SHARP(ening the) view of unresolved globular clusters in ultra diffuse galaxies

Ultra-Diffuse Galaxies (UDGs) challenge current galaxy formation models within the Λ CDM framework, particularly regarding their dark matter content and formation histories. Globular Clusters (GCs) serve as excellent tracers for probing the halos of these faint systems; however, current spectroscopic facilities struggle to reach the depth required to fully characterize GC populations beyond the local neighborhood. In this work, we present the scientific potential of NEXUS@SHARP, a near-infrared multi-slit spectrograph proposed on the upcoming Extremely Large Telescope (ELT). We demonstrate that NEXUS is uniquely positioned to overcome current observational limitations by combining high spatial resolution with efficient multiplexing. We show that NEXUS can efficiently help to characterize the GC population in UDGs across diverse environments– out to 60 to 70 Mpc–with a few hours of ELT time. These capabilities will allow for precise measurements of radial velocities and stellar populations, enabling robust dynamical mass estimates and distinguishing between competing UDG formation scenario.