Chandra and XMM-Newton observations of the merging cluster of galaxies PLCK G036.7+14.9

TL;DR

This study uses Chandra and XMM-Newton X-ray observations to analyze the merging galaxy cluster PLCK G036.7+14.9, revealing two subclusters and highlighting the importance of high-resolution imaging for accurate mass estimation in cosmology.

Contribution

First detailed high-resolution X-ray analysis of PLCK G036.7+14.9 revealing subcluster structure and merger dynamics, addressing mass estimation discrepancies in Planck cluster data.

Findings

Two subclusters identified with different cool-core properties.

Mass estimates from Planck are biased due to unresolved substructure.

Merger is likely at an early stage with line-of-sight orientation.

Abstract

We present Chandra and XMM-Newton observations of PLCK G036.7+14.9 from the Chandra-Planck Legacy Program. The high resolution X-ray observations reveal two close subclusters, G036N and G036S, which were not resolved by previous ROSAT, optical, or recent Planck observations. We perform detailed imaging and spectral analyses and use a simplified model to study the kinematics of this system. The basic picture is that PLCK G036.7+14.9 is undergoing a major merger (mass ratio close to unity) between the two massive subclusters, with the merger largely along the line-of-sight and probably at an early stage. G036N hosts a small, moderate cool-core, while G036S has at most a very weak cool-core in the central 40 kpc region. The difference in core cooling times is unlikely to be caused by the ongoing merger disrupting a pre-existing cool-core in G036S. G036N also hosts an unresolved radio source in the center, which may be heating the gas if the radio source is extended. The Planck derived mass is higher than the X-ray measured mass of either subcluster, but is lower than the X-ray measured mass of the whole cluster, due to the fact that Planck does not resolve PLCK G036.7+14.9 into subclusters and interprets it as a single cluster. This mass discrepancy could induce significant bias to the mass function if such previously unresolved systems are common in the Planck cluster sample. High resolution X-ray observations are necessary to identify the fraction of such systems and correct such a bias for the purpose of precision cosmological studies.