The EoR is an important, yet still largely unexplored, cosmic epoch that started shortly after inflation (the cosmic “dark ages”) and ended with the complete (re-)ionisation of intergalactic space about 1 billion years after the big bang. Since the cosmological era of recombination in which protons and electrons combined to form hydrogen for the first time (several hundred thousands years after the big bang), the intergalactic medium was almost entirely composed of neutral hydrogen. During the EoR the neutral intergalactic medium underwent a transition from completely neutral to largely ionised. The ionisation of neutral hydrogen requires photons with wavelengths shorter than 912Å (or, equivalently, energies higher than 13.6 eV), which was produced by the first stars and galaxies, and, probably to a lesser extent, radiation from the first active black holes. Hence, the EoR is also the epoch during which we find the first stars, galaxies and black holes that formed in the universe. Some fraction of these first objects are still expected to be around today, for example in the form of Galactic metal-poor stars or in the form of dwarf satellites of the Milky Way. The remainder, however, has been incorporated in larger objects (galaxies and black holes) or reprocessed by future generation of stars. A proper understanding of the EoR is therefore important in order to understand the formation history of most objects in the universe.
In recent years, deep observations with the Hubble Space Telescope (HST) have uncovered small samples of galaxies at high redshift that probe the final phase of the EoR or somewhat later. Wide sky surveys have also found already over a hundred luminous quasars at z ~ 6–7, extreme objects believed to be powered by the accretion of matter around supermassive black holes that had already reached masses of one billion solar masses or more so short after the big bang. Some information can be inferred from these samples, for example by extrapolating the number counts, the levels of star formation or the rate of black hole accretion observed to even earlier phases of the universe. However, in order to directly probe the EoR, it will be necessary to detect and study the first generations of stars and galaxies deep into the EoR, as well as the “phase-change” of the intergalactic medium. In the coming decade, this can be achieved using new instrumentation that will allow us to directly detect the emission from the first stars, galaxies and black holes, study the properties of the ionised gas seen in absorption against the spectra of background galaxies and quasars, and study the neutral gas detected through the redshifted 21-cm hyperfine transition of hydrogen with new radio telescopes.
The astrophysics of the EoR is therefore one of the primary science drivers of new instrumentation currently in development, such as the Low-frequency Array (LOFAR), the Murchison Wide-field Array (MWA), the Subaru HyperSuprimeCam (HSC) and Prime Focus Spectrograph (PFS), the James Webb Space Telescope (JWST), the Giant Magellan Telescope (GMT), the Thirty Meters Telescope (TMT), the Extremely Large Telescope (ELT), and the Square Kilometre Array (SKA).
The Institute for Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo in São Paulo, Brazil, will organize an intensive school to introduce the future generation of young astronomers (advanced undergraduate and graduate students and postdocs) to the forefront of the theoretical and observational developments of the astrophysics of the epoch of re-ionisation (EoR) including the following topics all taught by international experts:
- Reionization
- The First Stars
- The First Galaxies
- The First Black holes
- Gravitational lensing
- The development of structure
- The later evolution of galaxies
- The history of the Milky Way
- Observational techniques of the EoR
- Large instrumentation projects