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

TL;DR

This study uses radiative transfer simulations to analyze how intergalactic systems at redshift 3 distort the UV background, revealing significant spatial fluctuations in ion ratios due to density and metal enrichment effects.

Contribution

It introduces a multi-frequency radiative transfer simulation to self-consistently model UV background fluctuations caused by metal-enriched systems at z~3.

Findings

Significant spatial fluctuations in $rac{ m HeII}{ m HI}$ ratio in over-dense regions.

Fluctuations in metal ion ratios are present in a substantial fraction of enriched domains.

Both radiative transfer effects and metal enrichment contribute to observed ion ratio variations.

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, $\eta$, and the ratio of C$\,{\rm {\scriptstyle IV\ }}$ and Si$\,{\rm {\scriptstyle IV\ }}$ optical depths, $\zeta$. We find that: (i) $\eta$ spatially fluctuates through over-dense systems ($\Delta$) with statistically significant deviations $\delta\eta >25$\% in 18\% of the volume ; (ii) same fluctuations in $\zeta$ 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 $\Delta > 1.5$.