Aligned metal absorbers and the ultraviolet background at the end of reionization

Caitlin Doughty, Kristian Finlator, Benjamin D. Oppenheimer, Romeel Davé, Erik Zackrisson

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


We use observations of spatially aligned CII, CIV, SiII, SiIV, and OI absorbers to probe the slope and intensity of the ultraviolet background (UVB) at z ~ 6. We accomplish this by comparing observations with predictions from a cosmological hydrodynamic simulation using three trial UVBs applied in post-processing: a spectrally soft, fluctuating UVB calculated using multifrequency radiative transfer; a soft, spatially uniform UVB; and a hard, spatially uniform 'quasars-only' model. When considering our paired high-ionization absorbers (CIV/Si IV), the observed statistics strongly prefer the hard, spatially uniform UVB. This echoes recent findings that cosmological simulations generically underproduce strong C IV absorbers at z > 5. A single low/high ionization pair (Si II/Si IV), by contrast, shows a preference for the HM12 UVB, whereas two more (CII/C IV and OI/C IV) show no preference for any of the three UVBs. Despite this, future observations of specific absorbers, particularly Si IV/C IV, with next-generation telescopes probing to lower column densities should yield tighter constraints on the UVB.

Original languageEnglish (US)
Pages (from-to)4717-4727
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Apr 21 2018


  • Cosmology: theory
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift
  • Intergalactic medium
  • Quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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