Global 21-cm signal and its implications

The claimed discovery of the sky-averaged global 21-cm signal by the EDGES group at redshift z ≃ 12 − 22 has opened up a new window to investigate the Physics of this epoch. The redshift and strength of this signal give us an ideal opportunity to obtain constraints on the allowed Warm Dark Matter particle mass at redshifts currently inaccessible by any other means. We find that WDM models with m_x ≤ 3 keV can be ruled out since the global signal obtained using them are unable to match either the redshift range or the amplitude of the EDGES signal. Another application of this discovery is to study “First stars” (Pop III) formed at this high redshift. Though this metal-free PopIII stars have long been postulated to explain the metallicity gap between Big Bang Nucleosynthesis and the metal-rich PopII stars, they lack any observational support. With the assumption that this signal is driven by a combination of PopII and PopIII stars, we provide for the first time a data constrained estimate of the SFRD for PopIII stars at redshifts z ≃ 12 − 22. Finally, for the first time, we manage to include this global 21-cm observation along with the CMB data (from Planck) and Reionization related observations to jointly constrain the cosmological and astrophysical parameters. To this aim, we develop a Markov Chain Monte Carlo (MCMC)-based parameter estimation package, CosmoReionMC, and find that inclusion of more data indeed enables us to put tighter constraints on some of the cosmological parameters compared to the previous constraints obtained from Planck Observations.