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The assumptions inherent to global 21-cm signal analyses are rarelydelineated. In this paper, we formulate a general list of suppositionsunderlying a given claimed detection of the global 21-cm signal. Then, wespecify the form of these assumptions for two different analyses: 1) the oneperformed by the EDGES team showing an absorption trough in brightnesstemperature that they modeled separately from the sky foreground and 2) a new,so-called Minimum Assumption Analysis (MAA), that makes the most conservativeassumptions possible for the signal. We show fits using the EDGES analysis onvarious beam-weighted foreground simulations from the EDGES latitude with nosignal added. Depending on the beam used, these simulations produce large falsetroughs due to the invalidity of the foreground model to describe thecombination of beam chromaticity and the shape of the Galactic plane in thesky, the residuals of which are captured by the ad hoc flattened Gaussiansignal model. On the other hand, the MAA provides robust fits by including manyspectra at different time bins and allowing any possible 21-cm spectrum to bemodeled exactly. We present uncertainty levels and example signalreconstructions found with the MAA for different numbers of time bins. Withenough time bins, one can determine the true 21-cm signal with the MAA to $<10$times the noise level.

astrophysical journal/the astrophysical journal

Formulating and critically examining the assumptions of global 21-cm  signal analyses: How to avoid the false troughs that can appear in single  spectrum fits