Optical galaxies within 8000 km s-1 - II. The peculiar velocity of the Local Group

Abstract

Optical galaxies within 8000 km s −1 are used to predict the peculiar velocity of the Local Group. Our sample is drawn from the UGC and ESO catalogues. The predicted motion is 28°-32° away from the motion of the Local Group in the CMB frame, and the predicted velocity is 760±160 β 0 km s −1 , where β 0 ≡Ω 0.6 b 0 −1 . The direction of the optical dipole agrees with the directions of the IRAS dipoles, and is misaligned from the CMB dipole in the same sense. If it is assumed that the galaxies within 8000 km s −1 are responsible for all of the 606 km s −1 velocity of the Local Group, then β 0 =0.80 −0.13 +0.21 (1σ errors). The density of mass clustered with optical galaxies is then Ω=0.69 −0.18 +0.33 , if mass traces optical light (b 0 =1)