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A survey of submillimeter C and CO lines in nearby galaxies

Bayet, E. and Gerin, M. and Phillips, T. G. and Contursi, A. (2006) A survey of submillimeter C and CO lines in nearby galaxies. Astronomy and Astrophysics, 460 (2). pp. 467-485. ISSN 0004-6361. doi:10.1051/0004-6361:20053872.

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Aims. While the search for molecular gas in distant galaxies is based on the detection of submillimeter CO rotational lines, the current CO surveys of nearby galaxies are restricted to the millimeter CO lines. The submillimeter CO lines are formed in warm and dense molecular gas and are therefore sensitive to the physical conditions whereas the CO (J = 1 → 0) line is a tracer of the total molecular gas mass. In order to be able to compare the properties of molecular gas in nearby and distant galaxies, we have observed C and CO submillimeter lines (including the ^(12)CO(6-5) and ^(12)CO(7-6) lines) in a sample of nearby galaxies using the Caltech Submillimeter Observatory (CSO). Methods. We have obtained a complete view of the CO cooling curve (also called CO spectral energy distribution) by combining the submillimeter CSO data with previous observations found in the literature. We made use of Large Velocity Gradient (LVG) models to analyse the observed CO cooling curve, predict CO line intensities from J = 1 → 0 to J = 15 → 14 in the studied galaxies, and derive the physical properties of the warm and dense molecular gas : the kinetic temperature (T_K); the gas density (n(H2)); the CO column density divided by the line width N(^(12)CO)/Δv. The predictions for the line intensities and for the total CO cooling power, obtained from LVG modelling have been compared with predictions from Photo Dissociation Regions (PDR) models. Results. We show how the CO SED varies according to the galaxy star forming activity. For active nuclei, the peak is located near the ^(12)CO(6-5) or ^(12)CO(7-6) rotational lines, while, for normal nuclei, most of the energy is carried by the ^(12)CO(4-3) and ^(12)CO(5-4) lines. Whatever the spectral type of the nucleus, the observed C cooling rate is lower than the observed CO cooling rate (by a factor of ≥ 4). The CO cooling curve of nearby starburst galaxies (e.g. NGC 253) has a quite similar shape to the CO cooling curve of distant galaxies. Therefore, the CO cooling curves are useful diagnostics for the star forming activity in distant objects.

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Additional Information:© 2006 ESO. Received 21 July 2005. Accepted 21 August 2006. This work has benefitted from financial support from the CNRS/INSU research programs PCMI & PNG. We thank J. Cernicharo and M. Perault for letting us use their CO LVG models and J. Le Bourlot for introducing us to the Meudon PDR model. We made use of the SIMBAD and NED data base for helping us finding basic galaxy properties. The CSO is funded by the NSF under contract # AST 9980846.
Funding AgencyGrant Number
Centre National de la Recherche Scientifique/Institut national des sciences de l'Univers (CNRS/INSU)UNSPECIFIED
NSFAST 9980846
Subject Keywords:galaxies: starburst; galaxies: ISM; galaxies: nuclei; submillimeter; ISM: molecules
Issue or Number:2
Record Number:CaltechAUTHORS:20110216-095905891
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Official Citation:A survey of submillimeter C and CO lines in nearby galaxies E. Bayet, M. Gerin, T. G. Phillips and A. Contursi A&A 460 (2) 467-485 (2006) DOI: 10.1051/0004-6361:20053872
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22239
Deposited By: Ruth Sustaita
Deposited On:16 Feb 2011 18:37
Last Modified:09 Nov 2021 16:04

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