A Multiwavelength Look at Galactic Massive Star Forming Regions
  We present a multiwavelength study of 28 Galactic massive star-forming H II
regions. For 17 of these regions, we present new distance measurements based on
Gaia DR2 parallaxes. By fitting a multicomponent dust, blackbody, and power-law
continuum model to the 3.6 $\mu$m through 10 mm spectral energy distributions,
we find that ${\sim}34$% of Lyman continuum photons emitted by massive stars
are absorbed by dust before contributing to the ionization of H II regions,
while ${\sim}68$% of the stellar bolometric luminosity is absorbed and
reprocessed by dust in the H II regions and surrounding photodissociation
regions. The most luminous, infrared-bright regions that fully sample the upper
stellar initial mass function (ionizing photon rates $N_C \ge 10^{50}~{\rm
s}^{-1}$ and dust-processed $L_{\rm TIR}\ge 10^{6.8}$ L$_{\odot}$) have on
average higher percentages of absorbed Lyman continuum photons ($\sim$51%) and
reprocessed starlight ($\sim$82%) compared to less luminous regions. Luminous H
II regions show lower average PAH fractions than less luminous regions,
implying that the strong radiation fields from early-type massive stars are
efficient at destroying PAH molecules. On average, the monochromatic
luminosities at 8, 24, and 70 $\mu$m combined carry 94% of the dust-reprocessed
$L_{\rm TIR}$. $L_{70}$ captures ${\sim}52$% of $L_{\rm TIR}$, and is therefore
the preferred choice to infer the bolometric luminosity of dusty star-forming
regions. We calibrate SFRs based on $L_{24}$ and $L_{70}$ against the Lyman
continuum photon rates of the massive stars in each region. Standard
extragalactic calibrations of monochromatic SFRs based on population synthesis
models are generally consistent with our values.
