An improved measurement of the Hubble Constant using the Sunyaev -Zeldovich Effect

We present an improved measurement of the Hubble Constant (H 0) based on observations of the Sunyaev-Zeldovich Effect (SZE) in 5 nearby galaxy clusters from an x-ray flux-limited sample. This measurement incorporates cluster observations from the Owens Valley Radio Observatory (OVRO) 5.5-meter radio telescope, improved cluster models based on public ROSAT PSPC data, and an improved radio frequency absolute calibration based on observations with the OVRO 1.5-meter telescope. A 90% volume complete x-ray sample of 31 clusters with F x \u3c 1.0 × 10–11 erg cm –1 sec–1, Lx \u3e 1.13 × 1044 h–2 erg s–1, and z \u3c 0.1 is defined based on an x-ray duster sample existent in the literature. We analyze ROSAT PSPC data for 22 of these clusters, deriving masses and SZE predictions accurate to ∼5%. In conjunction with electron temperatures from the literature we find a mean gas mass fraction of (7.02 ± 0.28) h –3/2 × 10–2 at a radius of ∼1 h–1 Mpc. Our absolute calibration yields a flux density [special characters omitted] Jy at 32.0 GHz for the bright supernova remnant Cas-A, which becomes the basis for our SZE calibration. New observations of A399 were conducted from October 1996 through March 1997, yielding ΔTobs = –187 ± 21 μK. With our ROSAT model, this gives [special characters omitted] km s–1 Mpc–1. Observations of A478, Coma, A2142, and A2256, together with our models, yield [special characters omitted] and [special characters omitted] km s–1 Mpc–1 respectively. The sample average is [special characters omitted] km s–1 Mpc–1. This is the most accurate measurement of H0 from the SZE to date, and the only one based on an unbiased duster sample. Our result is in agreement with recent Cepheid-based determinations of the Hubble constant, as well as the results of other more traditional measurements, confirming the integrity of the local distance ladder