Deep Chandra observations of PLCKG287.0+32.9: A clear detection of a shock front in a heated former cool core

¹ Dipartimento di Fisica e Astronomia (DIFA), Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
² Istituto Nazionale di Astrofisica (INAF) – Istituto di Radioastronomia (IRA), Via Gobetti 101, I-40129 Bologna, Italy
³ University of California Observatories/Lick Observatory, Dept. of Astronomy and Astrophysics, Santa Cruz, CA 95064, USA
⁴ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano, Via A. Corti 12, 20133 Milano, Italy
⁵ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁶ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
⁷ University of Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

^⋆ Corresponding author: myriam.gitti@unibo.it

Received: 14 December 2024
Accepted: 17 March 2025

Abstract

Context. The massive, hot galaxy cluster PSZ2 G286.98+32.90 (hereafter PLCKG287, z = 0.383) hosts a giant radio halo and two prominent radio relics that are signs of a disturbed dynamical state. Gravitational lensing analysis shows a complex cluster core with multiple components. However, despite optical and radio observations indicating a clear multiple merger, the X-ray emission of the cluster, derived from XMM-Newton observations, shows only moderate disturbance.

Aims. The aim of this work is to study the X-ray properties and investigate the core heating of such a massive cluster by searching for surface brightness discontinuities and associated temperature jumps that would indicate the presence of shock waves.

Methods. We present new 200 ks Chandra X-ray Observatory ACIS-I observations of PLCKG287 and perform a detailed analysis to investigate the morphological and thermodynamical properties of the region inside R₅₀₀ (∼1.5 Mpc).

Results. The global X-ray morphology of the cluster has a comet-like shape, oriented in the NW-SE direction, with an ∼80 kpc offset between the X-ray peak and the brightest cluster galaxy (BCG). We detect a shock front in the NW direction at a distance of ∼390 kpc from the X-ray peak, characterized by a Mach number of ℳ ∼ 1.3, as well as a cold front at a distance of ∼300 kpc from the X-ray peak, nested in the same direction as the shock in a typical configuration expected for a merger. We also find evidence for X-ray depressions to the E and W, which could be the signature of feedback from the active galactic nucleus (AGN). The radial profile of the thermodynamic quantities shows a temperature and abundance peak in the cluster’s center, where the pressure and entropy also exhibit a rapid increase.

Conclusions. Based on these properties, we argue that PLCKG287 is what remains of a cool core after a heating event. We estimate that both the shock energy and the AGN feedback energy, implied by the analysis of the X-ray cavities, are sufficient to heat the core to the observed temperature of ∼17 keV in the central ≈160 kpc. We discuss the possible origin of the detected shock by investigating alternative scenarios of merger and AGN outburst, finding that they are both energetically viable. However, no single model seems able to explain all the X-ray features detected in this system. This suggests that the combined action of merger and central AGN feedback is likely necessary to explain the reheated cool core, the large-scale shock, and the cold front. The synergy of these two processes may act to shape the distribution of cool core and non-cool core clusters.