Study of neutral and ionized gas of the Wolf-Rayet ring nebula NGC 2359

Based on H I 21 cm line and radio continuum observations performed with the Very Large Array of the National Radio Astronomy Observatory and on optica l narrowband images obtained at the Cerro Tololo Inter-American Observatory , we investigate the distribution of the ionized and neutral gas in the reg ion of the ring nebula NGC 2359 surrounding the Wolf-Rayet star HD 56925 at a distance of 5 kpc. The radio continuum data, obtained at 1465 MHz with a n angular resolution of approximate to 30 ", have the same morphology as th e optical H alpha nebular line emission. An ionized mass of 70 M. and an el ectron density (corrected for filling factor) of 120 cm(-3) were estimated for the filamentary shell, while the mass in the whole ionized complex is i n the range 850-1100 M,. The H I 21 cm line data, with angular and velocity resolutions of approximate to 45 " and 1.3 km s(-1), respectively, reveal for the first time neutral hydrogen clearly interacting with the optical ri ng nebula at its systemic velocity of 54 km s(-1) and at 63 km s(-1). The H I gas distribution at 54 km s(-1) indicates the location of the ionization fronts. The estimated total neutral mass is approximate to 320 M.. Most of this mass seems to be located in a hemispherical shell expanding at 6-7 km s(-1) Taking into account the ionized, neutral, and molecular components, the mass associated with the NGC 2359 complex is about 2200 M.. The dynamic s of the nebula are consistent with momentum conservation or with an interm ediate stage between energy and momentum conservation.