Cosmic Flow From Two Micron All-Sky Redshift Survey: The Origin of Cosmic Microwave Background Dipole and Implications for Λcdm Cosmology

Abstract

We generate the peculiar velocity field for the 2MASS Redshift Survey (2MRS) catalog (Huchra et al. 2005) 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 −1 . We estimate the mean matter density to be Ω m = 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 −1 agrees with the observed motion and is generated by fluctuations within this volume, in agreement with observations. Having tested our method against observed distances, 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 40h −1 Mpc. Although most of the amplitude of the CMB dipole seems to be recovered by 120h −1 Mpc, the direction does not agree and hence we observe no convergence up to this scale. Due to dominant superclusters such as Shapley or Horologium-Reticulum in the southern hemisphere at scales above 120h −1 Mpc, one might need to go well beyond 200h −1 Mpc to fully recover the dipole vector.We develop a statistical model which allows us to estimate cosmological parameters from the reconstructed growth of convergence of the velocity of the Local Group towards the CMB dipole motion. For scales up to 60h −1 Mpc, assuming a Local Group velocity of 627 km s −1 , we estimate Ω m h 2 = 0.11 ± 0.06 and σ 8 = 0.9 ± 0.4, in agreement with WMAP5 measurements at the 1-σ level. However, for scales up to 100h −1 Mpc, we obtain Ω m h 2 = 0.08 ± 0.03 and σ 8 = 1.0 ± 0.4, which agrees at the 1 to 2-σ level with WMAP5 results.

The Virgo Cluster

“…Replacing Virgo with the ensemble of local supercluster distances Figure 2 shows the velocity field that allows Local Supercluster distances to be used as an ensemble to supplement the Virgo cluster distance in the traditional distance scale ladder. A similar velocity field has been calculated by Lavaux & Tully (2010) also from the 2MRS survey. The corresponding distance catalog is compiled from the following sources.…”

Cosmological parameters from the comparison of peculiar velocities with predictions from the 2M++ density field

“…• found by , or the ∼ 45 • misalignment found by Lavaux et al (2010). The 2M++ density field at various slices of SGZ.…”

“…Past studies constraining cosmological parameters through comparison of predicted motion of the LG using linear theory and that derived from the CMB include Erdogdu et al (2006), and . Recently such an analysis has been extended to the non-linear regime using a novel orbit-reconstruction algorithm to predict motions of nearby objects (Lavaux et al 2010).…”

Cosmic Flows surveys and CLUES simulations

“…Alternative approaches are explored, they are based on the reconstruction of galaxy orbits to today's observed positions and velocities from initial conditions that globally minimize the action. One procedure developed by colleagues in France that goes by the acronym MAK, Monge-AmpereKantorovich (Lavaux et al 2010), finds straight-line orbits for very large samples. This method can be used to roughly determine the initial conditions of redshift surveys of hundreds of thousands of galaxies.…”