Unveiling the Origins of Local Group Galaxies with ELT-SHARP: An Overview of Science Cases

Abstract

The $Λ$CDM paradigm successfully describes large-scale cosmic structure, yet tensions possibly persist on galactic and sub-galactic scales. The Milky Way and the Local Universe offer a uniquely accessible laboratory to probe these discrepancies through chemo-dynamical studies of resolved stellar populations. Understanding disk assembly, dynamical heating, and galactoseismology requires wide-field coverage and high-angular-resolution near-infrared spectroscopy capable of penetrating dust-obscured regions and resolving crowded stellar environments. We propose science cases exploiting \textsc{SHARP}, a multi-mode near-infrared spectrograph for Extremely Large Telescopes and future space facilities. Operating over $0.95$--$2.45\,μ$m in a single exposure, \textsc{SHARP} enables efficient access to key stellar and gas tracers across the Galactic bulge, disk, halo, and nearby galaxies. The \textsc{NEXUS} mode provides adaptive-optics-assisted multi-object spectroscopy over a $1.2'\times1.2'$ field with spectral resolutions up to $R\sim17{,}000$, enabling gas and stellar kinematics. Complementarily, the \textsc{VESPER} multi-IFU mode delivers spatially resolved spectroscopy in crowded regions, allowing reconstruction of internal kinematics and stellar population gradients on sub-arcsecond scales. Combined with surveys such as \textit{Gaia}, APOGEE, LAMOST, LSST, 4MOST, and ELT--MOSAIC, this project will map six-dimensional phase-space structures of disk and bulge stars, stellar streams, and nearby disk galaxies (e.g. LMC, SMC). The data will enable investigations of bars, spiral arms, warps, flares, and satellite interactions, providing critical constraints on disk evolution, merger history, and dark matter substructure, and providing stringent tests of $Λ$CDM on the smallest accessible scales.