Dark matter from cosmic flows: how much? where? what is it?

The large-scale dynamics of matter is inferred from the observed peculiar velocities of galaxies via the POTENT procedure. The smoothed fields of velocity and mass-density fluctuations are recovered from the current data of ∼ 3,000 galaxies. The cosmological density parameter Ω is constrained in three ways: (a) by comparing the density fields of mass and galaxies, (b) by using the velocity field in voids, and (c) by investigating quasilinear deviations from Gaussian fluctuations. The results indicate a high value for Ω, of order unity; values of 0.3 and lower are rejected with high confidence. If neutrinos contribute Ω_ν ≈ 0.2 as indicated by preliminary experimental results, and if baryonic matter is indeed strongly limited by nucleosynthesis constraints, the high value of Ω suggests the existence of yet another dark-matter component. Such a hybrid of cold and hot dark matter, though inelegant a priori, has been proposed earlier based on apparently-conflicting observational constraints on galactic and supergalactic scales. Highresolution POTENT analysis may help discriminating between dark-matter models.