Column density distribution and cosmological mass density of neutral
  gas: Sloan Digital Sky Survey-III Data Release 9
  We present the first results from an ongoing survey for Damped Lyman-alpha
systems (DLAs) in the spectra of z>2 quasars observed in the course of the
Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the Sloan
Digital Sky Survey (SDSS) III. Our full (non-statistical) sample, based on Data
Release 9, comprises 12,081 systems with log N(HI)>=20, out of which 6,839 have
log N(HI)>=20.3. This is the largest DLA sample ever compiled, superseding that
from SDSS-II by a factor of seven. Using a statistical sub-sample and
estimating systematics from realistic mock data, we probe the N(HI)
distribution at <z> = 2.5. Contrary to what is generally believed, the
distribution extends beyond 10^22 cm^-2 with a moderate slope of
index\approx-3.5. This result matches surprisingly well the opacity-corrected
distribution observed at z = 0. The cosmological mass density of neutral gas in
DLAs is found to be Omega_g_DLA~10^-3, evolving only mildly over the past 12
billion years.
