We have imaged the H92 \alpha ( 8.3 GHz ) , H75 \alpha ( 15 GHz ) , and H166 \alpha ( 1.4 GHz ) Radio Recombination Lines ( RRLs ) from NGC 253 at resolutions of 4.5 pc ( 0.4 ^ { \prime \prime } ) , 2.5 pc ( 0.2 ^ { \prime \prime } ) and 53 pc ( 4.5 ^ { \prime \prime } ) respectively .
The H92 \alpha line arises from individual compact sources , most of which possess radio continuum counterparts .
The line widths range from \sim 200 km s ^ { -1 } for the sources near the radio nucleus to 70-100 km s ^ { -1 } for the extranuclear ones .
These lines are emitted by gas at a density \sim 10 ^ { 4 } cm ^ { -3 } .
The remainder of the cm-wave RRLs arise in lower density gas ( \sim 500 cm ^ { -3 } ) with a higher area filling factor and with ten times higher mass .
A third component of higher density gas ( > 10 ^ { 4 } cm ^ { -3 } ) is required to explain the mm-wave RRLs .