1201.5371 (David L. Wiltshire et al.)

Hubble flow variance and the cosmic rest frame    [PDF]

David L. Wiltshire, Peter R. Smale, Teppo Mattsson, Richard Watkins

We characterize 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 decisive Bayesian evidence (ln B >> 5) that the Hubble constant
averaged in spherical radial shells is closer to its global value when referred
to the rest frame of the Local Group rather than to the standard rest frame of
the Cosmic Microwave Background (CMB) radiation. Angular averages reveal a
dipole structure in the Hubble flow variance, correlated with structures within
a sphere of radius 30/h - 60/h Mpc. Furthermore, the angular map of Hubble flow
variance is found to coincide with the angular map of the residual CMB
temperature dipole in the Local Group rest frame, with correlation coefficient
-0.92. This suggests a new mechanism for the origin of the CMB dipole: in
addition to a local boost it is generated by differences in the distance to the
surface of last scattering, of a maximum +/- 0.35/h Mpc, which arise from
foreground structures within 60/h Mpc, a 0.6% effect. The dipole feature is
accounted for by our position in a filamentary sheet between Local Voids and
Local Walls, producing a foreground density gradient on scales up to 60/h Mpc
on opposite sides of the sky. This result potentially eliminates problems of
interpretation of "bulk flows". Furthermore, anomalies associated with large
angles in the CMB anisotropy spectrum, and also the dark flow inferred from the
kinetic Sunyaev-Zel'dovich effect on small angular scales, need to be
critically re-examined.

View original: http://arxiv.org/abs/1201.5371