Proximate Molecular Quasar Absorbers: Excess of damped H2 systems at zabs~zQSO in SDSS DR14

Abstract

We present results from a search for strong H2 absorption systems proximate to quasars (zabs~zem) in the Sloan Digital Sky Survey (SDSS) Data Release 14. The search is based on the Lyman-Werner band signature of damped H2 absorption lines without any prior on the associated metal or neutral hydrogen content. This has resulted in the detection of 81 systems with log N(H2)~19-20 located within a few thousand km/s from the quasar. Compared to a control sample of intervening systems, this implies an excess of proximate H2 systems by about a factor of 4 to 5. The incidence of H2 systems increases steeply with decreasing relative velocity, reaching an order of magnitude higher than expected from intervening statistics at Delta_v<1000 km/s. The most striking feature of the proximate systems compared to the intervening ones is the presence of Ly-alpha emission in the core of the associated damped HI absorption line in about half of the sample. This puts constraints on the relative projected sizes of the absorbing clouds to those of the quasar line emitting regions. Using the SDSS spectra, we estimate the HI, metal and dust content of the systems, which are found to have typical metallicities of one tenth Solar, albeit with a large spread among individual systems. We observe trends between the fraction of leaking Ly-alpha emission and the relative absorber-quasar velocity as well as with the excitation of several metal species, similar to what has been seen in metal-selected proximate DLAs. With the help of theoretical HI-H2 transition relations, we show that the presence of H2 helps to break the degeneracy between density and strength of the UV field as main sources of excitation and hence provides unique constraints on the possible origin and location of the absorbing clouds. We suggest that most of these systems originate from galaxies in the quasar group. [truncated]

accepted for publication in A&A

References in corpus (21)

• Metallicity Evolution of Damped Lyman-alpha Systems out to z~5
• Velocity-Metallicity Correlation for high-z DLA Galaxies: Evidence for a Mass-Metallicity Relation?
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• The Atomic to Molecular Transition in Galaxies. I: An Analytic Approximation for Photodissociation Fronts in Finite Clouds
• Molecular hydrogen in high-redshift Damped Lyman-alpha systems: The VLT/UVES database
• On the Nature of Velocity Fields in High z Galaxies
• Discovery of a Perseus-like cloud in the early Universe: HI-to-H2 transition, carbon monoxide and small dust grains at zabs=2.53 towards the quasar J0000+0048
• Mining for Dust in Type 1 Quasars
• CO-dark molecular gas at high redshift: very large H${}_2$ content and high pressure in a low metallicity damped Lyman-alpha system
• The SDSS-DR5 Survey for Proximate Damped Lya Systems
• Physical conditions in the neutral interstellar medium at z=2.43 toward Q2348-011
• The color excess of quasars with intervening DLA systems- Analysis of the SDSS data release five
• Molecular hydrogen absorption systems in Sloan Digital Sky Survey
• [CII] 158 Micron Emission from z~4 HI Absorption-Selected Galaxies
• HI-to-H2 Transition Layers in the Star-Forming Region W43
• The Magellan Uniform Survey of Damped Lyman alpha Systems II: Paucity of Strong Molecular Hydrogen Absorption
• A ghostly damped Ly$\alpha$ system revealed by metal absorption lines
• Partial covering of emission regions of Q 0528-250 by intervening H${}_2$ clouds
• Deep optical spectroscopy of extended Lyman alpha emission around three radio-quiet z=4.5 quasars
• MUSE-inspired view of the quasar Q2059-360, its Lyman alpha blob, and its neighborhood
• Extent and structure of intervening absorbers from absorption lines redshifted on quasar emission lines

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