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Astron. Astrophys. 347, 37-46 (1999)

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13CO(1-0) and 12CO(2-1) in the center of the barred galaxy NGC 1530

D. Reynaud 1,2 and D. Downes 1

1 Institut de Radio Astronomie Millimétrique, F-38406 Saint Martin d'Hères, France
2 CEA/DSM/DAPNIA/SAp, C.E. Saclay, F-91191 Gif-sur-Yvette Cedex, France

Received 23 November 1998 / Accepted 15 April 1999

Abstract

We present 13CO(1-0) and 12CO(2-1) aperture synthesis maps of the barred spiral galaxy NGC 1530. The angular resolutions are respectively [FORMULA] and [FORMULA]. Both transitions show features similar to the 12CO(1-0) map, with a nuclear feature (a ring or unresolved spiral arms) surrounded by two curved arcs. The average line ratios are 12CO(1-0)/13CO(1-0)[FORMULA] and 12CO(2-1)/12CO(1-0)[FORMULA]. The 12CO/13CO ratio is lower in the circumnuclear ring (6-8) than in the arcs (11-15). We fit the observed line ratios by escape probability models, and deduce that the gas density is probably higher in the nuclear feature ([FORMULA] cm-3) than in the arcs ([FORMULA] cm-3), confirming earlier HCN results. The kinetic temperatures are in the range 20-90 K, but are weakly constrained by the model. The average filling factor of the 12CO(1-0) emitting gas is low, [FORMULA]. The cm-radio continuum emission also peaks in the nuclear feature, indicating a higher rate of star formation than in the arcs. We derive values for the CO luminosity to molecular gas mass conversion factor between 0.3 and [FORMULA](K [FORMULA] pc2)-1, significantly lower than the standard Galactic value.

Key words: galaxies: structure – galaxies: individual: NGC 1530 – galaxies: ISM – galaxies: kinematics and dynamics – radio lines: galaxies

Send offprint requests to: D. Reynaud (dreynaud@discovery.saclay.cea.fr)

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© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999
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