CO (J= 3 → 2) observations of the starburst galaxy NGC 1808 with ASTE
In: Publications of the Astronomical Society of Japan, Jg. 66 (2014-10-01), Heft 5
Online
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Zugriff:
We present the first map of 12CO (J= 3 → 2) and the first detection of 13CO (J= 3 → 2) in the nearby starburst galaxy with a superwind, NGC 1808. The molecular gas is concentrated in the inner 2 kpc region of the galaxy with extended structure along the galactic bar and along the minor galactic axis. The minor-axis structure can be explained as molecular gas entrained in a galactic wind observed as a dust outflow at optical wavelengths. We have carried out a radiative transfer analysis of the excitation conditions of molecular gas in the starburst region (radius 550 pc) by using the ratios of J= 1 → 0, J= 2 → 1, and J= 3 → 2 emission lines of 12CO and 13CO, and the large velocity gradient approximation. The beam-averaged density and kinetic temperature of molecular gas can be fitted at nH2≃ 103.5cm−3and Tk≃ 35 K, indicating the presence of warm molecular gas, close to the estimated dust temperature of Td≃ 34–37 K. The abundance ratio of the CO isotopologues is found to be [12CO]/[13CO] ≃ 34. The calculations show that, for the derived physical parameters, J= 2 → 1 and J= 3 → 2 transitions of 12CO are optically thick, 12CO J= 1 → 0 is moderately optically thick, and all transitions of 13CO are optically thin. We have estimated an average CO–H2conversion factor of XCO≃ 0.8 × 1020cm−2(K km s−1)−1in the central 550 pc by using a simple theoretical model assuming homogeneous, gravitationally bound gas clouds with turbulent velocities. In the same region the molecular gas mass is 3.0 × 108M⊙available to fuel the nuclear starburst.
Titel: |
CO (J= 3 → 2) observations of the starburst galaxy NGC 1808 with ASTE
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Autor/in / Beteiligte Person: | Salak, Dragan ; Nakai, Naomasa ; Kitamoto, Shoko |
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Zeitschrift: | Publications of the Astronomical Society of Japan, Jg. 66 (2014-10-01), Heft 5 |
Veröffentlichung: | 2014 |
Medientyp: | serialPeriodical |
ISSN: | 0004-6264 (print) ; 2053-051X (print) |
DOI: | 10.1093/pasj/psu074 |
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