Dark Matter Deficient Galaxies From High-velocity Galaxy Collisions

The recent discovery of diffuse dwarf galaxies that are deficient in dark matter appears to challenge the current paradigm of structure formation in our Universe. We describe the numerical experiments 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 kms-1. Using idealized high-resolution simulations with both mesh-based and particle-based gravito-hydrodynamics codes, we find that DMDGs can form as high-velocity galaxy collisions separate dark matter from the warm disk gas which subsequently is compressed by shock and tidal interaction to form stars. Then 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 TNG100-1 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.

How Metals Are Transported In And Out Of A Galacticc Disk: Dependence On The Hydrodynamic Schemes In Numerical Simulations

Metallicity is a fundamental probe for understanding the baryon physics in a galaxy. Since metals are intricately associated with radiative cooling, star formation and feedback, reproducing the observed metal distribution through numerical experiments will provide a prominent way to examine our understandings ofgalactic baryon physics. In this study, we analyze the dependence of the galactic metal distribution on the numerical schemes, and quantify the differences in metal mixing among modern galaxy simulation codes (the mesh-based code Enzo and the particle-based codes Gadget-2 and Gizmo-PSPH). In particular, we examine different stellar feedback strengths and an explicit metal diffusion scheme in particle-based codes, as a way to alleviate the well-known discrepancy in metal transport between mesh-based and particle-based simulations. We demonstrate that a sufficient number of gas particles is needed in the gas halo to properly investigate the metal distribution therein.Including an explicit metal diffusion scheme does not significantly affect the metal distribution in the galactic disk, but does change the amount of low-metallicity gas in the hot diffuse halo. We also find that the spatial distribution of metals depends strongly on how the stellar feedback is modeled. We demonstrate that the previously reported discrepancy in metals between mesh-based and particle-based simulations can be mitigated with our proposed prescription, enabling these simulations to be reliably utilized in the study of metals in galactic halos and in the circumgalactic medium.

Star Cluster Formation In Galaxy Mergers In high-resolution model