Journal Article

The myth of the molecular ring

C. L. Dobbs and A. Burkert

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 421, issue 4, pages 2940-2946
Published in print April 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI:
The myth of the molecular ring

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We investigate the structure of the Milky Way by determining how features in a spatial map correspond to CO features in a velocity map. We examine structures including logarithmic spiral arms, a ring and a bar. We explore the available parameter space, including the pitch angle of the spiral arms, radius of a ring and rotation curve. We show that, surprisingly, a spiral arm provides a better fit to the observed molecular ring than a true ring feature. This is because both a spiral arm and the observed feature known as the molecular ring are curved in velocity–longitude space. We find that much of the CO emission in the velocity–longitude map can be fitted by a nearly symmetric two‐armed spiral pattern. One of the arms corresponds to the molecular ring, whilst the opposite arm naturally reproduces the Perseus arm. Multiple arms also contribute to further emission in the vicinity of the molecular ring and match other observed spiral arms. Whether the Galactic structure consists primarily of two or several spiral arms, the presence of two symmetric logarithmic spirals, which begin in the vicinity of the ends of the bar, suggests a spiral density wave associated with the bar.

Keywords: Galaxy: kinematics and dynamics; Galaxy: structure

Journal Article.  4780 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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