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

作者：Doughty Caitlin^*; Finlator Kristian; Oppenheimer Benjamin D; Dave Romeel; Zackrisson Erik

来源：Monthly Notices of the Royal Astronomical Society, 2018, 475(4): 4717-4727.

DOI：10.1093/mnras/sty156

• galaxies: evolution
• galaxies: formation
• galaxies: high-redshift
• intergalactic medium
• quasars: absorption lines
• cosmology: theory

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 similar to 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 (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, whereas 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.

• 出版日期2018-4