Program: GN-2010A-C-3

We propose to measure the metallicities of z=3.1 \lya\ emitting galaxies. \lya\ emitters are the youngest class of high redshift galaxies, with typical ages of only $10^7$ years and stellar masses of $10^7 - 10^9 \msun$, even though their spatial clustering indicates halo masses of $10^{11} \msun$. By measuring the [OII], [OIII], and H$\beta$ line fluxes with NIRI, we will estimate metallicities for these galaxies for the first time ever. By doing so, we will {\bf(a)} supply one of the missing pieces in understanding \lya\ galaxies, whose stellar populations, masses of halos and ages have been constrained {\bf (b)} pin down the low-mass end of the mass-metallicity relation at z=3, and {\bf (c)} differentiate the kinematics of the resonantly scattered \lya\ line from other nebular lines, e.g. [OII] and [OIII]. This will allow us to {\bf (d)} distinguish scenarios where the \lya\ escape is due to special kinematics from those where the galaxies are relatively dust-free. {\bf (e)} We will cross-calibrate the star-formation rates derived from various emission lines. Finally, {\bf (f)} we will determine the velocity offset between the resonantly scattered \lya\ line and other lines. This is a critical parameter in determining how much of the blue wing of the \lya\ line is absorbed by intergalactic gas. By establishing this quantity directly, we will lay a firm foundation for tests of reionization based on \lya\ galaxy statistics at $z > 6$.