the intracluster medium over two decades in radius in the X-COP sample
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Added by
Vittorio Ghirardini
Publication date
2018
fields
Physics
and research's language is
English
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The hot plasma in galaxy clusters is expected to be heated to high temperatures through shocks and adiabatic compression. The thermodynamical properties of the gas encode information on the processes leading to the thermalization of the gas in the clusters potential well as well as non-gravitational processes such as gas cooling, AGN feedback and kinetic energy. In this work we present the radial profiles of the thermodynamic properties of the intracluster medium (ICM) out to the virial radius for a sample of 12 galaxy clusters selected from the Planck all-sky survey. We determine the universal profiles of gas density, temperature, pressure, and entropy over more than two decades in radius. We exploit jointly X-ray information from XMM and Sunyaev-Zeldovich constraints from Planck to recover thermodynamic properties out to 2 R500. We provide average functional forms for the radial dependence of the main quantities and quantify the slope and intrinsic scatter of the population as a function of radius. We find that gas density and pressure profiles steepen steadily with radius, in excellent agreement with previous observational results. Entropy profiles beyond R500 closely follow the predictions for the gravitational collapse of structures. The scatter in all thermodynamical quantities reaches a minimum in the range [0.2-0.8] R500 and increases outwards. Somewhat surprisingly, we find that pressure is substantially more scattered than temperature and density. Our results indicate that once accreting substructures are properly excised, the properties of the ICM beyond the cooling region R > 0.3 R500) follow remarkably well the predictions of simple gravitational collapse and require little non-gravitational corrections.
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In this work, we investigate the relation between the radially-resolved thermodynamic quantities of the intracluster medium in the X-COP cluster sample, aiming to assess the stratification properties of the ICM. We model the relations between radius, gas temperature, density and pressure using a combination of power-laws, also evaluating the intrinsic scatter in these relations. We show that the gas pressure is remarkably well correlated to the density, with very small scatter. Also, the temperature correlates with gas density with similar scatter. The slopes of these relations have values that show a clear transition from the inner cluster regions to the outskirts. This transition occurs at the radius $r_t = 0.19(pm0.04)R_{500}$ and electron density $n_t = (1.91pm0.21)cdot10^{-3} cm^{-3} E^2 (z)$. We find that above 0.2 $R_{500}$ the radial thermodynamic profiles are accurately reproduced by a well defined and physically motivated framework, where the dark matter follows the NFW potential and the gas is represented by a polytropic equation of state. By modeling the gas temperature dependence upon both the gas density and radius, we propose a new method to reconstruct the hydrostatic mass profile based only on the quite inexpensive measurement of the gas density profile.
We present the joint analysis of the X-ray and SZ signals in A2319, the galaxy cluster with the highest signal-to-noise ratio in Planck maps and that has been surveyed within our XMM Cluster Outskirts Project (X-COP). We recover the thermodynamical profiles by the geometrical deprojection of the X-ray surface brightness, of the SZ comptonization parameter, and an accurate and robust spectroscopic measurements of the temperature. We resolve the clumpiness of the density to be below 20 per cent demonstrating that most of this clumpiness originates from the ongoing merger and can be associated to large-scale inhomogeneities. This analysis is done in azimuthally averaged radial bins and in eight independent angular sectors, enabling us to study in details the azimuthal variance of the recovered properties. Given the exquisite quality of the X-ray and SZ datasets, we constrain at $R_{200}$ the total hydrostatic mass, modelled with a NFW profile, with very high precision ($M_{200} = 9.76 pm 0.16^{stat.} pm 0.31^{syst.} times 10^{14} M_odot$). We identify the ongoing merger and how it is affecting differently the gas properties in the resolved azimuthal sectors. We have several indications that the merger has injected a high level of non-thermal pressure in this system: the clumping free density profile is above the average profile obtained by stacking Rosat observations; the gas mass fraction exceeds the expected cosmic gas fraction beyond $R_{500}$; the pressure profile is flatter than the fit obtained by the Planck collaboration; the entropy profile is flatter than the mean one predicted from non-radiative simulations; the analysis in azimuthal sectors has revealed that these deviations occur in a preferred region of the cluster. All these tensions are resolved by requiring a relative support of about 40 per cent from non-thermal to the total pressure at $R_{200}$.
