Sharp HI edges at high z: the gas distribution from Damped Lyman-alpha to Lyman-limit absorption systems

Abstract

We derive the distribution of neutral and ionized gas in high redshift clouds which are optically thick to hydrogen ionizing radiation, using published data on Lyman-limit and Damped Lyman-alpha absorption systems in the redshift range 1.75 < z < 3.25. We assume that the distribution of the hydrogen total (HI+HII) column density in the absorbers follows a power law K N_H^{-alpha}, whereas the observed HI column density distribution deviates from a pure power law as a result of ionization from a background radiation field. Comparison of the models and observations give Maximum Likelihood solutions for the exponent alpha and for X, the value of log(N_H/N_HI) when the Lyman-limit optical depth is unity: alpha=2.7^{+1.0}_{-0.7} and X=2.75\pm0.35. X is much lower than what would be obtained for a gaseous distribution in equilibrium under its own gravity but the ratio of dark matter to gas density is not well constrained being log(eta_0)=1.1\pm 0.8. An extrapolation of our derived power law distribution towards systems of lower column density, the Lyman-alpha forest, favours models with log(eta_0) < 1.1 and alpha=2.7-3.3. With alpha appreciably larger than 2, Lyman-limit systems contain more gas than Damped Lyman-alpha systems and Lyman-alpha forest clouds even more. Estimates of the cosmological gas and dark matter density due to absorbers of different column density around z=2.5 are also given.

arXiv comment21 pages, 6 figures. Accepted for publication in ApJ

References in corpus (14)

• Radiative Transfer in a Clumpy Universe: II. The Utraviolet Extragalactic Background
• The Star Formation History of Field Galaxies
• The Opacity of the Lyman Alpha Forest and Implications for Omega_{baryon} and the Ionizing Background
• Discovery of Damped Lyman-Alpha Systems at Redshifts Less Than 1.65 and Results on their Incidence and Cosmological Mass Density
• Field Galaxy Evolution Since Z~1 from a Sample of QSO Absorption-Selected Galaxies
• Surveys for z > 3 Damped Lyman-alpha Absorption Systems
• The Distribution of Column Densities and b Values in the Lyman-Alpha Forest
• Protogalactic Disk Models of Damped Lya Kinematics
• The Proximity Effect, the UV Background and the Statistics of the Lyman-Alpha Lines at High Resolution
• Sharp Hi Edges in the Outskirts of Disk Galaxies
• Damped Lyman alpha absorber and the faint end of the galaxy luminosity function at high redshift
• APM z>4 QSO Survey: Distribution and Evolution of High Column Density HI Absorbers
• A Minihalo Model for the Lyman Limit Absorption Systems at High Redshift
• Star formation in disk galaxies driven by primordial H_2

Cited by in corpus (14)

• An updated analytic model for the attenuation by the intergalactic medium
• The 1000 Brightest HIPASS Galaxies: HI Mass Function and Omega_HI
• The Column Density Distribution and Continuum Opacity of the Intergalactic and Circumgalactic Medium at Redshift <z>=2.4
• A Homogeneous Sample of Sub-DLAs II: Statistical, Kinematic and Chemical Properties
• The 21cm Power Spectrum After Reionization
• Self-shielding Effects on the Column Density Distribution of Damped Lyman Alpha Systems
• HI clouds in the proximity of M33
• A catalogue of damped Lyman alpha absorption systems and radio flux densities of the background quasars
• The effects of an ionizing background on the HI column density distribution in the local Universe
• Neutral Hydrogen Mapping of Virgo Cluster Blue Compact Dwarf Galaxies
• Mini High Velocity Clouds
• High Velocity Cloud Edges and Mini-HVCs
• A Comprehensive Statistical Analysis of the Gas Distribution in Lyman-limit and Damped Lyman-alpha Absorption Systems
• The faint HI environment of galaxies: a laboratory for testing galaxy formation