Evolution of the cosmological mass density of neutral gas from Sloan
  Digital Sky Survey II - Data Release 7
  We present the results of a search for damped Lyman-alpha (DLA) systems in
the Sloan Digital Sky Survey II (SDSS), Data Release 7. We use a fully
automatic procedure to identify DLAs and derive their column densities. The
procedure is checked against the results of previous searches for DLAs in SDSS.
We discuss the agreements and differences and show the robustness of our
procedure. For each system, we obtain an accurate measurement of the absorber's
redshift, the HI column density and the equivalent width of associated metal
absorption lines, without any human intervention. We find 1426 absorbers with
2.15 < z < 5.2 with log N(HI)>=20, out of which 937 systems have log N(HI)>=
20.3. This is the largest DLA sample ever built, made available to the
scientific community through the electronic version of this paper. In the
course of the survey, we discovered the intervening DLA with highest HI column
density known to date with log N(HI)=22.0+/-0.1. This single system provides a
strong constraint on the high-end of the N(HI) frequency distribution now
measured with high accuracy. We show that the presence of a DLA at the blue end
of a QSO spectrum can lead to important systematic errors and propose a method
to avoid them. This has important consequences for the measurement of the
cosmological mass density of neutral gas at z~2.2 and therefore on our
understanding of galaxy evolution over the past 10 billion years. [truncated]
