2025MNRAS.543L...1F

The stellar mass-halo mass relation and the globular cluster (GC) number-halo mass relation are two scaling relations that relate fundamental properties of normal galaxies. Ultra-diffuse galaxies (UDGs), some of which, have rich GC systems and relatively low stellar masses can not follow the mean trend of both relations simultaneously - it is thus important to understand which relationship is followed by UDGs. Using independent halo masses determined from kinematic fitting to large radii, we identify three UDGs and two UDG-like galaxies from the literature and examine which scaling relation they follow. We find that the galaxies follow the GC number-halo mass relation but deviate in a systematic way from the stellar mass-halo mass relation, which depends on their GC count. This scatter off the relation is towards higher halo masses, or equivalently lower stellar masses. The galaxies exhibiting the largest offsets may represent 'failed galaxies' that have experienced quenched star formation with later assembly.