2MTF IV. A bulk flow measurement of the local Universe

TL;DR

This study measures the bulk flow of the local universe using the 2MASS Tully-Fisher survey, finding results consistent with the ΛCDM model and providing detailed velocity field maps within 100 h^{-1}Mpc.

Contribution

It presents new bulk flow measurements based on a comprehensive all-sky galaxy sample, combining multi-band data and advanced analysis methods to improve understanding of local cosmic motions.

Findings

Bulk flow at 20, 30, 40 h^{-1}Mpc is approximately 280-310 km/s.

Bulk flow directions align with previous measurements.

Results are consistent with ΛCDM predictions at 1σ level.

Abstract

Using the 2MASS near-infrared photometry and high signal-to-noise HI 21-cm data from the Arecibo, Green Bank, Nancay, and Parkes telescopes, we calculate the redshift-independent distances and peculiar velocities of 2,018 bright inclined spiral galaxies over the whole sky. This project is part of the 2MASS Tully-Fisher survey (2MTF), aiming to map the galaxy peculiar velocity field within 100 h^{-1}Mpc, with an all-sky coverage apart from Galactic latitudes |b|< 5 deg. A \chi^2 minimization method was adopted to analyze the Tully-Fisher peculiar velocity field in J, H and K bands, using a Gaussian filter. We combine information from the three wavebands, to provide bulk flow measurements of 310.9 +/- 33.9 km/s, 280.8 +/- 25.0 km/s, and 292.3 +/- 27.8 km/s at depths of 20 h^{-1}Mpc, 30 h^{-1}Mpc and 40 h^{-1}Mpc, respectively. Each of these bulk flow vectors points in a direction similar to those found by previous measurements. At each of the three depths, the bulk flow magnitude is consistent with predictions made by the $\Lambda$CDM model at the 1$\sigma$ level. The maximum likelihood and minimum variance method were also used to analyze the 2MTF samples, giving similar results.