A VLA Census of the Galactic H II Region Population
  The Milky Way contains thousands of H II region candidates identified by
their characteristic mid-infrared morphology, but lacking detections of ionized
gas tracers such as radio continuum or radio recombination line emission. These
targets thus remain unconfirmed as H II regions. With only $\sim$2500 confirmed
H II regions in the Milky Way, Galactic surveys are deficient by several
thousand nebulae when compared to external galaxies with similar star formation
rates. Using sensitive 9 GHz radio continuum observations with the Karl G.
Jansky Very Large Array (VLA), we explore a sample of H II region candidates in
order to set observational limits on the actual total population of Galactic H
II regions. We target all infrared-identified "radio quiet" sources from the
WISE Catalog of Galactic H II regions between
$245^{\circ}\geq\ell\geq90^{\circ}$ with infrared diameters less than
80$^{\prime\prime}$. We detect radio continuum emission from 50% of the
targeted H II region candidates, providing strong evidence that most of the
radio quiet candidates are bona fide HII regions. We measure the peak and
integrated radio flux densities and compare the inferred Lyman continuum fluxes
using models of OB-stars. We conclude that stars of approximately spectral type
B2 and earlier are able to create H II regions with similar infrared and radio
continuum morphologies as the more luminous H II regions created by O-stars.
From our 50% detection rate of "radio quiet" sources, we set a lower limit of
$\sim$7000 for the H II region population of the Galaxy. Thus the vast majority
of the Milky Way's H II regions remain to be discovered.
