Large‐Scale Correlations in the Lyα Forest at z = 3–4

Abstract

We present a study of the spatial coherence of the intergalactic mediumtoward two pairs of high-redshift quasars with moderate angularseparations observed with Keck ESI, Q1422+2309A/Q1424+2255(z$_{em}$~3.63, {$Δ$}{\thetas}=39$^{''}$) and Q1439-0034A/B(z$_{em}$~4.25, {$Δ$}{\thetas}=33$^{''}$). Thecross-correlation of transmitted flux in the Ly{$α$} forest shows a5-7 {$σ$} peak at zero velocity lag for both pairs. This stronglysuggests that at least some of the absorbing structures span the230-300h$^{-1}$$_{70}$ proper kpc transverse separationbetween sight lines. We also statistically examine the similaritybetween paired spectra as a function of transmitted flux, a measure thatmay be useful for comparison with numerical simulations. Ininvestigating the dependence of the correlation functions on spectralcharacteristics, we find that photon noise has little effect for asignal-to-noise ratio of $\gt$~10 per resolution element. However, theagreement between the autocorrelation along the line sight and thecross-correlation between sight lines, a potential test of cosmologicalgeometry, depends significantly on instrumental resolution. Finally, wepresent an inventory of metal lines. These include a pair of strong C IVsystems at z~3.4, appearing only toward Q1439B, and an Mg II + Fe IIsystem present toward Q1439A/B at z~1.68.The observations were made at the W. M. Keck Observatory, which isoperated as a scientific partnership between the California Institute ofTechnology and the University of California; it was made possible by thegenerous support of the W. M. Keck Foundation.