The dust obscuration bias in Damped Lyman alpha systems

Abstract

We present a new study of the effects of quasar obscuration on the statistics of Damped Ly alpha (DLA) systems. We show that the extinction of any Galactic or extragalactic HI region increases with the column density of zinc with a turning point above which background sources are suddenly obscured. We derive a relation between the extinction of a DLA system and its HI column density, N, metallicity, Z, fraction of iron in dust, f_Fe(Z), and redshift, z. From this relation we estimate the fraction of DLA systems missed as a consequence of their own extinction in magnitude-limited surveys. We derive a method for recovering the true frequency distributions of N and Z in DLAs, f_N and f_Z, using the biased distributions measured in the redshift range where the observations have sufficient statistics (1.8 </= z </= 3). By applying our method we find that the well-known empirical thresholds of DLA column densities, N(ZnII) </~ 10^13.1 cm^-2 and N(HI) </~ 10^22 cm^-2 can be successfully explained in terms of the obscuration effect without tuning of the local dust parameters. The obscuration has a modest effect on the distribution of quasar apparent magnitudes, but plays an important role in shaping the statistical distributions of DLAs. The exact estimate of the bias is still limited by the paucity of the data (~40 zinc measurements at 1.8 </~ z </~ 3). We find that the fraction of DLAs missed as a consequence of obscuration is \~30% to 50%, consistent with the results of surveys of radio-selected quasars. By modelling the metallicity distribution with a Schechter function we find that the mean metallicity can be ~5 to 6 times higher than the value commonly reported for DLAs at z~2.3.

Astronomy and Astrophysics, in press, 20 pages, 10 figures; abridged abstract; improved figs. 3 and 5; most of mathematical formulation moved to the Appendix; minor changes

References in corpus (38)

• Interstellar Dust Grains
• A Quantitative Comparison of SMC, LMC, and Milky Way UV to NIR Extinction Curves
• The Galaxy Luminosity Function and Luminosity Density at Redshift z=0.1
• Abundances for metal-poor stars with accurate parallaxes I. Basic data
• The Metallicity of High Redshift Galaxies: The Abundance of Zinc in 34 Damped Lyman Alpha Systems from z = 0.7 to 3.4
• The Age-Metallicity Relation of the Universe in Neutral Gas: The First 100 Damped Lya Systems
• The VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems
• 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
• Metal Abundances at z < 1.5: Fresh Clues to the Chemical Enrichment History of Damped Lyman alpha Systems
• The UCSD HIRES/KeckI Damped Lya Abundance Database: II. The Implications
• The Sloan Digital Sky Survey Quasar Catalog II. First Data Release
• The CORALS Survey I: New Estimates of the Number Density and Gas Content of Damped Lyman Alpha Systems Free from Dust Bias
• The Luminosity-Metallicity relation in the local universe from the 2dF Galaxy Redshift Survey
• Chemistry and Kinematics in the Solar Neighborhood: Implications for Stellar Populations and for Galaxy Evolution
• Heavy Element Abundances and Dust Depletions in the Host Galaxies of Three Gamma-Ray Bursts
• Abundances of Cu and Zn in metal-poor stars: clues for Galaxy evolution
• A physical upper limit on the HI column density of gas clouds
• Sulphur and zinc abundances in Galactic stars and damped Lyman-alpha systems
• Ionization Properties and Elemental Abundances in Damped Ly alpha Systems
• Zn and Cr abundances in damped Lyman alpha systems from the CORALS survey
• CII* Absorption in Damped Lyman Alpha Systems: (II) A New Window on the Star Formation History of the Universe
• Dust-reddening and gravitational lensing of SDSS QSOs due to foreground damped Lyman-alpha systems
• Star formation rate and metallicity of damped Lyman-alpha absorbers in cosmological SPH simulations
• Chemical abundances of Damped Ly alpha systems: A new method for estimating dust depletion effects
• The evolution of the galaxy luminosity function in the rest frame blue band up to z=3.5
• Metallicity Evolution of Damped Lyman Alpha Systems In Lambda CDM Cosmology
• The early build-up of dust in galaxies: A study of Damped Ly alpha Systems
• The Number Density of 0.6 < z < 1.7 MgII Systems from CORALS: Observational Biases at Intermediate Redshift
• Metallicity in damped Lyman-alpha systems: evolution or bias?
• Chemical evolution and depletion pattern in Damped Lyman-alpha (DLA) systems
• An Excess of C IV Absorbers in Luminous QSOs: Evidence for Gravitational Lensing?
• Investigating lensing by absorbers in the 2dF-Quasar survey
• Dust obscuration studies along quasar sight lines using simulated galaxies
• Occlusion Effects and the Distribution of Interstellar Cloud Sizes and Masses
• Dust obscuration of DLA galaxies

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