# An Introductory Review on Cosmic Reionization

## TL;DR

This paper provides an introductory overview of cosmic reionization, discussing its theoretical background, observational evidence, and significance in understanding early galaxy formation and cosmology.

## Contribution

It offers a comprehensive review of the current knowledge and uncertainties about cosmic reionization, highlighting future observational prospects.

## Key findings

- Reionization ended about one billion years after the Big Bang.
- Observational evidence supports the timing of reionization.
- Upcoming facilities will clarify remaining uncertainties.

## Abstract

The universe goes through several phase transitions during its formative stages. Cosmic reionization is the last of them, where ultraviolet and X-ray radiation escape from the first generations of galaxies heating and ionizing their surroundings and subsequently the entire intergalactic medium. There is strong observational evidence that cosmic reionization ended approximately one billion years after the Big Bang, but there are still uncertainties that will be clarified with upcoming optical, infrared, and radio facilities in the next decade. This article gives an introduction to the theoretical and observational aspects of cosmic reionization and discusses their role in our understanding of early galaxy formation and cosmology.