The bulk motion of flat galaxies on scales of 100 Mpc in the quadrupole and octupole approximations

Abstract

The peculiarities of non-Hubble bulk motions of galaxies are studied by analyzing a sample of 1271 thin edge-on spirals with distances determined using a multiparametric Tully-Fisher relation that includes the amplitude of the galaxy rotation, the blue and red diameters, surface brightness, and morphological type. In the purely dipole approximation, the bulk motion of galaxies relative to the cosmic microwave background frame can be described by the velocity of 336±96 km s−1 in the direction l=321°, b=−1° within radius Rmax=10000 km s−1. An analysis of more complex velocity field models shows that the anisotropy of the Hubble expansion described by the quadrupole term is equal to ∼5% on scale lengths Rmax=6000–10000 km s−1. The amplitude within the Local Supercluster (Rmax=3000 km s−1) is as high as ∼20%. The inclusion of the octupole component reduces the dipole amplitude to 134±111 km s−1 on scale lengths of ∼8000 km s−1. The most remarkable feature of the galaxy velocity field within Rmax=8000 km s−1 is the zone of minimum centered on l=80°, b=0° (the constellation of Cygnus) whose amplitude reaches 18% of the mean Hubble velocity.