Radiative transfer of Lyα photons with realistic gas physics

The cosmological global 21-cm signal provides an unprecedented view of our  cosmic history. It can provide insights into the epoch of cosmic dawn for which no other direct probes exist. An accurate model of the 21-cm signal at cosmic dawn hinges on the accuracy of the Lyman-α (Lyα) coupling, which in turn requires one to calculate the specific intensity of Lyα photons. Resonant lines, such as Lyα, have a finite spread in their absorption probability which makes solving the radiative transfer (RT) equation quite expensive. Due to this complexity, traditional calculations do not account for the broad line nature of the Lyα photons at all (as in 21cmFAST). Attempts to improve upon this traditional approach using numerical RT have recently emerged. However, the RT computation in these treatments suffers from assumptions such as a uniform density of intergalactic gas, zero gas temperature, and absence of gas bulk motion, or numerical approximations such as core skipping. I will present the results on Lyα coupling and the corresponding 21-cm signal done with the most accurate RT simulations devoid of any assumptions taken in previous works. Additionally, I will show that we find a 40% difference compared to previous works in the cosmic dawn 21-cm signal.