On the direct detectability of the cosmic dark ages: 21 centimeter emission from minihalos

In the standard cold dark matter (CDM) theory of structure formation, virialized minihalos (with T-vir less than or similar to 10(4) K) form in abundance at high redshift (z>6), during the cosmic "dark ages." The hydrogen in these minihalos, the first nonlinear baryonic structures to form in the universe, is mostly neutral and sufficiently hot and dense to emit strongly at the 21 cm line. We calculate the emission from individual minihalos and the radiation background contributed by their combined effect. Minihalos create a "21 cm forest" of emission lines. We predict that the angular fluctuations in this 21 cm background should be detectable with the planned Low Frequency Array (LOFAR) and Square Kilometer Array (SKA), thus providing a direct probe of structure formation during the dark ages. Such a detection will serve to confirm the basic CDM paradigm while constraining the shape of the power spectrum of primordial density fluctuations down to much smaller scales than have previously been constrained, the onset and duration of the reionization epoch, and the conditions that led to the first stars and quasars. We present results here for the currently favored, flat LambdaCDM model, for different tilts of the primordial power spectrum.