Evidence for Large Scale Structure in the Ly $\alpha$ Forest at z > 2.6

Abstract

We present a search for spatial and redshift correlations in a A resolution spectroscopic survey of the Lyα forest at 2.15 < z < 3.37 toward ten QSOs concentrated within a 1 • diameter field. We find a signal at 2.7σ significance for correlations of the Lyα absorption line wavelengths between different lines of sight over the whole redshift range. The significance rises to 3.2σ if we restrict the redshift range to 2.60 < z < 3.37, and to 4.0σ if we further restrict the sample to lines with rest equivalent width 0.1 ≤ W 0 A < 0.9. We conclude that a significant fraction of the Lyα forest arises in structures whose correlation length extends at least over 30 arcmin (∼ 26 h −1 comoving Mpc at z = 2.6 for H 0 ≡ 100h km s −1 Mpc −1 , Ω = 1.0, Λ = 0). We have also calculated the three dimensional two point correlation function for Lyα absorbers; we do not detect any significant signal in the data. However, we note that line blending prevents us from detecting the signal produced by a 100% overdensity of Lyα absorbers in simulated data. We find that the Lyα forest redshift distribution provides – 2 – a more sensitive test for such clustering than the three dimensional two point correlation function.