Mr. Atrideb Chatterjee

The discovery of a global 21-cm signal by the EDGES group at a redshift z ~17:2 has opened up a new window to investigate the Physics of this epoch. Surprisingly, the amplitude of the signal is twice as that expected from any "standard model" and hence has raised questions about our current under-standing of the Universe. The redshift and strength of this signal allow an ideal opportunity to obtain constraints on the allowed Warm Dark Matter particle mass at redshifts currently inaccessible by any other means. This is because WDM models with low mass will find it increasingly hard to explain the signal given the lack of low-mass structures at such high-z. We find that WDM models with mx <= 3 keV can be ruled out since they 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-z. Though this metalfree PopIII stars are postulated to explain the metallicity gap between Big Bang Nucleosynthesis and the metal-rich PopII stars, it has not yet been detected in any observation. 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). Our result suggests a rise in PopIII SFRD at z ~ 20 - 21 followed by a sharp fall at z ~ 15 - 16. Further, we are currently exploring the possibility of com-bining this observation with the Planck observations to put a joint constraint on the cosmological (to model the temperature and polarization anisotropies of the CMB radiation) and astrophysical parameters (to model the 21-cm signal) of our Universe.