Dark satellites and the morphology of dwarf galaxies

TL;DR

Dark satellites predicted by LambdaCDM can significantly influence dwarf galaxy morphology, potentially transforming disky dwarfs into spheroidal systems and triggering starbursts through dynamical heating.

Contribution

This study demonstrates through simulations that dark satellites can cause morphological transformations in dwarf galaxies, a process not previously well understood.

Findings

Dark satellites can induce spheroidal morphology in dwarf galaxies.

Mergers with dark satellites are more frequent in dwarf galaxies than in larger galaxies.

Dark satellite interactions may trigger starbursts in gas-rich dwarfs.

Abstract

One of the strongest predictions of the LambdaCDM cosmological model is the presence of dark satellites orbiting all types of galaxies. We focus here on the dynamical effects of such satellites on disky dwarf galaxies, and demonstrate that these encounters can be dramatic. Although mergers with M_sat > M_d are not very common, because of the lower baryonic content they occur much more frequently on the dwarf scale than for L_*-galaxies. As an example, we present a numerical simulation of a 20% (virial) mass ratio merger between a dark satellite and a disky dwarf (akin to the Fornax dwarf galaxy in luminosity) that shows that the merger remnant has a spheroidal morphology. We conclude that perturbations by dark satellites provide a plausible path for the formation of dSph systems and also could trigger starbursts in gas rich dwarf galaxies. Therefore the transition from disky to the often amorphous, irregular, or spheroidal morphologies of dwarfs could be a natural consequence of the dynamical heating of hitherto unobservable dark satellites.