2017MNRAS.471.2174B

We present an analysis of the spatial distribution and dynamics of neutral hydrogen gas around galaxies using new X-Shooter observations of z ∼ 2.5-4 quasars. Adding the X-Shooter data to our existing data set of high-resolution quasar spectroscopy, we use a total sample of 29 quasars alongside ∼1700 Lyman Break Galaxies (LBGs) in the redshift range 2 <= z <= 3.5. We measure the Lyα forest auto-correlation function, finding a clustering length of s₀ = 0.081 ± 0.006 h^–1 Mpc, and the cross-correlation function with LBGs, finding a cross-clustering length of s₀ = 0.27 ± 0.14 h^–1 Mpc and power-law slope γ = 1.1 ± 0.2. Our results highlight the weakly clustered nature of neutral hydrogren systems in the Lyα forest. Building on this, we make a first analysis of the dependence of the clustering on absorber strength, finding a clear preference for stronger Lyα forest absorption features to be more strongly clustered around the galaxy population, suggesting that they trace on average higher mass haloes. Using the projected and 2-D cross-correlation functions, we constrain the dynamics of Lyα forest clouds around z ∼ 3 galaxies. We find a significant detection of large-scale infall of neutral hydrogen, with a constraint on the Lyα forest infall parameter of β_F = 1.02 ± 0.22.