Limits and challenges of the detection of cluster-scale diffuse radio emission at high redshift

Abstract

Diffuse radio emission in galaxy clusters is a tracer of ultra-relativistic particles and μG-level magnetic fields, and is thought to be triggered by cluster merger events. In the distant Universe (i.e. z > 0.6), such sources have been observed only in a handful of systems, and their study is important to understand the evolution of large-scale magnetic fields over the cosmic time. Previous studies of nine Planck clusters up to z ∼ 0.9 suggest a fast amplification of cluster-scale magnetic fields, at least up to half of the current Universe’s age, and steep spectrum cluster scale emission, in line with particle re-acceleration due to turbulence. In this paper, we investigate the presence of diffuse radio emission in a larger sample of galaxy clusters reaching even higher redshifts (i.e. z ≳ 1). We selected clusters from the Massive and Distant Clusters of WISE Survey (MaDCoWS) with richness λ_{15 > 40 covering the area of the second data release of the LOFAR Two-Meter Sky Survey (LoTSS-DR2) at 144 MHz. These selected clusters are in the redshift range 0.78 − 1.53 (with a median value of 1.05). We detect the possible presence of diffuse radio emission, with the largest linear sizes of 350 − 500 kpc, in five out of the 56 clusters in our sample. If this diffuse radio emission is due to a radio halo, these radio sources lie on or above the scatter of the Pν − M500 radio halo correlations (at 150 MHz and 1.4 GHz) found at z < 0.6, depending on the mass assumed. We also find that these radio sources are at the limit of the detection by LoTSS, and therefore deeper observations are important for future studies.}