Bulk flows and CMB dipole anisotropy in cosmological void models

Abstract

The observational behavior of spherically symmetric inhomogeneous cosmological models is studied, which consist of inner and outer homogeneous regions connected by a shell or an intermediate self-similar region. It is assumed that the present matter density parameter in the inner region is smaller than that in the outer region, and the present Hubble parameter in the inner region is larger than that in the outer region. Then galaxies in the inner void-like region can be seen to have a bulk motion relative to matter in the outer region, when we observe them at a point O deviated from the center C of the inner region. Their velocity $v_p$ in the CD direction is equal to the difference of two Hubble parameters multiplied by the distance between C and O. It is found also that the velocity $v_d$ corresponding to CMB dipole anisotropy observed at O is by a factor $\approx 10$ small compared with $v_p$. This behavior of $v_d$ and $v_p$ may explain the puzzling situation of the cosmic flow of cluster galaxies, when the radius of the inner region and the distance CD are about 200 $h^{-1}$ Mpc and 40 $h^{-1}$ Mpc, respectively ($H_0 = 100 h^{-1} km/sec Mpc^{-1}$), and when the gaps of density and Hubble parameters are $\approx 0.5$ and 18%, respectively.