2005A&A...435..831R

We have detected the radio recombination lines H91α and H92α with rest frequencies of 8.6GHz and 8.3GHz from the starburst nucleus NGC 3256 at an angular resolution of 16.4''x9.6'' using the Australia Telescope Compact Array and at an angular resolution of 12.0''x2.9'' using the VLA. The line was detected at ∼1mJy/beam peak with a width of 160km/s with the ATCA and at ∼0.5mJy/beam peak with a width of 114km/s with the VLA. Modelling the line emitting region as a collection of H II regions, we derive constraints on the required number of H II regions, their temperature, density, and distribution. We find that a collection of 10 to 300 H II regions with temperatures of 5000K, densities of 1000cm^–3 to 5000cm^–3 and diameters of 15pc produced good matches to the line and continuum emmission. The Lyman continuum production rate required to maintain the ionization is 2x10⁵²s^–1 to 6x10⁵³s^–1, which requires 600 to 17000 O5 stars to be produced in the starburst.