Peculiar velocities of field spiral galaxies near and beyond the Great Attractor

Abstract

We measure peculiar velocities for a sample of 48 late-type spiral galaxies which are located in the general vicinity of the Great Attractor (GA). Relative distances are derived using the I-band Tully-Fisher relation. We confirm the existence of positive velocity residuals, with amplitude 500-2000 km s^-1^ in the Hydra-Centaurus region, for galaxies located at kinematic distances of 20-30 Mpc. Beyond 45 Mpc, we have a very weak signal of negative velocity residuals whose amplitude is very sensitive to the form of the Malmquist correction. However, positive velocity residuals can be detected in galaxies with distances as large as 80 Mpc. We test the origin of these motions by the use of a nonlinear spherical infall model which predicts the position of the caustic surface as a function of distance from the GA. We also use all available velocities to search for the caustics in redshift space. We explicitly incorporate distance errors into the models and adopt a correction which is appropriate for a highly clustered distribution. Comparison of the data with the model yields the following results: (1) we cannot identify a symmetric infall pattern centered on the GA (2) & bulk flow " infall pattern, centered on a kinematic distance of 4350 km s^-1^ provides the best means of correcting the observed velocity so as to produce a Tully- Fisher relation with the least amount of scatter, and (3) galaxies in the vicinity of OCA 3574 appear to participate in a small-scale infall pattern. The overall behavior of the data shows that we have not yet obtained a sample over a sufficiently large volume to isolate the true source of the observed peculiar velocities. The possibility of large peculiar motions on the scale of 10,000 km s^-1^ remains viable. However, the morphology in redshift space of the Centaurus Cluster, coupled with the large observed peculiar velocities in this region, strongly suggests that this structure is a main contributor to the observed flow.