The PDR structure and kinematics around the compact H ii regions S235 A and S235 C with [C ii], [13C ii], [O i], and HCO+line profiles

M. S. Kirsanova, V. Ossenkopf-Okada, L. D. Anderson, P. A. Boley, J. H. Bieging, Ya N. Pavlyuchenkov, M. Luisi, N. Schneider, M. Andersen, M. R. Samal, A. M. Sobolev, C. Buchbender, R. Aladro, Y. Okada

Research output: Contribution to journalArticlepeer-review

Abstract

The aim of this work is to study structure and gas kinematics in the photodissociation regions (PDRs) around the compact H ii regions S235 A and S235 C. We observe the [C ii], [13C ii], and [O i] line emission, using SOFIA/upGREAT, and complement them by data of HCO+ and CO. We use the [13C ii] line to measure the optical depth of the [C ii] emission, and find that the [C ii] line profiles are influenced by self-absorption, while the [13C ii] line remains unaffected by these effects. Hence, for dense PDRs, [13C ii] emission is a better tracer of gas kinematics. The optical depth of the [C ii] line is up to 10 in S235 A. We find an expanding motion of the [C ii]-emitting layer of the PDRs into the front molecular layer in both regions. Comparison of the gas and dust columns shows that gas components visible neither in the [C ii] nor in low-J CO lines may contribute to the total column across S235 A. We test whether the observed properties of the PDRs match the predictions of spherical models of expanding H ii region + PDR + molecular cloud. Integrated intensities of the [13C ii], [C ii], and [O i] lines are well represented by the model, but the models do not reproduce the double-peaked [C ii] line profiles due to an insufficient column density of C+. The model predicts that the [O i] line could be a more reliable tracer of gas kinematics, but the foreground self-absorbing material does not allow using it in the considered regions.

Original languageEnglish (US)
Pages (from-to)2651-2669
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Volume497
Issue number3
DOIs
StatePublished - Sep 1 2020

Keywords

  • H ii regions
  • ISM: Kinematics and dynamics
  • infrared: ISM
  • line: Profiles
  • photodissociation region (PDR)
  • radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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