LOCAL GRAVITY AND LARGE-SCALE STRUCTURE

The magnitude and direction of the observed dipole anisotropy of the galaxy distribution can in principle constrain the amount of large-scale power present in the spectrum of primordial density fluctuations. We here confront the data, provided by a recent redshift survey of galaxies detected by the IRAS satellite, with the predictions of two cosmological models with very different levels of large-scale power: the biased Cold Dark Matter dominated model (CDM) and a baryon-dominated model (BDM) with isocurvature initial conditions. We investigate model predictions for the Local Group peculiar velocity, VR, induced by mass inhomogeneities distributed out to a given radius, R, for R ≲ 10,000 km s-1. We develop several convergence measures for VR, which can become powerful cosmological tests when deep enough samples become available. For the present data sets, the CDM and BDM predictions are indistinguishable at the 2 σ level and both are consistent with observations. A promising discriminant between cosmological models is the misalignment angle between VR and the apex of the dipole anisotropy of the microwave background.