Jeans Instability in a Tidally Disrupted Halo Satellite Galaxy

TL;DR

This study demonstrates that Jeans instability can explain clumping in tidal tails of disrupted satellite galaxies, with implications for understanding dark matter halo substructure and observable stellar velocities.

Contribution

The paper provides the first detailed simulation-based evidence that Jeans instability causes clumping in tidal tails, linking tail substructure to dark matter properties.

Findings

Jeans instability explains observed clumping in tidal tails.

Velocity perturbations due to instability are around 10 km/s.

Halo particle mass influences tail substructure and Jeans wavelength.

Abstract

We use a hybrid test particle/N-body simulation to integrate 4 million massless test particle trajectories within a fully self-consistent 10^5 particle N-body simulation. The number of massless particles allows us to resolve fine structure in the spatial distribution and phase space of a dwarf galaxy as it is disrupted in the tidal field of a Milky Way type galaxy. The tidal tails exhibit nearly periodic clumping or a smoke-like appearance. By running simulations with different satellite particle mass, halo particle mass, number of massive and massless particles and with and without a galaxy disk, we have determined that the instabilities are not due to numerical noise, amplification of structure in the halo, or shocking as the satellite passes through the disk of the Galaxy. We measure Jeans wavelengths and growth timescales in the tidal tail and show that the Jeans instability is a viable explanation for the clumps. We find that the instability causes velocity perturbations of order 10 km/s. Clumps in tidal tails present in the Milky Way could be seen in stellar radial velocity surveys as well as number counts. We find that the unstable wavelength growth is sensitive to the simulated mass of dark matter halo particles. A simulation with a smoother halo exhibits colder and thinner tidal tails with more closely spaced clumps than a simulation with more massive dark matter halo particles. Heating by the halo particles increases the Jeans wavelength in the tidal tail affecting substructure development, suggesting an intricate connection between tidal tails and dark matter halo substructure.