The origin of large peculiar motions of star-forming regions and spiral structures of our Galaxy

TL;DR

This study uses advanced simulations to show that the transient and recurrent nature of spiral arms causes large peculiar motions of star-forming regions, explaining recent VLBI observations and highlighting systematic errors in galactic mapping.

Contribution

It demonstrates through simulations that spiral arms are transient, leading to large peculiar motions of star-forming regions, challenging the quasi-stationary spiral arm theory.

Findings

Star-forming regions have large, complex non-circular motions.

Transient spiral arms cause significant systematic errors in galactic distance estimates.

Simulation results align qualitatively with VLBI observations.

Abstract

Recent VLBI (Very Long Baseline Interferometer) observations determined the distances and proper motions of star-forming regions in spiral arms directly. They showed that star-forming regions and young stars have large peculiar motions, as large as 30 km/s with complex structures. Such a large peculiar motion is incompatible with the prediction of the standard theory of quasi-stationary spiral arms. We use a high-resolution, self-consistent N-body+hydrodynamical simulation to explore how the spiral arms are formed and maintained, and how star-forming regions move. We found that arms are not quasi-stationary but transient and recurrent, as suggested in alternative theories of spiral structures. Because of this transient nature of the spiral arms, star-forming regions exhibit a trend of large and complex non-circular motions, which is qualitatively consistent with the VLBI observations. Owing to this large non-circular motion, a kinematically estimated gas map of our Galaxy has a large systematic errors of ~2-3 kpc in the distance from the Sun.