Gas rotation and turbulence in the galaxy cluster Abell 2029

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 SRON Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA, Leiden, The Netherlands
⁴ INFN, Sezione di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
⁵ Department of Physics, University of Arkansas, 825 W Dickson st, Fayetteville, AR, USA
⁶ MIT Kavli Institute for Astrophysics and Space Research, 70 Vassar st., Cambridge, MA, USA
⁷ Department of Physics and Astronomy, The University of Alabama in Huntsville, Huntsville, AL 35899, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 December 2025
Accepted: 19 March 2026

Abstract

Aims. We constrain the rotation and turbulent support of the intracluster medium (ICM) in Abell 2029 (A2029) using dynamical equilibrium models and a combination of state-of-the-art X-ray and microwave datasets.

Methods. The rotating turbulent ICM in the model has a composite polytropic distribution in equilibrium in a spherically symmetric, cosmologically motivated dark halo. The profile of rotation velocity and the distribution of turbulent velocity dispersion are described with flexible functional forms, which are consistent with the properties of synthetic clusters formed in cosmological simulations. Adopting realistic profiles for the metallicity distribution of the ICM and for the point spread function of XRISM and XMM-Newton, we tuned the observables of the intrinsic quantities of the plasma in our model via a Markov chain Monte Carlo algorithm to reproduce the radial profiles of the thermodynamic quantities as derived from the spectral analysis of the XMM-Newton and Planck maps and the measurements of the line-of-sight (LOS) nonthermal velocity dispersion and redshift (probing the LOS velocity) in the XRISM pointings.

Results. Our model accurately reproduces the measurements of redshift and LOS nonthermal velocity dispersion, and this was further demonstrated by simulating and analyzing synthetic counterparts of the XRISM spectra, in accordance with the posterior distributions we obtained. We measured the turbulence-to-total pressure ratio to be ≈2% across the 0–650 kpc radial range, and, under the hypothesis that rotation is the only bulk motion, we report a rotation-to-dispersion velocity ratio peaking at 0.15 between 200–600 kpc. The hydrostatic-to-total mass ratio is ≈0.97 at r₂₅₀₀, i.e., the radius enclosing an overdensity of 2500 times the average value. Further constraints on the presence and amount of rotation could be obtained through a full azimuthal coverage of A2029 with XRISM.