The Galactic warp revealed by Gaia DR2 kinematics

TL;DR

This study uses Gaia DR2 data to map the Milky Way's stellar warp through kinematic signatures, revealing a gravitationally induced warp extending up to 14 kpc from the Sun.

Contribution

It provides the first detailed kinematic mapping of the Galactic warp using Gaia DR2 data, combining photometry and astrometry without individual extinction estimates.

Findings

Detected a 5-6 km/s vertical velocity gradient indicating the warp.

Mapped the warp out to 14 kpc from the Sun.

Confirmed the warp's gravitational origin across different stellar populations.

Abstract

Using Gaia DR2 astrometry, we map the kinematic signature of the Galactic stellar warp out to a distance of 7 kpc from the Sun. Combining Gaia DR2 and 2MASS photometry, we identify, via a probabilistic approach, 599 494 upper main sequence stars and 12 616 068 giants without the need for individual extinction estimates. The spatial distribution of the upper main sequence stars clearly shows segments of the nearest spiral arms. The large-scale kinematics of both the upper main sequence and giant populations show a clear signature of the warp of the Milky Way, apparent as a gradient of 5-6 km/s in the vertical velocities from 8 to 14 kpc in Galactic radius. The presence of the signal in both samples, which have different typical ages, suggests that the warp is a gravitationally induced phenomenon.