2007ApJ...670..295R

We present observations in the H53α line and radio continuum at 43 GHz carried out with the VLA in the D configuration (2" angular resolution) toward the starburst galaxy NGC 5253. VLA archival data have been reprocessed to produce a uniform set of 2, 1.3, and 0.7 cm high angular (0.2"x0.1") radio continuum images. The radio recombination line (RRL) H53α, a previously reported measurement of the H92α RRL flux density, and the reprocessed high angular resolution radio continuum flux densities have been modeled using a collection of H II regions. Based on the models, the ionized gas in the nuclear source has an electron density of ∼6x10⁴/cm3 and a volume filling factor of 0.05. A Lyman continuum photon production rate of 2x10⁵²/s is necessary to sustain the ionization in the nuclear region. The number of required O7 stars in the central 1.5 pc of the supernebula is ∼2000. The H53α velocity gradient (10 km/s/arcsec) implies a dynamical mass of ∼3x10⁵ M_☉; this mass suggests that the supernebula is confined by gravity.