Abstract
This thesis project intends to study the known substructures in the galactic halo and search for new ones using data from the QUEST collaboration. These substructures are believed to be remnants of globular clusters or accreted dwarf galaxies, similar to the Sagittarius dwarf spheroidal galaxy. RR Lyrae stars will be used to trace the halo because they are relatively easy to detect and because they are excellent standard candles whose distances are better determined than alternative tracers,e.g., M giants. Part of the project involves spectroscopic observation of RR Lyrae stars in the leading stream from the Sgr dSph galaxy, which will better determine its spatial dimensions, structure, radial velocity and velocity dispersion. These properties constrain models of the stream that assume different shapes for the dark matter halo.
