Analysing the large-scale bulk flow using cosmicflows4: increasing tension with the standard cosmological model

Abstract

ABSTRACT We present an estimate of the bulk flow in a volume of radii 150−200 h−1 Mpc using the minimum variance method with data from the CosmicFlows-4 (CF4) catalogue. The addition of new data in the CF4 has resulted in an increase in the estimate of the bulk flow in a sphere of radius 150 h−1 Mpc relative to the CosmicFlows-3 (CF3). This bulk flow has an $\sim 0.015~{{\ \rm per\ cent}}$ chance of occurring in the standard cosmological model with cosmic microwave background derived parameters. Given that the CF4 is deeper than the CF3, we were able to use the CF4 to accurately estimate the bulk flow on scales of 200 h−1 Mpc (equivalent to 266 Mpc for Hubble constant H0 = 75 km s−1 Mpc−1) for the first time. This bulk flow is in even greater tension with the standard model, having $\sim 1.5\times 10^{-4}\ \%$ probability of occurring. To estimate the bulk flow accurately, we introduce a novel method to calculate distances and velocities from distance moduli that is unbiased and accurate at all distances. Our results are completely independent of the value of H0.