MDense gas in nearby galaxies VIII. OCS
Dense gas in nearby galaxies
VIII. The detection of OCS
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R. Mauersberger
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Max-Planck-Institut für Radioastronomie
- Auf dem Hügel 69, D-53121 Bonn, Germany
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C. Henkel
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Max-Planck-Institut für Radioastronomie
- Auf dem Hügel 69, D-53121 Bonn, Germany
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Y.-N. Chin
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Radioastronomisches Institut der Universität Bonn
- Auf dem Hügel 71, D-53121 Bonn, Germany
Paper published in 1995 by the Main Journal of
Astronomy and Astrophysics in vol. 294, pp. 23 - 32.
If you want to have a look at the complete paper (without figures) please click
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Abstract.
The detection of extragalactic OCS, the heaviest molecule identified outside the
Galaxy, is reported in three rotational transitions toward the bulge of NGC253.
Toward M82, OCS has been tentatively detected.
Abundances are consistent with models for warm, dense clouds which have not yet
reached chemical equilibrium or with the frequent erosion of grain mantles
by C-shocks.
This can also explain the large abundances of complex molecules in NGC253.
Densities and temperatures of the OCS emitting gas are compared with results
from other molecular tracers.
From model computations, OCS in the center of NGC253 is emitted by a moderately
dense molecular component with n(H2) ~
103.4 /cm3.
This component makes up the bulk of the molecular gas mass.
Other molecules also reveal the presence of a much denser component
with 10(5-5.5) /cm3.
A molecular gas mass of ~ 2 × 108 solar masses is estimated for
a 180pc sized molecular cloud toward the center of NGC253; the mean
H2 density is ~ 2000 /cm3; and the mean H2
column density, 7 × 1023 /cm2, corresponds to a
visual extinction of 700m.
The relative OCS abundance is X(OCS) ~ 10-8.9.
From detections of the J=2-1 and 3-2 transitions of C34S, the density of
the dense molecular gas toward the nuclear region of IC342 is
n(H2) ~ 104.6 /cm3.
Also presented are a possible detection of the HC3N J=16-15
line toward IC342 and upper limits for the emission of the DCN J=2-1
line toward NGC253 and IC342.
For NGC253, [DCN]/[HCN] <= 4 × 10-3.
Any suggestion or comments please
e-mail to einmann@asiaa.sinica.edu.tw.
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