The properties of the Elqui stellar stream and its progenitor

Stellar streams - formed through the tidal disruptions and gravitational instabilities of dwarf galaxies and star clusters - can tell us about the nature of their progenitors as well as the distribution of mass inside their orbits. The Southern Stream Stellar Spectroscopic Survey (S⁵) employs the Anglo-Australian Telescope (AAT) to study stellar streams, using photometric and proper-motion data to identify candidate member stars and AAT spectra to obtain radial velocities and abundance information. Work done by S⁵ has explored stream membership, orbit models and progenitors in great detail. S⁵ also takes high resolution followup spectra for confirmed stream members to analyse their detailed properties and better understand the evolutionary processes of progenitor dwarf galaxies and globular clusters. This thesis presents the results of an in-depth study and membership analysis of a metal-poor, distant stellar stream originally found and discussed in the Dark Energy Survey footprint: Elqui. Previouswork using the line of sight velocity and metallicity dispersions of the streams showed that Elqui had most likely originated as an ultrafaint dwarf galaxy. We perform a detailed kinematic, chemical and membership analysis of the stream, estimating the total mass and luminosity to understand the properties of the initial progenitor dwarf galaxy. Elqui exhibits a metallicity range of [Fe/H] = -3.2 to -1.19 and has an estimated mass of 3.77 × 10⁴  +2.8×10³  −2.4×10² 𝑀_⊙. Elqui also likely experiences perturbations from the gravitational influences of the Large Magellanic Cloud and the bar of the Milky Way.