Brian Scott Mason

A Measurement of H0 from the Sunyaev-Zeldovich Effect

We present a determination of the Hubble constant, H0, from measurements of the Sunyaev-Zeldovich effect in an orientation-unbiased sample of seven z < 0.1 galaxy clusters. With improved X-ray models and a more accurate 32 GHz calibration, we obtain H0 = 64 ± 14sys km s-1 Mpc-1 for a standard cold dark matter (CDM) cosmology, or H0 = 66 ± 15sys km s-1 Mpc-1 for a flat ΛCDM cosmology. In combination with X-ray cluster measurements and the big bang nucleosynthesis value for ΩB, we find ΩM = 0.32 ± 0.05.

An Absolute Flux Density Measurement of the Supernova Remnant Cassiopeia A at 32 GHz

We report 32 GHz absolute flux density measurements of the supernova remnant Cas A, with an accuracy of 2.5%. The measurements were made with the 1.5 m telescope at the Owens Valley Radio Observatory. The antenna gain had been measured by NIST in May 1990 to be 0.505 ± 0.007 mK Jy-1. Our observations of Cas A in May 1998 yield Scas,1998 = 194 ± 5 Jy. We also report absolute flux density measurements of 3C 48, 3C 147, 3C 286, Jupiter, Saturn, and Mars.

Mass Models and Sunyaev-Zeldovich Effect Predictions for a Flux-Limited Sample of 22 Nearby X-Ray Clusters

We define a 90% complete, volume-limited sample of 31 z < 0.1 X-ray clusters and present a systematic analysis of public ROSAT PSPC data on 22 of these objects. Our efforts are undertaken in support of the Penn/OVRO Sunyaev-Zeldovich Effect (SZE) survey, and to this end we present predictions for the inverse Compton optical depth toward all 22 of these clusters. We have performed detailed Monte Carlo simulations in order to understand the effects of the cluster profile uncertainties on the SZE predictions given the OVRO 5.5 m telescope beam and switching patterns. We also present a similar analysis for the upcoming ACBAR experiment. For most of the clusters in the sample, we find less than a 5% uncertainty in the SZE predictions due to an imperfect knowledge of the profile. A comparison of different cooling-flow modeling strategies shows that our results are robust in this respect. The profile uncertainties are then one of the least significant components of our error budget for SZE-based distance measurements. The density models that result from this analysis also yield baryonic masses and, under the assumption of hydrostatic equilibrium, total masses and baryon mass fractions. Our Monte Carlo profile analysis indicates that the baryon masses within 1 h Mpc for these clusters are accurate to better than ~5% and unaffected by realistic PSPC systematics. In the sample as a whole, we find a mean gas mass fraction of (7.02 ? 0.28)h ? 10-2 internal to R500 ~ 1 h Mpc. This is in agreement with previous X-ray cluster analyses, which indicate an overabundance of baryons relative to the prediction of big bang nucleosynthesis for an ?M = 1 universe. Our analysis of the X-ray spectra confirms a previous claim of an excess absorbing column density toward A478, but we do not find evidence for anomalous column densities in the other 21 clusters. We also find some indications of an excess of soft counts in the ROSAT PSPC data. A measurement of H0 using these models and OVRO SZE determinations will be presented in a second paper.