Burton's Curse: The Impact of Bulk Flows on the Galactic Longitude-Velocity Diagram and the Illusion of a Continuous Perseus Arm

Abstract

In this work we demonstrate that the Perseus Arm is not a continuous structure of molecular gas in the second quadrant. We first show that the observed, distanced-resolved velocity structure of the Galaxy in the outer disk is capable of creating illusory spiral arms, as was first proposed by Burton (1971). Second, we measure the distances to a collection of CO clouds at velocities consistent with the Perseus arm with $135^{\circ }<l<160^{\circ }$. We find these distances using 3D dust maps from Green et al. (2019). We determine that these molecular cloud do not preferentially lie at the distance of a purported Perseus arm, but rather extend over 3 kpc in distance, with some evidence for a closer, high pitch angle structure between 1 and 1.5 kpc away. Finally, we demonstrate that velocity perturbations of the amplitude found near the Perseus arm can wreak havoc on our interpretation of the longitude-velocity diagram for more than half of the Milky Way disk.

14 pages, 7 figures. Accepted to the Astrophysical Journal

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• The Galactic dynamics revealed by the filamentary structure in atomic hydrogen emission
• SRG/eROSITA discovery of a radio faint X-ray candidate supernova remnant SRGe J003602.3+605421=G121.1-1.9
• The Radcliffe Wave as the gas spine of the Orion Arm
• Dependence of Molecular Cloud Samples on Angular Resolution, Sensitivity, and Algorithms