Speaker
Description
We propose a novel method to probe the spectral evolution of the global 21-cm background. Late-time evolution of our universe drives relic backgrounds to be correlated with low-redshift density tracers. This phenomena, the integrated Sachs-Wolfe effect (ISW), has been measured extensively for the cosmic microwave background (CMB) but never for the 21-cm background. We show that the 21-cm background also experiences ISW, and due to its dependence on the (1) sky-averaged amplituded and (2) the spectral shape, measuring the 21-cm ISW in conjunction with the CMB ISW can directly probe the time evolution of the global 21-cm background. A huge benefit over the single-element detectors such as EDGES and SARAS is that the 21-cm ISW is blind to the Milky Way contamination, thus naturally mitigating the ambiguity caused by the foreground removal process. We also show that, as long as SKA1-LOW conducts a full-sky observation for a few 1000s of hours, a new constraint on the evolution of the global 21-cm background can be made with high significance.
