IRAS versus POTENT Density Fields on Large Scales: Biasing Parameter and Ω

The galaxy density field as extracted from the IRAS 1.2 Jy redshift survey is compared to the mass-density field as reconstructed by the POTENT method from the Mark III catalog of peculiar velocities. The reconstruction is done with Gaussian smoothing of radius 12 h-1 Mpc, and the comparison is carried out within volumes of effective radii 31-46 h-1 Mpc, containing ≈ 10-26 independent samples. Random and systematic errors are estimated from multiple realizations of mock catalogs drawn from a simulation that mimics the observed density field in the local universe. The relationship between the two density fields is found to be consistent with gravitational instability theory in the mildly nonlinear regime and a linear biasing relation between galaxies and mass. We measure βI ≡ Ω0.6/bI = 0.89 ± 0.12 within a volume of effective radius 40 h-1 Mpc, where bI is the IRAS galaxy biasing parameter at 12 h-1 Mpc. This result is only weakly dependent on the comparison volume, suggesting that cosmic scatter is no greater than ±0.1. These data are thus consistent with Ω = 1 and bI ≃ 1. If bI > 0.75, as theoretical models of biasing indicate, then Ω > 0.33 at 95% confidence. A comparison with other estimates of βI, if not dominated by unaccounted-for systematic errors, may provide hints for scale dependence in the biasing relation for IRAS galaxies.