Milky Way Kinematics. II. A uniform inner Galaxy HI terminal velocity curve

Abstract

Using atomic hydrogen (HI) data from the VLA Galactic Plane Survey we measure the HI terminal velocity as a function of longitude for the first quadrant of the Milky Way. We use these data, together with our previous work on the fourth Galactic quadrant, to produce a densely sampled, uniformly measured, rotation curve of the Northern and Southern Milky Way between $3\mathrm{kpc}<R<8\mathrm{kpc}$. We determine a new joint rotation curve fit for the first and fourth quadrants, which is consistent with the fit we published in McClure-Griffiths \& Dickey (2007) and can be used for estimating kinematic distances interior to the solar circle. Structure in the rotation curves is now exquisitely well defined, showing significant velocity structure on lengths of $\sim 200$ pc, which is much greater than the spatial resolution of the rotation curve. Furthermore, the shape of the rotation curves for the first and fourth quadrants, even after subtraction of a circular rotation fit shows a surprising degree of correlation with a roughly sinusoidal pattern between $4.2<R<7$ kpc.

24 pages, 8 figures. Accepted for publication in the Astrophysical Journal

References in corpus (7)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• The VLA Galactic Plane Survey
• The Structure of the Milky Way's Bar Outside the Bulge
• The Vertical Structure of the Outer Milky Way HI Disk
• Milky Way Kinematics: Measurements at the Subcentral Point of the Fourth Quadrant
• The morphology of the Milky Way - I. Reconstructing CO maps from simulations in fixed potentials
• The incorrect rotation curve of the Milky Way

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• The odd primordial halo of the Milky Way implied by Gaia. A shallow core, but a steep decline