Radio recombination lines ( RRLs ) are powerful , extinction-free diagnostics of the ionized gas in young , star-forming regions .
Unfortunately , these lines are difficult to detect in external galaxies .
We present the results of EVLA observations of the RRL and radio continuum emission at 33 GHz from NGC 253 , a nearby nuclear starburst galaxy .
We detect the previously unobserved H58 \alpha and H59 \alpha RRLs and make simultaneous sensitive measurements of the continuum .
We measure integrated line fluxes of 44.3 \pm 0.7 W m ^ { -2 } and 39.9 \pm 0.8 W m ^ { -2 } for the H58 \alpha and H59 \alpha lines , respectively .
The thermal gas in NGC 253 is kinematically complex with multiple velocity components .
We constrain the density of the thermal gas to 1.4 - 4 \times 10 ^ { 4 } cm ^ { -3 } and estimate an ionizing photon flux of 1 \times 10 ^ { 53 } s ^ { -1 } .
We use the RRL kinematics and the derived ionizing photon flux to show that the nuclear region of NGC 253 is not gravitationally bound , which is consistent with the outflow of gas inferred from the X-ray and { H } \alpha measurements .
The line profiles , fluxes , and kinematics of the H58 \alpha and H59 \alpha lines agree with those of RRLs at different frequencies confirming the accuracy of the previous , more difficult , high frequency observations .
We find that the EVLA is an order of magnitude more efficient for extragalactic RRL observations than the VLA .
These observations demonstrate both the power of the EVLA and the future potential of extragalactic RRL studies with the EVLA .