Probing the Astrophysics of Cluster Outskirts

TL;DR

This paper models the entropy and temperature profiles of galaxy cluster outskirts, predicting steep declines in ICP temperature at low redshift, consistent with recent X-ray observations.

Contribution

It introduces a formalism linking entropy production reduction at boundary shocks to the cosmological evolution of cluster outskirts.

Findings

Predicted ICP temperature profiles steepen in cluster outskirts.

Model agrees with X-ray data for five observed clusters.

Steep temperature declines are expected at low redshift.

Abstract

In galaxy clusters the entropy distribution of the IntraCluster Plasma modulates the latter's equilibrium within the Dark Matter gravitational wells, as rendered by our Supermodel. We argue the entropy production at the boundary shocks to be reduced or terminated as the accretion rates of DM and intergalactic gas peter out; this behavior is enforced by the slowdown in the outskirt development at late times, when the Dark Energy dominates the cosmology while the outer wings of the initial perturbation drive the growth. In such conditions, we predict the ICP temperature profiles to steepen into the cluster outskirts. The detailed expectations from our simple formalism agree with the X-ray data concerning five clusters whose temperature profiles have been recently measured out to the virial radius. We predict steep temperature declines to prevail in clusters at low redshift, tempered only by rich environs including adjacent filamentary structures.