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Title:
1051 erg less: the Galactic H II region OA 184
Authors:
Foster, T.; Kothes, R.; Sun, X. H.; Reich, W.; Han, J. L.
Affiliation:
AA(National Research Council of Canada, Herzberg Institute of Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton, BC, V2A 6J9, Canada ), AB(National Research Council of Canada, Herzberg Institute of Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton, BC, V2A 6J9, Canada; Department of Physics and Astronomy, University of Calgary, 2500 University Drive N.W., Calgary, AB, Canada), AC(National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China), AD(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), AE(National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China)
Publication:
Astronomy and Astrophysics, Volume 454, Issue 2, August I 2006, pp.517-526 (A&A Homepage)
Publication Date:
08/2006
Origin:
EDP Sciences
Keywords:
polarization, ISM: supernova remnants, H II regions
DOI:
10.1051/0004-6361:20064881
Bibliographic Code:
2006A&A...454..517F

Abstract

Aims.The identification of the object OA 184 as a Galactic Supernova Remnant (SNR) is re-examined, and evidence to the contrary is presented. The aim is to show definitively that OA 184 is actually a Galactic H II region, and to estimate some physical parameters for the nebula (e.g. temperature, density, and magnetic field in the ionized shell).
Methods: .To determine the broad spectral properties of OA 184 a multiwavelength approach is used, with historical and new radio data, and existing X-ray and IR data on OA 184 considered. Radio continuum 408 and 1420 MHz Canadian Galactic Plane Survey (CGPS) data, Effelsberg 2695 MHz data, and new Urumqi 5 GHz radio observations in Stokes I, Q, and U are presented. As well, we present CGPS H I line data, and eight radio recombination lines (RRL, H103-110α) observed for this study with the Green Bank Telescope.
Results: .An integrated radio spectrum of index α=-0.14 to -0.2 (S(Jy) ∝ να) is determined from four radio frequencies. RRL emission appears at vLSR=-25.8 km s-1 and at the intensity predicted for free-free thermal emission. Q and U maps at λ~6 cm show OA 184 as a depolarizing source, affecting a background filament of polarized non-thermal Galactic emission. An H II shell of thickness less than 0.2° is indicated by this depolarization. CGPS ~1-arcminute resolution H I line maps are presented, and the systemic velocity of the ISM immediately surrounding OA 184 is -26.8 km s-1. The distance of OA 184 is 2.2±0.4 kpc, obtained from a new distance method based on a Galactic H I modelling procedure. A simple model as a shell of ionized hydrogen 4 pc thick is considered, and the RRL observations are used to estimate (under conditions of non-thermodynamic equilibrium) the electron temperature Te=8300 K and density ne=5.3 cm-3. The line of sight magnetic field in the ionized shell is found to be < B∥>≃-2.5~μG (directed away from the Sun).
Conclusions: .We conclude that OA 184 is a Galactic H II region energized by the lone O7.5V star BD+41°1144.
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