ClG 0217+70: A massive merging galaxy cluster with a large radio halo and relics

Abstract

We present an analysis of archival Chandra data of the merging galaxy cluster ClG 0217+70. The Fe XXV He$\alpha$ X-ray emission line is clearly visible in the 25 ks observation, allowing a precise determination of the redshift of the cluster as $z=0.180\pm0.006$. We measure $kT_{500}=8.3\pm0.4$ keV and estimate $M_{500}=(1.06\pm0.11)\times10^{15}\ M_\odot$ based on existing scaling relations. Correcting both the radio and X-ray luminosities with the revised redshift reported here, which is much larger than previously inferred based on sparse optical data, this object is no longer an X-ray underluminous outlier in the $L_\mathrm{X}-P_\mathrm{radio}$ scaling relation. The new redshift also means that, in terms of physical scale, ClG 0217+70 hosts one of the largest radio halos and one of the largest radio relics known to date. Most of the relic candidates lie in projection beyond $r_{200}$. The X-ray morphological parameters suggest that the intracluster medium is still dynamically disturbed. Two X-ray surface brightness discontinuities are confirmed in the northern and southern parts of the cluster, with density jumps of $1.40\pm0.16$ and $3.0\pm0.6$, respectively. We also find a $700\times200$ kpc X-ray faint channel in the western part of the cluster, which may correspond to compressed heated gas or increased non-thermal pressure due to turbulence or magnetic fields.