Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sf2a.conf..489b&link_type=abstract
SF2A-2004: Semaine de l'Astrophysique Francaise, meeting held in Paris, France, June 14-18, 2004. Edited by F. Combes, D. Barret
Astronomy and Astrophysics
Astrophysics
Scientific paper
We observed galaxies (NGC 253, Henize 2-10, M83, IC342 and NGC 6946) with the Caltech Submillimeter Observatory in various rotational lines of carbon monoxide: 12CO(J=3-2), (J=4-3), (J=6-5) and (J=7-6) and also 13CO(J=3-2) and in the 3P2-3P1 and 3P1-3P0 fine-structure transitions of atomic carbon [CI] at 809 GHz and 492 Ghz, respectively. 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 these 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 NGC 253, Henize 2-10, M83 and IC342 and predicted integrated line properties} of all CO transitions up to CO(15-14). We found the observations to be in good agreement with a medium defined by Tk≈ 50-10 0 K, 12CO/13CO ≈ 30, n(H2) ≳ 104 cm-3 and N(12CO)= 3.5 ±1 — 1018 cm-2 for Henize 2-10 and defined by Tk≈ 70-150 K, 12CO/13CO ≈ 40, n(H2) ≳ 104 cm-3 and N(12CO)=1.5 ± 0.5 —1019 cm-2 for NGC 253. A PDR model has also been used and here the data are well fitted by a model cloud (within 20 %) with a gas density of n(H)= 8.0± 1 — 105 cm-3 and an incident FUV flux of chi ≈20000 for Henize 2-10. For NGC 253, we deduced n(H)= 3.0±0.5 — 105 cm-3 and chi ≈20000 for the modelled cloud. M83 and IC342 have just finished to be studied with a LVG model. For M83, we found the observations well fitted with the following models: Tk≈ 100-150 K, 12CO/13CO ≈ 40, n(H2) ≳ 104 cm-3 and N(12CO)=3.0±1 —1018 cm-2. For IC342, We reproduced well observations with a LVG model of Tk≈ 100 K, 12CO/13CO ≈ 40, n(H2)=1000 cm-3 and N(12CO)=5 —1018 cm-2 or with a LVG model of Tk ≈ 170 K, 12CO/13CO ≈ 40, n(H2)=562.3 cm-3 and N(12CO)=6.0 —1018 cm-2. We compared our results (physical properties of warm gas) with those obtained for the nucleus of Milky Way and the Cloverleaf QSO
Bayet Estelle
Contursi Alessandra
Gerin Maryvonne
Phillips Thomas G.
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