Prospects for Probing Feedback from the First Black Holes and Stars During Reionization

The feasibility of making highly redshifted HI 21‐cm (rest frame) measurements from an early epoch of the Universe between the Dark Ages and Reionization (i.e., z>6 and $v<200 MHz$⁠) to probe the effects of feedback from the first stars and quasars is assessed in this paper. It may be possible to determine the distribution of hydrogen through the Universe and to constrain the birth of the first stars and black holes via HI tomography. Such observations may also place limits on the properties of Inflation and any exotic heating mechanisms before the first star formation begins (e.g., dark matter decay). The global (all‐sky) HI signal after Recombination has distinct features at different frequencies between 30 and 200 MHz that change as the relative balance between the CMB and spin temperatures changes due to the expansion of the Universe and the ignition of stars and/or black holes. A technology roadmap to approach these observations beginning with ground‐based arrays and ending with a low frequency radio array on the lunar farside is described.