Unveiling the birth and evolution of the H ii region Sh2-173

Abstract

Based on a multiwavelength study, the interstellar medium around the H II region Sh2-173 has been analysed. The ionized region is clearly detected in the optical and the radio continuum images. The analysis of the H I data shows a region of low emissivity that has an excellent morphological correlation with the radio continuum emission. The H II region is partially bordered by a photodissociation region, which, in turn, is encircled by a molecular structure. The H I and CO structures related to Sh2-173 are observed in the velocity ranges from -25 to -31 km s -1 and from -27 to -39 km s -1 , respectively. Taking into account the presence of non-circular motions in the Perseus spiral arm, together with previous distance estimates for the region, we adopt a distance of 2.5 0.5 kpc for Sh2-173. Seven hot stars were identified in the field of Sh2-173, being only one O-type star. The amount of energetic photons emitted by this star is enough to keep the region ionized and heat the dust. Given that an expanding H II region may trigger star formation, a search for young stellar object (YSO) candidates was made using different infrared point source catalogues. A population of 46 YSO candidates was identified, projected on to the molecular clouds.