Issue |
A&A
Volume 427, Number 1, November III 2004
|
|
---|---|---|
Page(s) | 45 - 59 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20035614 | |
Published online | 25 October 2004 |
The submillimeter C and CO lines in Henize 2-10 and NGC 253
1
Laboratoire de Radioastronomie (LRA), Observatoire de Paris and École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France (CNRS-UMR 8112) e-mail: estelle.bayet@lra.ens.fr
2
California Institute of Technology, Downs Laboratory of Physics 320-47, Pasadena, CA 91125, USA
3
Max Planck Institute für Extraterrestrische Physik, Postfach 1312, 85741, Garching, Germany
Received:
3
November
2003
Accepted:
5
July
2004
The purpose of this paper is to describe a method for
determining a cooling template for galaxies, using nearby galaxies,
and applicable to future observations of distant galaxies.
We observed two starburst galaxies (NGC 253 and Henize 2-10) with
the Caltech Submillimeter Observatory in the rotational lines
of carbon monoxide 12CO(–2), (
–5) and (
–6) for both,
and also 12CO(
–3) and 13CO(
–2) for Henize 2-10 and in the 3P2–3P1 fine-structure
transitions of atomic carbon [CI] at 809 GHz for NGC 253. Some of
these observations have been made previously, but the present
multitransition study (including data found in the
literature) is the most complete to date for the two galaxies.
From these observations, we have derived the properties of the warm
and dense molecular gas in the galaxy nuclei. We used an LTE analysis and an LVG radiative transfer model to determine physical
conditions of the interstellar medium in both sources and predicted
integrated line properties of all CO transitions up to
12CO(15–14). We found the observations to be in good agreement with a
medium characterized by
–100 K,
,
cm-3 and
cm-2 for Henize 2-10 and characterized by
–150 K,
,
cm-3 and
cm-2
for NGC 253. A PDR model has also been used and here the data are
well fitted (within 20%) by a model cloud with a gas density of
cm-3 and an incident FUV flux
of
for Henize 2-10. For NGC 253, we deduced
cm-3 and
for
the modelled cloud. The physical properties of warm gas and
CO cooling curves of the target galaxies are compared
with those measured for the nucleus of the Milky Way and the Cloverleaf QSO. The gas properties and CO cooling curve are similar for the two starburst galaxies and the Cloverleaf QSO while the Milky Way nucleus exhibits lower excitation molecular gas.
Key words: galaxies: starburst / galaxies: individual: NGC 253 / galaxies: individual: Henize 2-10 / submillimeter / ISM: molecules / galaxies: ISM
© ESO, 2004
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