Detection of the 205 m [NII] Line from the Carina Nebula. G. J. Stacey 1 , T. E. Oberst 1 , A. Loehr 2 , S. C. Parshley 1 , T. Nikola 1 , N. F. H. Tothill 2 , J. I. Harnett 2 , A. P. Lane 2 , A. A. Stark 2 , and C. R. Tucker 3 1 Department of Astronomy, Cornell University
Detection of the 205 m [NII] Line from the Carina Nebula
G. J. Stacey1, T. E. Oberst1, A. Loehr2, S. C. Parshley1, T. Nikola1, N. F. H. Tothill2, J. I. Harnett2, A. P. Lane2, A. A. Stark2, and C. R. Tucker3
1Department of Astronomy, Cornell University
2Harvard-Smithsonian Center for Astrophysics
We report the first detection of the [NII] 205 m (1.46 THz) fine structure line from the ground using a direct detection spectrometer. The line was detected and mapped in emission from the Carina star formation region in the Galaxy using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) on the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole. The [NII] line is an important coolant for the diffuse ionized ISM, and (together with the 122 m [NII] line) is an excellent probe of gas density. The [NII] 205 m line emission peaks at the Carina II HII region, and its strength indicates low density (n ~ 30 cm-3) low ionization state gas envelopes the HII region. When compared with the ISO [CII] observations of this region, we find that a surprising large fraction (~ 50%) of the [CII] line emission arises from this low density ionized gas, a result with implications for [CII] studies of photodissociation regions (PDRs). The detection of this line demonstrates the utility of Antarctic sites for THz spectroscopy.
The Carina Nebula
The [NII] maps entailed ~ 20 pointings, or > 400 spectra covering the two regions:
Figure 1. 5 5 pixel SPIFI footprint (red square) and regions mapped (blue outlines) superposed on Digital Sky Survey image (from Mizutani et al. 2002).
The [NII] Lines
[NII] contours: fraction of peak (0.51 K)
Figure 3. SPIFI [NII] 205 m contours (blue & red) superposed on (black) 21 cm continuum contours (Retallack, 1983)
Figure 2. N+ Energy level diagram.
[NII] 205 n
Figure 5. Theoretical, and observed [NII] 122/205 m line ratio (blue line and dot) and [CII] 158 m/ [NII] 205 m line ratio (red line and dot) as a functions of ionized gas density.
Figure 4. [NII] 205 m line detected from G287.57-0.59 (Carina II).
Aurora over the South Pole August 22, 2005 (photo by Stephen Parshley)
The SPIFI instrument mounted on the Nasmyth arm of the AST/RO telescope.
Prior ISO Results
The [NII] Line Ratio
[NII] and [CII]
-- However, [CII] can also arise from low density ionized gas
Trec(DSB) ~ 150 K
This work was supported by NSF grants OPP-0094605, OPP-0338149, and NASA grant NNG05GK70H. We are indebted to the Cardiff group under P. A. R. Ade for their excellent filters, to the GSFC group (S.H. Moseley, D. J. Benford, & J. G. Staguhn) for their excellent bolometers, and to J.W. Kooi who set up LO’s for our frequency calibration at the pole. We also thank the many people who have contributed to the success of SPIFI both at AST/RO and the JCMT including, and especially C. M. Bradford, A. D. Bolatto, J.A. Davidson, & M. L. Savage
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