Multiple beads-on-a-string : dark matter-deficient galaxy information in a mini-bullet satellite-satellite galaxy collision

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Dark-matter deficient galaxies (DMDGs) discovered in the search for ultra-diffuse galaxies (UDGs), in apparent conflict with standard CDM, may be produced by high-velocity galaxy-galaxy collisions, the Mini-bullet scenario. Recent observations of an aligned trail of UDGs near NGC1052, including DMDGs DF2 and DF4, suggesting a common formation site and time, ∼8.9±1.5 Gyr ago, provide a test. Hydro/N-body simulations are presented here with initial conditions for colliding satellites tailored to match the observed UDGs in the NGC1052 group, supplemented by galaxy orbit integrations. We demonstrate the formation of a trail of DMDGs, including two massive ones that replicate the observed motions of DF2 and DF4. The linear relation, v=Ax+v₀, conjectured previously to relate positions (x) and velocities (v) of the aligned DMDGs as a signature of the collision event, is approximately obeyed, but individual DMDGs can deviate significantly from it. The progenitors whose collision spawned the trail of DMDGs survive the collision without, themselves, becoming DMDGs. We predict one progenitor is located at the end of the trail, testable by observing the difference between its stars, formed pre-collision, from those of the DMDGs, formed post-collision. By contrast, stellar ages and metallicities of the DMDGs are nearly identical. We further offer a hint that the tidal field of host NGC1052 may contribute to making DMDGs diffuse. ΛCDM simulation in a 100 cMpc box finds our required initial conditions ∼10 times at z<3. These results indicate current observations are consistent with the Mini-bullet scenario, encouraging further study.



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