GALACTIC ACCRETION AND ANGULAR-MOMENTUM REORIENTATION

The generation of galactic angular momentum by tidal forces is re-examined. We calculate the tidal torques in linear theory on a spherical shell centred either on a random point or on a peak in the smoothed density field. We show that when the torque is decomposed into contributions from multipoles, the dipole term is more important than the quadrupole, and higher multipoles are unimportant. When the dipole contribution is taken into account, the torques of thin shells of radii r and r' are anticorrelated for r/r' greater-than-or-similar-to 2. Significant contributions to the torque on any shell come from shells that are more than five times as big. The magnitude of the torque on a shell does not depend greatly on whether the shell is centred on a peak in the smoothed density field rather than on a random point. The dimensionless angular momentum parameter-lambda of virialized objects remains fairly constant at lambda congruent-to 0.05 as the object grows as a result of cosmic infall.