Statistical Determination of Bulk Flow Motions

TL;DR

This paper introduces a new statistical method to measure galaxy bulk flows using the two-point correlation function, applying it to SDSS data, and finds results consistent with standard cosmological models, challenging claims of excessive motions.

Contribution

The paper presents a novel parameterization for bulk motions and a model-independent velocity dispersion measure, applied to SDSS data, providing new insights into cosmic flow measurements.

Findings

Measured v_p=270^{+433} km/s for SDSS clusters at z=0.1.

Results are consistent with LCDM predictions, not supporting claims of large bulk flows.

Developed a technique to reconstruct the perturbed potential from v_p evolution.

Abstract

We present here a new parameterization for the bulk motions of galaxies and clusters (in the linear regime) that can be measured statistically from the shape and amplitude of the two-dimensional two-point correlation function. We further propose the one-dimensional velocity dispersion (v_p) of the bulk flow as a complementary measure of redshift-space distortions, which is model-independent and not dependent on the normalisation method. As a demonstration, we have applied our new methodology to the C4 cluster catalogue constructed from Data Release Three (DR3) of the Sloan Digital Sky Survey. We find v_p=270^{+433}km/s (also consistent with v_p=0) for this cluster sample (at z=0.1), which is in agreement with that predicted for a WMAP5-normalised LCDM model (i.e., v_p(LCDM=203km/s). This measurement does not lend support to recent claims of excessive bulk motions (\simeq1000 km/s) which appear in conflict with LCDM, although our large statistical error cannot rule them out. From the measured coherent evolution of v_p, we develop a technique to re-construct the perturbed potential, as well as estimating the unbiased matter density fluctuations and scale--independent bias.