OMEGA AND BIASING FROM OPTICAL GALAXIES VERSUS POTENT MASS

The mass density field in the local universe, recovered by the POTENT method from peculiar velocities of $\sim$3000 galaxies, is compared with the density field of optically-selected galaxies. Both density fields are smoothed with a Gaussian filter of radius 12 $h^{-1}$ Mpc. Under the assumptions of gravitational instability and a linear biasing parameter b\sbo between optical galaxies and mass, we obtain \beta\sbo \equiv \om^{0.6}/b\sbo = 0.74 \pm 0.13. This result is obtained from a regression of POTENT mass density on optical density after correcting the mass density field for systematic biases in the velocity data and POTENT method. The error quoted is just the $1\sigma$ formal error estimated from the observed scatter in the density--density scatterplot; it does not include the uncertainty due to cosmic scatter in the mean density or in the biasing relation. We do not attempt a formal analysis of the goodness of fit, but the scatter about the fit is consistent with our estimates of the uncertainties.Comment: Final revised version (minor typos corrected). 13 pages, gzipped tar file containing LaTeX and figures. The Postscript file is available at ftp://dust0.dur.ac.uk/pub/mjh/potopt/potopt.ps.Z or (gzipped) at ftp://xxx.lanl.gov/astro-ph/ps/9501/9501074.ps.gz or via WWW at http://xxx.lanl.gov/ps/astro-ph/9501074 or as separate LaTeX text and encapsulated Postscript figures in a compressed tar'd file at ftp://dust0.dur.ac.uk/pub/mjh/potopt/latex/potopt.tar.

Shellflow. I. The Convergence of the Velocity Field at 6000 km/s

We present the first results from the Shellflow program, an all-sky Tully-Fisher (TF) peculiar velocity survey of 276 Sb-Sc galaxies with redshifts between 4500 and 7000 km/s. Shellflow was designed to minimize systematic errors between observing runs and between telescopes, thereby removing the possibility of a spurious bulk flow caused by data inhomogeneity. A fit to the data yields a bulk flow amplitude V_bulk = 70{+100}{-70} km/s (1 sigma error) with respect to the Cosmic Microwave Background, i.e., consistent with being at rest. At the 95% confidence level, the flow amplitude is < 300 km/s. Our results are insensitive to which Galactic extinction maps we use, and to the parameterization of the TF relation. The larger bulk motion found in analyses of the Mark III peculiar velocity catalog are thus likely to be due to non-uniformities between the subsamples making up Mark III. The absence of bulk flow is consistent with the study of Giovanelli and collaborators and flow field predictions from the observed distribution of IRAS galaxies.Comment: Accepted version for publication in ApJ. Includes an epitaph for Jeffrey Alan Willick (Oct 8, 1959 - Jun 18, 2000