Outflow-Confined H II Regions. I. First Signposts of Massive Star
  Formation
  We present an evolutionary sequence of models of the photoionized disk-wind
outflow around forming massive stars based on the Core Accretion model. The
outflow is expected to be the first structure to be ionized by the protostar
and can confine the expansion of the HII region, especially in lateral
directions in the plane of the accretion disk. The ionizing luminosity
increases as Kelvin-Helmholz contraction proceeds, and the HII region is formed
when the stellar mass reaches ~10-20Msun depending on the initial cloud core
properties. Although some part of outer disk surface remains neutral due to
shielding by the inner disk and the disk wind, almost the whole of the outflow
is ionized in 1e3-1e4 yr after initial HII region formation. Having calculated
the extent and temperature structure of the HII region within the immediate
protostellar environment, we then make predictions for the strength of its
free-free continuum and recombination line emission. The free-free radio
emission from the ionized outflow has a flux density of ~(20-200)x(nu/10GHz)^p
mJy for a source at a distance of 1 kpc with a spectral index p~0.4-0.7, and
the apparent size is typically ~500AU at 10GHz. The H40alpha line profile has a
width of about 100km/s. These properties of our model are consistent with
observed radio winds and jets around forming massive protostars.
