IRAS-GALAXIES VERSUS POTENT MASS - DENSITY FIELDS, BIASING, AND OMEGA

The galaxy density field extracted from a complete redshift survey of IRAS galaxies brighter than 1.936 Jy is compared with the mass-density field reconstructed by the POTENT procedure from the observed peculia r velocities of 493 objects. Both density fields have been filtered wi th a Gaussian of smoothing length 1200 km s-1. Noise considerations li mit the present analysis to a volume approximately (5300 km s-1)3 cont aining approximately 12 independent density samples. We find a strong correlation between the galaxy and mass-density fields; both feature t he Great Attractor, part of the Perseus-Pisces supercluster, and the l arge void between them. Monte Carlo noise simulations show that the da ta are consistent with the hypotheses that the smoothed fluctuations o f galaxy and mass densities at each point are proportional to each oth er with a '' biasing '' factor of IRAS galaxies b(I), and that the pec uliar velocity field is related to the mass-density field as expected according to gravitational instability theory. Under these hypotheses, the two density fields can be related by specifying two parameters, b (I), and the cosmological density parameter OMEGA. The Monte Carlo sim ulations are then used to estimate the random errors, to correct for s ystematic errors in POTENT, and to constrain the parameters via a like lihood analysis. Our strongest result is OMEGA0.6/b(I) = 1.28(+0.75/-0 .59) at 95% confidence. Small nonlinear effects allow weaker, separate constraints on OMEGA and on b(I). Thus, if OMEGA = 1, then b(I) = 0.7 (+0.6/-0.2), and if b(I) > 0.5, then OMEGA > 0.46, both at the 95% con fidence level. Inhomogeneous Malmquist bias could cause an overestimat e of OMEGA; our 95% confidence limit for b(I) > 0.5 could be reduced b y correction for this bias at most to OMEGA > 0.3. The constraints on OMEGA are limited to the simple biasing relation assumed, but the effe ct of undersampling cluster cores by IRAS is negligible, and the resul ts are independent of the cosmological constant LAMBDA.