| Abstract: |
The redshifted 21-cm signal from neutral hydrogen gas in the intergalactic medium is expected to trace the large-scale evolution of the Universe between the surface of last scattering (z=1100) and the end of the Epoch of Reionization (z=5.5). Models for the sky-averaged, or global, component of this signal consist of two absorption features in the radio spectrum: one below 50 MHz, from the Dark Ages, and the second one between 50 and 150 MHz, produced by the appearance of the first stars at the Cosmic Dawn. Several challenges make the measurement of this signal extremely difficult, including: (1) strong astrophysical foregrounds, (2) very strict instrumental calibration requirements, (3) effects from the environment and the Earth's ionosphere, and (4) anthropogenic radio-frequency interference. Considering all these challenges, a multifaceted strategy is necessary to reliably detect the global 21-cm signal from the early Universe. In this talk, I will describe the status of three global 21-cm experiments in which I participate: EDGES, MIST, and LuSEE-night. The EDGES experiment, after its 2018 result, continues taking data in Western Australia with different instrumental configurations. The new MIST experiment started conducting observations in 2022 from the US and the Canadian High Arctic. Finally, the LuSEE-night space mission will land on the lunar farside in 2026 to observe the sky below 50 MHz from that extreme environment. |
