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For refcode 2001ApJ...548..564W:
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2001ApJ...548..564W A Determination of the Hubble Constant from Cepheid Distances and a Model of the Local Peculiar Velocity Field Jeffrey A. Willick and Puneet Batra Department of Physics, 382 Via Pueblo Mall, Varian Physics Building, Stanford University, Stanford, CA 94305; pbatra@perseus.stanford.edu Received 2000 May 22; accepted 2000 October 18 ABSTRACT We present a measurement of the Hubble constant based on Cepheid distances to 27 galaxies within 20 Mpc. We take the Cepheid data from published measurements by the Hubble Telescope Key Project on the Distance Scale (H_0_KP). We calibrate the Cepheid period-luminosity (PL) relation with data from over 700 Cepheids in the LMC obtained by the OGLE collaboration; we assume an LMC distance modulus of 18.50 mag (d_LMC_ = 50.1 kpc). Using this PL calibration, we obtain new distances to the H_0_KP galaxies. We correct the redshifts of these galaxies for peculiar velocities using two distinct velocity field models: the phenomenological model of Tonry et al. and a model based on the IRAS density field and linear gravitational instability theory. We combine the Cepheid distances with the corrected redshifts for the 27 galaxies to derive H_0_, the Hubble constant. The results are H_0_ = 85 +/- 5 km s^-1^ Mpc^-1^ (random error) at 95% confidence when the IRAS model is used, and 92 +/- 5 km s^-1^ Mpc^- 1^ when the phenomenological model is used. The IRAS model is a better fit to the data, and the Hubble constant it returns is more reliable. Systematic error stems mainly from LMC distance uncertainty, which is not directly addressed by this paper. Our value of H_0_ is significantly larger than that quoted by the H_0_KP, H_0_ = 71 +/- 6 km s^-1^ Mpc^-1^. Cepheid recalibration explains ~30% of this difference, and velocity field analysis accounts for ~70%. We discuss in detail possible reasons for this discrepancy and future studies needed to resolve it. Subject headings: cosmology: observations-distance scale-galaxies: distances and redshifts
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