WMAP constraints on the Intra-Cluster Medium

Abstract

We devise a Monte-Carlo based, optimized filter match method to extract the thermal Sunyaev-Zel&#39;dovich (SZ) signature of a catalog of 116 low-redshift X-ray clusters from the first year data release of the Wilkinson Microwave Anisotropy Probe (WMAP). We detect an over-all amplitude for the SZ signal at the ~ 8-sigma level, yielding a combined constraint of f_{gas}h = 0.08 +/- 0.01 (ran) +/- 0.01 (sys) on the gas mass fraction of the Intra-Cluster Medium. We also compile X-ray estimated gas fractions from the literature for our sample, and find that they are consistent with the SZ estimates at the 2-sigma level, while both show an increasing trend with X-ray temperature. Nevertheless, our SZ estimated gas fraction is 30-40% smaller than the concordance LCDM cosmic average. We also express our observations in terms of the SZ flux-temperature relation, and compare it with other observations, as well as numerical studies. Based on its spectral and spatial signature, we can also extract the microwave point source signal of the clusters at the 3-sigma level, which puts the average microwave luminosity (at ~ 41 GHz) of bright cluster members (M_K < -21) at (2.4 +/- 0.8) x 10^{27} h^{-2} erg/s/Hz. Furthermore, we can constrain the average dark matter halo concentration parameter to c_{vir}=3.4+0.6-0.9, for clusters with T_x > 5 kev. Our work serves as an example for how correlation of SZ surveys with cluster surveys in other frequencies can significantly increase our physical understanding of the intra-cluster medium.