2017ApJ...846...64M

We derive infrared and radio flux densities of all ∼1000 known Galactic H II regions in the Galactic longitude range 17○ / . 5 ℓ65^○. Our sample comes from the Wide-Field Infrared Survey Explorer (WISE) catalog of Galactic H II regions. We compute flux densities at six wavelengths in the infrared (Spitzer GLIMPSE 8 µm, WISE 12 µm and 22 µm, Spitzer MIPSGAL 24 µm, and Herschel Hi-GAL 70 µm and 160 µm) and two in the radio (MAGPIS 20 cm and VGPS 21 cm). All H II region infrared flux densities are strongly correlated with their ∼20 cm flux densities. All H II regions used here, regardless of physical size or Galactocentric radius, have similar infrared to radio flux density ratios and similar infrared colors, although the smallest regions (r < 1 pc), have slightly elevated IR to radio ratios. The colors log₁₀(F_24µm_/F12µm_) 0 and log₁₀(F_70µm_/F12µm_) 1.2, and log₁₀(F_24µm_/F12µm_) 0 and log₁₀(F_160µm_/F70µm_) 0.67 reliably select H II regions, independent of size. The infrared colors of ∼22% of H II regions, spanning a large range of physical sizes, satisfy the IRAS color criteria of Wood & Churchwell for H II regions, after adjusting the criteria to the wavelengths used here. Because these color criteria are commonly thought to select only ultra-compact H II regions, this result indicates that the true ultra-compact H II region population is uncertain. Compared to a sample of IR color indices from star-forming galaxies, H II regions show higher log₁₀(F_70µm_/F12µm_) ratios. We find a weak trend of decreasing infrared to ∼20 cm flux density ratios with increasing R_gal, in agreement with previous extragalactic results, possibly indicating a decreased dust abundance in the outer Galaxy.