The Dark Ages of the Universe and Hydrogen Reionization

TL;DR

This paper reviews the epoch of hydrogen reionization, discussing its significance in cosmic history, current observational signatures, recent simulation results, and future prospects for understanding the universe's first luminous objects.

Contribution

It provides a comprehensive review of recent studies, observations, and simulations related to hydrogen reionization and explores future research directions.

Findings

Reionization signatures are imprinted in the cosmic microwave background.

Simulations offer insights into the timing and sources of reionization.

Future experiments will enhance understanding of the early universe.

Abstract

One of the milestones in the cosmic history is the formation of the first luminous objects and Hydrogen reionization. The standard theory of cosmic structure formation predicts that the first generation of stars were born about a few hundred million years after the Big Bang. The dark Universe was then lit up once again, and eventually filled with ultraviolet photons emitted from stars, galaxies, and quasars. The exact epoch of the cosmic reionization and the details of the process, even the dominant sources, are not known except the fact that the universe was reionized early on. Signatures of reionization are expected to be imprinted in the cosmic microwave background radiation, especially in its large scale polarization. Future CMB experiments, together with other probes such as 21 cm surveys, will provide rich information on the process of reionization. We review recent studies on reionization. The implications from available observations in a wide range of wavelengths are discussed. Results from state-of-the-art computer simulations are presented. Finally, we discuss prospects for exploring the first few hundred million years of the cosmic history.