On the Radiative Acceleration of Quasar Absorption Line Clouds

Abstract

Radiation may expel dense gas clouds from quasar emission line regions. Small clouds can be accelerated to velocities approaching c if they are confined so as to maintain high densities. The kinetic energies, inferred from the spectra, of low to medium excitation quasar absorption clouds are too large for radiation pressure to have played a dominant role in their acceleration. If these clouds are physically associated with the quasars, they are probably accelerated by the same stresses that are responsible for their confinement. Models for absorption clouds based on radiatively driven instabilities in expanding quasar envelopes predict column densities that are much larger than those deduced from observation.