2004ApJ...613...61B

We present a study of the spatial coherence of the intergalactic medium toward two pairs of high-redshift quasars with moderate angular separations observed with Keck ESI, Q1422+2309A/Q1424+2255 (z_em~3.63, Δθ=39'') and Q1439-0034A/B (z_em~4.25, Δθ=33''). The cross-correlation of transmitted flux in the Lyα forest shows a 5-7 σ peak at zero velocity lag for both pairs. This strongly suggests that at least some of the absorbing structures span the 230-300/h₇₀proper kpc transverse separation between sight lines. We also statistically examine the similarity between paired spectra as a function of transmitted flux, a measure that may be useful for comparison with numerical simulations. In investigating the dependence of the correlation functions on spectral characteristics, we find that photon noise has little effect for a signal-to-noise ratio of ≳10 per resolution element. However, the agreement between the autocorrelation along the line sight and the cross-correlation between sight lines, a potential test of cosmological geometry, depends significantly on instrumental resolution. Finally, we present an inventory of metal lines. These include a pair of strong C IV systems at z~3.4, appearing only toward Q1439B, and an Mg II + Fe II system present toward Q1439A/B at z~1.68.