Abstract
Strong emission in the (CO)-C-12 J = 1-0 and 2-1 lines is reported from the lenticular galaxy NGC 3593. A deconvolution of the data to a nominal angular resolution of 8" (corresponding to 270 pc at d = 7 Mpc) shows that the molecular gas is distributed in a ring-like configuration of radius 200-350pc, located at the turning point of the rotation curve. The kinematical center and the center of the molecular ring, as well as the center of the radio continuum emission, are offset approximately 15" from the optical center position. This difference is most likely caused by extinction at optical wavelengths. The diameter of the J = 1-0 ring is larger than both the 2-1 ring and the angular separation between the peaks of the radio continuum emission, suggesting either the presence of optically thin CO near the inner boundary of the ring, a radial gradient in density or in kinetic temperature with the highest values near the center. The total molecular masses derived from the far infrared flux and the (CO(1-0))-C-12 integrated intensity, approximately 3 10(8) M. and approximately 4.5 10(8) M., indicate that dust and molecular cloud properties do not differ drastically from those in the Milky Way. The M(H-2)/M(tot) ratio is 1% for the entire galaxy and 8% inside a radius of 10" (350pc). The M(H-2)/M(HI) ratio is approximately 2.5. Toward the central region, (CO(2-1))-C-13 data infer an optical depth of 0.2. The beam averaged (CO)-C-13 column density is of order 7 10(15) cm-2 and the beam filling factor less than or similar 0.1. This is the first time that the three-dimensional 'Lucy rectification' has been applied to analyse the detailed spatial morphology and velocity distribution of extragalactic molecular gas. An alternative approach, 'Simulated Annealing', is also tested for one- and three-dimensional applications, yielding consistent results with respect to the velocity field and the emissivity distribution of NGC 3593.