The Distribution and Evolution of Quasar Proximity Zone Sizes

TL;DR

This study uses advanced simulations to analyze how quasar proximity zone sizes evolve over time and are affected by intervening absorbers, revealing growth patterns and the impact of DLAs and LLSs.

Contribution

It provides new insights into the evolution of quasar proximity zones using high-resolution simulations that resolve key absorption systems.

Findings

Proximity zones grow steadily before reionization and rapidly after.

Most old quasars have small proximity zones due to DLAs or LLSs.

Metal contamination helps distinguish absorber-induced small zones.

Abstract

In this paper, we study the sizes of quasar proximity zones with synthetic quasar absorption spectra obtained by post-processing a Cosmic Reionization On Computers (CROC) simulation. CROC simulations have both relatively large box sizes and high spacial resolution, allowing us to resolve Lyman limit systems, which are crucial for modeling the quasar absorption spectra. We find that before reionization most quasar proximity zone sizes grow steadily for $\sim 10$ Myr, while after reionization they grow rapidly but only for $\sim 0.1$ Myr. We also find a slow growth of $R_{\rm obs}$ with decreasing turn-on redshift. In addition, we find that $\sim 1-2\%$ of old quasars ($30$ Myr old) display extremely small proximity zone sizes ($<1$ proper Mpc), of which the vast majority are due to the occurrence of a damped Ly$\alpha$ absorber (DLA) or a Lyman limit system (LLS) along the line of sight. These DLAs and LLSs are contaminated with metal, which offers a way to distinguish them from the normal proximity zones of young quasars.