We have observed seven ultracompact HII regions in hydrogen recombination
lines in the millimeter band. Toward four of these regions, there is a high
velocity (full width to half maximum 60-80 km/s) component in the line
profiles. The high velocity gas accounts for 35-70% of the emission measure
within the beam. We compare these objects to an additional seven similar
sources we have found in the literature. The broad recombination line objects
(BRLOs) make up about 30% of all sources in complexes containing ultracompact
HII regions. Comparison of spectral line and continuum data implies that the
BRLOs coincide with sources with rising spectral indices, >=0.4 up to 100 GHz.
Both the number of BRLOs and their frequency of occurrence within HII region
complexes, when coupled with their small size and large internal motions, mean
that the apparent contradiction between the dynamical and population lifetimes
for BRLOs is even more severe than for ultracompact HII regions. We evaluate a
number of models for the origin of the broad recombination line emission. The
lifetime, morphology, and rising spectral index of the sources argue for photo-
evaporated disks as the cause for BRLOs. Existing models for such regions,
however, do not account for the large amounts of gas observed at supersonic
velocities.Comment: 36 pages, 8 figure