Spherical Infall in G10.6-0.4: Accretion through an Ultracompact H ii Region

We present high resolution (0.''12 x 0.''079) observations of theultracompact HII region G10.6-0.4 in 23 GHz radio continuum and the NH3(3,3)line. Our data show that the infall in the molecular material is largelyspherical, and does not flatten into a molecular disk at radii as small as 0.03pc. The spherical infall in the molecular gas matches in location and velocitythe infall seen in the ionized gas. We use a non-detection to place a stringentupper limit on the mass of an expanding molecular shell associated withpressure driven expansion of the HII region. These data support a scenario inwhich the molecular accretion flow passes through an ionization front andbecomes an ionized accretion flow onto one or more main sequence stars, not theclassical pressure-driven expansion scenario. In the continuum emission we seeevidence for externally ionized clumps of molecular gas, and cavities evacuatedby an outflow from the central source.Comment: Accepted for publication in Astrophysical Journal Letter