CO observations of NGC 2359: The molecular clouds revisited

Based on CO (2-1) observations obtained with the Swedish-ESO Submillimeter Telescope, the distribution of molecular material associated with the Wolf- Rayet ring nebula NGC 2359 has been determined. The angular resolution is 2 2 ", and the velocity resolution is 0.33 km s(-1). Three molecular componen ts are detected in the direction of the nebula. The bulk of the molecular g as is observed at 54 km s(-1) and follows the southeastern border of the ne bula. Adopting a distance d = 5 kpc for NGC 2359, an H-2 mass of about 1200 +/- 500 M. appears to be related to the southern part of the nebula, while 140 +/- 50 M. are linked to the filamentary windblown bubble. The volume d ensity of the molecular gas related to the southern bar is greater than or equal to 10(3) H-2 molecules cm(-3), while lower densities were estimated f or the material associated with the filamentary windblown bubble. From the present data, it is not clear if the molecular gas at 37 km s(-1) (similar or equal to 380 +/- 120 M., d = 5 kpc) is associated with the nebula, but t he molecular material observed at 67 km s(-1) (similar or equal to 70 +/- 2 5 M., d = 5 kpc) seems to be unconnected. The comparison between ionized, H I, and molecular distributions indicates that the H I filament detected wi th the Very Large Array is located at the interface between the ionized and molecular material, and that the H I filament at 54 km s(-1) has originate d in the photodissociation of the H-2. Most of the molecular gas associated with the filamentary bubble seems to be interstellar in origin. The dynami cs of the nebula is reanalyzed based on these new molecular results. It is consistent with either momentum conservation or an intermediate stage betwe en energy and momentum conservation.