THE GALAXY VELOCITY-FIELD AND COLD DARK-MATTER MODELS

We consider a composite sample of 1184 optically selected galaxies wit h known peculiar motions, grouped in 704 objects that we assume as fai r tracers of the underlying velocity field. We perform a detailed stat istical analysis, calculating both the bulk flow and the velocity corr elation function. The same tests are applied to mock catalogs extracte d from Monte Carlo simulations of the linear velocity field in CDM mod els. We sample this field at the same locations of the observed galaxi es, placing the ''observer'' in a point with properties similar to tho se of the Local Group. The density parameter OMEGA0, the primordial sp ectral index n, and the linear bias parameter b are allowed to vary in suitable intervals. By a maximum likelihood analysis we assess the re lative merits of the models in fitting the observations as measured by the above statistics and reproducing the Local Group properties. Our main results are the following. For a fixed value OMEGA0 = 0.2 the ''b est'' values correspond to b = 1 and n = 0-0.5; for a flat universe th e likelihood function peaks at (n = 0, b = 2), while the unbiased stan dard CDM model (OMEGA0 = n = b = 1) is rejected at about 90% confidenc e level. By allowing only one parameter to vary we get a maximum aroun d b = 1.3-1.5 in the standard CDM model (OMEGA0 = n = 1) and we can ex clude b < 0.8 with 90% confidence. For a model with fixed n = b = 1 th e preferred model has OMEGA0 = 0.3, while the allowed range is [0.1, 0 .85] (still at 90%). Only a weak dependence on n is found in models wi th OMEGA0 = b = 1. Our prediction for the linear bias parameter in the standard CDM model is strongly affected by the Local Group constraint : by dropping this condition, the lower value b = 0.8-1.0 would result , for the likelihood maximum, and b > 1.8 values would be rejected at the 90% confidence level.