Ionized Gas Towards Molecular Clumps: Physical Properties of Massive
  Star Forming Regions
  We have conducted a search for ionized gas at 3.6 cm, using the Very Large
Array, towards 31 Galactic intermediate- and high-mass clumps detected in
previous millimeter continuum observations. In the 10 observed fields, 35 HII
regions are identified, of which 20 are newly discovered. Many of the HII
regions are multiply peaked indicating the presence of a cluster of massive
stars. We find that the ionized gas tends to be associated towards the
millimeter clumps; of the 31 millimeter clumps observed, 9 of these appear to
be physically related to ionized gas, and a further 6 have ionized gas emission
within 1'. For clumps with associated ionized gas, the combined mass of the
ionizing massive stars is compared to the clump masses to provide an estimate
of the instantaneous star formation efficiency. These values range from a few
percent to 25%, and have an average of 7 +/- 8%. We also find a correlation
between the clump mass and the mass of the ionizing massive stars within it,
which is consistent with a power law. This result is comparable to the
prediction of star formation by competitive accretion that a power law
relationship exists between the mass of the most massive star in a cluster and
the total mass of the remaining stars.
