13CO(1-0) and 12CO(2-1) in the center of the barred galaxy NGC 1530
Received 23 November 1998 / Accepted 15 April 1999
We present 13CO(1-0) and 12CO(2-1) aperture synthesis maps of the barred spiral galaxy NGC 1530. The angular resolutions are respectively and . 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) and 12CO(2-1)/12CO(1-0). 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 ( cm-3) than in the arcs ( 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, . 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 (K 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 (firstname.lastname@example.org)
© European Southern Observatory (ESO) 1999
Online publication: June 18, 1999