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Tracking the Outer Spiral Arms of the Galaxy in H I Absorption


Strasser, ST and Dickey, JM and Taylor, AR and Boothroyd, AI and Gaensler, BM and Green, AJ and Kavars, DW and Lockman, FJ and Martin, PG and McClure-Griffiths, NM and Rothwell, TA and Stil, JM, Tracking the Outer Spiral Arms of the Galaxy in H I Absorption, The Astronomical Journal, 134, (6) pp. 2252-2271. ISSN 0004-6256 (2007) [Refereed Article]

DOI: doi:10.1086/522794


We have analyzed 793 atomic hydrogen emission and absorption spectrum pairs toward continuum background sources in the northern and southern Galactic plane. In this paper we focus on absorption features from cold gas in the outermost arms of the Galaxy. We find H I absorption associated on a global scale with the outer spiral arm (first and second Galactic quadrants). To a lesser extent we also see absorption associated with the most distant spiral arm in the third and fourth Galactic quadrants. In total, 236 spectra contain clear absorption features associated with the outermost spiral arms. Cool-phase gas therefore exists throughout these spiral arms. The mean distances between absorbing clouds are on the order of 90-220 pc. We identify a number of striking H I structures with masses on the order of 10 5-10 6 M ⊙ containing cool H I gas with temperatures below 100 K. These clouds are only marginally stable against gravitational collapse. © 2007. The American Astronomical Society. All rights reserved.

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:48753
Year Published:2007
Web of Science® Times Cited:38
Deposited By:Physics
Deposited On:2007-08-01
Last Modified:2008-04-04

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