Chandra Measurements of a Complete Sample of X-ray Luminous Galaxy Clusters: the Gas Mass Fraction

TL;DR

This study uses Chandra X-ray data to measure the gas mass fraction in luminous galaxy clusters, finding values consistent with the cosmic baryon fraction at r500, resolving previous discrepancies.

Contribution

It provides the first comprehensive measurement of gas mass fractions in a complete sample of luminous clusters at z=0.15-0.30 using independent analyses.

Findings

Gas mass fraction at r500 is 0.163 +/- 0.032.

Measured gas fractions agree with cosmic baryon fraction.

Results reconcile previous conflicting measurements.

Abstract

We present Chandra X-ray measurements of the gas mass fraction out to r500 for a complete sample of the 35 most luminous clusters from the Brightest Cluster Sample and the Extended Brightest Cluster Sample at redshift z=0.15-0.30. The sample includes relaxed and unrelaxed clusters, and the data were analysed independently using two pipelines and two different models for the gas density and temperature. We measure an average of fgas(r500) = 0.163 +/- 0.032, which is in agreement with the cosmic baryon fraction (Omega_b / Omega_M = 0.167 +/- 0.006) at the 1-sigma level, after adding the stellar baryon fraction. Earlier studies reported gas mass fractions significantly lower than the cosmic baryon fraction at r500, and in some cases higher values that are consistent with the cosmic baryon fraction towards the virial radius.In this paper we show that the most X-ray luminous clusters in the redshift range z=0.15-0.30 have a gas mass fraction that is consistent with the cosmic value at r500.