The Las Campanas Observatory/Palomar 10,000 Kilometer per Second Cluster Survey. II. Constraints on Large‐Scale Streaming

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Abstract
The LCO/Palomar 10,000 km s-1 (LP10K) Tully-Fisher (TF) data set is used to test for bulk streaming motions on a ~150 h-1 Mpc scale. The sample consists of 172 cluster galaxies in the original target range of the survey, 9000-13,000 km s-1, plus an additional 72 galaxies with cz ≤ 30,000 km s-1. A maximum likelihood analysis that is insensitive to Malmquist and selection bias effects is used to constrain the bulk velocity parameters, and realistic Monte Carlo simulations are carried out to correct residual biases and determine statistical errors. When the analysis is restricted to the original target range, the bias-corrected bulk flow is vB = 720 ± 280 km s-1 (1 σ error) in the direction l = 266°, b = 19°, with an overall 1 σ directional error of 38°. When all objects out to z = 0.1 are included, the result is virtually unchanged, vB = 700 ± 250 km s-1 toward l = 272°, b = 10° with a directional uncertainty of 35°. The hypothesis that the Hubble flow has converged to the cosmic microwave background (CMB) frame at distances 100 h-1 Mpc is ruled out at the 97% confidence level. The data are inconsistent with the flow vector found by Lauer & Postman; though similar in amplitude, the LP10K and Lauer-Postman flow vectors are nearly orthogonal. However, the LP10K bulk flow is consistent with that obtained from the Streaming Motions of Abell Clusters (SMAC) survey of elliptical galaxies recently described by Hudson et al. If correct, the LP10K results indicate that the convergence depth for the Hubble flow is 150 h-1 Mpc. However, the modest statistical significance of these results, together with contrasting claims recently made in the literature, suggest that further observational data are required before firm conclusions are drawn.
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