2MTF V. Cosmography, Beta, and the residual bulk flow

TL;DR

This paper analyzes the velocity field of the nearby Universe using the Tully-Fisher relation, comparing models based on galaxy surveys, and finds that accounting for monopole offsets improves model agreement and reduces residual bulk flow, aligning with theoretical expectations.

Contribution

It introduces a detailed comparison of velocity field reconstructions from 2MASS and IRAS surveys, highlighting the impact of monopole offsets on bulk flow estimates and model accuracy.

Findings

PSCz model fits the velocity data better than 2MRS.

Removing monopole offsets reduces residual bulk flow to ~150 km/s.

Models largely account for major structures influencing bulk velocity.

Abstract

Using the Tully-Fisher relation, we derive peculiar velocities for the 2MASS Tully-Fisher Survey and describe the velocity field of the nearby Universe. We use adaptive kernel smoothing to map the velocity field, and compare it to reconstructions based on the redshift space galaxy distributions of the 2MASS Redshift Survey (2MRS) and the IRAS Point Source Catalog Redshift Survey (PSCz). With a standard $\chi^2$ minimization fit to the models, we find that the PSCz model provides a better fit to the 2MTF velocity field data than does the 2MRS model, and provides a value of $\beta$ in greater agreement with literature values. However, when we subtract away the monopole deviation in the velocity zeropoint between data and model, the 2MRS model also produces a value of $\beta$ in agreement with literature values. We also calculate the `residual bulk flow': the component of the bulk flow not accounted for by the models. This is $\sim 250$ km/s when performing the standard fit, but drops to $\sim 150$ km/s for both models when the aforementioned monopole offset between data and models is removed. This smaller number is more in line with theoretical expectations, and suggests that the models largely account for the major structures in the nearby Universe responsible for the bulk velocity.