Reconstructing positions and peculiar velocities of galaxy clusters within 25,000 kilometers per second: The cluster real space dipole

Starting from the observed distribution of Abell/ACO galaxy clusters in redshift space, we use a two-step procedure to recover their distances and peculiar velocities. After statistically correcting for the unobserved cluster distribution in the zone of avoidance and also for a smooth absorption at higher latitudes, we use a dynamical iterative algorithm, based on that published by Strauss & Davis in 1988, to recover the real-space duster positions by minimizing the redshift-space distortions. The whole procedure assumes that clusters trace the mass, that peculiar velocities are caused by gravity, and that linear perturbation theory applies. The amplitude of the cluster dipole measured in real space turns out to be similar to 23% less than that measured in redshift space. In both cases the dipole direction is aligned with the cosmic microwave background dipole within similar to 10 degrees, taking into account the Virgocentric infall component of the Local Group motion. Using linear theory we obtain beta(c)(=Omega(0)(0.6)/b(c)) approximate to 0.21(+/-0.03), where the uncertainty is due to observational errors and limitations in the reconstruction procedure, while the intrinsic cosmological variance amounts to similar to 0.07. This beta(c) value implies that for a cluster-mass bias parameter of b(c) less than or similar to 5, a flat universe is not excluded, contrary to previous cluster-dipole z-space analysis. A more stringent determination of beta(c) will be obtained from the analysis of the peculiar velocity field in a forthcoming paper

Reconstructing positions and peculiar velocities of galaxy clusters within 25,000 kilometers per second: The cluster real space dipole

Starting from the observed distribution of Abell/ACO galaxy clusters in redshift space, we use a two-step procedure to recover their distances and peculiar velocities. After statistically correcting for the unobserved cluster distribution in the zone of avoidance and also for a smooth absorption at higher latitudes, we use a dynamical iterative algorithm, based on that published by Strauss & Davis in 1988, to recover the real-space duster positions by minimizing the redshift-space distortions. The whole procedure assumes that clusters trace the mass, that peculiar velocities are caused by gravity, and that linear perturbation theory applies. The amplitude of the cluster dipole measured in real space turns out to be similar to 23% less than that measured in redshift space. In both cases the dipole direction is aligned with the cosmic microwave background dipole within similar to 10 degrees, taking into account the Virgocentric infall component of the Local Group motion. Using linear theory we obtain beta(c)(=Omega(0)(0.6)/b(c)) approximate to 0.21(+/-0.03), where the uncertainty is due to observational errors and limitations in the reconstruction procedure, while the intrinsic cosmological variance amounts to similar to 0.07. This beta(c) value implies that for a cluster-mass bias parameter of b(c) less than or similar to 5, a flat universe is not excluded, contrary to previous cluster-dipole z-space analysis. A more stringent determination of beta(c) will be obtained from the analysis of the peculiar velocity field in a forthcoming paper

Reconstructing cluster peculiar velocities within 20000 km/sR

none2noneBranchini E.F.; Plionis M.Branchini, E. F.; Plionis, M

On the least action principle in cosmology

Given the present distribution of mass tracing objects in an expanding universe, we develop and test a fast method for recovering their past orbits using the least action principle. In this method, termed FAM for fast action minimization, the orbits are expanded in a set of orthogonal time basis functions satisfying the appropriate boundary conditions at the initial and final times. The conjugate gradient method is applied to locate the extremum of the action in the space of the expansion coefficients of the orbits. The treecode gravity solver routine is used for computing the gravitational field appearing in the action and the potential field appearing in the gradient of the action. The time integration of the Lagrangian is done using Gaussian quadratures. FAM allows us to increase the number of galaxies over previous numerical action principle implementations by more than one order of magnitude. For example, orbits for the similar to 15 000 IRAS PSCz galaxies can be recovered in similar to 12 000 CPU seconds on a 400-MHz DEC-Alpha machine. FAM can recover the present peculiar velocities of particles and the initial fluctuations field. It successfully recovers the flow field down to cluster scales, where deviations of the flow from the Zel'dovich solution are significant. We also show how to recover orbits from the present distribution of objects in redshift space by direct minimization of a modified action, without iterating the solution between real and redshift spaces

Growth Rate of Cosmological Perturbations at z~0.1 from a New Observational Test

Spatial variations in the distribution of galaxy luminosities, estimated from redshifts as distance proxies, are correlated with the peculiar velocity field. Comparing these variations with the peculiar velocities inferred from galaxy redshift surveys is a powerful test of gravity and dark-energy theories on cosmological scales. Using ~2 ×105 galaxies from the SDSS Data Release 7, we perform this test in the framework of gravitational instability to estimate the normalized growth rate of density perturbations f sigma8=0.37 ±0.13 at z ~0.1 , which is in agreement with the cold dark matter model with a cosmological constant. This unique measurement is complementary to those obtained with more traditional methods, including clustering analysis. The estimated accuracy at z ~0.1 is competitive with other methods when applied to similar data sets

COLORS, LUMINOSITIES, AND MASSES OF DISK GALAXIES .2. ENVIRONMENTAL DEPENDENCIES

The B-band and near-infrared (H) luminosity functions of spiral galaxies are derived for the Coma and A1367 clusters and for a reference population of ''field'' galaxies in the Coma supercluster. They are consistent at the bright end, but they differ significantly at the faint end, indicating an overdensity of spirals with blue color (B-H < 3.0) and faint H luminosity (H > -21.5) in clusters with respect to the field. These objects have disturbed morphology and peculiar velocities significantly larger than the rest of the cluster sample. We discuss these results in the framework of a possible environmental dependence of galaxy evolution, and we conclude that enhanced current star formation in cluster spiral galaxies might occur due to molecular gas collapse stimulated by the ram-pressure mechanism