Observations of the Ionized, Neutral, and Molecular Components Associated with an Expanding HiiRegion

Abstract

We present H92α, HI 21 cm, NH3 (1, 1) and NH3 (2, 2) lines and radio continuum observations toward the compact HII region G111.61+0.37, located in the region Sharpless 159. The dense molecular gas (traced by the ammonia lines) in the vicinity of G111.61+0.37 is distributed in clumps indicating considerable inhomogeneity in the molecular gas. A warm (Trot = 47 K) ammonia clump is located just in front of the head of the cometary HII region. The photodissociated region associated to this compact HII region was detected in the HI 21 cm line. The neutral region is extended in the direction opposite to the dense molecular gas. The velocity distribution of the neutral gas suggests that the HI region is expanding in a champagne flow resembling that of the HII region, although with much lower velocities.