Program: GN-2011A-Q-17

Galaxies are surrounded by metal-enriched gaseous halos whose statistical absorption properties provide useful constraints on galaxy formation. Previously, absorption-line studies have used unresolved quasars as light sources, or at best a few such `pencil beams' in quasar pairs or lenses. We propose a proof-of-concept experiment to use a galaxy gravitationally lensed into an arc as an extended light source for spatially resolved spectroscopy of an intervening galaxy halo. Using R~1130 spectra of the high surface brightness 'Clone' arc, we will confirm and characterize variations along the arc in the rest-frame equivalent width of a MgII system seen in one knot of the arc (and search for other intervening absorption systems, and variations in them, all along the arc). These variations will directly test the Chen & Tinker (2008) universal profile for MgII absorbing halos. Our spectroscopy will simultaneously provide a spatially resolved (and high-S/N coadded) spectrum of the z=2 lensed galaxy with which to study in detail the properties of this >L* Lyman-break galaxy.