Distances and peculiar velocities of spiral galaxies in the 2MFGC and SFI++ samples

TL;DR

This study compares infrared Tully-Fisher distances and peculiar velocities of spiral galaxies from the 2MFGC and SFI++ datasets, finding high agreement and characterizing their bulk motion with a dipole model.

Contribution

It provides a detailed comparison of two large galaxy samples' distances and velocities, revealing their correlation and bulk motion characteristics.

Findings

Approximately 10% of galaxies deviate from the TF relation.

TF distances from both samples are highly correlated (r=+0.95).

Bulk motion is characterized by a dipole with amplitude 297 km/s.

Abstract

We compare infrared Tully-Fisher (TF) distances and peculiar velocities derived for spiral galaxies from the two largest datasets: the 2MASS selected Flat Galaxy Catalog, 2MFGC [19, 20] and the Arecibo General Catalog with I-band photometry, SFI++ [30,7]. These samples contain peculiar velocities for ~3000 and ~4000 objects, respectively. Based on a sub-sample of ~1000 common deeply inclined galaxies, we reach the following conclusions. Irrespective to high (SFI++) or low (2MFGC) quality of the used photometric data, about 10% of the galaxies in both samples deviate considerably from the main body of the TF relation. After their deletion, the standard TF scatters drops to 0.47^m (2MFGC) and 0.40^m (SFI++). The TF distances, derived from two the samples, demonstrate a high degree of mutual agreement with a correlation coefficient \ro=+0.95 and \sigma(H_0r)=837 km/s. Peculiar velocities of the galaxies are also correlated with \ro=0.56-0.59 and \sigma(V_pec)=610 km/s. We find that the bulk motion of the 2MFGC and SFI++ galaxies on a typical scale of H_0r~5700 km/s can be represented by a dipole solution with the amplitude V=297+/-23 km/s directed towards l=292+/-4 degr., b=-12+/-3 degr., being only slightly sensitive to different modifications of the TF relaton.