Galaxies lacking dark matter produced by close encounters in a cosmological simulation

TL;DR

This paper demonstrates through advanced cosmological simulations that close encounters with massive galaxies can produce low-mass galaxies lacking dark matter, aligning with recent observations and challenging previous assumptions.

Contribution

It reveals that standard cosmological models can naturally produce dark-matter-deficient galaxies via galaxy interactions, supported by detailed simulations.

Findings

Approximately 30% of massive galaxies have dark-matter-deficient satellites.

Close encounters with massive neighbors can strip dark matter from low-mass galaxies.

Simulation results match observed properties of dark-matter-deficient galaxies.

Abstract

The standard cold dark matter plus cosmological constant model predicts that galaxies form within dark-matter haloes, and that low-mass galaxies are more dark-matter dominated than massive ones. The unexpected discovery of two low-mass galaxies lacking dark matter immediately provoked concerns about the standard cosmology and ignited explorations of alternatives, including self-interacting dark matter and modified gravity. Apprehension grew after several cosmological simulations using the conventional model failed to form adequate numerical analogues with comparable internal characteristics (stellar masses, sizes, velocity dispersions and morphologies). Here we show that the standard paradigm naturally produces galaxies lacking dark matter with internal characteristics in agreement with observations. Using a state-of-the-art cosmological simulation and a meticulous galaxy-identification technique, we find that extreme close encounters with massive neighbours can be responsible for this. We predict that approximately 30 percent of massive central galaxies (with at least 1e11 solar masses in stars) harbour at least one dark-matter-deficient satellite (with 1e8 - 1e9 solar masses in stars). This distinctive class of galaxies provides an additional layer in our understanding of the role of interactions in shaping galactic properties. Future observations surveying galaxies in the aforementioned regime will provide a crucial test of this scenario.