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[Ne II] Observations of Gas Motions in Compact and Ultracompact H II Regions | | Qingfeng Zhu
; John H. Lacy
; Daniel T. Jaffe
; Matthew J. Richter
; Thomas K. Greathouse
; | | Date: |
2 Apr 2008 | | Abstract: | We present high spatial and spectral resolution observations of sixteen
Galactic compact and ultracompact H II regions in the [Ne II] 12.8 microns fine
structure line. The small thermal width of the neon line and the high dynamic
range of the maps provide an unprecedented view of the kinematics of compact
and ultracompact H II regions. These observations solidify an emerging picture
of the structure of ultracompact H II regions suggested in our earlier studies
of G29.96-0.02 and Mon R2 IRS1; systematic surface flows, rather than
turbulence or bulk expansion, dominate the gas motions in the H II regions. The
observations show that almost all of the sources have significant (5-20 km/s)
velocity gradients and that most of the sources are limb-brightened. In many
cases, the velocity pattern implies tangential flow along a dense shell of
ionized gas. None of the observed sources clearly fits into the categories of
filled expanding spheres, expanding shells, filled blister flows, or cometary H
II regions formed by rapidly moving stars. Instead, the kinematics and
morphologies of most of the sources lead to a picture of H II regions confined
to the edges of cavities created by stellar wind ram pressure and flowing along
the cavity surfaces. In sources where the radio continuum and [Ne II]
morphologies agree, the majority of the ionic emission is blue-shifted relative
to nearby molecular gas. This is consistent with sources lying on the near side
of their natal clouds being less affected by extinction and with gas motions
being predominantly outward, as is expected for pressure-driven flows. | | Source: | arXiv, 0804.0439 | | Services: | Forum | Review | PDF | Favorites | |
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