Talk detail

Participant	Wiltshire, David
Institution	University of Canterbury - Dept of Physics & Astronomy, Private Bag 4800 - Christchurch - Canterbury - New Zealand

Session	TC3	Accepted	Yes	Order	7	Time	15:45 - 16:00
Talk	Oral abstract	Title	Hubble flow variance and the cosmic rest frame
Co-authors	P.R. Smale, T. Mattsson and R. Watkins
Abstract	I present an analysis of the radial and angular variance of the Hubble flow in the COMPOSITE sample of 4534 galaxy distances. Independent of any cosmological assumptions other than the existence of a suitably averaged linear Hubble law, we find with very strong Bayesian evidence that the Hubble constant averaged in spherical radial shells is closer to its global value when referred to the rest frames of the Local Group and Local Sheet rather than to the standard rest frame of the Cosmic Microwave Background (CMB) radiation. Furthermore, we find a dipole structure in angular averages, correlated with structures within a sphere of radius 65/h Mpc, and correlated with the residual CMB temperature dipole in the Local Group rest frame. It is suggested that rather than being entirely due to a local boost, there is a contribution to the CMB dipole from foreground structures which generate an anisotropy in the distance-redshift relation, at the level of 0.5%. Although quite natural from the point of inhomogeneous cosmologies, this suggestion would change a number of key aspects of the standard approach to observational cosmology, including in particular the interpretation of "bulk flows".