2018ApJS..234...24M

We present 33 GHz imaging for 112 pointings toward galaxy nuclei and extranuclear star-forming regions at ≃2'' resolution using the Karl G. Jansky Very Large Array (VLA) as part of the Star Formation in Radio Survey. A comparison with 33 GHz Robert C. Byrd Green Bank Telescope single-dish observations indicates that the interferometric VLA observations recover 78% ± 4% of the total flux density over 25'' regions (≃kpc scales) among all fields. On these scales, the emission being resolved out is most likely diffuse non-thermal synchrotron emission. Consequently, on the ≃30-300 pc scales sampled by our VLA observations, the bulk of the 33 GHz emission is recovered and primarily powered by free-free emission from discrete H II regions, making it an excellent tracer of massive star formation. Of the 225 discrete regions used for aperture photometry, 162 are extranuclear (i.e., having galactocentric radii r_G >= 250 pc) and detected at >3σ significance at 33 GHz and in Hα. Assuming a typical 33 GHz thermal fraction of 90%, the ratio of optically-thin 33 GHz to uncorrected Hα star formation rates indicates a median extinction value on ≃30-300 pc scales of A_Hα ≃ 1.26 ± 0.09 mag, with an associated median absolute deviation of 0.87 mag. We find that 10% of these sources are "highly embedded" (i.e., A_Hα >= 3.3 mag), suggesting that on average, H II regions remain embedded for <=1 Myr. Finally, we find the median 33 GHz continuum-to-Hα line flux ratio to be statistically larger within r_G < 250 pc relative to the outer disk regions by a factor of 1.82 ± 0.39, while the ratio of 33 GHz to 24 µm flux densities is lower by a factor of 0.45 ± 0.08, which may suggest increased extinction in the central regions.