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