The Distribution and Evolution of Quasar Proximity Zone Sizes
  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.
