Probing large-scale UV background inhomogeneity associated with quasars using metal absorption

We study large-scale UV background inhomogeneity in three-dimensions associated with the observed quasar populations at high redshift. We do this by measuring metal absorption through quasar absorption spectrum stacking as a function distance to closest quasar in SDSS-IV/eBOSS on 10s of comoving megaparsec scales. We study both intergalactic medium absorbers and mixed circumgalactic medium absorbers and probe absorption in Ovi, Civ, and Siiv, and Siiii. Overall, stronger high ionization species absorption is seen closer to quasars at 2.4 < z < 3.1. Ovi absorption shows a particularly strong change, with effects in Civ evident in some cases, and more marginal effects in Siiii and Siiv. We further study 2.05 < z < 2.4 (with weak signs of increasing homogeneity with time) and explore the study of metal absorption as a function of integrated SDSS-r band flux quasar flux (yielding consistent but less significant results). While the metal absorption does show sensitivity to large-scale 3D quasar proximity, the current incomplete quasar samples limit detailed interpretation. This work does, however, demonstrate that UV background inhomogeneities exist on scales of several 10s of comoving megaparsecs associated with quasars and that they can be measured with precision by examining metal absorption in the intergalactic medium.

Automated summary

The study investigates large-scale UV background inhomogeneities associated with high redshift quasar populations by measuring metal absorption in quasar absorption spectrum stacking. Stronger high ionization species absorption is observed closer to quasars at 2.4 < z < 3.1. Additionally, weak signs of increasing homogeneity with time are explored in the range of 2.05 < z < 2.4. Limitations of incomplete quasar samples are noted in the interpretation of results.