We report the first detection of the 205 \mu m ^ { 3 } P _ { 1 } \rightarrow ^ { 3 } P _ { 0 } [ NII ] line from a ground-based observatory using a direct detection spectrometer .
The line was detected from the Carina star formation region using the South Pole Imaging Fabry-Perot Interferometer ( SPIFI ) on the Antarctic Submillimeter Telescope and Remote Observatory ( AST/RO ) at South Pole .
The [ NII ] 205 \mu m line strength indicates a low-density ( n \sim 32 ~ { } { cm } ^ { -3 } ) ionized medium , similar to the low-density ionized halo reported previously in its [ OIII ] 52 and 88 \mu m line emission .
When compared with the ISO [ CII ] observations of this region , we find that 27 \% of the [ CII ] line emission arises from this low-density ionized gas , but the large majority ( \sim 73 \% ) of the observed [ CII ] line emission arises from the neutral interstellar medium .
This result supports and underpins prior conclusions that most of the observed [ CII ] 158 \mu m line emission from Galactic and extragalactic sources arises from the warm , dense photodissociated surfaces of molecular clouds .
The detection of the [ NII ] line demonstrates the utility of Antarctic sites for THz spectroscopy .