Estimation of physical conditions in the cold phase of the ISM in the sub-DLA system at z = 2.06 in the spectrum of the quasar J2123-0050

Abstract

An independent analysis of the molecular hydrogen absorption system at z = 2.059 in the spectrum of the quasar J2123-0050 is presented. The H_2 system consists of two components (A and B) with column densities log N^A(H_2) = 17.94+/-0.01 and log N^B(H_2) = 15.16+/-0.02. The spectrum exhibits the lines of HD molecules (log N^A(HD) = 13.87+/-0.06) and the neutral species C I and Cl I associated with the H_2 absorption system. For the molecular hydrogen lines near the quasar's Ly_beta and O VI emission lines, we detect a nonzero residual flux, ~3% of the total flux, caused by the effect of partial coverage of the quasar's broad-line region by an H_2 cloud. The uniqueness of the system being investigated is manifested in a high abundance of the neutral species H_2 and C I at the lowest H I column density, log N(H I) = 19.18+/-0.15, among the high redshift systems. The N(HD)/2N(H_2) ratio for component A has turned out to be also unusually high, (4.26+/-0.60)x10^{-5}. We have investigated the physical conditions in components A and B. Component A represents the optically thick case; the gas has a low number density (n~30 cm^{-3}) and a temperature T~140 K. In component B, the medium is optically thin with n<100 cm^{-3} and T<100 K. The ultraviolet (UV) background intensity in the clouds exceeds the mean intensity in our Galaxy by almost an order of magnitude. A high gas ionization fraction, n(H+)/n(H)~10^{-2}, which can be the result of partial shielding of the system from hard UV radiation, is needed to describe the high HD and C I column densities. Using our simulations with the PDR Meudon code, we can reconstruct the observed column densities of the species within the model with a constant density n(H)=40 cm^{-3}. A high H_2 formation rate (higher than the mean Galactic value by a factor of 10-40) and high gas ionization fraction and UV background intensity are needed in this case.

arXiv comment23 pages, 15 figures, 6 tables

References in corpus (50)

• The Sloan Digital Sky Survey: Technical Summary
• The chemical composition of the Sun
• Radiative Transfer in a Clumpy Universe: II. The Utraviolet Extragalactic Background
• Information criteria for astrophysical model selection
• Structure of Stationary Photodissociation Fronts
• Primordial Nucleosynthesis in the Precision Cosmology Era
• Modelling Primordial Gas in Numerical Cosmology
• A model for atomic and molecular interstellar gas: The Meudon PDR code
• Column density distribution and cosmological mass density of neutral gas: Sloan Digital Sky Survey-III Data Release 9
• On the (Non)Evolution of HI Disks over Cosmic Time
• The Distribution of Thermal Pressures in the Interstellar Medium from a Survey of C I Fine-Structure Excitation
• Molecular Hydrogen in the FUSE Translucent Lines of Sight: The Full Sample
• Molecular hydrogen in high-redshift Damped Lyman-alpha systems: The VLT/UVES database
• The Chemistry of Interstellar OH+, H2O+, and H3O+: Inferring the Cosmic Ray Ionization Rates from Observations of Molecular Ions
• The VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems: Physical conditions in the neutral gas
• The First Positive Detection of Molecular Gas in a GRB Host Galaxy
• Surface chemistry in the interstellar medium - I - H2 formation by Langmuir-Hinshelwood and Eley-Rideal mechanisms
• H2 formation and excitation in the diffuse interstellar medium
• First detection of CO in a high-redshift DLA
• Keck telescope constraint on cosmological variation of the proton-to-electron mass ratio
• Chemical Rates on Small Grains and PAHs: C^+ Recombination and H_2 Formation
• Molecular Hydrogen in the Damped Lyman-alpha System towards GRB 120815A at z=2.36
• Diffuse molecular gas at high redshift: Detection of CO molecules and the 2175 Å dust feature at z=1.64
• Physical conditions in QSO absorbers from fine-structure absorption lines
• Interstellar H I and H_2 in the Magellanic Clouds: An Expanded Sample Based on UV Absorption-Line Data
• The warm, the excited, and the molecular gas: GRB 121024A shining through its star-forming galaxy
• High-Resolution Observations of Interstellar Ca I Absorption -- Implications for Depletions and Electron Densities in Diffuse Clouds
• On the sizes of z>2 Damped Lyman-alpha Absorbing Galaxies
• First constraint on cosmological variation of the proton-to-electron mass ratio from two independent telescopes
• VLT/X-shooter spectroscopy of the GRB 120327A afterglow
• Physical conditions in the neutral interstellar medium at z=2.43 toward Q2348-011
• Partial coverage of the Broad Line Region of Q1232+082 by an intervening H2-bearing cloud
• VLT/UVES observations of extremely strong intervening damped Lyman-alpha systems: Molecular hydrogen and excited carbon, oxygen and silicon at log N(HI)=22.4
• Molecular hydrogen in the z = 2.66 damped Lyman-alpha absorber toward Q J0643-5041
• HD Molecular Lines in an Absorption System at Redshift z = 2.3377
• Molecular hydrogen absorption systems in Sloan Digital Sky Survey
• Deuterated molecular hydrogen in the Galactic ISM. New observations along seven translucent sightlines
• New abundance determinations in z < 1.5 QSO absorbers: seven sub-DLAs and one DLA
• HD/H2 Molecular Clouds in the Early Universe: The Problem of Primordial Deuterium
• Molecular hydrogen in damped Ly-alpha systems: clues to interstellar physics at high-redshift
• The Magellan Uniform Survey of Damped Lyman alpha Systems II: Paucity of Strong Molecular Hydrogen Absorption
• Cosmological concordance or chemical coincidence? Deuterated molecular hydrogen abundances at high redshift
• A New FUSE Survey of Interstellar HD
• Element Abundances at High-redshift: Magellan MIKE Observations of sub-Damped Lyman-alpha Absorbers at 1.7 < z <2.4
• HD/H2 as a probe of the roles of gas, dust, light, metallicity and cosmic rays in promoting the growth of molecular hydrogen in the diffuse interstellar medium
• Ionization corrections in a multi-phase interstellar medium: Lessons from a z~2 sub-DLA
• Directional Radiation and Photodissociation Regions in Molecular Hydrogen Clouds
• Neutral chlorine and molecular hydrogen at high redshift
• Partial covering of emission regions of Q 0528-250 by intervening H${}_2$ clouds
• Effect of a partial coverage of quasar broad-line regions by intervening H${}_2$-bearing clouds

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• Spotting high-z molecular absorbers using neutral carbon: Results from a complete spectroscopic survey with the VLT
• X-shooter observations of strong H${}_2$-bearing DLAs at high redshift
• Physical conditions in diffuse interstellar medium of local and high redshift galaxies: measurements based on excitation of H${}_2$ rotational and CI fine-structure levels
• HD molecules at high redshift: cosmic-ray ionization rate in the diffuse interstellar medium
• Multicomponent H2 in DLA at zabs = 2.05: physical conditions through observations and numerical models
• HD/H${}_2$ ratio in the diffuse interstellar medium
• Neutral carbon in diffuse interstellar medium: abundance matching with H2 for DLAs at high redshifts
• Influence of radiative pumping on the HD rotational level populations in diffuse molecular clouds of the interstellar medium