CHEX-MATE: New detections and properties of the radio diffuse emission in massive clusters with MeerKAT

Abstract

Modern radio telescopes are revolutionising our understanding of non-thermal phenomena in galaxy clusters, collecting large samples of extended sources with unprecedented sensitivity and angular resolution. In this work, we present novel MeerKAT observations for a sample of 21 galaxy clusters that are part of the CHEX-MATE project. These systems were selected based on their high mass and displaying signs of dynamical activity. Thanks to the high-quality data at hand, we were able to detect extended radio emission in every target considered. We report two new halos, one new relic, and two new candidate relics. We also confirm a previous candidate halo and two candidate relics. After investigating the scaling relations with the cluster properties, we confirmed the presence of a radio halo power-mass correlation and relate it to a higher radio halo emissivity in more massive clusters. For radio relics, we highlight the MeerKAT capabilities to significantly extend the depth of radio observations to a new, unexplored field of low-radio power sources ($\lesssim 10^{23} ~ {\rm W~Hz^{-1}} $ at 1.28 GHz). Thanks to such high-sensitivity data, we have found that the radio relic power can be characterised by a wide range of values for a given cluster mass and relic size. Ultimately, we discuss how current radio observations, in combination with large radio surveys, are increasingly capable of testing numerical simulation predictions and coming close to performing direct comparisons with their data, enabling new insights on the evolution of radio relics.

Figures (26)

• Figure 1: Visual comparison of the whole CHEX-MATE sample and the studied cluster sample. Top: Mass-redshift distribution of the CHEX-MATE clusters (grey) with highlighted in red the targets considered in this work, alongside Tier-1 ($0.05 < \rm{z} < 0.2$ ; $M_{500}> 2 \times 10^{14}~M_{\odot}$) and Tier-2 (z$<0.6$; $\rm{M_{500}}>7.25 \times 10^{14}~M_{\odot}$ sub-samples. Bottom: Same comparison as the top panel, but for the $c-w$ plane. The dynamical classification is taken from C22, with up (down) triangles indicating objects with $\delta>0{\degree} ~ (<0{\degree})$, while the two dashed lines are the median value of the $c$ and $w$ parameters of CHEX-MATE.
• Figure 2: Radio (red with white contours) and X-ray (blue) overlays of the diffuse emission in the galaxy clusters covered by our new MeerKAT observations. We also report the cluster $R_{500}$ with a dashed white line.
• Figure 3: MeerKAT image of PSZ2G008.31-04.74. Top: Radio emission above $3\sigma_{\rm RMS}$ after the source subtraction of discrete sources (at 22 resolution and $\sigma_{RMS} = 12.6 ~\mu \rm{Jy ~ beam^{-1}}$) and with an inset showing the high-resolution ($\sim$ 7) map for the radio galaxy complex. X-ray contours are overlayed in black, starting at $2\times10^{-6}$ cts/s and spaced by a factor of $2$. Bottom: Spectral index map considering only the signal above $3\sigma_{\rm RMS}$ in the two bands used to derive $\alpha$, with overlayed the contours of the radio emission of the left image. Spectral index uncertainty maps are shown in Fig \ref{['fig:1err']}.
• Figure 4: Same as Fig. \ref{['fig:1']} but for PSZ2G056.93-55.08 (at 18 resolution and $\sigma_{RMS} = 11.6 ~\mu \rm{Jy ~ beam^{-1}}$), showing the spectral index map of the region B and C (at $\sim 7\arcsec$) and for the relic in the west. The spectral index uncertainty maps are shown in Fig \ref{['fig:2err']}.
• Figure 5: Same as Fig. \ref{['fig:1']}, but for PSZ2G172.98-53.55 (at 40 resolution and $\sigma_{RMS} = 40.8 ~\mu \rm{Jy ~ beam^{-1}}$)