Velocity-density correlations from the cosmicflows-3 distance catalogue and the 2MASS Redshift Survey

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 catalogue and the dipole moment of the 2MRS galaxy distribution in concentric spherical shells centred on these objects. Limiting the analysis to cosmicflows-3 objects with distances of 100h^-1 Mpc, the correlation function is detected at a confidence level of ≳4σ. The measurement is found consistent with the standard ΛCDM model at the ≲1.7σ level. We formally derive the constraints 0.32 < Ω ^0.55 σ8 < 0.48 (68 per cent confidence level) or equivalently 0.34 < Ω^0.55/b < 0.52, where b is the galaxy bias factor. Deeper and improved peculiar velocity catalogues will substantially reduce the uncertainties, allowing tighter constraints from this type of correlations.