Influence of measurement errors and deviations from Tully‐Fisher relationship on multipole structure of bulk galaxy motion

Abstract

The velocity field of large-scale non-Hubble galaxy motion recovered from peculiar velocities of spiral galaxies is distorted due to measurement errors and deviations from Tully-Fisher relationship. To figure out how this affects the multipole structure we use the Monte-Carlo approach and simulate errors and deviations. We use the galaxies from the Revised Flat Galaxy Catalogue subsample and the generalized Tully-Fisher relationship in the 'H I line width-angular diameter' version. The analysis of the multipole structure has shown that the dipole velocity component (bulk motion) is underestimated, and the characteristic values of the quadrupole component are overestimated. The directions of the quadrupole component's eigenvectors can be determined precisely enough. Typical deviation angles of bulk motion apices lie between 17 and 40• . The main input is caused by errors in the measurement of the angular diameter. The probability of the quadrupole component being incidental can be estimated at the 4 per cent level. For the octopole component, it can be estimated at the 7-10 per cent level. This is essentially higher than the estimations less than 1 per cent due to the Fisher test.

Yet another sample of RFGC galaxies

“…One can see that the non-relativistic DQO-model gives the apex closest to the results of most authors. This is consistent with our earlier results (Parnovsky & Parnowski 2008 of Monte Carlo simulations, which demonstrate that the DQO-model gives the best fit to the data. However, the apex in the semi-relativistic DQOmodel is way beyond all reasonable confidence boundaries.…”

Large-scale collective motion of RFGC galaxies

“…The data on HI line widths for RFGC galaxies in the HyperLeda (Paturel et al 2003a) catalogue are based on 149 sources, which have different reliability. The main sources used in previous versions of our samples are listed in the papers (Parnovsky et al 2001;Parnovsky & Tugay 2004;Karachentsev et al 2000a,b;Parnovsky & Tugay 2005). Since that time new large volumes of data on radial velocities and HI linewidths of galaxies were published (e.g., ?).…”

“…Four years later, the number of galaxies with available data increased and reached 1561 (Parnovsky & Tugay 2004); 1493 of them entered the sample. A new version of the list of peculiar velocities was prepared by Parnovsky & Tugay (2005). This list was the basis for solving the two abovementioned problems, namely mapping the matter density and estimation of cosmological parameters.…”

Large-scale collective motion of RFGC galaxies in curved space-time

“…They are due to the errors in angular diameters and H I line widths and deviations from the Tully-Fisher relation. These errors were analyzed in the paper (Parnovsky & Parnowski 2008). Here we will briefly mention the main points of the routine used.…”

“…Thus, it can help avoiding undernoising and overnoising. Other constraints used and details of the procedure are described in the paper (Parnovsky & Parnowski 2008). Naturally, we do not try to find a unique set of noise parameters.…”