Sh2-205 - I: the surrounding interstellar medium

Abstract

We investigate the distribution of the interstellar matter in the environs of the H II region Sh2-205, based on neutral hydrogen 21-cm-line data and radio continuum images at 408 and 1420 MHz obtained from the CGPS, 12CO (J=1 →0) observations, high-resolution IRAS data (HIRES), and MSX data. Sh2-205 can be separated into three distinct optical structures: SH 149.25-0.0, SH 148.83-0.67, and LBN 148.11-0.45. The three regions are detected at both 408 and 1420 MHz. The derived spectral indices show the thermal nature of SH 148.83-0.67 and LBN 148.11-0.45. LBN 148.11-0.45 is a classical H II region surrounded by an H i shell. The associated neutral atomic and ionized masses are 65 M⊙ and 70 M⊙, respectively. Dust and molecular gas (∼6 × 104 M⊙) related to this ionized region have been found. In particular, a photodissociation region is detected at the interface between the ionized and molecular regions. If the proposed exciting star HD 24094 were an O8-O9 type star, as suggested by its near-infrared colours, its UV photon flux would be strong enough to explain the ionization of the nebula. The optical, radio continuum, and 21-cm-line data allow us to conclude that SH 148.83-0.67 is an interstellar bubble powered by the energetic action of HD 24431. The associated neutral atomic and ionized masses are 180 M⊙ and 300 M⊙, respectively. The emission of SH 149.25-0.0 is too faint to derive the dust and gas parameters. An H I shell centred at (l, b) = (149°0', -1°30') was also identified. It correlates morphologically with the molecular gas emission. The neutral atomic and molecular masses of the shell are 1600 M⊙ and 2.6 × 104 M⊙, respectively. The open cluster NGC 1444 is probably responsible for shaping this H I structure.