Program: GN-2007A-Q-18

To try to find out the evolutionary sequence by connecting galaxy samples at different epochs, different selection methods is an upcoming key science in the study of galaxy evolution. We recently found the differential evolution of galaxies through the comparison of UV luminosity function (LF) of Lyman break galaxy samples at z~5, 4 and 3. Properties of LBGs at z~5 such as clustering, Ly-alpha equivalent widths (EWs) also show dependence on UV/optical luminosity. These findings suggest that mechanism driving galaxy evolution works differentially depending on UV luminosity and/or mass. However, despite these intriguing results, there remains controversy about the evolution of UVLF especially at z~5. In order to clarify the situation, we propose a deep spectroscopy of a large sample of z~5 LBGs using GMOS-N. The primary goals are (1) spectroscopic identification of redshifts to obtain indubitable number density of bright LBGs and (2) improvement of statistical significance of Ly-alpha EW distribution as a function of UV luminosity and stellar mass. The latter is also valuable to explore the relation between LBGs and Ly-alpha emitters. Efficient sky subtraction with the nod-and-shuffle technique available in GMOS-N is a key feature to improve the S/N at lambda>7000AA.