Constraining gas motions in the Centaurus cluster using X-ray surface brightness fluctuations and metal diffusion

TL;DR

This study uses X-ray brightness fluctuations and metal diffusion analysis to constrain gas motion velocities and scales in the Centaurus cluster, finding velocities of 100-150 km/s on 4-10 kpc scales, with two methods in agreement.

Contribution

It introduces a combined approach using surface brightness fluctuations and metal diffusion to constrain gas motions in galaxy clusters, providing consistent velocity estimates.

Findings

Gas velocities are 100-150 km/s on 4-10 kpc scales.

Surface brightness fluctuation power spectrum is flatter than Kolmogorov expectations.

Two independent methods yield consistent constraints on gas motions.

Abstract

We compare two different methods of constraining the characteristic velocity and spatial scales of gas motions in the X-ray bright, nearby Centaurus cluster, using new deep (760ks) Chandra observations. The power spectrum of excess surface brightness fluctuations in the 0.5-6.0 keV band in a sector to the west is measured and compared to theoretical expectations for Kolmogorov index fluctuations. The observed power spectrum is flatter than these expectations, and the surface brightness fluctuations are around the 8 percent level on length scales of 2 kpc. We convert the 2D power spectrum of fluctuations into a 3D power spectrum using the method of Churazov et al., and then convert this into constraints on the one-component velocity of the gas motions as a function of their length scale. We find one-component velocities in the range 100-150 km/s on spatial scales of 4-10 kpc. An independent constraint on the characteristic velocity and length scales of the gas motions is then found by considering the diffusion coefficient needed to explain the distribution of metals in the Centaurus cluster, combined with the need to balance the rate of gas cooling with the rate of heat dissipated by the gas motions. We find that these two methods of constraining the velocity and length scales of the gas motions are in good agreement.