Dynamical Properties of Collisionless Star Streams

TL;DR

This paper investigates the dynamical behavior of collisionless star streams created by tidal disruption of satellites, revealing how their structures and gaps evolve depending on orbital eccentricity and satellite mass.

Contribution

It introduces a scaling method using action-angle variables to predict stream features across different satellite masses and analyzes gap evolution in streams with varying eccentricities.

Findings

Low eccentricity streams are smoother with less differential motion.

High eccentricity streams develop shell-like features at apocenter.

Gaps in streams blur over time, with the rate depending on eccentricity.

Abstract

A sufficiently extended satellite in the tidal field of a host galaxy loses mass to create nearly symmetric leading and trailing tidal streams. We study the case in which tidal heating drives mass loss from a low mass satellite. The stream effectively has two dynamical components, a common angular momentum core superposed with episodic pulses with a broader angular momentum distribution. The pulses appear as spurs on the stream, oscillating above and below the stream centerline, stretching and blurring in configuration space as they move away from the cluster. Low orbital eccentricity streams are smoother and have less differential motion than high eccentricity streams. The tail of a high eccentricity stream can develop a fan of particles which wraps around at apocenter in a shell feature. We show that scaling the essentially stationary action-angle variables with the cube root of the satellite mass allows a low mass satellite stream to accurately predict the features in the stream from a satellite a thousand times more massive. As a practical astrophysical application, we demonstrate that narrow gaps in a moderate eccentricity stream, such as GD-1, blur out to 50\% contrast over approximately 6 radial periods. A high eccentricity stream, such as Pal~5, will blur small gaps in only radial 2 orbits as can be understood from the much larger dispersion of angular momentum in the stream.