Formation of globular cluster-rich ultra-diffuse galaxies through mergers

Abstract

We use high-resolution, idealized hydrodynamic simulations of gas-rich dwarf-galaxy mergers to test whether such encounters can form ultra-diffuse galaxies (UDGs) with globular cluster (GC) systems. We simulate 1:1 and 1:2 mergers alongside an isolated control model and identify stellar overdensities as GC candidates (GCCs). The remnants evolve into dispersion-supported, UDG-like systems with three-dimensional stellar half-mass radii $r^{3D} \sim 1.9-2.6$ kpc, while the isolated dwarf remains rotationally supported and forms no GCCs. Tidal heating and stellar feedback expel a large fraction of the gas beyond the dark matter (DM) halo, leaving stellar-dominated remnants whose DM haloes remain cuspy. Merger-driven star formation is highly clustered: the fraction of newly formed stellar mass bound in massive clusters exceeds 0.5 after the first pericentric passage and remains elevated thereafter. By the final snapshot, the remnants host GC populations numbering 20 (1:1) and 39 (1:2), more centrally concentrated than the field stars and consistent with the observed GC number-halo mass relation. The GCCs match observed star clusters in the planes of mass versus size, velocity dispersion, and density. More massive clusters exhibit stronger internal rotation and broader metallicity spreads. In one case, the merger produces a nucleated UDG via cluster inspiral followed by sustained in-situ star formation. These results demonstrate that gas-rich dwarf mergers are a viable pathway to GC-rich (and sometimes nucleated) UDGs, and predict correlated cluster mass, rotation, and metallicity-dispersion trends testable with observations.