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Title: DISSECTING THE PROPERTIES OF OPTICALLY THICK HYDROGEN AT THE PEAK OF COSMIC STAR FORMATION HISTORY

We present the results of a blind survey of Lyman limit systems (LLSs) detected in absorption against 105 quasars at z ∼ 3 using the blue sensitive MagE spectrograph at the Magellan Clay telescope. By searching for Lyman limit absorption in the wavelength range λ ∼ 3000-4000 Å, we measure the number of LLSs per unit redshift l(z) = 1.21 ± 0.28 at z ∼ 2.8. Using a stacking analysis, we further estimate the mean free path of ionizing photons in the z ∼ 3 universe λ{sub mfp}{sup 912} = 100 ± 29 h{sub 70.4}{sup -1} Mpc. Combined with our LLS survey, we conclude that systems with log N{sub HI} ≥ 17.5 cm{sup –2} contribute only ∼40% to the observed mean free path at these redshifts. Furthermore, with the aid of photoionization modeling, we infer that a population of ionized and metal poor systems is likely required to reproduce the metal line strengths observed in a composite spectrum of 20 LLSs with log N{sub HI} ∼ 17.5-19 cm{sup –2} at z ∼ 2.6-3.0. Finally, with a simple toy model, we deduce that gas in the halos of galaxies can alone account for the totality of LLSs at z ∼< 3,more » but a progressively higher contribution from the intergalactic medium is required beyond z ∼ 3.5. We also show how the weakly evolving number of LLSs per unit redshift at z ∼< 3 can be modeled either by requiring that the spatial extent of the circumgalactic medium is redshift invariant in the last ∼10 Gyr of cosmic evolution or by postulating that LLSs arise in halos that are rare fluctuations in the density field at each redshift.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
  2. Department of Chemistry and Physics, Saint Michael's College, Colchester, VT 05439 (United States)
  3. University of California Observatories-Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
  4. Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
Publication Date:
OSTI Identifier:
22270965
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 775; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ABSORPTION SPECTRA; ASTROPHYSICS; COSMOLOGY; FLUCTUATIONS; GALAXIES; HYDROGEN; LYMAN LINES; MEAN FREE PATH; PHOTOIONIZATION; QUASARS; RED SHIFT; STAR EVOLUTION; STARS; TELESCOPES; UNIVERSE