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Resolving the Kinematic Distance Ambiguity Toward Galactic H II Regions


Kolpak, MA and Jackson, JM and Bania, TM and Clemens, DP and Dickey, JM, Resolving the Kinematic Distance Ambiguity Toward Galactic H II Regions, The Astrophysical Journal, 582, (2) pp. 756-769. ISSN 0004-637X (2003) [Refereed Article]

DOI: doi:10.1086/344752


Kinematic distance determinations in the inner Galaxy are hampered by the near-far kinematic distance ambiguity. Here we resolve the ambiguity for 49 H II region complexes with known recombination-line velocities in the first Galactic quadrant. We measured the 21 cm H I absorption spectrum toward each source with the Very Large Array in the C array. The maximum velocity of H I absorption was used to discriminate between the near and far kinematic distances. The number ratio of far to near sources, ∼3, can be entirely explained as a geometrical effect. The kinematic distances that we derive are compared with previous determinations for the same sources. Although our distance determinations are largely in agreement with previous measurements, there are 22 discrepancies that we discuss. Using our distance determinations, we create a face-on Galactic map of the H II region complexes and compare it with a kinematically derived profile of the distribution of CO-traced molecular hydrogen. The H II region complexes delineate the large-scale features seen in the molecular gas. The 5 kpc molecular ring and the Sagittarius spiral arm are clearly evident, and a few H II region complexes lie in the Perseus arm.

Item Details

Item Type:Refereed Article
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Galactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Dickey, JM (Professor John Dickey)
ID Code:35938
Year Published:2003
Web of Science® Times Cited:95
Deposited By:Physics
Deposited On:2005-09-20
Last Modified:2011-11-29

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