Evaluating the QSO contribution to the 21-cm signal from the Cosmic Dawn

The upcoming radio interferometer Square Kilometre Array (SKA) is expected to detect the redshifted 21-cm signal from the neutral hydrogen present the Cosmic Dawn. Temperature fluctuations from X-ray heating of the intergalactic medium can dominate the fluctuations in the 21-cm signal this time. This heating depends on the abundance, clustering, and of the X-ray sources present, which remain highly uncertain. We a suite of three new large-volume, 349\\, Mpc a side, fully numerical transfer simulations including QSO-like sources, extending the work presented in Ross et al. (2017). The results show that our QSOs have modest contribution to the heating budget, yet significantly impact the 21-cm. Initially, the power spectrum is boosted on large scales by heating the biased QSO-like sources, before decreasing on all scales. Fluctuations images of the 21-cm signal with resolutions corresponding to SKA1-Low at appropriate redshifts are well above the expected noise for deep, indicating that imaging could be feasible for all the X-ray models considered. The most notable contribution of the QSOs is a increase in non-Gaussianity of the signal, as measured by the skewness kurtosis of the 21-cm probability distribution functions. However, in the of late Lyman-\ saturation, this non-Gaussianity could be decreased particularly when heating occurs earlier. We conclude increased non-Gaussianity is a promising signature of rare X-ray sources this time, provided that Lyman-\ saturation occurs before heating the 21-cm signal.