The SFRS: 3-33GHz VLA obs. of star-forming regions

With 3-33GHz radio spectra, we measured the spectral indices and corresponding thermal (free-free) emission fractions for a sample of 335 discrete regions having significant detections in at least two radio bands. After removing 14 likely background galaxies, we find that the median thermal fraction at 33GHz is 92%+/-0.8% with a median absolute deviation of 11%, when a two-component power-law model is adopted to fit the radio spectrum.

Limiting the sample to 238 sources that are confidently identified as star-forming regions and not affected by potential AGN contamination (i.e., having galactocentric radii r_G_>=250pc) results in a median thermal fraction of 93%+/-0.8% with a median absolute deviation of 10%. We further measure the thermal fraction at 33GHz for 163 regions identified at 7" resolution to be 94%+/-0.8% with a median absolute deviation of 8%.