UV background fluctuations traced by metal ions at z ≈ 3

Here we investigate how LyC-opaque systems present in the intergalactic medium at z ≈ 3 can distort the spectral shape of a uniform UV background (UVB) through radiative transfer (RT) effects. With this aim in mind, we perform a multifrequency RT simulation through a cosmic volume of 10 h-1 cMpc scale polluted by metals, and self-consistently derive the ions of all the species. The UVB spatial fluctuations are traced by the ratio of He II and H I column density, η, and the ratio of C IV and Si IV optical depths, ξ . We find that: (i) η spatially fluctuates through overdense systems (Δ) with statistically significant deviations δη > 25 per cent in 18 per cent of the volume; (ii) same fluctuations in ξ are also present in 34 per cent of the enriched domain (only 8 per cent of the total volume) and derive from a combination of RT induced effects and in-homogeneous metal enrichment, both effective in systems with Δ > 1.5.