Quasars Enlightening the Reionization Epoch

Dear Colleagues,

The first quasars are at the forefront of research in the rapidly advancing field of galaxy formation and evolution, and intergalactic medium (IGM) evolution at the reionization epoch. In the last few years, the number of quasars discovered at a redshift larger than 6 has seen a rapid increase, and now exceeds 200, with the record holder at z = 7.54. There are many new discoveries in this field, as well as open questions. The very existence of the first quasars is a conundrum, because they are powered by super-massive black holes (SMBH) whose seeds and growth processes are still uncertain. On the other hand, state-of-the-art observations have shown that quasars are hosted by massive star-forming galaxies, and some suggest that they may be the signposts of overdense regions. Yet, it is still debated as to which physical processes drive the evolution of the first SMBH and their host galaxies, which is the role of intense star formation, of AGN-driven winds and of the environment. Finally, quasars at z~6 are one of the few fundamental probes of the (final stages of the) reionization process, thanks to the information on the physical status of the IGM imprinted in their absorption spectrum. The metal absorption lines detected in the quasar spectra are a key feature to investigate the early chemical enrichment and the possible signature of PopIII stars. This Special Issue welcomes papers and reviews on any aspect of these issues.

Dr. Valentina D'Odorico
Dr. Chiara Feruglio
Guest Editors

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• Reionization epoch
• QSO host galaxies and environment
• Super-massive black holes
• Intergalactic medium
• Early metal enrichment