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

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 and the Arecibo General Catalog with I-band photometry, SFI++. These samples contain peculiar velocities for ~3000 and ~4000 objects, respectively. Based on a sub-sample of ~1000 common very inclined galaxies, we reach the following conclusions. Irrespective of high (SFI++) or low (2MFGC) quality of the photometric data used, both the samples have ~10% fraction of galaxies deviating considerably from the main body of the TF relation. After their deletion, the standard TF scatter drops to 0m.47 (2MFGC) and 0m.40 (SFI++). The TF distances, derived from two samples, demonstrate a high degree of mutual agreement with a correlation coefficient ρ = +0.95 and σ(H 0 r ) = 837 km/s. Peculiar velocities of the galaxies are also correlated with ρ = 0.56−0.59 and σ(V pec ) = 610 V pec km/s. We find that the bulk motion of the 2MFGC and SFI++ galaxies on a typical scale of H 0 r ≈ 5700 km/s can be represented by a dipole solution with the amplitude V = (297 ± 23) km/s directed towards {l = 2920 ± 40, b = −120 ± 30}, being only slightly sensitive to different modifications of the TF relaton.