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

We present high-resolution (0.12"×0.079") observations of the ultracompact H II 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 largely spherical and does not flatten into a thin disk at radii as small as 0.03 pc. The spherical infall in the molecular gas matches in location and velocity the infall seen in the ionized gas. We use a nondetection to place a stringent upper limit on the mass of an expanding molecular shell associated with pressure-driven expansion of the H II region. These data support a scenario in which the molecular accretion flow passes through the ionization front and becomes an ionized accretion flow onto one or more main-sequence stars, not the classical pressure-driven expansion scenario. In the continuum emission, we see evidence for externally ionized clumps of molecular gas and cavities evacuated by an outflow from the central source.