Program: GS-2006A-Q-3

We have obtained high S/N moderate and high resolution Gemini and Keck spectra of the Ly$\alpha$ forests of a large sample of projected pairs of quasars with $z>2$ and sub-arcminute separations. In these extremely rare sightlines, Ly$\alpha$ absorption, as measured in the \emph{background} quasar spectrum, can be used to study the environment, emission geometry, and radiative history of the \emph{foreground} quasar, provided that the systemic redshift of the foreground quasar is known accurately. We propose to obtain low dispersion ($R\sim 1700$) H-band spectra of 24 sub-arcminute $z > 2$ projected pairs of quasars, with NIRI and GNIRS to determine systemic redshifts from the narrow [OIII]~$\lambda 5008$ emission line accurate to $<100\rm \,km\,s^{-1}$. This will eliminate the current $\sim 5~\hmpc$ uncertainty in the foreground quasars' radial position, resolving transverse length scales as small as $\sim 25\hkpc$. We will then be able to characterize the transverse proximity effect, measure the cross-correlation function of quasars with neutral gas, constrain the isotropy of quasar emission, and the emission history of the quasars on timescales from $8 \times 10^4$ to $3 \times 10^6$ years, as well as gain insights into the fluorescent recombination radiation emitted by Lyman limit systems illuminated by ultraviolet photons.