The clustering properties of the Lyman clouds

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Abstract
We analyse the clustering properties of a high-resolution ( ∼ 10 km s−1) sample of about 1600 Lyman α lines in the spectra of 15 quasars, obtained in the framework of an ESO key programme with the addition of literature data. The two-point correlation function in velocity space shows a significant signal on small velocity scales (Δv≲300 km s−1) with amplitude and significance increasing with increasing column density. The correlation scale at z ∼ 3 turns out to be 200-300 h50−1 kpc. A trend of increasing correlation with decreasing redshift is apparent. The existence of over- and underdensities on scales of a few tens of Mpc is confirmed with a high confidence level and a number of possible structures are identified. The present observations are found to be consistent with models of gravitationally induced correlations. A continuity scenario between Lyman α and metal systems emerges, with a suggested physical association between the Lyman α clouds with log NHi, ≳ 14 and the haloes of protogalactic systems.

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