Recognizing the first radiation sources through their 21 cm signature

At the beginning of the reionization epoch, radiation sources produce fluctuations in the redshifted 21 cm background. We show that different types of sources ( such as miniquasars, Population II and III stars, supernovae, etc.) produce distinct signatures in the 21 cm signal radial profiles and statistical fluctuations, through which they can be identified. Furthermore, we show that the 21 cm signal from X-ray-emitting sources is much easier to observe than was expected, due to a previously neglected pumping mechanism.