Millimetre and submillimetre observations of the emission from dust in compact H II regions

The authors report observations at 0.35, 0.8, 1.1 and 3.3 mm with almost identical beamsizes between 0.8 - 3.3 mm of a small sample of compact H II regions selected from the IRAS catalogue. They find (1) a mean long-wavelength emissivity law β = 1.75±0.20; (2) a short-wavelength emissivity law β ≤ 1; (3) the transition between the two regimes occurring at a wavelength somewhat longer than generally assumed; (4) a substantial contribution to the 3.3-mm fluxes from free-free emission