The imprint of the relative velocity between baryons and dark matter on
  the 21-cm signal from reionization
  The post-recombination streaming of baryons through dark matter keeps baryons
out of low mass (<10^6 solar masses) halos coherently on scales of a few
comoving Mpc. It has been argued that this will have a large impact on the
21-cm signal before and after reionization, as it raises the minimum mass
required to form ionizing sources. Using a semi-numerical code, we show that
the impact of the baryon streaming effect on the 21-cm signal during
reionization (redshifts z approximately 7-20) depends strongly on the cooling
scenario assumed for star formation, and the corresponding virial temperature
or mass at which stars form. For the canonical case of atomic hydrogen cooling
at 10^4 Kelvin, the minimum mass for star formation is well above the mass of
halos that are affected by the baryon streaming and there are no major changes
to existing predictions. For the case of molecular hydrogen cooling, we find
that reionization is delayed by a change in redshift of approximately 2 and
that more relative power is found in large modes at a given ionization
fraction. However, the delay in reionization is degenerate with astrophysical
assumptions, such as the production rate of UV photons by stars.
