Imprints of the first billion years: Lyman limit systems at z ∼ 5
Abstract
Lyman limit systems (LLSs) trace the lowdensity circumgalactic medium and the most dense regions of the intergalactic medium, so their number density and evolution at highredshift, just after reionization, are important to constrain. We present a survey for LLSs at high redshifts, z_{LLS} = 3.55.4, in the homogeneous data set of 153 optical quasar spectra at z ∼ 5 from the Giant Gemini GMOS survey. Our analysis includes detailed investigation of survey biases using mock spectra which provide important corrections to the raw measurements. We estimate the incidence of LLSs per unit redshift at z ≈ 4.4 to be ℓ(z) = 2.6 ± 0.4. Combining our results with previous surveys at z_{LLS} < 4, the bestfit powerlaw evolution is ℓ(z) = ℓ_{*}[(1 + z)/4]^{α} with ℓ_{*} = 1.46 ± 0.11 and α = 1.70 ± 0.22 (68 per cent confidence intervals). Despite hints in previous z_{LLS} < 4 results, there is no indication for a deviation from this single powerlaw soon after reionization. Finally, we integrate our new results with previous surveys of the intergalactic and circumgalactic media to constrain the hydrogen column density distribution function, f(N_{HI}, X), over 10 orders of magnitude. The data at z ∼ 5 are not welldescribed by the f(N_{HI}, X) model previously reported for z ∼ 23 (after rescaling) and a 7pivot model fitting the full z ∼ 25 data set is statistically unacceptable. We conclude that there is significant evolution in the shape of f(N_{HI}, X) over this ∼2billionyear period.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 January 2019
 DOI:
 10.1093/mnras/sty2762
 arXiv:
 arXiv:1810.10040
 Bibcode:
 2019MNRAS.482.1456C
 Keywords:

 quasars: absorption lines;
 cosmological parameters;
 cosmology: observations;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 16 pages, 19 figures, accepted to MNRAS