Modelling Population III stars for semi-numerical simulations
  Theoretically modelling the 21-cm signals caused by Population III stars (Pop
III stars) is the key to extracting fruitful information on Pop III stars from
current and forthcoming 21-cm observations. In this work we develop a new
module of Pop III stars in which the escape fractions of ionizing photons and
Lyman-Werner (LW) photons, photo-heating by UV radiation, and LW feedback are
consistently incorporated. By implementing the module into a public 21-cm
semi-numerical simulation code, 21CMFAST, we demonstrate 21-cm signal
calculations and investigate the importance of Pop III star modelling. What we
find is that the contribution from Pop III stars to cosmic reionization
significantly depends on the treatment of the escape fraction. With our escape
fraction model, Pop III stars hardly contribute to reionization because less
massive halos, whose escape fraction are high, cannot host Pop III stars due to
LW feedback. On the other hand, Pop III stars well contribute to reionization
with the conventional constant escape fraction. We also find that UV
photo-heating has non-negligible impact on the 21-cm global signal and the
21-cm power spectrum if the ionization fraction of the Universe is higher than
roughly 1 percent. In this case, the strength of the 21-cm global signal
depends on the photo-heating efficiency and thus on the Pop III star mass. We
conclude that detailed modelling of Pop III stars is imperative to predict
21-cm observables accurately for future observations.
