Are stellar over-densities in dwarf galaxies the "smoking gun" of triaxial dark matter haloes?

TL;DR

This study uses N-body simulations to demonstrate that stellar over-densities in dwarf spheroidal galaxies can be caused by the triaxial shape of dark matter haloes, providing observable signatures for their shape.

Contribution

It shows that stellar debris from disrupted clusters forms persistent over-densities due to triaxial dark matter halos, linking observed substructures to halo shape.

Findings

Stellar over-densities can be shells, clumps, or elongated features at low surface brightness.

Debris features are long-lasting and linked to halo triaxiality.

Kinematic signatures include a double-peak in velocity distribution depending on viewing angle.

Abstract

We use N-body simulations to study the tidal evolution of globular clusters (GCs) in dwarf spheroidal (dSph) galaxies. Our models adopt a cosmologically motivated scenario in which the dSph is approximated by a static NFW halo with a triaxial shape. For a large set of orbits and projection angles we examine the spatial and velocity distribution of stellar debris deposited during the complete disruption of stellar clusters. Our simulations show that such debris appears as shells, isolated clumps and elongated over-densities at low surface brightness (>26 mag/arcsec^2), reminiscent of substructure observed in several MW dSphs. Such features arise from the triaxiality of the galaxy potential and do not dissolve in time. Stellar over-densities reported in several MW dSphs may thus be the telltale evidence of dark matter haloes being triaxial in shape. We explore a number of kinematic signatures that would help to validate (or falsify) this scenario. The mean angular momentum of the cluster debris associated with box and resonant orbits, which are absent in spherical potentials, is null. As a result, we show that the line-of-sight velocity distribution may exhibit a characteristic "double-peak" depending on the oriention of the viewing angle with respect to the progenitor's orbital plane. Kinematic surveys of dSphs may help to detect and identify substructures associated with the disruption of stellar clusters, as well as to address the shape of the dark matter haloes in which dSphs are embedded.