Abstract
The formation of the first galaxies during cosmic dawn and reionization (at
redshifts $z=5-30$), triggered the last major phase transition of our universe,
as hydrogen evolved from cold and neutral to hot and ionized. The 21-cm line of
neutral hydrogen will soon allow us to map these cosmic milestones and study
the galaxies that drove them. To aid in interpreting these observations, we
upgrade the public code 21cmFAST, improving the treatment of feedback in
molecular-cooling galaxies. We introduce a new, flexible parametrization of the
additive feedback from: (i) an inhomogeneous, $H_2$-dissociating (Lyman-Werner;
LW) background; and (ii) dark matter -- baryon relative velocities. We
demonstrate that our flexible model can recover results from recent,
small-scale hydrodynamical simulations. We perform a large (1.5 comoving Gpc on
a side), "best-guess" simulation as the 2021 installment of the Evolution of
21-cm Structure (EOS) project. This improves on the previous EOS release by
using an updated galaxy model that reproduces the observed UV luminosity
functions (UVLFs), and by including an additional population of
molecular-cooling galaxies. The resulting 21-cm global signal and power
spectrum are significantly weaker than in the 2016 EOS releases, due to a more
rapid evolution of the star-formation rate density required to match the UVLFs.
Nevertheless, we forecast high signal-to-noise detections for both HERA and the
SKA. We demonstrate how the stellar-to-halo mass relation of the unseen, first
galaxies can be inferred from the evolution of 21-cm fluctuations. Finally, we
show that the spatial modulation of X-ray heating due to the relative
velocities provides a unique acoustic signature that is detectable at $z
10-15$ in our fiducial model. Ours are the first public simulations
with joint inhomogeneous LW and relative-velocity feedback across cosmic dawn
and reionization.
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