Letter to the Editor

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

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: xyzhang@strw.leidenuniv.nl
² SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
³ Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
⁴ Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁵ Dipartimento di Fisica e Astronomia, Università di Bologna, via Gobetti 93/2, 40122 Bologna, Italy
⁶ INAF – Istituto di Radioastronomia di Bologna, Via Gobetti 101, 40129 Bologna, Italy
⁷ Minnesota Institute for Astrophysics, University of Minnesota, 116 Church St. S.E., Minneapolis, MN 55455, USA
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁹ Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, IA 52242, USA

Received: 24 July 2020
Accepted: 14 September 2020

Abstract

We present an analysis of archival Chandra data of the merging galaxy cluster ClG 0217+70. The Fe XXV Heα 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 ± 0.006. We measure kT₅₀₀ = 8.3  ±  0.4 keV and estimate M₅₀₀ = (1.06 ± 0.11) × 10¹⁵ M_⊙ 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_X − P_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 r₂₀₀. 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 ± 0.16 and 3.0 ± 0.6, respectively. We also find a 700 × 200 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.