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Published November 1, 2004 | Published + Accepted Version
Journal Article Open

An Unbiased Measurement of H_0 through Cosmic Background Imager Observations of the Sunyaev-Zel'dovich Effect in Nearby Galaxy Clusters


We present H_0 results from Cosmic Background Imager (CBI) observations of the Sunyaev-Zel'dovich effect (SZE) in seven galaxy clusters, A85, A399, A401, A478, A754, A1651, and A2597. These observations are part of a program to study a complete, volume-limited sample of low-redshift (z < 0.1), X-ray-selected clusters. Our focus on nearby objects allows us to study a well-defined, orientation-unbiased sample, minimizing systematic errors due to cluster asphericity. We use density models derived from ROSAT imaging data and temperature measurements from ASCA and BeppoSAX spectral observations. We quantify in detail sources of error in our derivation of H_0, including calibration of the CBI data, density, and temperature models from the X-ray data, cosmic microwave background primary anisotropy fluctuations, and residuals from radio point source subtraction. From these seven clusters we obtain a result of H_0 = 67_(-18-6)^(+30+15) km s^(-1) Mpc^(-1) for an unweighted sample average. The respective quoted errors are random and systematic uncertainties at 68% confidence. The dominant source of error is confusion from intrinsic anisotropy fluctuations.

Additional Information

© 2004. The American Astronomical Society. Receivved 2003 June 17; accepted 2004 July 7. We gratefully acknowledge Hans Böhringer and the REFLEX team for sharing with us their cluster data in advance of publication. We thank Jonathan Sievers and Monique Arnaud for useful discussions, and the anonymous referee for helpful suggestions that improved the organization of the paper. Steve Myers' early work in this field set the stage for this project, and we acknowledge his assistance throughout. We are most grateful to Steve Padin, Martin Shepherd and John Cartwright for their many invaluable contributions to the CBI. We acknowledge the invaluable efforts of Russ Keeney, Steve Miller, Angel Otarola, Walter Schaal, and John Yamasaki at various stages of the project. We gratefully acknowledge the generous support of Maxine and Ronald Linde, Cecil and Sally Drinkward, Barbara and Stanley Rawn, Jr., and Fred Kavli, and the strong support of the provost and president of the California Institute of Technology, the PMA division Chairman, the director of the Owens Valley Radio Observatory, and our colleagues in the PMA Division. This work was supported by the National Science Foundation under grants AST 94-13935, AST 98-02989, and AST 00-98734. P. S. U. acknowledges support from an NSF Graduate Student Fellowship. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

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