Cosmicflows-4 and the Cosmological Consistency of Large-Scale Motions

Abstract

We study coherent flows in Cosmicflows-4 (CF4) and its constituent catalogs. We fit monopole and dipole moments in nonoverlapping radial bins using a log-distance radial-velocity estimator. For each sample, the Planck 2018 $\Lambda$CDM prediction accounts for the actual positions, statistical weights, velocity covariance, and measurement covariance. Across six bins extending to $300,h^{-1},\mathrm{Mpc}$, the All Individual sample is broadly consistent with $\Lambda$CDM, with dipole and joint deviations of $2.29\sigma$ and $2.36\sigma$. The strongest localized feature occurs at $120$--$160,h^{-1},\mathrm{Mpc}$, where $|V_{\mathrm{dip}}|=628\pm 82,\mathrm{km},{\mathrm{s}}^{-1}$ and the dipole deviation reaches $3.40\sigma$. The excess is concentrated toward negative supergalactic X and depends strongly on the survey window. TFR and 6dFGS favor larger dipoles, while SDSS and SN favor smaller ones. Removing 6dFGS reduces the upper-bin dipole deviation to $1.56\sigma$, while removing SN raises it to $3.77\sigma$. Nevertheless, the SN and 6dFGS dipoles remain mutually consistent when their covariance is included. SDSS is consistent with $\Lambda$CDM through $160,h^{-1},\mathrm{Mpc}$ but shows a separate rise at larger radii whose significance depends on the treatment of the monopole and shared distance-scale covariance. Overall, CF4 does not show uniformly anomalous motion across its full radial range. Instead, it contains localized and window-dependent features that should be tested with selection-matched mock catalogs and correlated calibration uncertainties.

21 pages, 8 figures