Speaker
Description
The 21 cm line emitted by neutral hydrogen (HI) atoms is a valuable observable for investigating the high redshift universe. In particular, before cosmic reionization, the universe was filled with neutral hydrogen gas. Due to cosmic expansion, the redshifted 21 cm line before the reionization is observed at frequencies below 200 MHz. Therefore, low-frequency radio observations can map HI signals across multiple epochs. The physical state of HI gas strongly depends on radiation from the first stars and galaxies. The 21 cm signal reveals the history of gas heating, sources of reionization, birth of first stars, and fundamental cosmology. However, despite significant efforts of multiple observatory, the 21 cm fluctuations from the Epoch of Reionization (EoR) have not yet been detected, though several radio instruments have provided upper limits on the signal. The Murchison Widefield Array (MWA), a low-frequency radio interferometer located in Western Australia, has been conducting 21 cm line observations for the past 10 years. In this talk, I review recent and ongoing EoR 21cm line analyses, with a particular focus on the MWA.
