The Final 21-cm Cosmology Frontier

ongoing

"Radiation emitted by neutral hydrogen during the Universe's first billion years holds detailed information about its first stars, galaxies, black holes and fundamental physics. Achieving a detection of its faint ""21-cm signal"", currently redshifted to several meter wavelengths, has been extremely difficult due to the bright radio emission from other sources, human-made interference signals, the ionosphere, and telescope imperfections. It thus remains one of the hardest frontiers in present-day cosmology. In the past years, we made tremendous progress in mitigating these challenges, thanks to access to world-class low-frequency radio telescopes and research into innovative data analysis techniques. Using the Low-Frequency Array (LOFAR), we set the deepest limits on the 21-cm signal during the Epoch of Reionization, 500-1000 million years after the Big Bang, and the first limits during the early Cosmic Dawn. We started two innovative programs with AARTFAAC and NenuFAR, targeting the entire span of the Cosmic Dawn (100-500 million years), covering the recently-announced global 21-cm signal from EDGES. Last but not least, we launched the Netherlands-China Low-Frequency Explorer (NCLE) space-mission, currently in lunar L2 as part of the Chinese Chang-e' 4 mission, to set the first limits on the global 21-cm signal from the Dark Ages (20-100 million years).  CoDEX draws together these state-of-the-art observational programs and their expertise into a single program, improving current 21-cm power spectrum limits by three to six orders of magnitude, advancing them into the domain of standard astrophysical models from z~8 to ~80. To achieve this, we will process petabytes of data, strengthen efforts in the signal- and data-processing domain and enhance processing capacity. ERC funding enables us to achieve this in the coming years before next-generation instruments, such as the SKA, come online."