Column density distribution and cosmological mass density of neutral gas: Sloan Digital Sky Survey-III Data Release 9

TL;DR

This study analyzes a large sample of Damped Lyman-alpha systems from SDSS-III to understand the distribution and evolution of neutral gas in the universe, revealing that high column density systems are more common than previously thought.

Contribution

It provides the largest DLA sample to date, extending the N(HI) distribution beyond 10^22 cm^-2 and showing mild evolution of neutral gas density over 12 billion years.

Findings

N(HI) distribution extends beyond 10^22 cm^-2 with a slope of approximately -3.5.

The cosmological mass density of neutral gas in DLAs is about 10^-3, with little evolution over 12 billion years.

The distribution matches the opacity-corrected distribution observed at z=0.

Abstract

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.