On the Cluster Physics of Sunyaev-Zel'dovich Surveys II: Deconstructing the Thermal SZ Power Spectrum

TL;DR

This paper investigates the thermal Sunyaev-Zel'dovich (tSZ) effect's power spectrum using simulations to understand how intracluster medium structure influences cosmological measurements, highlighting the importance of substructure and cluster radii.

Contribution

It provides a detailed empirical pressure profile fit from simulations and compares analytical, semi-analytical, and numerical methods for calculating the tSZ power spectrum.

Findings

Substructure and asphericity increase the tSZ power spectrum by 10-20%.

Most of the tSZ power at ell ~2000-8000 comes from cluster substructures.

Cluster interiors (r < R_500) dominate the tSZ power spectrum at relevant angular scales.

Abstract

Secondary anisotropies in the cosmic microwave background are a treasure-trove of cosmological information. Interpreting current experiments probing them are limited by theoretical uncertainties rather than by measurement errors. Here we focus on the secondary anisotropies resulting from the thermal Sunyaev-Zel'dovich (tSZ) effect; the amplitude of which depends critically on the average thermal pressure profile of galaxy groups and clusters. To this end, we use a suite of SPH simulations that include radiative cooling, star formation, supernova feedback, and energetic feedback from active galactic nuclei (AGN). We examine in detail how the pressure profile depends on cluster radius, mass, and redshift and provide an empirical fitting function. We employ three different approaches for calculating the tSZ power spectrum: an analytical approach that uses our pressure profile fit, a semi-analytical method of pasting our pressure fit onto simulated clusters, and a direct numerical integration of our simulated volumes. We demonstrate that the detailed structure of the intracluster medium and cosmic web affect the tSZ power spectrum. In particular, the substructure and asphericity of clusters increase the tSZ power spectrum by 10-20% at ell ~2000-8000, with most of the additional power being contributed by substructures. The contributions to the power spectrum from radii larger than R_500 is ~ 20% at ell = 3000, thus clusters interiors (r < R_500) dominate the power spectrum amplitude at these angular scales.