  The formation of the first stars is an exciting frontier area in astronomy.
Early redshifts z ~ 20 have become observationally promising as a result of a
recently recognized effect of a supersonic relative velocity between the dark
matter and gas. This effect produces prominent structure on 100 comoving Mpc
scales, which makes it much more feasible to detect 21-cm fluctuations from the
epoch of first heating. We use semi-numerical hybrid methods to follow for the
first time the joint evolution of the X-ray and Lyman-Werner radiative
backgrounds, including the effect of the supersonic streaming velocity on the
cosmic distribution of stars. We incorporate self-consistently the negative
feedback on star formation induced by the Lyman-Werner radiation, which
dissociates molecular hydrogen and thus suppresses gas cooling. We find that
the feedback delays the X-ray heating transition by a Delta z ~ 2, but leaves a
promisingly large fluctuation signal over a broad redshift range. The
large-scale power spectrum is predicted to reach a maximal signal-to-noise
ratio of S/N ~ 3-4 at z ~ 18 (for a projected first-generation instrument),
with S/N > 1 out to z ~ 22-23. We hope to stimulate additional numerical
simulations as well as observational efforts focused on the epoch prior to
cosmic reionization.
