SIMBAD references

We present the results of a survey of damped (DLA, log N(HI)>20.3) and sub-damped Lyman-α systems (19.5<logN(HI)<20.3) at z>2.55 along the lines-of-sight to 77 quasars with emission redshifts in the range 4<z_em<6.3. Intermediate resolution (R∼4300) spectra were obtained with the Echellette Spectrograph and Imager (ESI) mounted on the Keck telescope. A total of 100 systems with logN(HI)>19.5 were detected of which 40 systems are damped Lyman-α systems for an absorption length of ΔX=378. About half of the lines of sight of this homogeneous survey have never been investigated for DLAs. We study the evolution with redshift of the cosmological density of the neutral gas and find, consistent with previous studies at similar resolution, that Ω_DLA,HI decreases at z>3.5. The overall cosmological evolution of Ω_HI shows a peak around this redshift. The HI column density distribution for logN(HI)≥20.3 is fitted, consistent with previous surveys, with a single power-law of index α~-1.8±0.25. This power-law overpredicts data at the high-end and a second, much steeper, power-law (or a gamma function) is needed. There is a flattening of the function at lower HI column densities with an index of α~-1.4 for the column density range logN(HI)=19.5-21. The fraction of HI mass in sub-DLAs is of the order of 30%. The HI column density distribution does not evolve strongly from z∼2.5 to z∼4.5.