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First detection of ...
First detection of [NII] 205 μm absorption in interstellar gas. Herschel-HIFI observations towards W31C, W49N, W51, and G34.3+0.1.
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- Persson, Carina, 1964 (author)
- Chalmers tekniska högskola,Chalmers University of Technology
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- Gerin, M. (author)
- Ecole Normale Superieure (ENS)
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- Mookerjea, Bhaswati (author)
- Tata Institute of Fundamental Research
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- Black, John H, 1949 (author)
- Chalmers tekniska högskola,Chalmers University of Technology
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- Olberg, Michael, 1956 (author)
- Chalmers tekniska högskola,Chalmers University of Technology
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- Goicoechea, J.R. (author)
- CSIC - Instituto de Ciencia de Materiales de Madrid (ICMM)
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- Hassel, G.E. (author)
- Siena College
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- Falgarone, E. (author)
- Ecole Normale Superieure (ENS)
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- Levrier, F. (author)
- Ecole Normale Superieure (ENS)
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- Menten, K.M. (author)
- Max Planck Gesellschaft zur Förderung der Wissenschaften e.V. (MPG),Max Planck Society for the Advancement of Science (MPG)
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- Pety, J. (author)
- Institut de Radioastronomie Millimétrique (IRAM)
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(creator_code:org_t)
- 2014-08-08
- 2014
- English.
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 568, s. 37-
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Abstract
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- We present high resolution [N II] 205 μm (3^P_1 − 3^P_0) spectra obtained with Herschel-HIFI towards a small sample of far-infrared bright star forming regions in the Galactic plane: All sources display an emission line profile associated directly with the H II regions themselves. For the first time we also detect absorption of the [N II] 205 μm line by extended low-density foreground material towards W 31C and W 49N over a wide range of velocities. We attribute this absorption to the warm ionised medium (WIM) and find N(N+) ≈ 1.5×10^17 cm^-2 towards both sources. This is in agreement with recent Herschel-HIFI observations of [C II] 158 μm, also observed in absorption in the same sight-lines, if ≈7–10% of all C + ions exist in the WIM on average. Using an abundance ratio of [N]/[H] = 6.76×10^-5 in the gas phase we find that the mean electron and proton volume densities are ∼0.1–0.3 cm^-3 assuming a WIM volume filling fraction of 0.1–0.4 with a corresponding line-of-sight filling fraction of 0.46–0.74. A low density and a high WIM filling fraction are also supported by RADEX modelling of the [N II] 205 μm absorption and emission together with visible emission lines attributed mainly to the WIM. The detection of the 205 μm line in absorption emphasises the importance of a high spectral resolution, and also offers a new tool for investigation of the WIM.
Subject headings
- NATURVETENSKAP -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)
Keyword
- atomic processes
- ISM: atoms
- line formation
- ISM: structure
- Galaxy: general
- ISM: abundances
Publication and Content Type
- art (subject category)
- ref (subject category)
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Persson, Carina, ...
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Gerin, M.
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Mookerjea, Bhasw ...
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Black, John H, 1 ...
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Olberg, Michael, ...
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Goicoechea, J.R.
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Hassel, G.E.
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Falgarone, E.
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Levrier, F.
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Menten, K.M.
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Pety, J.
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- NATURAL SCIENCES
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NATURAL SCIENCES
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and Physical Science ...
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Chalmers University of Technology