Measuring the Hubble constant and our Virgo-infall velocity independently

Details Measuring the Hubble constant and our Virgo-infall velocity independently Measuring the Hubble constant and our Virgo-infall velocity independently

May 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...426..473l&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 426, no. 2, p. 473-485

Astronomy and Astrophysics

Astrophysics

13

Cosmology, Hubble Constant, Radio Emission, Spiral Galaxies, Velocity Measurement, Virgo Galactic Cluster, Astrophysics, Distance, Errors, Red Shift

Scientific paper

A sample of spiral galaxies with BT less than 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: HAB, the mean Hubble ratio between AV and BV, and delta vparallel, 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 sub-samples. The two sampled volumes, separated by a velocity interval of 5600 km/s, 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 HAB without increasing the Malmquist bias. By limiting our sample to spiral galaxies having large velocity widths WR, 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 disperison. 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 sigmaTF0 approximately 0.33 mag for WR approximately equal to or greater than 180 km/s. Our numerical results are delta vparallel approximately equals 414 +/- 82 km/s and HAB approximately equals (84.0 +/- 2.4)(1 + epsilon) km/s Mpc, 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 HAB of the uncertainties in the local velocity field. Constrained by our observed delta vparallel as well as other observational quantities, we found that the rms deviation from unity of HAB/H0 (where H0 is the Hubble constant for each model) is 5%, making HAB a good indicator for H0. Taking this variation as an additional error, our formal estimate for the Hubble constant is H0 approximately equals (84 +/- 5)(1 + epsilon) km/s Mpc.

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