The Sunyaev-Zel'dovich effect in WMAP data

TL;DR

This study analyzes WMAP 5-year data to detect the average Sunyaev-Zel'dovich effect in galaxy clusters, comparing observations with X-ray based models, and explores the impact of gas profiles and point source contamination on the measurements.

Contribution

It provides the first high-significance detection of the average SZE in WMAP data and investigates the discrepancies with X-ray models, considering point source contamination and alternative gas profiles.

Findings

Detected the average SZE at high significance in WMAP data.

Standard beta-models underestimate the SZE signal compared to X-ray predictions.

Point source contamination may account for part of the SZE signal discrepancy.

Abstract

Using WMAP 5 year data, we look for the average Sunyaev-Zel'dovich effect (SZE) signal from clusters of galaxies by stacking the regions around hundreds of known X-ray clusters. We detect the average SZE at a very high significance level. The average cluster signal is spatially resolved in the W band. This mean signal is compared with the expected signal from the same clusters calculated on the basis of archival ROSAT data. From the comparison we conclude that the observed SZE seems to be less than the expected signal derived from X-ray measurements when a standard beta-model is assumed for the gas distribution. This conclusion is model dependent. Our predictions depend mostly on the assumptions made about the core radius of clusters and the slope of the gas density profile. Models with steeper profiles are able to simultaneously fit both X-ray and WMAP data better than a beta-model. However, the agreement is not perfect and we find that it is still difficult to make the X-ray and SZE results agree. A model assuming point source contamination in SZE clusters renders a better fit to the one-dimensional SZE profiles thus suggesting that contamination from point sources could be contributing to a diminution of the SZE signal. Selecting a model that better fits both X-ray and WMAP data away from the very central region, we estimate the level of contamination and find that on average, the point source contamination is on the level of 16 mJy (at 41 GHz), 26 mJy (at 61 GHz) and 18 mJy (at 94 GHz). These estimated fluxes are marginally consistent with the estimated contamination derived from radio and infrared surveys thus suggesting that the combination of a steeper gas profile and the contribution from point sources allows us to consistently explain the X-ray emission and SZE in galaxy clusters as measured by ROSAT and WMAP.