Velocity-Density Correlations from the cosmicflows-3 Distance Catalog and the 2MASS Redshift Survey

Abstract

The peculiar velocity of a mass tracer is on average aligned with the dipole modulation of the surrounding mass density field. We present a first measurement of the correlation between radial peculiar velocities of objects in the cosmicflows-3 catalog and the dipole moment of the 2MRS galaxy distribution in concentric spherical shells centered on these objects. Limiting the analysis to cosmicflows-3 objects with distances of $100 \rm Mpc h^{-1}$, the correlation function is detected at a confidence level $> 4σ$. The measurement is found consistent with the standard $Λ$CDM model at $< 1.7σ$ level. We formally derive the constraints $0.32<Ω^{0.55}σ_8<0.48$ ($68\% $ confidence level) or equivalently $0.34<Ω^{0.55}/b<0.52$, where $b$ is the galaxy bias factor. Deeper and improved peculiar velocity catalogs will substantially reduce the uncertainties, allowing tighter constraints from this type of correlations.