Can 21-cm observations discriminate between high-mass and low-mass
  galaxies as reionization sources?
  The prospect of detecting the first galaxies by observing their impact on the
intergalactic medium as they reionized it during the first billion years leads
us to ask whether such indirect observations are capable of diagnosing which
types of galaxies were most responsible for reionization. We attempt to answer
this by considering a set of large-scale radiative transfer simulations of
reionization in sufficiently large volumes to make statistically meaningful
predictions of observable signatures, while also directly resolving all
atomically-cooling halos down to 10^8 M_solar. We focus here on predictions of
the 21-cm background, to see if upcoming observations are capable of
distinguishing a universe ionized primarily by high-mass halos from one in
which both high-mass and low-mass halos are responsible, and to see how these
results depend upon the uncertain source efficiencies. We find that 21-cm
fluctuation power spectra observed by the first generation EoR/21-cm radio
interferometer arrays should be able to distinguish the case of reionization by
high-mass halos alone from that by both high- and low-mass halos, together.
Some reionization scenarios yield very similar power spectra and rms evolution
and thus can only be discriminated by their different mean reionization history
and 21-cm PDF distributions. We find that the skewness of the 21-cm PDF
distribution smoothed over LOFAR-like window shows a clear feature correlated
with the rise of the rms due to patchiness. Measurements of the mean
photoionization rates are sensitive to the average density of the regions being
studied and therefore could be strongly skewed in certain cases. (abridged)
