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

Abstract

We use observations of spatially-aligned C II, C IV, Si II, Si IV, and O I absorbers to probe the slope and intensity of the ultraviolet background (UVB) at $z\sim 6$. 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 multi-frequency radiative transfer; a soft, spatially-uniform UVB; and a hard, spatially-uniform "quasars-only" model. When considering our paired high-ionization absorbers (C IV/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, while two more (C II/C IV and O I/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.

13 pages, 4 figures, accepted by MNRAS

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• A deep search for metals near redshift 7: the line-of-sight towards ULAS J1120+0641
• The Reionization of Carbon
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Cited by in corpus (8)

• The contribution from stars stripped in binaries to cosmic reionization of hydrogen and helium
• The XQR-30 Metal Absorber Catalog: 778 Absorption Systems Spanning 2 < z < 6.5
• The evolution of the Si IV content in the Universe from the epoch of reionization to cosmic noon
• The Faint Host Galaxies of C IV Absorbers at z > 5
• Metal enrichment and evolution in four z > 6.5 quasar sightlines observed with JWST/NIRSpec
• The effects of binary stars on galaxies and metal-enriched gas during reionization
• The environments and hosts of metal absorption at z>5
• Cospatial 21 cm and metal-line absorbers in the epoch of reionization -- I : Incidence and observability