The Epoch of Reionization
The Universe has changed...
The cosmic epoch that is relevant in the context of my research happened thousands of million years after the first atoms formed. At this time, the Universe was a very dark and opaque place (the Dark Age), pervaded mainly by neutral hydrogen (H I) atoms. This is drastically different from today’s Universe, populated by astronomical sources such as stars, galaxies, black holes, and quasars, where almost all of the hydrogen gas is ionized (i.e., the electron has been ejected from the hydrogen atom). The formation of the first stars and galaxies marks the beginning of a key phase transition in the Universe history referred to as the Cosmic Dawn. These light sources emitted the first ionizing photons, i.e., photons with enough energy to knock electrons off of atoms and molecules. The increasing amount of ionizing photons produced during these epochs progressively ionized the hydrogen in the entire Universe. This latter era is referred to as the Epoch of Reionization (see Figure above) and this period is a crucial milestone in the history of the Universe.
Exploring the Epoch of Reionization
The Epoch of Reionization has critical implications for the formation of stars and galaxies, yet many fundamental issues related to this epoch remain poorly understood. For example, it is still unclear when cosmic reionization started and ended, what physical processes dominated the formation of the first objects, or which of these objects (e.g., low-mass galaxies, black holes, quasars) dominantly contributed to the ionizing photons budget. Answering these questions is a complex process because it requires knowledge in diverse astrophysical domains and because the observational support to explore these distant epochs is (for now) very limited.
In short:
The Epoch of Reionization is a key phase transition in the Universe history, and we still have little information about
The cosmic epoch that is relevant in the context of my research happened thousands of million years after the first atoms formed. At this time, the Universe was a very dark and opaque place (the Dark Age), pervaded mainly by neutral hydrogen (H I) atoms. This is drastically different from today’s Universe, populated by astronomical sources such as stars, galaxies, black holes, and quasars, where almost all of the hydrogen gas is ionized (i.e., the electron has been ejected from the hydrogen atom). The formation of the first stars and galaxies marks the beginning of a key phase transition in the Universe history referred to as the Cosmic Dawn. These light sources emitted the first ionizing photons, i.e., photons with enough energy to knock electrons off of atoms and molecules. The increasing amount of ionizing photons produced during these epochs progressively ionized the hydrogen in the entire Universe. This latter era is referred to as the Epoch of Reionization (see Figure above) and this period is a crucial milestone in the history of the Universe.
Exploring the Epoch of Reionization
The Epoch of Reionization has critical implications for the formation of stars and galaxies, yet many fundamental issues related to this epoch remain poorly understood. For example, it is still unclear when cosmic reionization started and ended, what physical processes dominated the formation of the first objects, or which of these objects (e.g., low-mass galaxies, black holes, quasars) dominantly contributed to the ionizing photons budget. Answering these questions is a complex process because it requires knowledge in diverse astrophysical domains and because the observational support to explore these distant epochs is (for now) very limited.
In short:
The Epoch of Reionization is a key phase transition in the Universe history, and we still have little information about
- The properties of the light-sources that dominantly contributed to the Reionization
- How the ionizing photons propagated from the light-sources to the inter-galactic medium in the Universe