Bulk flow and shear in the local Universe: 2MTF and COSMICFLOWS-3

The low-order kinematic moments of galaxies, namely bulk flow and shear, enables us to test whether theoretical models can accurately describe the evolution of the mass density field in the nearby Universe. We use the so-called ηMLE maximum likelihood estimator in log-distance space to measure these moments from a combined sample of the 2MASS Tully-Fisher (2MTF) survey and the COSMICFLOWS-3 (CF3) compilation. Galaxies common between 2MTF and CF3 demonstrate a small zero-point difference of -0.016 ± 0.002 dex. We test the ηMLE on 16 mock 2MTF survey catalogues in order to explore how well the ηMLE recovers the true moments, and the effect of sample anisotropy. On the scale size of 37 h^-1 Mpc, we find that the bulk flow of the local Universe is 259 ± 15 km s^-1 in the direction is (l, b) = (300 ± 4°, 23 ± 3°) (Galactic coordinates). The average shear amplitude is 1.7 ± 0.4 h km s^-1 Mpc^-1. We use a variable window function to explore the bulk and shear moments as a function of depth. In all cases, the measurements are consistent with the predictions of the Λ cold dark matter (ΛCDM) model.