Metal Enrichment in the Circumgalactic Medium and Lyα Halos around Quasars at z ∼ 3

<jats:title>Abstract</jats:title> <jats:p>Deep observations have detected extended Ly<jats:italic>α</jats:italic> emission nebulae surrounding tens of quasars at redshift 2–6. However, the metallicity of such extended halos is still poorly understood. We perform a detailed analysis on a large sample of 80 quasars at <jats:italic>z</jats:italic> ∼ 3 based on MUSE-VLT data. We find clear evidence of extended emission of the UV nebular lines such as  C <jats:sc>iv</jats:sc> <jats:italic>λ</jats:italic>1549 or  He <jats:sc>ii</jats:sc> <jats:italic>λ</jats:italic>1640 for about 20% of the sample, while  C <jats:sc>iii</jats:sc>] <jats:italic>λ</jats:italic>1909 is only marginally detected in a few objects. By stacking the cubes, we detect emission of C <jats:sc>iv</jats:sc>, He <jats:sc>ii</jats:sc>, and C <jats:sc>iii</jats:sc>] out to a radius of about 45 kpc. C <jats:sc>iv</jats:sc> and He <jats:sc>ii</jats:sc>  show a radial decline much steeper than Ly<jats:italic>α</jats:italic>, while C <jats:sc>iii</jats:sc>] shows a shallower profile similar to Ly<jats:italic>α</jats:italic> in the inner 45 kpc. We infer that the average metallicity of the circumgalactic gas within the central 30–50 kpc is ∼0.5 solar, or even higher. However, we also find evidence of a component of the Ly<jats:italic>α</jats:italic> halos, which has much weaker metal emission lines relative to Ly<jats:italic>α</jats:italic>. We suggest that the high metallicity of the circumgalactic medium within the central 30–50 kpc is associated with chemical pre-enrichment by past quasar-driven outflows and that there is a more extended component of the circumgalactic medium that has much lower metallicity and is likely associated with near-pristine gas accreted from the intergalactic medium. We show that our observational results are in good agreement with the expectations of the FABLE zoom-in cosmological simulations.</jats:p>