The Large Scale Galaxy Peculiar Velocity Field

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Session 121 -- Cosmology and CMB
Oral presentation, Saturday, January 15, 2:15-3:45, Salon III Room (Crystal Gateway)

[121.05] The Large Scale Galaxy Peculiar Velocity Field

Andrew Connolly (Johns Hopkins University), Bob Joseph (Institute for Astronomy, Hawaii), Chris Collins (Durham University), Phil James (Edinburgh University)

The amplitude, scale and coherence of the galaxy peculiar velocity field provide a direct probe of the mass distribution in the Universe. By comparing the predictions of cosmological models with the observed velocity field, we can determine some of the severest constraints for galaxy formation theories. We present here the initial results of an all-sky survey of the galaxy peculiar velocity field, from a sample of 218 ScI spiral galaxies extending out to a depth of 100 $h^{-1}$ Mpc.

Multi--color observations were undertaken for the galaxy sample, and their kinematic properties extracted from the astronomical literature. From these data, the Tully--Fisher and color--magnitude relations were investigated as potential distance indicators. Using a principal component analysis we show that the central surface brightness correlates with the magnitude and linewidth. We propose the inclusion of this extra dimension in the Tully--Fisher relation to improve its accuracy as a distance indicator.

From the ScI galaxy sample we derive a bulk dipole velocity of 376 km s$^{-1}$ towards $l=330$ and $b=31$, with respect to the Cosmic Background Radiation. The amplitude is consistent with that derived by Dressler et al.\ (1987), while the depth of the survey extends, 25\% deeper than that of Dressler et al.

Combining the present and published velocity field data we compare the observed velocity field with a number of Cold Dark Matter cosmological models. We find the data are best fitted by a flat, low density Cold Dark Matter universe with H$_o = 100$ Mpc$^{-1}$ km s$^{-1}$ and a cosmological constant of 0.8. We cannot, however, rule out the standard, low bias Cold Dark Matter model at greater than a 90\% confidence level.

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