High-frequency carbon recombination line as a probe to study the environment of Ultra-compact HII regions

Abstract

The far-ultra violet (6 – 13.6 eV) photons from the OB stars in Ultra-compact HII regions (UCHs) produce photo-dissociation regions (PDRs) at the interface between the ionized and the natal molecular material. In this paper, we show that carbon recombination lines (CRLs) at frequencies greater than a few GHz are detectable from these PDRs and such observations can be used to: (1) estimate the physical properties of the PDR material; (2) study the kinematics of the PDR material relative to the HII region gas; (3) constrain the magnetic fields in the vicinity of UCHs and (4) address the lifetime problem of UCHs.