Probing the origin of diffuse radio emission in the cool-core of the Phoenix galaxy cluster

TL;DR

This study investigates the origin of diffuse radio emission in the Phoenix galaxy cluster's cool core, revealing cold fronts, spiraling cool gas, and a minihalo, suggesting turbulence from gas sloshing as a potential source.

Contribution

It provides the first detailed radio and X-ray analysis of the Phoenix cluster's cool core, identifying cold fronts and a minihalo at a high redshift, and proposing turbulence as the origin of radio emission.

Findings

Detection of spiraling cool gas around the core.

Discovery of two cold fronts near the core.

Measurement of minihalo flux density and spectral index.

Abstract

Cool core galaxy clusters are considered to be dynamically relaxed clusters with regular morphology and highly X-ray luminous central region. However, cool core clusters can also be sites for merging events that exhibit cold fronts in X-ray and mini-halos in radio. We present recent radio/X-ray observations of the Phoenix Cluster or SPT-CL J2344-4243 at the redshift of $z=0.596$. Using archival {\it Chandra} X-ray observations, we detect spiraling cool gas around the cluster core as well as discover two cold fronts near the core. It is perhaps the most distant galaxy cluster to date known to host cold fronts. Also, we present JVLA\footnote{Jansky Very Large Array\\ \url{https://science.nrao.edu/facilities/vla}} 1.52 GHz observations of the minihalo, previously discovered at 610 MHz with GMRT\footnote{Giant Metrewave Radio Telescope\\ \url{http://www.gmrt.ncra.tifr.res.in}} observations in the center of the Phoenix galaxy cluster. The minihalo flux density at 1.52 GHz is $9.65 \pm 0.97$ mJy with the spectral index between 610 MHz and 1.52 GHz being $-0.98 \pm 0.16$\footnote{$S_{\nu} = \nu^{\alpha}$ where $S_{\nu}$}. A possible origin of these radio sources is turbulence induced by sloshing of the gas in the cluster core.