Program: GN-2005A-C-9

We propose to use Gemini GMOS and LRIS on Keck I to obtain moderate dispersion spectra of the Ly$\alpha$ forests of close quasar pairs discovered from the SDSS. Spectra with $\sim 100 \ {\rm km \ s^{-1}}$ resolution at high %($S/N$) signal to noise ratio will enable us to measure both line of sight and transverse Ly$\alpha$ forest absorption correlations on scales as small as $\sim 40 \ \rm{h^{-1} kpc}$ (comoving). This will allow us to study the thermal history of the IGM, measure the geometry of the universe at redshift $z\sim 2$, and study the transverse proximity effect. After an extensive follow up campaign to search for companions around SDSS quasars using the 3.5m telescope at APO, we have discovered 73 new close quasar pairs with separations, $2^{\prime\prime}<\Delta\theta<60^{\prime\prime}$ ($40 \ \rm{h^{-1} kpc}\lesssim R \lesssim 1 \rm{h^{-1} Mpc}$), spanning the redshift range, $1.8\lesssim z \lesssim 2.9$, the largest such sample in existence. We request 3 nights on Gemini to observe 10 high redshift pairs, and 2 nights on Keck I to observe 10 lower redshift blue pairs down to the atmospheric cutoff. Combined with data from previous NOAO allocations and other facilities, these 20 new pairs will provide us with the statistics we need for precision cosmological constraints competitive with and complementary to the CMB, supernovae, and large galaxy surveys.