XQ-100 survey neutral gas

The XQ-100 DLA sample is combined with major DLA surveys in the literature. The final combined sample consists of 742 DLAs over a redshift range approximately 1.6<z_abs_<5.0.

We develop a novel technique for computing {Omega}_HI_^DLA^ as a continuous function of redshift, and we thoroughly assess and quantify the sources of error therein, including fitting errors and incomplete sampling of the high column density end of the column density distribution function. There is a statistically significant redshift evolution in {Omega}_HI_^DLA^ (>=3{sigma}) from z~2 to z~5. In order to make a complete assessment of the redshift evolution of {Omega}_HI_, we combine our high-redshift DLA sample with absorption surveys at intermediate redshift and 21-cm emission line surveys of the local universe.