Stars and Reionization: The Cross-Correlation of the 21cm Line and the
  Near Infrared Background
  With improving telescopes, it may now be possible to observe the Epoch of
Reionization in multiple ways. We examine two of these observables - the excess
light in the near-infrared background that may be due to high redshift stars
and ionized HII bubbles, and the 21 cm emission from neutral hydrogen. Because
these two forms of emission should result from different, mutually exclusive
regions, an anticorrelation should exist between them. We discuss the strengths
of using cross-correlations between these observations to learn more about high
redshift star formation and reionization history. In particular, we create
simulated maps of emission from both the near-infrared background and 21 cm
emission. We find that these observations are anticorrelated, with the
strongest anticorrelation originating from times when the universe is half
ionized. This result is robust and does not depend on the properties of the
stars themselves. Rather, it depends on the ionization history.
Cross-correlations can provide redshift information, which the near-infrared
background cannot provide alone. In addition, cross-correlations can help
separate foreground emission from the true high redshift component, making it
possible to say with greater certainty that we are indeed witnessing the Epoch
of Reionization.
