On the Stability of Tidal Streams

TL;DR

This paper investigates the stability of galactic tidal streams, using analytical calculations and simulations, concluding that such streams are stable against gravitational instabilities across all scales and times.

Contribution

It provides a new analytical framework for assessing tidal stream stability and confirms stability through numerical simulations, challenging previous claims of instability.

Findings

Tidal streams are stable on all length scales.

Analytical and numerical methods agree on stability results.

Streams do not develop gravitational clumps as previously suggested.

Abstract

We explore the stability of tidal streams to perturbations, motivated by recent claims that the clumpy structure of the stellar streams surrounding the globular cluster Palomar 5 are the result of gravitational instability. We calculate the Jeans length of tidal streams by treating them as a thin expanding cylinder of collisionless matter. We also find a general relation between the density and the velocity dispersion inside a stream, which is used to determine the longitudinal Jeans criterion. Our analytic results are checked by following the time evolution of the phase space density within streams using numerical simulations. We conclude that tidal streams within our galactic halo are stable on all length scales and over all timescales.