EDP Sciences
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Volume 390, Number 1, July IV 2002
Page(s) 337 - 350
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20020671

A&A 390, 337-350 (2002)
DOI: 10.1051/0004-6361:20020671

Expanding shells of shocked neutral hydrogen around compact H ${\ion II}$ regions

R. Kothes1, 2 and C. R. Kerton1

1  National Research Council of Canada, Herzberg Institute of Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton, British Columbia, V2A 6K3, Canada
2  Department of Physics and Astronomy, The University of Calgary, 2500 University Dr. NW, Calgary, AB, T2N 1N4 Canada
    e-mail: charles.kerton@nrc.ca

(Received 20 February 2002 / Accepted 30 April 2002 )

By comparing radial velocities of radio bright compact $\ion{H}{ii}$ regions with their $\ion{H}{i}$ absorption profiles, we discovered expanding shells of neutral hydrogen around them. These shells are revealed by absorption of the radio continuum emission from the $\ion{H}{ii}$ regions at velocities indicating greater distances than the observed radial velocity. We believe that these shells are shock zones at the outer edge of the expanding ionized region. Additionally we found evidence for a velocity inversion inside the Perseus arm caused by a spiral shock, which results in a deep absorption line in the spectra of compact $\ion{H}{ii}$ regions behind it. - ISM: kinematics and dynamics

Key words: ISM: circumstellar matter -- ISM: $\ion{H}{ii}$ regions

Offprint request: R. Kothes, roland.kothes@nrc.ca

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