Detection of the 205 μm [N ii ] Line from the Carina Nebula

We report the first detection of the 205 um 3P1 - 3P0 [NII] line from aground-based observatory using a direct detection spectrometer. The line wasdetected from the Carina star formation region using the South Pole ImagingFabry-Perot Interferometer (SPIFI) on the Antarctic Submillimeter Telescope andRemote Observatory (AST/RO) at South Pole. The [NII] 205 um line strengthindicates a low-density (n ~ 32 cm^-3 ionized medium, similar to thelow-density ionized halo reported previously in its [OIII] 52 and 88 um lineemission. When compared with the ISO [CII] observations of this region, we findthat ~27% of the [CII] line emission arises from this low-density ionized gas,but the large majority ~ 73% of the observed [CII] line emission arises fromthe neutral interstellar medium. This result supports and underpins priorconclusions that most of the observed [CII] 158 um line emission from Galacticand extragalactic sources arises from the warm, dense photodissociated surfacesof molecular clouds. The detection of the [NII] line demonstrates the utilityof Antarctic sites for THz spectroscopy.Comment: 8 pages, 2 figures. To appear in the Astrophysical Journal Letter