Peculiar Velocities for Galaxies in the Great Wall.II.Analysis

We analyze the peculiar velocity field in the vicinity of the Great Wall (GW) using a sample of 172 spiral galaxies with reliable IRTF distance estimates (Dell'Antonio et al. 1996). We examine three main issues: (1) the infall onto the GW, (2) large-scale flow, and (3) shear. We use a Monte Carlo method to remove selection-based biases from the peculiar velocity sample. For the GW sample, the velocity bias is small (<150 km s^-1^). We use the bias-corrected velocities to constrain the infall towards the Great Wall. We thus have the first limits on the true spatial thickness of this structure. The data are best fit by an infall velocity <= 150 km s^-1^. The 90% upper limit on the mean infall velocity is ~500 km s^-1^. Consequently, the upper limit on the real-space full width of the GW is d<11.2h^-1^ Mpc. Thus, the Great Wall is a thin, two- dimensional structure in real space as well as in redshift space. We calculate the best-fit estimate of the motion of the Local Group with respect to the galaxy distribution: ν_flow_ ~ 725+/-400 km s^-1^ towards a 11.7 +/- 1.5 hr, δ = 36.8deg^+/-55^deg^. Because our δ constraints are quite weak, this flow is consistent with the CMB dipole (Smoot et al. 1992) and with the flow vector of Riess et al. (1995). The data are also consistent at the 25% confidence level with the direction of large-scale flow reported by Lauer & Postman (1994). We calculate the improvement in sensitivity expected for a sample extending over the full declination range of the GW. We also calculate the shear across the right ascension range of the GW. The GW region is quiet: the detected the shear across the range of the GW is -70+/-210 km s^-1^. The absence of large shear constrains the amplitude of large-scale density fluctuations (Feldman & Watkins 1995).