Universal thermodynamic properties of the intracluster medium over two decades in radius in the X-COP sample

¹ Dipartimento di Fisica e Astronomia Università di Bologna, Via Piero Gobetti, 93/2, 40129 Bologna, Italy
e-mail: vittorio.ghirardini2@unibo.it
² INAF, Osservatorio di Astrofisica e Scienza dello Spazio, via Pietro Gobetti 93/3, 40129 Bologna, Italy
³ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
⁴ INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
⁵ IRAP, Université de Toulouse, CNRS, CNES, UPS, Toulouse, France
⁶ INAF – IASF Milano, via Bassini 15, 20133 Milano, Italy
⁷ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ, 08544-1001 USA
⁸ Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milano, Italy
⁹ INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
¹⁰ Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, 02138 USA
¹¹ Dipartimento di Fisica, Università degli Studi di Roma Tor Vergata, via della Ricerca Scientifica, 1, 00133 Roma, Italy
¹² INAF, Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy
¹³ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

Received: 30 April 2018
Accepted: 4 October 2018

Abstract

Context. The hot plasma in a galaxy cluster 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 cluster’s potential well and on non-gravitational processes such as gas cooling, AGN feedback, shocks, turbulence, bulk motions, cosmic rays and magnetic field.

Aims. 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, from 0.01R₅₀₀ to 2R₅₀₀.

Methods. We exploited X-ray information from XMM-Newton and Sunyaev-Zel’dovich constraints from Planck to recover thermodynamic properties out to 2R₅₀₀. 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.

Results. 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 outward. Somewhat surprisingly, we find that pressure is substantially more scattered than temperature and density.

Conclusions. Our results indicate that once accreting substructures are properly excised, the properties of the ICM beyond the cooling region (R > 0.3R₅₀₀) follow remarkably well the predictions of simple gravitational collapse and require few non-gravitational corrections.