CO(2−1) and λ20 cm Radio Continuum Observations of NGC3628

Extract

We have mapped the edge-on galaxy NGC3628 in the ¹²CO(2−1) and ¹³CO(2−1) lines with the IRAM 30m MRT and in radio continuum at λ20 cm with the VLA. The ¹²CO(2−1) spectra were obtained out to a distance of 3 kpc east and 2 kpc west of the edge-on galaxy (resolution 0.4 kpc) with supplementary spectra ≃ 9 kpc east and west (1 arcmin ≃ 2 kpc at a distance of 6.7 Mpc). The resulting map shows a central peak of CO emission but also a multiple peaked structure from which we deduce a ringlike enhancement of molecular gas with a diameter of ≃ 400 pc and two outer maxima likely indicating spiral arms of the galaxy. The view of a molecular “ring” is supported by the fact that the maxima of the CO intensity are located close to the turnover radius where rigid rotation passes into differential rotation. Lesch et al. (1990) found for a number of galaxies with molecular rings that these rings can be formed by viscous accretion of molecular gas even at these radii. We find for the rigid rotating disk a molecular mass of m ≃ 10⁸M_⊙ assuming a conventional conversion factor. From our channelmaps we were able to distinguish between six unresolved clumps in the central region with comparable CO emissivity and masses of ≃ 10⁶M_⊙.