On the Tidal Formation of Dark Matter Deficient Galaxies

TL;DR

This study uses high-resolution simulations to demonstrate that tidal stripping of cored dark matter halos can produce dark matter deficient galaxies like DF2 with properties and globular cluster populations consistent with observations.

Contribution

It shows that tidal stripping of cored dark matter halos can explain the formation of dark matter deficient galaxies with their observed globular cluster features.

Findings

Tidal stripping can produce DF2-like galaxies with realistic properties.

Only about 20% of GCs are stripped if their initial distribution is twice that of stars.

Stellar outskirts of such galaxies should have shallow metallicity gradients.

Abstract

Previous studies have shown that dark matter deficient galaxies (DMDG) such as NGC1052-DF2 (hereafter DF2) can result from tidal stripping. An important question, though, is whether such a stripping scenario can explain DF2's large specific frequency of globular clusters (GCs). After all, tidal stripping and shocking preferentially remove matter from the outskirts. We examine this using idealized, high-resolution simulations of a regular dark matter dominated galaxy that is accreted onto a massive halo. As long as the initial (pre-infall) dark matter halo of the satellite is cored, which is consistent with predictions of cosmological, hydrodynamical simulations, the tidal remnant can be made to resemble DF2 in all its properties, including its GC population. The required orbit has a peri-centre at the 8.3 percentile of the distribution for subhaloes at infall, and thus is not particularly extreme. On this orbit the satellite loses 98.5 (30) percent of its original dark matter (stellar) mass, and thus evolves into a DMDG. The fraction of GCs that is stripped off depends on the initial radial distribution. If, at infall, the median projected radius of the GC population is roughly two times that of the stars, consistent with observations of isolated galaxies, only $\sim 20$ percent of the GCs are stripped off. This is less than for the stars, which is due to dynamical friction counteracting the tidal stirring. We predict that, if indeed DF2 was crafted by strong tides, its stellar outskirts should have a very shallow metallicity gradient.