Probing the He <scp>ii</scp> Reionization ERa via Absorbing C <scp>iv</scp> Historical Yield (HIERACHY). IV. A Complex Redshifted Absorption System Intrinsic to Quasar

Abstract High-resolution spectra provide a powerful tool in studying the associated absorption lines in quasars. We present a case study of the quasar J014741-030247 at z ∼ 4.75, which hosts complex intrinsic absorption lines revealed by the high-resolution Magellan/MIKE spectrum obtained from the HIERACHY program. We focus on one of the strongest absorption systems ( z ∼ 4.7804) and determine the column densities of multiple ionization species. We find that the apparent optical depth method may significantly underestimate the column densities of high ions. Decomposing the absorption into multiple components yields a better fit and reveals clear evidence of partial coverage. The variation in covering fractions among different ions suggests that high ions are distributed more extensively in this system. We estimate electron densities of different components (630–4070 cm −3 ), these are based on the column densities of Si ii * and C ii *. By combining these with the hydrogen number density and ionization parameter derived from photoionization modeling, we infer that the different components are located at distances of 2.3–9.5 kpc from the quasar. The derived N H / n e and the partial coverage observed in low ions all require cloud sizes smaller than 1 pc, even down to 0.01 pc. Finally, the low kinetic luminosity of the gas (&lt;0.5% L bol ) indicates that it is insufficient to drive significant AGN feedback and may only suppress star formation via “multistage” mechanism.