Properties of gas clumps and gas clumping factor in the intra cluster medium

TL;DR

This study uses high-resolution cosmological simulations to analyze gas clumping in galaxy clusters, revealing how unresolved clumping biases X-ray measurements and assessing the detectability of bright gas clumps with current X-ray instruments.

Contribution

It provides new insights into the impact of gas clumping on X-ray derived cluster parameters and evaluates the observability of bright gas clumps in the nearby universe.

Findings

Unresolved gas clumping causes 10-20% uncertainty in baryon fraction estimates.

Some bright gas clumps are already detectable with current X-ray instruments.

Preheating, AGN feedback, and cosmic rays minimally affect gas clump statistics.

Abstract

The spatial distribution of gas matter inside galaxy clusters is not completely smooth, but may host gas clumps associated with substructures. These overdense gas substructures are generally a source of unresolved bias of X-ray observations towards high density gas, but their bright luminosity peaks may be resolved sources within the ICM, that deep X-ray exposures may be (already) capable to detect. In this paper we aim at investigating both features, using a set of high-resolution cosmological simulations with ENZO. First, we monitor how the bias by unresolved gas clumping may yield incorrect estimates of global cluster parameters and affects the measurements of baryon fractions by X-ray observations. We find that based on X-ray observations of narrow radial strips, it is difficult to recover the real baryon fraction to better than 10 - 20 percent uncertainty. Second, we investigated the possibility of observing bright X-ray clumps in the nearby Universe (z<=0.3). We produced simple mock X-ray observations for several instruments (XMM, Suzaku and ROSAT) and extracted the statistics of potentially detectable bright clumps. Some of the brightest clumps predicted by simulations may already have been already detected in X- ray images with a large field of view. However, their small projected size makes it difficult to prove their existence based on X-ray morphology only. Preheating, AGN feedback and cosmic rays are found to have little impact on the statistical properties of gas clumps.