Cool Core Bias in Sunyaev-Zel'dovich Galaxy Cluster Surveys

TL;DR

This paper investigates how cool cores and radio emissions in galaxy clusters bias Sunyaev-Zel'dovich survey measurements, quantifying the impact on cluster detection significance across different redshifts and properties.

Contribution

It provides the first detailed quantitative analysis of cool core and radio emission biases on SZ cluster detection, with estimates applicable to various surveys.

Findings

Cool cores can increase SZ significance by up to 10% at z > 0.3.

Bias in SZ signal depends on cuspiness, redshift, and radio luminosity.

For the Phoenix cluster, cool core bias inflates SZ significance by about 6%.

Abstract

Sunyaev-Zeldovich (SZ) surveys find massive clusters of galaxies by measuring the inverse Compton scattering of cosmic microwave background off of intra-cluster gas. The cluster selection function from such surveys is expected to be nearly independent of redshift and cluster astrophysics. In this work, we estimate the effect on the observed SZ signal of centrally-peaked gas density profiles (cool cores) and radio emission from the brightest cluster galaxy (BCG) by creating mock observations of a sample of clusters that span the observed range of classical cooling rates and radio luminosities. For each cluster, we make simulated SZ observations by the South Pole Telescope and characterize the cluster selection function, but note that our results are broadly applicable to other SZ surveys. We find that the inclusion of a cool core can cause a change in the measured SPT significance of a cluster between 0.01% - 10% at z > 0.3, increasing with cuspiness of the cool core and angular size on the sky of the cluster (i.e., decreasing redshift, increasing mass). We provide quantitative estimates of the bias in the SZ signal as a function of a gas density cuspiness parameter, redshift, mass, and the 1.4 GHz radio luminosity of the central AGN. Based on this work, we estimate that, for the Phoenix cluster (one of the strongest cool cores known), the presence of a cool core is biasing the SZ significance high by ~ 6%. The ubiquity of radio galaxies at the centers of cool core clusters will offset the cool core bias to varying degrees.