JVLA Observations of IC 342: Probing Star Formation in the Nucleus

IC 342 is a nearby, late-type spiral galaxy with a young nuclear star cluster surrounded by several giant molecular clouds. The IC 342 nuclear region is similar to the Milky Way and therefore provides an interesting comparison. We explore star formation in the nucleus using radio recombination line (RRL) and continuum emission at 5, 6.7, 33, and 35 GHz with the JVLA. These radio tracers are largely unaffected by dust and therefore sensitive to all of the thermal emission from the ionized gas produced by early-type stars. We resolve two components in the RRL and continuum emission within the nuclear region that lie east and west of the central star cluster. These components are associated both spatially and kinematically with two giant molecular clouds. We model these regions in two ways: a simple model consisting of uniform gas radiating in spontaneous emission, or as a collection of many compact H II regions in non-local thermodynamic equilibrium. The multiple H II region model provides a better fit to the data and predicts many dense ({n}_{{e}}∼ {10}⁴{--}{10}⁵ {{cm}}^-3), compact (≲ 0.1 pc) H II regions. For the whole nuclear region as defined by RRL emission, we estimate a hydrogen-ionizing rate of {N}_{{L}} ∼ 2× {10}⁵² {{{s}}}^-1, corresponding to the equivalent of ∼2000 O6 stars and a star formation rate of ∼0.15 M _⊙ yr^-1. We detect radio continuum emission west of the southern mini molecular spiral arm, consistent with trailing spiral arms.