Large-Scale Mass Distribution Behind the Galactic Plane

Abstract

We map the smoothed mass-density distribution in the Galactic zone of avoidance (zoa), within $6000\kms$ of the Local Group, using potent reconstruction from peculiar velocities of galaxies. The interpolation into the zoa is based on the assumed gravitational nature of the velocity field implying a potential flow. The main dynamical features at a distance r=4000 km/s are (a) the peak of the Great Attractor connecting Centaurus and Pavo at l=330, (b) a moderate bridge connecting Perseus-Pisces and Cepheus at l= 140, and (c) an extension of a large void from the southern Galactic hemisphere into the zoa near the direction of Puppis, l=220-270. We find a strong correlation between the mass density and the IRAS and optical galaxy density at $b=+-20, which indicates that the main dynamical features in the zoa should also be seen in galaxy surveys through the Galactic plane. The gravitational acceleration at the Local Group, based on the mass distribution out to 6000 km/s, is strongly affected by the mass distribution in the zoa: its direction changes by 31 when the |b| < 20 zoa is included, bringing it to within 4 +- 19 of the CMB dipole.