We use atomic hydrogen (H I) data from the Southern Galactic Plane Survey to study the kinematics of the fourth quadrant of the Milky Way. By measuring the terminal velocity as a function of longitude throughout the fourth Galactic quadrant we have derived the most densely sampled rotation curve available for the Milky Way between 3 kpc ≤ R ≤ 8 kpc. We determine a new joint rotation curve fit for the first and fourth quadrants, which can be used for kinematic distances interior to the solar circle. From our data we place new limits on the peak-to-peak variation of streaming motions in the fourth quadrant to be ∼10 km s -1. We show that the shape of the average H I profile beyond the terminal velocity is consistent with gas of three velocity dispersions, a cold component with Î"v = 6.3 km s -1, a warmer component with Î"v = 12.3 km s _1, and a fast component with Î"v = 25.9 km s _1. By examining the widths with Galactic radius we find that the narrowest two components show little variation with radius and their small-scale fluctuations track each other very well, suggesting that they share the same cloud-to-cloud motions. The width of the widest component is constant until R < 4 kpc, where it increases sharply. © 2007. The American Astronomical Society. All rights reserved.

Item Type:	Refereed Article
Research Division:	Physical Sciences
Research Group:	Astronomical and Space Sciences
Research Field:	Galactic Astronomy
Objective Division:	Expanding Knowledge
Objective Group:	Expanding Knowledge
Objective Field:	Expanding Knowledge in the Physical Sciences
Author:	Dickey, JM (Professor John Dickey)
ID Code:	50110
Year Published:	2007
Web of Science® Times Cited:	77
Deposited By:	Physics
Deposited On:	2007-08-01
Last Modified:	2008-04-04
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