APM z>4 QSO Survey: Distribution and Evolution of High Column Density HI Absorbers

Abstract

Eleven candidate damped Lya absorption systems were identified in 27 spectra of the quasars from the APM z>4 survey covering the redshift range 2.8<z(abs)<4.4 (8 with z(abs)>3.5). High resolution echelle spectra (0.8A FWHM) have been obtained for three quasars, including 2 of the highest redshift objects in the survey. Two damped systems have confirmed HI column densities of N(HI) >= 10^20.3 atoms cm^-2, with a third falling just below this threshold. We have discovered the highest redshift damped Lya absorber known at z=4.383 in QSO BR1202-0725. The APM QSOs provide a substantial increase in the redshift path available for damped surveys for z>3. We combine this high redshift sample with other quasar samples covering the redshift range 0.008 < z < 4.7 to study the redshift evolution and the column density distribution function for absorbers with log N(HI)>=17.2. In the HI column density distribution f(N)=kN^-beta we find evidence for breaks in the power law, flattening for 17.2< log N(HI)<21 and steepening for log N(HI)>21.2. The column density distribution function for the data with log N(HI)>=20.3 is better fit with the form f(N)=(f*/N*)(N/N*)^-beta exp(-N/N*). Significant redshift evolution in the number density per unit redshift is evident in the higher column density systems with an apparent decline in N(z) for z>3.5.

To appear in MNRAS. Latex file (10 pages of text) plus 14 separate postscript figure files. Requires mn.sty. Postscript version with figures embedded is available at http://www.ociw.edu/~lisa/publications.html

Cited by in corpus (46)

• Evidence for Reionization at z ~ 6: Detection of a Gunn-Peterson Trough in a z=6.28 Quasar
• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• The SDSS Damped Lya Survey: Data Release 3
• Evolution of the cosmological mass density of neutral gas from Sloan Digital Sky Survey II - Data Release 7
• Cosmic Histories of Stars, Gas, Heavy Elements, and Dust
• Discovery of Damped Lyman-Alpha Systems at Redshifts Less Than 1.65 and Results on their Incidence and Cosmological Mass Density
• Surveys for z > 3 Damped Lyman-alpha Absorption Systems
• The evolution of Omega(HI) and the epoch of formation of damped Lyman-alpha absorbers
• The HI Mass Function of Galaxies from a Deep Survey in the 21cm Line
• The UCSD HIRES/KeckI Damped Lya Abundance Database: II. The Implications
• The CORALS Survey I: New Estimates of the Number Density and Gas Content of Damped Lyman Alpha Systems Free from Dust Bias
• Reconciling the local galaxy population with damped Ly-alpha cross sections and metal abundances
• A Homogeneous Sample of Sub-DLAs III: Total Gas Mass Omega_(HI+HeII) at z>2
• The UCSD HIRES/KeckI Damped Lya Abundance Database: I. The Data
• The Star Formation Rate Intensity Distribution Function--Implications for the Cosmic Star Formation Rate History of the Universe
• Dust and Diffuse Interstellar Bands in the z_a = 0.524 Absorption System toward AO 0235+164
• The effects of UV background correlations on LyA forest flux statistics
• A Homogeneous Sample of Sub-DLAs II: Statistical, Kinematic and Chemical Properties
• Absorption Systems in the Spectra of 66 z > 4 Quasars
• A comprehensive set of elemental abundances in damped Ly-alpha systems: revealing the nature of these high-redshift galaxies
• The Building the Bridge survey for z=3 Ly-alpha emitting galaxies I: method and first results
• The Baryonic Mass Function of Spiral Galaxies: Clues to Galaxy Formation
• The Last Eight-Billion Years of Intergalactic CIV Evolution
• The Population of Damped Lyman-alpha and Lyman Limit Systems in the Cold Dark Matter Model
• Simulations of Damped Lyman-Alpha and Lyman Limit Absorbers in Different Cosmologies: Implications for Structure Formation at High Redshift
• The evolution of neutral gas in damped Lyman $\alpha$ systems from the XQ-100 survey
• Galaxy Formation and the Kinematics of Damped Lyman Alpha Systems
• Self-shielding Effects on the Column Density Distribution of Damped Lyman Alpha Systems
• Testing Cosmological Models Against the Abundance of Damped Lyman-Alpha Absorbers
• The spatial distribution of cold gas in hierarchical galaxy formation models
• The Building the Bridge survey for z=3 Ly-alpha emitting galaxies II: Completion of the survey
• An excess of damped Lyman alpha galaxies near QSOs
• The Spatial, Ionization, and Kinematic Conditions of the z=1.39 Damped Ly-alpha Absorber in Q0957+561 A,B
• NICMOS Snapshot Survey of Damped Lyman Alpha Quasars
• MM-Newton Observations of two high redshift quasars: RX J1028-0844 and BR 0351-1034
• A new measurement of zinc metallicity in a DLA at z=3.35
• Cosmological Constraints from High-Redshift Damped Lyman-Alpha Systems
• The Chemical Evolution of the Universe I: High Column Density Absorbers
• Sharp HI edges at high z: the gas distribution from Damped Lyman-alpha to Lyman-limit absorption systems
• The HI Column Density Distribution Function at z=0: the Connection to Damped Ly alpha Statistics
• Soft X-ray Absorption by High-Redshift Intergalactic Helium
• Supermassive Objects as Gamma-Ray Bursters
• Unified model for quasar absorption line systems
• Microlensing of Quasars By Stars In Their Damped Lyman alpha Absorbers
• A Comprehensive Statistical Analysis of the Gas Distribution in Lyman-limit and Damped Lyman-alpha Absorption Systems
• Are Damped Ly-alpha Systems Large, Galactic Disks ?