Vertical Structure and Kinematics of the Galactic Outer Disk

TL;DR

This study measures parallax and proper motion of water maser sources to analyze the Galactic outer disk's vertical structure and kinematics, revealing the warp's extent and oscillatory vertical motions likely caused by satellite interactions.

Contribution

It provides new measurements of maser sources in the outer Galaxy, demonstrating the warp's increasing height with distance and evidence of bending waves in the disk.

Findings

Galactic warp reaches 200-400 pc, with signatures up to 600 pc.

Vertical velocities show oscillatory behavior, indicating bending waves.

Warp height increases with Galactocentric distance.

Abstract

We report measurements of parallax and proper motion for four 22 GHz water maser sources as part of VERA Outer Rotation Curve project. All sources show Galactic latitudes of $>$ 2$^{\circ}$ and Galactocentric distances of $>$ 11 kpc at the Galactic longitude range of 95$^{\circ}$ $< l <$ 126$^{\circ}$. The sources trace the Galactic warp reaching to 200$\sim$400 pc, and indicate the signature of the warp to 600 pc toward the north Galactic pole. The new results along with previous results in the literature show the maximum height of the Galactic warp is increased with Galactocentric distance. Also, we examined velocities perpendicular to the disk for the sample, and found an oscillatory behavior between the vertical velocities and Galactic heights. This behavior suggests the existence of the bending (vertical density) waves, possibly induced by a perturbing satellite (e.g. passage of the Sagittarius dwarf galaxy).