Streaming Motions and Kinematic Distances to Molecular Clouds

Abstract

We present high-resolution smoothed particle hydrodynamics simulations of a region of gas flowing in a spiral arm and identify dense gas clouds to investigate their kinematics with respect to a Milky Way model. We find that, on average, the gas in the arms can have a net radial streaming motion of $v_R\approx -9km/s$ and rotate $\approx 6km/s$ slower than the circular velocity. This translates to average peculiar motions towards the Galaxy centre and opposite to Galactic rotation. These results may be sensitive to the assumed spiral arm perturbation, which is $\approx 3\%$ of the disc potential in our model. We compare the actual distance and the kinematic estimate and we find that streaming motions introduce systematic offsets of $\approx 1$ kpc. We find that the distance error can be as large as $\pm 2$ kpc and the recovered cloud positions have distributions that can extend significantly into the inter-arm regions. We conclude that this poses a difficulty in tracing spiral arm structure in molecular cloud surveys.

12 pages, 14 figures, accepted for publication in MNRAS

References in corpus (18)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• SPLASH: An interactive visualisation tool for Smoothed Particle Hydrodynamics simulations
• Physical properties of molecular clouds for the entire Milky Way disk
• Molecular Cloud Evolution II. From cloud formation to the early stages of star formation in decaying conditions
• Kinematic Distances to Molecular Clouds identified in the Galactic Ring Survey
• A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry
• Trigonometric parallaxes of star forming regions in the Sagittarius spiral arm
• The frequency and nature of `cloud-cloud collisions' in galaxies
• The formation of molecular clouds in spiral galaxies
• Trigonometric Parallaxes of Star Forming Regions in the Perseus Spiral Arm
• 3D Distribution of Molecular Gas in the Barred Milky Way
• ATLASGAL - Kinematic distances and the dense gas mass distribution of the inner Galaxy
• The origin of large peculiar motions of star-forming regions and spiral structures of our Galaxy
• Trigonometric Parallaxes of Star Forming Regions in the Scutum Spiral Arm
• Parallaxes of Star Forming Regions in the Outer Spiral Arm of the Milky Way
• The morphology of the Milky Way - II. Reconstructing CO maps from disc galaxies with live stellar distributions
• The prevalence of star formation as a function of Galactocentric radius
• Errors in kinematic distances and our image of the Milky Way Galaxy

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• The SEDIGISM survey: The influence of spiral arms on the molecular gas distribution of the inner Milky Way
• The historical record of massive star formation in Cygnus
• HI Vertical Structure of Nearby Edge-on Galaxies from CHANG-ES
• Energy estimation of high energy particles associated with the SS433/W50 system through radio observation at 1.4 GHz
• Autonomous Gaussian decomposition of the Galactic Ring Survey. II. The Galactic distribution of 13CO
• Insights into the structure and kinematics of a Milky Way-like galaxy