We present a detailed analysis of the baryonic and dark matter distribution in the lensing cluster Abell 611 (z=0.288), with the goal of determining the dark matter profile over an unprecedented range of cluster-centric distance. By combining three complementary probes of the mass distribution, weak lensing from deep multi-color imaging, strong lensing constraints based on the identification of multiply-imaged sources, and resolved stellar velocity dispersion measures for the brightest cluster galaxy (BCG), we extend the methodology for separating the dark and baryonic mass components introduced by Sand et al. (2008). Our resulting dark matter profile samples the cluster from ~3 kpc to 3.25 Mpc, thereby providing an excellent basis for comparisons with recent numerical models. We demonstrate that only by combining our three observational techniques can degeneracies in constraining the form of the dark matter profile be broken on scales crucial for detailed comparisons with numerical simulations. Our analysis reveals that a simple Navarro, Frenk, and White (NFW) profile is an unacceptable fit to our data. We confirm earlier claims that the inner profile of the dark matter profile deviates significantly from the NFW form and find a inner logarithmic slope beta flatter than 0.3 (68%; where rho_DM ~ r^{-beta} at small radii). In order to reconcile our data with cluster formation in a LambdaCDM cosmology, we speculate that it may be necessary to revise our understanding of the nature of baryon--dark matter interactions in cluster cores. Comprehensive weak and strong lensing data, when coupled with kinematic information on the brightest cluster galaxy, can readily be applied to a larger sample of clusters to test the universality of these results.
We conduct a joint X-ray and weak-lensing study of four relaxed galaxy clusters (Hydra A, A478, A1689 and A1835) observed by both Suzaku and Subaru out to virial radii, with an aim to understand recently-discovered unexpected feature of the ICM in cluster outskirts. We show that the average hydrostatic-to-lensing total mass ratio for the four clusters decreases from sim 70% to sim 40% as the overdensity contrast decreases from 500 to the virial value.The average gas mass fraction from lensing total mass estimates increases with cluster radius and agrees with the cosmic mean baryon fraction within the virial radius, whereas the X-ray-based gas fraction considerably exceeds the cosmic values due to underestimation of the hydrostatic mass. We also develop a new advanced method for determining normalized cluster radial profiles for multiple X-ray observables by simultaneously taking into account both their radial dependence and multivariate scaling relations with weak-lensing masses. Although the four clusters span a range of halo mass, concentration, X-ray luminosity and redshift, we find that the gas entropy, pressure, temperature and density profiles are all remarkably self-similar when scaled with the lensing M_200 mass and r_200 radius.The entropy monotonically increases out to sim 0.5r_200 following the accretion shock heating model K(r)propto r^1.1, and flattens at simgt 0.5r_200.The universality of the scaled entropy profiles indicates that the thermalization mechanism over the entire cluster region (>0.1r_200) is controlled by gravitation in a common to all clusters, although the heating efficiency in the outskirts needs to be modified from the standard law.The bivariate scaling functions of the gas density and temperature reveal that the flattening of the outskirts entropy profile is caused by the steepening of the temperature, rather than the flattening of the gas density.
The rich galaxy cluster Abell 2204 exhibits edges in its X-ray surface brightness at $sim 65$ and $35 {rm~ kpc}$ west and east of its center, respectively. The presence of these edges, which were interpreted as sloshing cold fronts, implies that the intracluster medium was recently disturbed. We analyze the properties of the intracluster medium using multiple Chandra observations of Abell 2204. We find a density ratio $n_{rm in}/n_{rm out} = 2.05pm0.05$ and a temperature ratio $T_{rm out}/T_{rm in} = 1.91pm0.27$ (projected, or $1.87pm0.56$ deprojected) across the western edge, and correspondingly $n_{rm in}/n_{rm out} = 1.96pm0.05$ and $T_{rm out}/T_{rm in} =1.45pm0.15$ (projected, or $1.25pm0.26$ deprojected) across the eastern edge. These values are typical of cold fronts in galaxy clusters. This, together with the spiral pattern observed in the cluster core, supports the sloshing scenario for Abell 2204. No Kelvin-Helmholtz eddies are observed along the cold front surfaces, indicating that they are effectively suppressed by some physical mechanism. We argue that the suppression is likely facilitated by the magnetic fields amplified in the sloshing motion, and deduce from the measured gas properties that the magnetic field strength should be greater than $24pm6$ $mu$G and $32pm8$ $mu$G along the west and east cold fronts, respectively.
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