The isolated dark matter-poor galaxy that ran away. An example from IllustrisTNG

Abstract

Since the discovery of dark matter-deficient galaxies, numerous studies have shown that these exotic galaxies naturally occur in the $Λ$CDM model due to stronger tidal interactions. They are typically satellites, with stellar masses in the $10^8-10^9\;\mathrm{M}_\odot$ range, of more massive galaxies. The recent discovery of a massive galaxy lacking dark matter and also lacking a more massive neighbor is puzzling. Two possible scenarios have been suggested in the literature: either the galaxy lost its dark matter early or it had been lacking ab initio. As a proof of concept for the former assumption, we present an example from IllustrisTNG300. At present, the galaxy has a stellar mass of $M_\star \simeq 6.8 \cdot 10^9\; \mathrm{M}_\odot$, with no gas, $M_\mathrm{DM}/M_\mathrm{B} \simeq 1.31$, and a stellar half-mass radius of $R_{0.5,\star} = 2.45\;\mathrm{kpc}$. It lost the majority of its dark matter early, between $z = 2.32$ and $z = 1.53$. Since then, it has continued to dwell in the cluster environment, interacting with the cluster members without merging, while accelerating on its orbit. Eventually, it left the cluster and it has spent the last $\sim 2\;\mathrm{Gyr}$ in isolation, residing just outside the most massive cluster in the simulation. Thus, the galaxy represents the first example found in simulations of both an isolated dark matter-poor galaxy that lost its extended envelope early and a fairly compact stellar system that has managed to escape.