What Velocities and Eccentricities tell us about Radial Migration

TL;DR

This paper analyzes how velocities and eccentricities of stars reveal insights into radial migration in the Galactic disc, comparing models with observations to understand the effects of angular momentum mixing and abundance gradients.

Contribution

It interprets recent velocity trends in low [alpha/Fe] stars and discusses how eccentricity distributions can constrain Galactic disc evolution models.

Findings

Velocity trend matches model predictions with adjusted radial abundance gradient.

Complete mixing of stars would eliminate the velocity trend.

Eccentricity distributions are useful for constraining Galactic structure.

Abstract

This note attempts to interpret some of the recent findings about a downtrend in the mean azimuthal velocity of low [alpha/Fe] thin disc stars with increasing metallicity. The presence of such a trend was predicted in the model of Schoenrich & Binney (2009), albeit with a slightly steeper slope. We show that in a simple picture a Galactic disc without mixing in angular momenta would display an exceedingly steep trend, while in the case of complete mixing of all stars the trend has to vanish. The difference between model and observational data can hence be interpreted as the consequence of the radial abundance gradient in the model being too high resulting in an underestimate of the migration strength. We shortly discuss the value of eccentricity distributions in constraining structure and history of the Galactic disc.