AAS 201st Meeting, January, 2003
Session 23. Cosmology: The Fundamental Parameter
Oral, Monday, January 6, 2003, 10:00-11:30am, 608-609

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[23.06D] The Enigmatic Local Hubble Flow: Probing the Nearby Peculiar Velocity Field with Consistent Distances to Neighboring Galaxies.

B. Mendez, M. Davis, J. Newman (UC Berkeley), B.F. Madore, W.L. Freedman (Carnegie Institute of Washington), J. Moustakas (Steward Observatory, U of Arizona)

The properties of the velocity field in the local volume (cz < 550 km s-1) have been difficult to constrain due to a lack of a consistent set of galaxy distances. The sparse observations available to date suggest a remarkably quiet flow, with little deviation from a pure Hubble law. However, velocity field models based on the distribution of galaxies in the 1.2 Jy IRAS redshift survey, predict a quadrupolar flow pattern locally with strong infall at the poles of the local Supergalactic plane. In an attempt to resolve this discrepency, we probe the local velocity field and begin to establish a consistent set of galactic distances. We have obtained images of nearby galaxies in I, V, and B bands from the W.M. Keck Observatory and in F814W and F555W filters from the {\em Hubble Space Telescope}. Where these galaxies are well resolved into stars we can use the Tip of the Red Giant Branch (TRGB) as a distance indicator. Using a maximum likelihood analysis to quantitatively measure the I magnitude of the TRGB we determine precise distances to several nearby galaxies. We supplement that dataset with published distances to local galaxies measured using Cepheids, Surface Brightness Fluctuations, and the TRGB. With these data we find that the amplitude of the local flow is roughly half that expected in linear theory and N-body simulations; thus the enigma of cold local flows persists.

This work was supported in part by NASA through a grant from the Space Telescope Science Institute and a Predoctoral Fellowship for Minorities from the Ford Foundation.

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