2020MNRAS.493.3223F

We explore the expected galaxy environments of C IV absorbers at z > 5 using the Technicolor Dawn simulations. These simulations reproduce the observed history of reionization, the z ∼ 6 galaxy stellar mass function, the Ly α forest transmission at z > 5, and the Si IV column density distribution (CDD) at z ≃ 5.5. None the less, the C IV CDD remains underproduced. Comparison with observed C II/Si II equivalent width ratios and the C II line incidence suggests that a low carbon yield accounts for some, but not all, of the C IV discrepancy. Alternatively, a density-bounded escape scenario could harden the metagalactic ionizing background more dramatically even than binary stellar evolution, boosting the C IV CDD into near agreement with observations. In this case, galaxies ionize more efficiently and fewer are required to host a given high-ionization absorber. Absorbers' environments therefore constrain ionizing escape. Regardless of the escape scenario, galaxies correlate with C IV absorbers out to 300 proper kpc (pkpc). The correlation strengthens independently with galaxy luminosity and C IV column density. Around strong systems (log(N_C IV_/ cm^–2)> 14)), the overdensity of galaxies with M_UV < -18 or log (L_Ly α_/erg s^–1) > 41.9 declines from 200-300 within 100 pkpc to 40-60 within 250 pkpc. The previously suggested association between strong C IV absorbers and Ly α emitters at z > 5 is not expected. It may arise if both populations inhabit large-scale voids, but for different reasons. Although most neighbouring galaxies are too faint for HST, JWST will, with a single pointing, identify ∼10 neighbouring galaxies per strong C IV absorber at z > 5. Ground-based tests of these predictions are possible via deep surveys for Ly α emission using integral field units.