Cosmic flow from 2MASS redshift survey: The origin of CMB dipole and implications for LCDM cosmology

Abstract

We generate the peculiar velocity field for the 2MASS Redshift Survey (2MRS) catalog using an orbit-reconstruction algorithm. The reconstructed velocities of individual objects in 2MRS are well-correlated with the peculiar velocities obtained from high-precision observed distances within 3,000 km/s. We estimate the mean matter density to be 0.31 +/- 0.05 by comparing observed to reconstructed velocities in this volume. The reconstructed motion of the Local Group in the rest frame established by distances within 3,000 km/s agrees with the observed motion and is generated by fluctuations within this volume, in agreement with observations. Then, we reconstruct the velocity field of 2MRS in successively larger radii, to study the problem of convergence towards the CMB dipole. We find that less than half of the amplitude of the CMB dipole is generated within a volume enclosing the Hydra-Centaurus-Norma supercluster at around 40 Mpc/h. Although most of the amplitude of the CMB dipole seems to be recovered by 120 Mpc/h, the direction does not agree and hence we observe no convergence up to this scale. We develop a statistical model which allows us to estimate cosmological para meters from the reconstructed growth of convergence of the velocity of the Local Group towards the CMB dipole motion. For scales up to 60 Mpc/h, assuming a Local Group velocity of 627 km/s, we estimate Omega_m h^2 = 0.11 +/- 0.06 and sigma_8=0.9 +/- 0.4, in agreement with WMAP5 measurements at the 1-sigma level. However, for scales up to 100 Mpc/h, we obtain Omega_m h^2 = 0.08 +/- 0.03 and sigma_8=1.0 +/- 0.4, which agrees at the 1 to 2-sigma level with WMAP5 results. (abridged)