Radio Recombination Lines from Starbursts: NGC 3256, NGC 4945 and the   Circinus Galaxy
  A renewed attempt to detect radio recombination lines from external galaxies has resulted in the measurement of lines from several bright starburst galaxies. The lines are produced by hydrogen ionized by young, high-mass stars and are diagnostic of the conditions and gas dynamics in the starburst regions without problems of dust obscuration. We present here detections of the lines H91alpha and H92alpha near 8.6 GHz from the starburst nuclei in NGC 3256, NGC 4945, and the Circinus galaxy using the ATCA and VLA. Modelling the line emitting region as a collection of H II regions, we derive the required number of H II regions, their temperature, density, and distribution. 
A.L. Roy, W.M. Goss, Niruj R. Mohan, T. Oosterloo, and K.R.   Anantharamaiah