Very Small Array observations of the SunyaevZel'dovich effect in nearby galaxy clusters
Abstract
We present Very Small Array (VSA) observations (centred on ~34 GHz) on scales ~20 arcmin towards a complete, Xray fluxlimited sample of seven clusters at redshift z < 0.1. Four of the clusters have significant SunyaevZel'dovich (SZ) detections in the presence of cosmic microwave background (CMB) primordial anisotropy. For all seven, we use a Bayesian Markov Chain Monte Carlo (MCMC) method for inference from the VSA data, with Xray priors on cluster positions and temperatures, and radio priors on sources. In this context, the CMB primordial fluctuations are an additional source of Gaussian noise, and are included in the model as a nondiagonal covariance matrix derived from the known angular power spectrum. In addition, we make assumptions of βmodel gas distributions and of hydrostatic equilibrium, to evaluate probability densities for the gas mass (M_{gas}) and total mass (M_{r}) out to r_{200}, the radius at which the average density enclosed is 200 times the critical density at the redshift of the cluster. This is further than has been done before and close to the classical value for a collapsed cluster. Our combined estimate of the gas fraction (f_{gas}=M_{gas}/M_{r}) is 0.08^{+0.06}_{0.04}h^{1}. The random errors are poor (note, however, that the errors are higher than would have been obtained with the usual χ^{2} method on the same data) but the control of bias is good. We have described the MCMC analysis method specifically in terms of SZ but hope the description will be of more general use. We find that the effects of primordial CMB contamination tend to be similar in the estimates of both M_{gas} and M_{r} over the narrow range of angular scales we are dealing with, so that there is little effect of primordials on f_{gas} determination. Using our M_{r} estimates we find a normalization of the masstemperature relation based on the profiles from the VSA cluster pressure maps, which is in good agreement with recent MT determinations from Xray cluster measurements.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 May 2005
 DOI:
 10.1111/j.13652966.2005.08696.x
 arXiv:
 arXiv:astroph/0405582
 Bibcode:
 2005MNRAS.359...16L
 Keywords:

 galaxies: clusters: general;
 cosmic microwave background;
 cosmology: observations;
 Xrays: galaxies: clusters;
 Astrophysics
 EPrint:
 Replaces earlier version. 16 pages, 5 figures, LaTeX. Minor revisions to content, accepted by MNRAS for publication