Observations of compact sources in galaxy clusters using MUSTANG2

TL;DR

This study uses MUSTANG2 observations at 90 GHz to measure compact sources in galaxy clusters, calibrates their impact on tSZE measurements, and highlights the need for high-resolution surveys to better understand source contamination.

Contribution

It provides the first empirical calibration between radio survey flux densities and source contamination in tSZE measurements using high-resolution data.

Findings

3% of ACT clusters have >20% decrease in Compton-y due to sources

3% of ACT clusters have >10% increase in Compton-y due to sources

High-resolution surveys are essential for accurate cluster detection and characterization

Abstract

Compact sources can cause scatter in the scaling relationships between the amplitude of the thermal Sunyaev-Zel'dovich Effect (tSZE) in galaxy clusters and cluster mass. Estimates of the importance of this scatter vary - largely due to limited data on sources in clusters at the frequencies at which tSZE cluster surveys operate. In this paper we present 90 GHz compact source measurements from a sample of 30 clusters observed using the MUSTANG2 instrument on the Green Bank Telescope. We present simulations of how a source's flux density, spectral index, and angular separation from the cluster's center affect the measured tSZE in clusters detected by the Atacama Cosmology Telescope (ACT). By comparing the MUSTANG2 measurements with these simulations we calibrate an empirical relationship between 1.4 GHz flux densities from radio surveys and source contamination in ACT tSZE measurements. We find 3 per cent of the ACT clusters have more than a 20 per cent decrease in Compton-y but another 3 per cent have a 10 per cent increase in the Compton-y due to the matched filters used to find clusters. As sources affect the measured tSZE signal and hence the likelihood that a cluster will be detected, testing the level of source contamination in the tSZE signal using a tSZE selected catalog is inherently biased. We confirm this by comparing the ACT tSZE catalog with optically and X-ray selected cluster catalogs. There is a strong case for a large, high resolution survey of clusters to better characterize their source population.