Line broadening in the W3(OH) champagne flow

High angular resolution H92 alpha recombination-line and 18 cm continuum observations of the ultracompact H II region W3(OH) indicate a supersonic champagne flow: a 12 km/s gradient in the recombination-line velocities across the H II region measures the acceleration of the ionized gas, while low-level contiuum emission traces the extent of the outflow to the northeast away from the compact core. The previously observed progressive blueshifting of lower frequency recombination lines may be due to variations in electron impact line broadening in the champagne flow. This systematic shifting of the recombination-line velocities can occur because the line broadening is coupled to the gas density through electron collisions while the gas velocity is also coupled to the density through mass flux conservation. Interpretation of observations of H II regions within the context of the champagne flow model rather than the ionization bounded nebula model has implications for theories of the sequential formation of massive stars in clusters and the dynamical evolution of molecular gas around newly formed stars.