Quasars in the Epoch of Reionization

 

ABSTRACT:

A prime objective of observational astrophysics is to characterize the earliest sources in the first Gyr of the universe, and to peer into the cosmic times when the first stars, black holes and galaxies formed. Although galaxy candidates are now identified up to redshifts of about 10, their faintness typically precludes detailed studies of their nature, and often, even their spectroscopic confirmation. Quasars, on the other hand, are the most luminous non-transient sources known and can be studied in detail at the earliest cosmic epochs. The discovery and characterization of a statistically significant sample of quasars at z>6 is crucial to further study the epoch of reionization, one of the current frontiers of astrophysical research. I will present our efforts on building such a statistical sample, which has led to tripling the number of these quasars in just the last three years. I will discuss the diverse range of physical properties of this quasar sample as well as our initial follow-up studies from optical to radio wavelengths, including a new quasar at a redshift record (z=7.5). In particular, recent observations with ALMA revealed the presence of far-infrared companions around the quasars, and provide key constraints on the properties of the quasar host galaxies. I will also talk about the future direction for distant quasar searches and discuss the potential of JWST and the next generation of 30m-class telescopes.