Dark-matter-deficient galaxies in hydrodynamical simulations

Low-mass galaxies are expected to be dark-matter-dominated even within their central regions. Recently, two observations reported two dwarf galaxies in a group environment with very little dark matter in their central regions. We explore the population and origins of dark-matter-deficient galaxies (DMDGs) using two state-of-the-art hydrodynamical simulations, the EAGLE and Illustris projects. For all satellite galaxies with 10⁹ < M_* < 10¹⁰ M_\odot in groups with M₂₀₀ > 10¹³ M_\odot, we find that about 2.6 {per cent} of them in EAGLE, and 1.5 {per cent} in Illustris are DMDGs with dark matter fractions below 50 {per cent} inside two times the half-stellar-mass radius. We demonstrate that DMDGs are highly tidally disrupted galaxies, and that because dark matter has a higher binding energy than stars, mass loss of the dark matter is much more rapid than that of stars in DMDGs during tidal interactions. If DMDGs were confirmed in observations, they are expected in current galaxy formation models.