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For refcode 1994ApJ...426..473L:
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1994ApJ...426..473L MEASURING THE HUBBLE CONSTANT AND OUR VIRGO-INFALL VELOCITY INDEPENDENTLY NANYAO Y. LU AND E. E. SALPETER Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853; lu@ipac.caltech.edu, hann@astrosun.tn.cornell.edu AND G. LYLE HOFFMAN Department of Physics, Lafayette College, Easton, PA 18042; hoffmang@astro.phys.lafayette.edu Received 1993 June 16; accepted 1993 November 11 ABSTRACT A sample of spiral galaxies with B_T_ < 14.5 located in two local volumes, one in the direction of, but behind, the Virgo Cluster (behind- Virgo volume [BV]) and the other in the opposite direction (anti-Virgo volume [AV]), were used via a Tully-Fisher (TF) relation to derive the following two parameters: H_AB_, the mean Hubble ratio between AV and BV, and {DELTA}{nu}_parallel_, the peculiar velocity of the Local Group in the direction of the Virgo Cluster (VC) with respect to a uniformly expanding reference system defined by our AV and BV subsamples. The two sampled volumes, separated by a velocity interval of 5600 km s^-1^, form an antipodal pair. This particular geometry not only allows us to derive the two parameters independently but also reduces the dynamical effect of the Local Supercluster on H_AB_ without increasing the Malmquist bias. By limiting our sample to spiral galaxies having large velocity widths W_R_, we effectively reduce the TF scatter and Malmquist bias in our sample. The TF zero point and dispersion were then determined by further correcting for the small residual Malmquist bias. An additional sample of fainter galaxies was used to test for a non-Gaussian tail to the TF dispersion. We found no evidence for such a tail and formally give an upper limit of about 18% for the fractional contribution of an unseen tail. The average intrinsic TF dispersion for the dominant Gaussian component is {sigma}_TF_^0^~0.33 mag for W_R_ ~> 180 km s^-1^. Our numerical results are {DELTA}{nu}_parallel_~ 414 +/- 82 km s^-1^ and H_AB_ ~(84.0 +/- 2.4)(1 + {epsilon}) km s^-1^ Mpc^-1^, where (1 + {epsilon}) accounts for any systematic error between the calibrators and the sample galaxies. Various dynamical models were tested to explore the effect on H_AB_ of the uncertainties in the local velocity field. Constrained by our observed {DELTA}{nu}_parallel_ as well as other observational quantities, we found that the rms deviation from unity of H_AB_/H_0_ (where H_0_ is the Hubble constant for each model) is 5%, making H_AB_ a good indicator for H_0_. Taking this variation as an additional error, our formal estimate for the Hubble constant is H_0_ ~ (84 +/- 5)(1 + {epsilon}) km s^-1^ Mpc^-1^. Subject headings: cosmology: observations - distance scale - galaxies: distances and redshifts - radio lines: galaxies
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