The Universal Gas Mass Fraction in Clusters of Galaxies

TL;DR

This study measures the gas mass fraction in galaxy cluster RCS 2318+0034 using deep Chandra X-ray observations, finding it consistent with X-ray selected clusters on large scales but lower in the core, possibly due to ongoing merger activity.

Contribution

First detailed measurement of gas mass fraction in an optically selected galaxy cluster using deep X-ray data, revealing scale-dependent variations and merger effects.

Findings

Gas mass fraction within r500 is typical of X-ray selected clusters.

Gas mass fraction within r2500 is lower than in most X-ray selected clusters.

Cluster undergoing a major merger affecting core gas properties.

Abstract

We obtained a deep 150ksec Chandra observation of the optically selected cluster of galaxies, RCS 2318+0034, to investigate the gas mass fraction in this system. Combining our deep {\it Chandra} observation with an archival 50ksec observation, we derive gas mass fractions of fgas=0.06 +- 0.02 and 0.10 +- 0.02 within r2500 and r500, respectively. The gas mass fraction in RCS 2318+0034 within r500 is typical of X-ray selected clusters. Further study shows that the large scale properties of RCS 2318+0034, including the relations between gas mass, X-ray luminosity and gas temperature are also consistent with the observed correlations of X-ray selected clusters. However, the gas mass fraction within r2500 is less than most X-ray selected clusters, as previously reported. The deep Chandra image of RCS 2318+0034 shows that this system is presently undergoing a major merger which may have an impact on the inferred gas mass fraction within r2500.