Testing Galaxy Formation Models with High Redshift 21-cm Signals and
Upcoming Galaxy Surveys

Current observations of galaxies at redshifts greater than z ~ 4 are
consistent with a relatively simple picture of galaxy evolution at
high-z in which star formation is fueled by the inflow of pristine gas
from the intergalactic medium but self-limiting due to feedback from
stellar winds and supernovae explosions. However, these observations are
limited to rather bright, rare galaxies, especially at the highest
redshifts, and as a result may not be informative of how most galaxies
evolve. Observations of the 21-cm background offer a new window into the
growth of structure at early times, and can thus provide a vital and
independent test of galaxy formation models. In this talk, I will
discuss galaxy formation theory in the context of the 21-cm detection
recently reported by the EDGES collaboration. This signal has received
much attention in the last year due to its anomalous depth, which has
led to a variety of exotic explanations including milli-charged dark
matter and as-yet-unidentified radio backgrounds in the early Universe.
I will first highlight the flurry of ideas that have arisen in the last
~year to explain the anomalous amplitude of the EDGES signal. Then, I
will turn to an under-appreciated aspect of the signal: its timing is
not consistent with empirically-calibrated models of high-z galaxies. If
confirmed, the EDGES signal may thus be evidence of new physics *and*
new astrophysics.