HI cosmological mass density at z=5

With this survey we make the most precise high-redshift measurement of the cosmological mass density of neutral hydrogen, Omega_HI_. At such high redshift, important systematic uncertainties in the identification of DLAs are produced by strong intergalactic medium absorption and QSO continuum placement.

These can cause spurious DLA detections, result in real DLAs being missed or bias the inferred DLA column density distribution. We correct for these effects using a combination of mock and higher resolution spectra, and show that for the GGG DLA sample the uncertainties introduced are smaller than the statistical errors on Omega_HI_. We find Omega_HI_=0.98^+0.20^_-0.18_x10^-3^ at <z>=4.9, assuming a 20 percent contribution from lower column density systems below the DLA threshold.