Detection of a dearth of stars with zero angular momentum in the solar neighbourhood

TL;DR

This paper identifies a lack of stars with zero angular momentum near the Sun using Gaia and RAVE data, models this phenomenon, and derives the Solar rotation velocity and Galactic center distance from it.

Contribution

It introduces a novel dynamical method to measure Solar velocity and Galactic center distance based on the observed star distribution dip.

Findings

Detected a dip in star angular momentum distribution near zero.

Estimated Solar rotation velocity as 239±9 km/s.

Measured the Galactic center distance as 7.9±0.3 kpc.

Abstract

We report on the detection in the combined $Gaia$-DR1/RAVE data of a lack of disk stars in the solar neighbourhood with velocities close to zero angular momentum. We propose that this may be caused by the scattering of stars with very low angular momentum onto chaotic, halo-type orbits when they pass through the Galactic nucleus. We model the effect in a Milky-Way like potential and fit the resulting model directly to the data, finding a likelihood ($\sim2.7\sigma$) of a dip in the distribution. Using this effect, we can make a dynamical measurement of the Solar rotation velocity around the Galactic center: $v_{\odot}=239\pm9$ km s$^{-1}$. Combined with the measured proper motion of Sgr A$^*$, this measurement gives a measurement of the distance to the Galactic centre: $R_0=7.9\pm0.3$ kpc.