CO observations in NGC 2359: the molecular cloud revisited

Abstract

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 22″, and the velocity resolution is 0.33 km s-1. Three molecular components are detected in the direction of the nebula. The bulk of the molecular gas is observed at 54 km s-1 and follows the southeastern border of the nebula. Adopting a distance d = 5 kpc for NGC 2359, an H2 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 density of the molecular gas related to the southern bar is > 103 H2 molecules cm-3, while lower densities were estimated for 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 (≃ 380 ± 120 M⊙, d = 5 kpc) is associated with the nebula, but the molecular material observed at 67 km s-1 (≃ 70 ± 25 M⊙, d = 5 kpc) seems to be unconnected. The comparison between ionized, H I, and molecular distributions indicates that the H I filament detected with 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 originated in the photodissociation of the H2. Most of the molecular gas associated with the filamentary bubble seems to be interstellar in origin. The dynamics of the nebula is reanalyzed based on these new molecular results. It is consistent with either momentum conservation or an intermediate stage between energy and momentum conservation.