Galactic rotation in Gaia DR1

TL;DR

This paper uses Gaia DR1 data to precisely measure the Oort constants, revealing non-axisymmetric features of the Milky Way's local stellar velocity field and providing new constraints on galactic models.

Contribution

It presents the first confident measurements of the Oort constants C and K using Gaia DR1 data, highlighting non-axisymmetry in the local velocity field.

Findings

Measured Oort constants with high precision.

Detected non-axisymmetric features in the velocity field.

Provided constraints on Milky Way models.

Abstract

The spatial variations of the velocity field of local stars provide direct evidence of Galactic differential rotation. The local divergence, shear, and vorticity of the velocity field---the traditional Oort constants---can be measured based purely on astrometric measurements and in particular depend linearly on proper motion and parallax. I use data for 304,267 main-sequence stars from the Gaia DR1 Tycho-Gaia Astrometric Solution to perform a local, precise measurement of the Oort constants at a typical heliocentric distance of 230 pc. The pattern of proper motions for these stars clearly displays the expected effects from differential rotation. I measure the Oort constants to be: A = 15.3+/-0.4 km/s/kpc, B = -11.9+/-0.4 km/s/kpc, C = -3.2+/-0.4 km/s/kpc and K = -3.3+/-0.6 km/s/kpc, with no color trend over a wide range of stellar populations. These first confident measurements of C and K clearly demonstrate the importance of non-axisymmetry for the velocity field of local stars and they provide strong constraints on non-axisymmetric models of the Milky Way.