Chandra measurements of gas homogeneity and turbulence at intermediate radii in the Perseus Cluster

TL;DR

This study uses Chandra X-ray data to analyze gas density fluctuations and turbulence in the Perseus Cluster, revealing low to moderate turbulence and slight gas clumping at intermediate radii, with implications for future X-ray observations.

Contribution

First detailed measurement of gas homogeneity and turbulence at intermediate radii in the Perseus Cluster using surface brightness fluctuations.

Findings

Density bias around 3% below 1.6r_2500

Turbulent velocity less than 400 km/s at these radii

Methodology accounts for background and Poisson noise

Abstract

We present a Chandra study of surface brightness fluctuations in the diffuse intracluster medium of the Perseus Cluster. Our study utilizes deep, archival imaging of the cluster core as well as a new mosaic of 29 short 5 ks observations extending in 8 different directions out to radii of r_500 ~ 2.2r_2500. Under the assumption that the distribution of densities at a given radius is log-normally distributed, two important quantities can be derived from the width of the log-normal density distribution on a given spatial scale: the density bias, which is equal to the square root of the clumping factor C; and the one-component turbulent velocity, v_(k, 1D). We forward-model all contributions to the measured surface brightness, including astrophysical and particle background components, and account for the Poisson nature of the measured signal. Measuring the distribution of surface brightness fluctuations in 1 arcmin^2 regions, spanning the radial range 0.3-2.2 r_2500 (7.8-57.3 arcmin), we find a small to moderate average density bias of around 3% at radii below 1.6r_2500. We also infer an average turbulent velocity at these radii of v_1D <400 km s^-1. Direct confirmation of our results on turbulent velocities inferred from surface brightness fluctuations should be possible using the X-ray calorimeter spectrometers to be flown aboard the XRISM and Athena. observatories.