A redshift survey of IRAS galaxies

We present the results of a full-sky flux-limited redshift survey of galaxies detected by the Infrared Astronomical Satellite (IRAS). Care is taken to correct the infrared flux densities for a variety of systematic biases of the IRAS database. The sample consists of 2636 galaxies covering 87.6% of the sky, and has a characteristic depth of 3500 km s$\sp{-1}$, or 35 Mpc for $H\sb0$ = 100 km s$\sp{-1}$ Mpc$\sp{-1}$. We use linear perturbation theory to relate the dipole moment of the galaxy distribution to the peculiar velocity of the Local Group; the angle between the two vectors is only 19$\sp\circ$. A comparison of the amplitudes of these two vectors yields an estimate of the cosmological density parameter $\Omega$ = 0.70 $\pm$ 0.16. The assumptions that enter into this calculation are critically examined, and the possibility of systematic errors is emphasized.

The relation between the dipole moment of the galaxy distribution, and the peculiar velocities of galaxies, allows us to predict the peculiar velocity field at every point within the volume enclosed by the sample; redshifts are corrected self-consistently for peculiar velocities using a robust iteration procedure. The velocity field shows strong infall into two major centers of mass concentration: the Pisces-Perseus supercluster and the Hydra-Centaurus supercluster. We make detailed comparisons of these predictions with directly observed peculiar velocities of galaxies from a variety of sources. There are systematic differences between observed and predicted peculiar velocities in various regions of the sky. In particular, the observations show a larger amplitude of infall towards the Hydra-Centaurus region than is predicted by the IRAS density distribution. This may indicate that the assumption that our sample traces the density distribution of dark matter is not correct in detail.