Cosmic velocity flows on large scales with SDSS DR7 early-type galaxies

In order to obtain a quantitative picture of the distribution of matter in the universe one needs to take into account both baryonic and dark matter. In particular, galactic peculiar velocities depend on the distribution of gravitational matter and thus peculiar velocities provide a probe of the distribution of dark matter.;If one looks at a large enough region, the bulk flow of galaxies should converge to the CMB dipole. There have been many studies of the convergence depth and the dipole direction and magnitude. All observations up to 60 h-1 Mpc beginning a decade ago have measured a bulk flow and these results agree with the theoretical expectation. In contrast, however, peculiar velocity surveys larger than 100h -1 Mpc provide results that vary between surveys.;This thesis presents a study of cosmic velocity flow in the region up to z ∼ 0:07 (≈ 200h-1 Mpc) using a sample of early-type galaxies taken from the Sloan Digital Sky Survey (SDSS) DR7. SDSS is currently the largest, extensive survey of the sky and provides a homogeneous and dense sample of galaxies which may help resolve the inconsistency of bulk flow measurements.;In this thesis, the distances of 189 galaxy clusters between ∼6000 and ∼21200 km s-1 were measured using the Fundamental Plane (FP). Both forward and inverse FPs were obtained using 2789 early-type galaxies, the members of the 189 galaxy clusters. The forward FP is found to have 7.68% mean and 7.71% median distance errors per cluster and the inverse FP gives 7.65% mean and 7.67% median errors in distance per cluster. The median number of galaxies per cluster is 15.;According to our results, the estimated distances are method dependent; the distances from the inverse FP show systematically higher values. The consistency between the distances from the two different methods is rejected at the 1% significance level based on the chi-square test. The source of the inconsistency was investigated by constructing mock data.;Cluster substructures were also studied and an adaptive kernal method was used to construct contours of galaxy cluster substructures. Galaxy cluster structures visualized by these contour are analyzed quantitatively by KMM method. We show that the existence of the substructures in a cluster is not significantly related to the size of the scatter around the fundamental plane of the cluster.;Finally, peculiar velocities of galaxy clusters were estimated and analyzed. Peculiar velocities are fitted by two attractor models. The double attractor model with the Great Attractor (GA) and the Shapley Super Cluster (SS) could help explain the peculiar velocity field better than the single attractor model with only GA. We investigated if the resultant bulk flow from this peculiar velocity field is consistent with the Λ Cold Dark Matter (Λ CDM) picture through chi-square statistics when the window function takes into account the spatial distribution of the data. The bulk flow from peculiar velocities was calculated by Maximum Likelihood Method (MLM) which gave the bulk flow of 970+/-130 km/s for the forward FP peculiar velocity data and 90+/-120 km/s for the inverse FP peculiar velocity. According to the chi-square values, the ΛCDM model is accepted at the 5% significance level when the bulk flow from peculiar velocities with the distances from inverse FP. However, when the bulk flow from peculiar velocities with the distances from forward FP, the ΛCDM model is rejected even at the 1% significance level. This different conclusion come from the fact that there is a significant inconsistency between the distances from the inverse and forward FP.