Program: GS-2007B-Q-206

Connecting galaxy samples at different epochs is a key tool for studying galaxy evolution. We recently found differential, luminosity-dependent galaxy evolution by comparing UV luminosity functions (UVLF) of Lyman break galaxies at z=5, 4 and 3. Clustering and LyA equivalent widths of z=5 LBGs likewise show dependence on UV/optical luminosity. These findings suggest that the mechanism driving galaxy evolution depends on UV luminosity and/or mass. However, despite these intriguing results, there remains controversy about the evolution of the UVLF especially at z=5. To clarify the situation, we propose deep spectroscopy of a large sample of z=5 LBGs using GMOS-S. The primary goals are (1) spectroscopic redshift identifications to obtain indubitable number density of bright LBGs and (2) improvement of statistical significance of LyA EW distribution as a function of UV luminosity and stellar mass. We will be working at >7000A, so bright-time is OK but efficient sky subtraction with the GMOS nod-and-shuffle technique is key.