A Caltech Library Service

[C II] absorption and emission in the diffuse interstellar medium across the Galactic plane

Gerin, M. and Ruaud, M. and Goicoechea, J. R. and Gusdorf, A. and Godard, B. and De Luca, M. and Falgarone, E. and Goldsmith, P. F. and Lis, D. C. and Menten, K. M. and Neufeld, D. and Phillips, T. G. and Liszt, H. (2015) [C II] absorption and emission in the diffuse interstellar medium across the Galactic plane. Astronomy and Astrophysics, 573 . Art. No. A30. ISSN 0004-6361. doi:10.1051/0004-6361/201424349.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


Aims. Ionized carbon is the main gas-phase reservoir of carbon in the neutral diffuse interstellar medium (ISM) and its 158 μm fine structure transition [C ii] is the most important cooling line of the diffuse ISM. We combine [C ii] absorption and emission spectroscopy to gain an improved understanding of physical conditions in the different phases of the ISM. Methods. We present high-resolution [C ii] spectra obtained with the Herschel/HIFI instrument towards bright dust continuum regions in the Galactic plane, probing simultaneously the diffuse gas along the line of sight and the background high-mass star forming regions. These data are complemented by single pointings in the 492 and 809 GHz fine structure lines of atomic carbon and by medium spectral resolution spectral maps of the fine structure lines of atomic oxygen at 63 and 145 μm with Herschel/PACS. Results. We show that the presence of foreground absorption may completely cancel the emission from the background source in medium spectral resolution PACS data and that high spectral resolution spectra are needed to interpret the [C ii] and [O i] emission and the [C ii]/FIR ratio. This phenomenon may explain part of the [C ii]/FIR deficit seen in external luminous infrared galaxies where the bright emission from the nuclear regions may be partially canceled by absorption from diffuse gas in the foreground. The C+ and C excitation in the diffuse gas is consistent with a median pressure of ~5900 K cm^(-3) for a mean kinetic temperature of ~100 K. A few higher pressure regions are detected along the lines of sight, as emission features in both fine structure lines of atomic carbon. The knowledge of the gas density allows us to determine the filling factor of the absorbing gas along the selected lines of sight. The derived median value of the filling factor is 2.4%, in good agreement with the properties of the Galactic cold neutral medium. The mean excitation temperature is used to derive the average cooling due to C^+ in the Galactic plane : 9.5 × 10^(-26) erg^(-1) H^(-1). Along the observed lines of sight, the gas phase carbon abundance does not exhibit a strong gradient as a function of Galacto-centric radius and has a weighted average of C/H = 1.5 ± 0.4 × 10^(-4).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Goldsmith, P. F.0000-0002-6622-8396
Lis, D. C.0000-0002-0500-4700
Menten, K. M.0000-0001-6459-0669
Neufeld, D.0000-0001-8341-1646
Additional Information:© 2014 ESO. Article published by EDP Sciences. Received 6 June 2014; accepted 14 October 2014. The Herschel spacecraft was designed, built, tested, and launched under a contract to ESA managed by the Herschel/Planck Project team by an industrial consortium under the overall responsibility of the prime contractor Thales Alenia Space (Cannes), and including Astrium (Friedrichshafen) responsible for the payload module and for system testing at spacecraft level, Thales Alenia Space (Turin) responsible for the service module, and Astrium (Toulouse) responsible for the telescope, with in excess of a hundred subcontractors. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France and the US. Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri-INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronmico Nacional (IGN), Centro de Astrobiologa (CSIC-INTA); Sweden: Chalmers University of Technology – MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University – Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS and SPIRE consortia. M.G., M.R., A.G. and E.F. acknowledge support from the Centre National de Recherche Spatiale (CNES). This work was partly funded by grant ANR-09-BLAN-0231-01 from the French Agence Nationale de la Recherche as part of the SCHISM project. J.R.G. thanks Spanish MINECO for funding support under grants CDS2009-00038, AYA2009-07304 and AYA2012-32032. M.R. is supported by the 3DICE project, funded by an ERC Starting grant (Agreement number 336474). NRAO is operated by Associated Universities, Inc., under contract with the National Science Foundation. This work was carried out in part at the Jet Propulsion Laboratory, which is operated by the California Institute of Technology for NASA.We thank the referee, E. Jenkins, for his comprehensive report which helped us to significantly improve this paper.
Funding AgencyGrant Number
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Agence Nationale pour la Recherche (ANR)ANR-09-BLAN-0231-01
Ministerio de Economía, Industria y Competitividad (MINECO)CDS2009-00038
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2009-07304
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2012-32032
European Research Council (ERC)336474
Subject Keywords:ISM: general; ISM: structure; Galaxy: disk; infrared: ISM
Record Number:CaltechAUTHORS:20150313-113313705
Persistent URL:
Official Citation:[C II] absorption and emission in the diffuse interstellar medium across the Galactic plane M. Gerin, M. Ruaud, J. R. Goicoechea, A. Gusdorf, B. Godard, M. de Luca, E. Falgarone, P. Goldsmith, D. C. Lis, K. M. Menten, D. Neufeld, T. G. Phillips and H. Liszt A&A 573 A30 (2015) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:55749
Deposited On:13 Mar 2015 21:28
Last Modified:10 Nov 2021 20:49

Repository Staff Only: item control page