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 O VI, C IV, and Si IV,
and Si III. Overall stronger high ionization species absorption is seen closer
to quasars at $2.4<z<3.1$. O VI absorption shows a particularly strong change,
with effects in C IV evident in some cases, and more marginal effects in Si III
and Si IV. 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.
