Searching for rotation in X-COP galaxy clusters

¹ Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum – Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
² INAF, Osservatorio di Astrofisica e Scienza dello Spazio, Via Gobetti 93/3, 40129 Bologna, Italy
³ INFN, Sezione di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy

^⋆ Corresponding author: tommaso.bartalesi3@unibo.it

Received: 10 January 2025
Accepted: 13 March 2025

Abstract

Aims. We searched for evidence of rotational support by analyzing the thermodynamic profiles of the intracluster medium (ICM) of a sample of nearby, massive galaxy clusters.

Methods. For each object of the XMM-Newton Cluster Outskirts Project (X-COP) sample, we present axisymmetric models of a rotating ICM with composite polytropic distributions, in equilibrium in spherically symmetric dark halos, exploring cases both with and without turbulent support in the ICM. The profile of rotation velocity and the distribution of turbulent velocity dispersion are described with flexible functional forms, consistent with the properties of synthetic clusters formed in cosmological simulations. The models are tuned via a Markov chain Monte Carlo algorithm to reproduce the radial profiles of the thermodynamic variables as resolved in the XMM-Newton and Planck maps, and to be consistent with the mass distributions estimated either from weak lensing observations (when available) or under the assumption of a “universal” baryon fraction value.

Results. Our models indicate that there is room for non-negligible rotation in the ICM of massive clusters, with a typical peak rotation speed ≈300 km s⁻¹ and a peak rotation-velocity-to-velocity-dispersion ratio u_ϕ/σ_gas,1D ≈ 0.3. According to our models, the ICM in Abell 2255 can have a rotation speed as high as 500 km s⁻¹, corresponding to u_ϕ/σ_gas,1D ≈ 0.4, at a distance of 100 kpc from the center, where the X-ray emissivity is still high. This makes Abell 2255 a very promising candidate for the presence of rotation in the ICM that could be detected with the currently operating XRISM observatory, as we demonstrate by computing and analyzing a mock X-ray spectrum.