H0 from an orientation-unbiased sample of SZ and X-ray clusters

We have observed the Sunyaev-Zel'dovich effect in a sample of five moderate-redshift clusters with the Ryle Telescope, and used them in conjunction with X-ray imaging and spectral data from ROSAT and ASCA to measure the Hubble constant. This sample was chosen with a strict X-ray flux limit using both the BCS and NORAS cluster catalogues to be well above the surface-brightness limit of the ROSAT All-Sky Survey, and hence to be unbiased with respect to the orientation of the cluster. This controls the major potential systematic effect in the SZ/X-ray method of measureing H0. Taking the weighted geometric mean of the results and including the main sources of random error, namely the noise in the SZ measurement, the uncertainty in the X-ray temperatures and the unknown ellipticity of the clusters, we find H0 = 59 +8/-7 km/s/Mpc assuming a standard CDM model with Omega_M = 1.0, Omega_Lambda = 0.0, or H0 = 65 +8/-7 km/s/Mpc if Omega_M = 0.3, Omega_Lambda = 0.7.