The large-scale velocity field from the Cosmicflows-4 data

Abstract

ABSTRACT The reconstruction of the large-scale velocity field from the grouped Cosmicflows-4 (CF4) database is presented. The lognormal bias of the inferred distances and velocities data is corrected by the Bias Gaussianization correction scheme, and the linear density and velocity fields are reconstructed by means of the Wiener filter and constrained realizations (CRs) algorithm. These tools are tested against a suite of random and constrained Cosmicflows-3-like mock data. The CF4 data consist of three main subsamples – the 6dFGS and the SDSS data – and the ‘others’. The individual contributions of the subsamples have been studied. The quantitative analysis of the velocity field is done mostly by the mean overdensity (ΔL(R)) and the bulk velocity (Vbulk(R)) profiles of the velocity field out to $300\, {{h^{-1}\, {\rm Mpc}}}$. The Vbulk(R) and ΔL(R) profiles of the CF4 data without its 6dFGS component are consistent with the cosmic variance to within 1σ. The 6dFGS sample dominates the Vbulk (ΔL) profile beyond $\sim 120\, {{h^{-1}\, {\rm Mpc}}}$, and drives it to roughly a 3.4σ (−1.9σ) excess (deficiency) relative to the cosmic variance at $R\sim 250\ (190)\ \, {{h^{-1}\, {\rm Mpc}}}$. The excess in the amplitude of Vbulk is dominated by its Supergalactic X component, roughly in the direction of the Shapley Concentration. The amplitude and alignment of the inferred velocity field from the CF4 data are at $\sim (2{-}3)\, \sigma$ discrepancy with respect to the Lambda cold dark matter model. Namely, it is somewhat atypical but yet there is no compelling tension with the model.