Measurement of the electron-pressure profile of galaxy clusters in Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data

TL;DR

This study uses WMAP 3-year data to measure the electron-pressure profile of galaxy clusters via the thermal Sunyaev-Zeldovich effect, revealing large-scale pressure distributions and dark matter dominance at cluster outskirts.

Contribution

It provides the first high-significance detection of the TSZ effect out to large radii and shows the baryon profile aligns with the Navarro-Frenk-White dark matter profile, challenging simple isothermal models.

Findings

TSZ effect detected at 15σ significance

Pressure profile extends to ~3 Mpc, larger than X-ray emitting region

Dark matter dominates cluster dynamics at large radii

Abstract

Using WMAP 3-year data at the locations of close to $\sim 700$ X-ray selected clusters we have detected the amplitude of the thermal Sunyaev-Zeldovich (TSZ) effect at the 15$\sigma$ level, the highest statistical significance reported so far. Owing to the large size of our cluster sample, we are able to detect the corresponding CMB distortions out to large cluster-centric radii. The region over which the TSZ signal is detected is, on average, four times larger in radius than the X-ray emitting region, extending to $\sim 3h_{70}^{-1}$Mpc. We show that an isothermal $\beta$ model does not fit the electron pressure at large radii; instead, the baryon profile is consistent with the Navarro-Frenk-White profile, expected for dark matter in the concordance $\Lambda$CDM model. The X-ray temperature at the virial radius of the clusters falls by a factor $\sim 3-4$ from the central value, depending on the cluster concentration parameter. Our results suggest that cluster dynamics at large radii is dominated by dark matter and is well described by Newtonian gravity.