Title: A Fundamental Physical Problem in 21cm Cosmology

Li-Zhi Fang
University of Arizona

Detecting the emission or absorption of redshifted 21 cm hyperfine line of neutral hydrogen with large low-frequency radio arrays is generally viewed as a frontier in observational cosmology of the coming decades. The 21 signals come from the first generation of stars formed at the end of dark age of the universe. It would be the most promising probe of the epoch of reionization. To estimate the 21 signal from early universe, we need to study a fundamental physical problem: how a system of photons and atoms approaches to statistical equilibrium when the resonant scattering between photon and atom is considered. This problem has been addressed on as early as 1950s (Wouthuysen 1952, Field 1958). However, the quantitative solutions of the Wouthuysen-Field (W-F) coupling, which is necessary for 21 cm cosmology, are obtained very recently. I will present the story of 21 cm cosmology and the time evolution of the W-F coupling.

UT Arlington Physics