Molecular distribution and kinematics in nearby galaxies II.
Molecular distribution and kinematics in nearby galaxies
II. Sub-mm observations of NGC4945
-
R. Mauersberger
-
Steward Observatory,
The University of Arizona
- Tucson,
AZ 85721, U.S.A.
- and
-
Max-Planck-Institut für Radioastronomie
- Auf dem Hügel 69, D-53121 Bonn, Germany
-
C. Henkel,
-
Max-Planck-Institut für Radioastronomie
- Auf dem Hügel 69, D-53121 Bonn, Germany
-
J.B. Whiteoak
-
Paul Wild Observatory,
Australia Telescope National Facility,
CSIRO
- Locked Bag 194, Narrabri NSW 2390, Australia
-
Y.-N. Chin
-
Radioastronomisches Institut der Universität Bonn
- Auf dem Hügel 71, D-53121 Bonn, Germany
-
A.R. Tieftrunk
-
Max-Planck-Institut für Radioastronomie
- Auf dem Hügel 69, D-53121 Bonn, Germany
Paper published in 1996 by the Main Journal of
Astronomy and Astrophysics in vol. 309, pp. 705 - 714.
If you want to have a look at the complete paper (without figures) please click
here (PostScript file of 2196379 bytes) or
here (gzip-compressed PostScript file
of 1778611 bytes).
Abstract.
The central 80 × 80 of the nearby edge-on starburst galaxy NGC4945 has been
mapped in the J=3-2 line of 12CO with a resolution of 15.
Also spectra of the J=3-2 transition of 13CO and tentative
detections of the J=4-3 line of HCN and the
J(Ka,Kc) = 3(1,2)-2(1,1) line of H2CO
are presented.
The CO J=3-2 emission is concentrated toward the kinematical center of
the galaxy with a deconvolved full width to half power (FWHP) size of
(11.5 ± 3) corresponding to (220 ± 50)pc at a distance D = 3.7 Mpc).
This is less than the extent of the nuclear molecular complex as derived
from the distributions of the lower rotational CO transitions.
Position-velocity maps reveal three condensations located at the center
and at offsets of 5 toward either side of the nucleus.
The dynamical mass in the inner R < 600 pc is ~
3 × 109 Msun.
Applying a `standard' N(H2)/I(CO) conversion factor of
2 × 1020 cm-2/(K km s-1), the central molecular
gas mass is ~ 9 × 108 Msun.
Like in the case of the central regions of the Milky Way and NGC253,
integrated 12CO line intensities combined with a standard conversion
factor yield a gas mass which is 6 to 14 times higher than that obtained from
multi-transition CO model and from the dust continuum emission.
If the latter results are correct, we find a conversion factor of only
0.15 ~ 0.35 × 1020 cm-2/(K km s-1) for the
central region of NGC4945.
An embedded active nucleus may contribute to the very high `star forming
efficiency' LIR/Mgas ~ 140 Lsun/Msun.
The contribution of the CO lines to the `continuum' flux density in
a 50GHz 1.3mm band is comparable to that of the dust.
From the strength of the CO J=3-2 emission and our tentative detection
of high density tracing molecules, bulk of the CO emitting gas should have a
high density (n(H2) = 103.5 ~ 104
cm-3) and is clumped with a beam filling factor of roughly 20%.
Any suggestion or comments please
e-mail to einmann@asiaa.sinica.edu.tw.
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