Merger-driven multiscale ICM density perturbations: testing cosmological simulations and constraining plasma physics

Monthly Notices of the Royal Astronomical Society, vol. 528, pp. 7274–7299

Abstract

ABSTRACT The hot intracluster medium (ICM) provides a unique laboratory to test multiscale physics in numerical simulations and probe plasma physics. Utilizing archival Chandra observations, we measure density fluctuations in the ICM in a sample of 80 nearby (z ≲ 1) galaxy clusters and infer scale-dependent velocities within regions affected by mergers (r < R2500c), excluding cool-cores. Systematic uncertainties (e.g. substructures, cluster asymmetries) are carefully explored to ensure robust measurements within the bulk ICM. We find typical velocities ∼220 (300) km s−1 in relaxed (unrelaxed) clusters, which translate to non-thermal pressure fractions ∼4 (8) per cent, and clumping factors ∼1.03 (1.06). We show that density fluctuation amplitudes could distinguish relaxed from unrelaxed clusters in these regions. Comparison with density fluctuations in cosmological simulations shows good agreement in merging clusters. Simulations underpredict the amplitude of fluctuations in relaxed clusters on length scales <0.75 R2500c, suggesting these systems are most sensitive to ‘missing’ physics in the simulations. In clusters hosting radio haloes, we examine correlations between gas velocities, turbulent dissipation rate, and radio emission strength/efficiency to test turbulent re-acceleration of cosmic ray electrons. We measure a weak correlation, driven by a few outlier clusters, in contrast to some previous studies. Finally, we present upper limits on effective viscosity in the bulk ICM of 16 clusters, showing it is systematically suppressed by at least a factor of 8, and the suppression is a general property of the ICM. Confirmation of our results with direct velocity measurements will be possible soon with XRISM.

Authors 6

1. Annie Heinrich

   University of Chicago

   Affiliation as printed

   Department of Astronomy and Astrophysics, University of Chicago , 5640 S Ellis Avenue, Chicago, IL 60637 , USA

2. Irina Zhuravleva

   University of Chicago

   Affiliation as printed

   Department of Astronomy and Astrophysics, University of Chicago , 5640 S Ellis Avenue, Chicago, IL 60637 , USA

3. Congyao Zhang

   University of Chicago

   Affiliation as printed

   Department of Astronomy and Astrophysics, University of Chicago , 5640 S Ellis Avenue, Chicago, IL 60637 , USA

4. E. Churazov

   Space Research Institute · Max Planck Institute for Astrophysics

   Affiliation as printed

   Max Planck Institute for Astrophysics , Karl-Schwwarzschild-Strasse 1, D-85478 Garching , Germany

   Space Research Institute (IKI) , Profsoyuznaya 84/32, Moscow 117997 , Russia

5. W. Forman

   Center for Astrophysics Harvard & Smithsonian

   Affiliation as printed

   Center for Astrophysics , Harvard and Smithsonian, 60 Garden St., MS-3, Cambridge, MA 02138 , USA

6. Reinout J. van Weeren Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University , PO Box 9513, NL-2300 RA Leiden , the Netherlands