OPTICAL GALAXIES WITHIN 8000 KM S(-1) .2. THE PECULIAR VELOCITY OF THE LOCAL GROUP

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-degrees-32-degrees away from the motion of the Local Group in the CMB frame, and the predicted velocity is 760 +/- 160 beta(o) km s-1, where beta(o) = OMEGA0.6 b(o)-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 beta(o) = 0.80(-0.13)+0.21 (1 sigma errors). The density of mass clustered with optical galaxies is then OMEGA = 0.69(-0.18)+0.33, if mass traces optical light (b(o) = 1). Alternatively, if OMEGA = 1 then optical galaxies are mildly biased with b(o) = 1.25 +/- 0.26. For cosmological models that fit the large-scale galaxy counts, however, we do not expect the mass within 8000 km s-1 to account for all of the motion of the Local Group, and a better estimate is beta(o) = 0.72(-0.18)+0.37. For the same model, but using only the galactic Z dipole, we obtain beta(o) = 0.49(-0.11)+0.18. Then, if mass traces light, OMEGA > 0.14 at the 95 per cent confidence level.