UV background fluctuations traced by metal ions at z ≈ 3

Abstract

ABSTRACT 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 $\,\small {II}$ and H $\,\small {I}$ column density, η, and the ratio of C $\, \small {IV}$ and Si $\, \small {IV}$ optical depths, ζ. 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 ζ 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.