The impact of halo concentration on the Sunyaev Zel'dovich effect signal from massive galaxy clusters

TL;DR

This paper explores how the concentration of galaxy clusters affects the Sunyaev Zel'dovich (SZ) signal, revealing that outer SZ profiles are influenced by gas pressure truncation near splashback radius, which impacts cosmological measurements.

Contribution

The study introduces a simple model for gas pressure truncation at splashback radius, improving the understanding of concentration effects on SZ signals in galaxy clusters.

Findings

Inner SZ profiles are well modeled by polytropic gas models.

Outer SZ profiles are affected by gas pressure truncation near splashback radius.

Ignoring concentration dependence can bias splashback radius measurements by up to 2%.

Abstract

The Sunyaev Zel'dovich (SZ) effect is sensitive to the pressure of ionized gas inside galaxy clusters, which is in turn controlled largely by the gravitational potential of the cluster. Changing the concentration parameter describing the cluster mass distribution impacts the gravitational potential and thus the cluster SZ signal, with implications for cosmological and other analyses of SZ-selected clusters. We investigate the concentration-SZ relation in theory and simulations. We find that the impact of concentration on the inner SZ profile ($R \lesssim 0.75 R_{200c}$) can be captured with standard polytropic gas models. However, we find that such models do a poor job of reproducing the outer SZ profiles ($R \gtrsim 0.75 R_{200c}$) and the relation between the integrated SZ signal, $Y$, and concentration. This disagreement results from a sharp truncation of the gas pressure profile near the splashback radius, likely caused by virial shocks. We develop a simple description of the truncation that leads to a good match with the simulated SZ profiles out to several $R_{200c}$ for clusters of varying mass and concentration, and that also accurately predicts the concentration-$Y$ relationship. Finally, we determine how inference of the linear bias parameter and splashback radius for SZ-selected clusters can be biased by ignoring the concentration dependence of the SZ signal, finding that bias to the former is essentially negligible, while bias to the latter can be as much as 2\%.