The Effect of Helium Sedimentation on Galaxy Cluster Masses and Scaling Relations

TL;DR

This study investigates how helium sedimentation in galaxy clusters affects mass estimates and scaling relations, finding minimal impact on large-scale measurements but notable effects at smaller radii.

Contribution

It provides empirical constraints on helium sedimentation effects using Chandra data, highlighting their limited influence on cluster mass estimates and scaling relations.

Findings

Negligible increase in gas mass within large radii due to sedimentation

Approximately 10% decrease in total mass inferred at large radii

Significant effects at small radii with over 10% variation in gas and total mass

Abstract

Recent theoretical studies predict that the inner regions of galaxy clusters may have an enhanced helium abundance due to sedimentation over the cluster lifetime. If sedimentation is not suppressed (e.g., by tangled magnetic fields), this may significantly affect the cluster mass estimates. We use Chandra X-ray observations of eight relaxed galaxy clusters to investigate the upper limits to the effect of helium sedimentation on the measurement of cluster masses and the best-fit slopes of the Y_X - M_500 and Y_X - M_2500 scaling relations. We calculated gas mass and total mass in two limiting cases: a uniform, un-enhanced abundance distribution and a radial distribution from numerical simulations of helium sedimentation on a timescale of 11 Gyrs. The assumed helium sedimentation model, on average, produces a negligible increase in the gas mass inferred within large radii (r < r500) (1.3 +/- 1.2 per cent) and a (10.2 +/- 5.5) per cent mean decrease in the total mass inferred within r < r500. Significantly stronger effects in the gas mass (10.5 +/- 0.8 per cent) and total mass (25.1 +/- 1.1 per cent) are seen at small radii owing to a larger variance in helium abundance in the inner region, r < 0.1 r500. We find that the slope of the Y_X -M_500 scaling relation is not significantly affected by helium sedimentation.