Formation of Dark Matter Deficient Galaxies during High-velocity Galaxy Collisions

Along with their luminous member globular clusters (GCs), the recent discovery of diffuse dwarf galaxies that are deficient in dark matter — such as NGC1052-DF2 and NGC1052-DF4 — appears to challenge the current paradigm of structure formation in our Universe. We describe the numerical experiments using the adaptive mesh refinement code (Enzo) and particle-based gravito-hydrodynamics code (Gadget-2) to determine if the so-called dark matter deficient galaxies (DMDGs) could be produced when two gas-rich, dwarf-sized galaxies collide with a high relative velocity of ~ 300 km/s. Using idealized high-resolution simulations, we demonstrate simultaneous formation of DMDGs and their star clusters (SCs) in high-velocity galaxy collisions that separate dark matter from the warm disk gas which subsequently is compressed by shock and tidal interaction to form stars efficiently. In particular, we show that the galaxy collision spawns multiple massive SCs () within 150 Myr after the collision. At the end of our ~ 800 Myr fiducial run, the resulting DMDG of hosts 10 luminous (), gravitational bound SCs with a line-of-sight velocity dispersion 11.2 km/s. Our study suggests that DMDGs and their luminous member SCs could form simultaneously in high-velocity galaxy collisions while being in line with the key observed properties of NGC1052-DF2 and NGC1052-DF4. Also, using a large simulated universe IllustrisTNG, we discover a number of high-velocity galaxy collision events in which DMDGs are expected to form. However, we did not find evidence that these types of collisions actually produced DMDGs in the IllustrisTNG100-1 run. We argue that the resolution of the numerical experiment is critical to realize the “collision-induced” DMDG formation scenario. Our results demonstrate one of many routes in which galaxies could form with unconventional dark matter fractions.