Interpreting the Global 21-cm Signal from High Redshifts. I. Model Independent Constraints

Understand

The sky-averaged (global) 21-cm signal is a powerful probe of the intergalactic medium (IGM) prior to the completion of reionization.

• However, it has so far been unclear that even in the best case scenario, in which the signal is accurately extracted from the foregrounds, that it will provide more than crude estimates of when the Universe's first stars and black holes form.
• In contrast to previous work, which has focused on predicting the 21-cm signatures of the first luminous objects, we investigate an arbitrary realization of the signal, and attempt to translate its features to the physical properties of the IGM.
• Within a simplified global framework, the 21-cm signal yields quantitative constraints on the Lyman-alpha background intensity, net heat deposition, ionized fraction, and their time derivatives, without invoking models for the astrophysical sources themselves.