Ultraviolet photon production rates of the first stars: Impact on the He II $\lambda$ 1640 Å emission line from primordial star clusters and the 21-cm signal from cosmic dawn

Joel Wasserman, Erik Zackrisson, Jiten Dhandha +3

The first stars, the chemically pristine Population III, likely played an important role in heating the intergalactic medium during the epoch of cosmic dawn. The very high effectiv…