The Flux Auto‐ and Cross‐Correlation of the Lyα Forest. I. Spectroscopy of QSO Pairs with Arcminute Separations and Similar Redshifts

Abstract

The Lyα forest has opened a new redshift regime for cosmological investigation. At z>2 it provides a unique probe of cosmic geometry and an independent constraint on dark energy that is not subject to standard candle or ruler assumptions. In Paper I of this series on using the Lyα forest observed in pairs of QSOs for a new application of the Alcock-Paczyński test, we present and discuss the results of a campaign to obtain moderate-resolution spectroscopy (FWHM ~= 2.5 Å) of the Lyα forest in pairs of QSOs with small redshift differences (Δz<0.25, z>2.2) and arcminute separations (θ<5'). This data set, composed of seven individual QSOs, 35 pairs, and one triplet, is also well suited for future investigations of the coherence of Lyα absorbers on ~1 Mpc transverse scales and the transverse proximity effect. We note seven revisions for previously published QSO identifications and/or redshifts. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution, and with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.