THE VALUE OF βFROM THE LG AND ABELL CLUSTER PECULIAR VELOCITIES

Abstract

Comparing the observed peculiar velocities of the Local Group and of nearby Abell clusters of galaxies with those predicted using linear perturbation theory and the 3-D reconstruction algorithm of Branchini \& Plionis (1995) the value of $β$ can be estimated. I show that the anisotropy that causes the LG motion does not only extend to very large depths ($\sim 160 \; h^{-1}$ Mpc) but it is also very coherent, which suggests that the value of $β\approx 0.21 \pm 0.015$, obtained from the LG velocity, should not be significantly affected by cosmic variance. Comparing the Abell cluster and QDOT galaxy dipoles in real space their relative biasing factor are estimated to be $b_{cI}\approx 3.5\pm0.5$. Finally, using a suitable set of available cluster peculiar velocities I obtain a somewhat lower value of $β\approx 0.15 - 0.17$ but with a large uncertainty ($\gtrsim 0.1$) when weighted by the large observational errors.