Tidal ribbons

TL;DR

Tidal debris near the Galactic disc forms ribbon-like structures due to amplitude-dependent vertical frequencies, enabling potential detection and insights into the Galaxy's vertical gravitational profile.

Contribution

This paper reveals that tidal debris near the Galactic disc forms ribbons instead of streams, due to amplitude-dependent vertical frequencies, providing a new method to probe the Galactic potential.

Findings

Tidal debris near the disc forms ribbons, not streams.

Ribbons are detectable as clumps in integrals-of-motion space.

Ribbons can help determine the Galactic potential vertically.

Abstract

Tidal debris from Galactic satellites generally forms one-dimensional elongated streams, since nearby Galactic orbits have almost identical frequency ratios. We show that the situation is different for orbits close to the Galactic disc, whose vertical frequency $\Omega_z$ is strongly amplitude dependent. As a consequence, stars stripped from a satellite obtain a range of values for $\Omega_z$ and hence of frequency ratios, and spread into two dimensions, forming a ribbon-like structure with vertical extent comparable to that of the progenitor orbit. In integrals-of-motion space, tidal ribbons are clumps, which offers the best chance of detection and allows the determination of the Galactic potential vertically across the disc.