COSMOLOGICAL DIPOLES IN-DEPTH

We review and discuss the problem of the convergence of the peculiar acceleration (proportional to the ''dipole'') felt by the Local Group (LG) of galaxies, as inferred by the motion with respect to the cosmic microwave background (CMB) frame. In the light of the conflicting results that appeared in the literature, the basic issue we discuss here is at what depth such convergence is achieved. By matching the dipole growth with radial distance obtained from galaxy samples, which map better the closer regions, to that obtained from samples of galaxy clusters, which map better the far regions, we estimate that almost 1/2 of the LG peculiar velocity with respect to the CMB, upsilon(LG), is due to mass fluctuations located at a distance greater than similar to 60 h(-1) Mpc (less than or similar to 30% of upsilon(LG), is due to fluctuations at depths greater than 100 h(-1) Mpc). This result is at variance with earlier claims which suggested that all of this velocity is generated within such inner sphere. Our results make a prediction for the final level of dipole anisotropy (scaled to IRAS galaxies) on the scale of similar to 180 h(-1) Mpc which should be found by future, fainter all-sky galaxy samples: the asymptotic expected value of the peculiar velocity should be upsilon(I)(infinity)similar or equal to(4/b(cI))(Omega(0)(0.6)/b(I rho))1100 +/- 150 km s(-1). This result favors an open universe, unless IRAS galaxies are biased with respect to the matter distribution (i.e., b(I rho)similar to 1.8). The growth with depth of the dipoIe favors models with a coherence length larger than standard CDM.