Neutral gas density in Damped Lyman Alpha systems

Abstract

We estimate the intrinsic neutral gas density in Damped Lyman Alpha systems (${\Omega }_{HI}^{(DLA)}$) in the redshift range $2.2\lesssim z\lesssim 5$ from the DLA SDSS DR_3 sample of optically selected quasars. We take into account self-consistently the obscuration on background quasars due to the dust present in Damped Lyman Alpha systems. We model the column density and redshift distribution of these systems by using both a non-parametric and a parametric approach. Under conservative assumptions on the dust content of Damped Lyman $\alpha$ systems, we show that selection effects lead to underestimating the intrinsic neutral gas density by at least $15\%$ with respect to the observed neutral gas density. Over the redshift range $[2.2;5.5]$ we find ${\Omega }_{HI}^{(DLA)}=0.97_{-0.06-0.15}^{+0.08+0.28}\cdot 10^{-3}$, where the first set of error bars gives the $1\sigma$ random errors and the second set gives the modeling uncertainty dependent on the fraction of metals in dust - from 0\% to 50\%. This value compares with ${\Omega }_{HI}^{(DLA)}=0.82_{-0.05}^{+0.05}$ ($1\sigma$ error bars), which is obtained when no correction for dust is introduced. In the model with half of the metals mass in dust we cannot constraint ${\Omega }_{HI}^{(DLA)}$ at a confidence level higher than $90\%$. In this case there is indeed a probability of about $10\%$ that the intrinsic column density distribution of DLA systems is a power law $f(N_{HI})\propto 1/N_{HI}^{1.95}$. In contrast, with $25\%$ of the metals in dust - the most realistic estimate - a power law is ruled out at $99.5\%$ of confidence level.

32 pages, 8 figures, accepted for publication in the Astrophysical Journal

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Cited by in corpus (8)

• Evolution of the cosmological mass density of neutral gas from Sloan Digital Sky Survey II - Data Release 7
• Metal-Free Gas Supply at the Edge of Reionization: Late-Epoch Population III Star Formation
• Dust Biasing of Damped Lyman Alpha Systems: a Bayesian Analysis
• The Mean Metal-line Absorption Spectrum of DLAs in BOSS
• A quasar hiding behind two dusty absorbers. Quantifying the selection bias of metal-rich, damped Lyman-alpha absorption systems
• The high A_V Quasar Survey: A z=2.027 metal-rich damped Lyman-alpha absorber towards a red quasar at z=3.21
• Assessing the dust selection bias in quasar absorbers at 0.7 < z< 1.6: Zn/Fe abundances in a radio-selected sample
• Dust absorption along the line of sight for high-redshift objects