Archival VLA data has been used to produce arcsecond-resolution 6- and 20-cm images of the region surrounding the nuclear 200-pc ( \sim 15 ^ { \prime \prime } ) starburst in NGC 253 .
Twenty-two discrete sources stronger than 0.4 mJy have been detected within \sim 2 kpc ( \sim 3′ ) of the galaxy nucleus ; almost all these sources must be associated with the galaxy .
None of the radio sources coincides with a detected X-ray binary , so they appear to be due to supernova remnants and H ii regions .
The region outside the central starburst has a derived radio supernova rate of \lesssim 0.1 yr ^ { -1 } , and may account for at least 20 % of the recent star formation in NGC 253 .
Most of the newly identified sources have steep , nonthermal radio spectra , but several relatively strong thermal sources also exist , containing the equivalent of tens of O5 stars .
These stars are spread over tens of parsecs , and are embedded in regions having average ionized gas densities of \sim 20–200 cm ^ { -3 } , much lower than in the most active nuclear star-forming regions in NGC 253 or in the super star clusters seen in other galaxies .
The strongest region of thermal emission coincides with a highly reddened area seen at near-infrared wavelengths , possibly containing optically obscured H ii regions .