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Milky Way Kinematics. I. Measurements at the Subcentral Point of the Fourth Quadrant


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McClure-Griffiths, NM and Dickey, JM 2007 , 'Milky Way Kinematics. I. Measurements at the Subcentral Point of the Fourth Quadrant' , The Astrophysical Journal, vol. 671, no. 1 , pp. 427-438 , doi: 10.1086/522297.

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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 s1.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 v ¼ 6:3 km s1, a
warmer component withv ¼ 12:3 km s1, and a fast component withv ¼ 25:9 km s1. 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.

Item Type: Article
Authors/Creators:McClure-Griffiths, NM and Dickey, JM
Keywords: Galaxy: kinematics and dynamics — ISM: kinematics and dynamics — radio lines: ISM
Journal or Publication Title: The Astrophysical Journal
Publisher: University of Chicago Press
ISSN: 0004-637X
DOI / ID Number: 10.1086/522297
Additional Information:

© 2007. The American Astronomical Society

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