Effect of Helium Sedimentation on X-ray Measurements of Galaxy Clusters

Understand

The uniformity of the helium-to-hydrogen abundance ratio in X-ray emitting intracluster medium (ICM) is one of the commonly adopted assumptions in X-ray analyses of galaxy clusters and cosmological constraints derived from these measurements.

• In this work, we investigate the effect of He sedimentation on X-ray measurements of galaxy clusters in order to assess this assumption and associated systematic uncertainties.
• By solving a set of flow equations for a H-He plasma, we show that the helium-to-hydrogen mass ratio is significantly enhanced in the inner regions of clusters.
• The effect of He sedimentation, if not accounted for, introduces systematic biases in observable properties of clusters derived using X-ray observations.