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Title:
Neutral Gas Density in Damped Lyα Systems
Authors:
Trenti, M.; Stiavelli, M.
Affiliation:
AA(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218; , ), AB(Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218; , )
Publication:
The Astrophysical Journal, Volume 651, Issue 1, pp. 51-60. (ApJ Homepage)
Publication Date:
11/2006
Origin:
UCP
ApJ Keywords:
ISM: Dust, Extinction, Galaxies: High-Redshift, Galaxies: ISM, Galaxies: Intergalactic Medium
DOI:
10.1086/507423
Bibliographic Code:
2006ApJ...651...51T

Abstract

We estimate the intrinsic neutral gas density in damped Lyα (DLA) systems (Ω(DLA)HI) in the redshift range 2.2<~z<~5 from the SDSS DR3 DLA sample of optically selected quasars. We take into account self-consistently the obscuration on background quasars due to the dust present in damped Lyα systems. We model the column density and redshift distribution of these systems by using both a nonparametric and a parametric approach. Under conservative assumptions on the dust content of DLA 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 Ω(DLA)HI=0.97+0.08+0.28-0.06-0.15×10-3, where the first set of error bars gives the 1 σ 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 Ω(DLA)HI=0.82+0.05-0.05×10-3 (1 σ 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 Ω(DLA)HI 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(NHI)~1/N1.95HI. In contrast, with 25% of the metals in dust, the most realistic estimate, a power law is ruled out at a 99.5% confidence level.
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