The Influence of Mergers on Scatter and Evolution in Sunyaev-Zel'dovich Effect Scaling Relations

TL;DR

This paper investigates how galaxy cluster mergers affect the Sunyaev-Zel'dovich effect scaling relation, revealing that accounting for non-thermal pressure from gas motions reduces bias and scatter, improving mass estimates for cosmology.

Contribution

It demonstrates that including non-thermal pressure from merger-induced gas motions significantly improves the accuracy of the SZE Y-M scaling relation.

Findings

Non-thermal pressure contributes to bias and scatter in the Y-M relation.

Post-merger, thermal SZE signal increases as turbulent energy dissipates.

Accounting for non-thermal energy reduces scatter by 20-30%.

Abstract

The Sunyaev-Zel'dovich effect (SZE) observable-mass (Y-M) scaling relation is a promising technique for obtaining mass estimates for large samples of galaxy clusters and holds a key to studying the nature of dark matter and dark energy. However, cosmological inference based on SZE cluster surveys is limited by our incomplete knowledge of bias, scatter, and evolution in the Y-M relation. In this work, we investigate the effects of galaxy cluster mergers on the scaling relation using the Omega500 high-resolution cosmological hydrodynamic simulation. We show that the non-thermal pressure associated with merger-induced gas motions contributes significantly to the bias, scatter, and evolution of the scaling relation. After the merger, the kinetic energy of merging systems is slowly converted into thermal energy through dissipation of turbulent gas motions, which causes the thermal SZE signal to increase steadily with time. This post-merger evolution is one of the primary source of bias and scatter in the Y-M relation. However, we show that when the missing non-thermal energy is accounted for, the resulting relation exhibits little to no redshift evolution and the scatter around the scaling relation is ~20-30 % smaller than that of the thermal SZE signal alone. Our work opens up a possibility to further improve the current robust mass proxy, Y, by accounting for the missing non-thermal pressure component. We discuss future prospect of measuring internal gas motions in galaxy clusters and its implication for cluster-based cosmological tests.