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2000ApJ...543..552S -
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Astrophys. J., 543, 552-576 (2000/November-2)
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Surveys for z>3 damped Lyα absorption systems: the evolution of neutral gas.
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STORRIE-LOMBARDI L.J. and WOLFE A.M.
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Abstract (from CDS):
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We have completed spectroscopic observations using LRIS on the Keck 1 telescope of 30 very high redshift quasars, 11 selected for the presence of damped Lyα absorption systems and 19 with redshifts z>3.5 not previously surveyed for absorption systems. We have surveyed an additional 10 QSOs with the Lick 120" and the Anglo-Australian Telescope. We have combined these with previous data, resulting in a statistical sample of 646 QSOs and 85 damped Lyα absorbers with column densities N_HI_≥2x10^{20} atoms.cm^{–2} covering the redshift range 0.008≤z≤4.694. Four main features of how the neutral gas in the universe evolves with redshift are evident from these data.

- (1. )
For the first time, we determine a

*statistically significant*steepening in the column density distribution function at redshifts z>4.0 (greater than 99.7% confidence). The steepening of the distribution function is due to both fewer very high column density absorbers (N_HI_≥10^{21}atoms.cm^{–2}) and more lower column density systems (N_HI_=2-4x10^{20}atoms.cm^{–2}). - (2. )
The frequency of very high column density absorbers (N_HI_≥10

^{21}atoms.cm^{–2}) reaches a peak in the redshift range 1.5<z<4, when the universe is 10%-30% of its present age. Although the sample size is still small, the peak epoch appears to be 3.0≤z≤3.5. The highest column density absorbers disappear rapidly toward higher redshifts in the range z=3.5⟶4.7 and lower redshifts z=3.0⟶0. None with column densities logN_HI_≥21 have yet been detected at z>4, although we have increased the redshift path surveyed by ~60%. - (3. )
With our current data set, the comoving mass density of neutral gas, Ω

_{g}, appears to peak at 3.0<z<3.5, but the uncertainties are still too large to determine the precise shape of Ω_{g}. The statistics are consistent with a constant value of Ω_{g}for 2<z<4. There is still tentative evidence for a drop-off at z>4, as indicated by earlier data sets. If we define R_{g*}≡Ω_{g}/Ω_{*}, where R_{g*}is the ratio of the peak value of Ω_{g}to Ω_{*}, the mass density in galaxies in the local universe, we find values of R_{g*}=0.25-0.5 at z∼3, depending on the cosmology. For an Ω=1 universe with a zero cosmological constant, R_{g*}~0.5. For an Ω=1 universe with a positive cosmological constant (Ω_{Λ}=0.7, Ω_{M}=0.3), we find R_{g*}~0.25. For a universe with Ω_{Λ}=0 and Ω_{M}=0.3, we find R_{g*}~0.3. - (4. )
Ω

_{g}decreases with redshift for the interval z=3.5⟶0.008 for our data set, but we briefly discuss new results from Rao & Turnshek for z<1.5 that suggest that Ω_{g}(z<1.5) may be higher than previously determined.

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Abstract Copyright:
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∼

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Journal keyword(s):
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Galaxies: Evolution - Galaxies: Intergalactic Medium - Galaxies: Quasars: Absorption Lines
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VizieR on-line data:
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<Available at CDS (J/ApJ/543/552): tables 1-6, refs>

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Nomenclature:
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Tables 2-5: [SW2000b] QSO JHHMM+DDMM abs N.NN, [SW2000b] QSO JHHMM+DDMM abs N.NNN, [SW2000b] QSO JHHMM+DDMM abs N.NNNN, N=116.

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Errata:
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erratum vol. 592, p. 1263 (2003)

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Simbad objects:
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729

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2019.09.17-03:09:33

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