UV background fluctuations traced by metal ions at $z\approx3$

Abstract

Here we investigate how LyC-opaque systems present in the intergalactic medium at $z\approx3$ can distort the spectral shape of a uniform UV background (UVB) through radiative transfer (RT) effects. With this aim in mind, we perform a multi-frequency RT simulation through a cosmic volume of $10h^{-1}$~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$\, \rm \scriptstyle II\ $ and H$\, \rm \scriptstyle I\ $ column density, $η$, and the ratio of C$\,{\rm {\scriptstyle IV\ }}$ and Si$\,{\rm {\scriptstyle IV\ }}$ optical depths, $ζ$. We find that: (i) $η$ spatially fluctuates through over-dense systems ($Δ$) with statistically significant deviations $δη>25$\% in 18\% of the volume ; (ii) same fluctuations in $ζ$ are also present in $34$\% of the enriched domain (only 8\% of the total volume) and derive from a combination of RT induced effects and in-homogeneous metal enrichment, both effective in systems with $Δ> 1.5$.

Accepted for pub. in MNRAS after very minor rev