Indirect Measurements of Gas Velocities in Galaxy Clusters: Effects of Ellipticity and Cluster Dynamic State

Irina Zhuravleva; Mandy C. Chen; Eugene Churazov; Alexander A. Schekochihin; Congyao Zhang; Daisuke Nagai

doi:10.1093/mnras/stad470

paper

Indirect Measurements of Gas Velocities in Galaxy Clusters: Effects of Ellipticity and Cluster Dynamic State

arXiv:2210.11544 · doi:10.1093/mnras/stad470

Abstract

While awaiting direct velocity measurement of gas motions in the hot intracluster medium, we rely on indirect probes, including gas perturbations in galaxy clusters. Using a sample of $\sim 80$ clusters in different dynamic states from Omega500 cosmological simulations, we examine scaling relations between the fluctuation amplitudes of gas density, $δ ρ / ρ$ , pressure, $δ P / P$ , X-ray surface brightness, Sunyaev-Zeldovich (SZ) y-parameter, and the characteristic Mach number of gas motions, $M_{1d}$ . In relaxed clusters, accounting for halo ellipticities reduces $δ ρ / ρ$ or $δ P / P$ by a factor of up to 2 within $r_{500 c}$ . We confirm a strong linear correlation between $δ ρ / ρ$ (or $δ P / P$ ) and $M_{1d}$ in relaxed clusters, with the proportionality coefficient $η \approx 1$ . For unrelaxed clusters, the correlation is less strong and has a larger $η \approx 1.3 \pm 0.5$ ( $1.5 \pm 0.5$ ) for $δ ρ / ρ$ ( $δ P / P$ ). Examination of the power-law scaling of $M_{1d}$ with $δ ρ / ρ$ shows that it is almost linear for relaxed clusters, while for the unrelaxed ones, it is closer to $δ ρ / ρ \propto M_{1d}^{2}$ , supporting an increasing role of non-linear terms and compressive modes. In agreement with previous studies, we observe a strong correlation of $M_{1d}$ with radius. Correcting for these correlations leaves a residual scatter in $M_{1d}$ of $\sim 4 (7)$ per cent for relaxed (perturbed) clusters. Hydrostatic mass bias correlates with $M_{1d}$ as strongly as with $δ ρ / ρ$ in relaxed clusters. The residual scatters after correcting for derived trends is $\sim 6 - 7$ per cent. These predictions can be verified with existing X-ray and SZ observations of galaxy clusters combined with forthcoming velocity measurements with X-ray microcalorimeters.

15 pages, 11 figures, submitted

Indirect Measurements of Gas Velocities in Galaxy Clusters: Effects of Ellipticity and Cluster Dynamic State

Abstract

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