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The REACH radiometer for detecting the 21-cm hydrogen signal from redshift 7.5 to 28
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Observations of the 21-cm line from primordial hydrogen promise to be one of the best tools to study the early epochs of the Universe: the Dark Ages, the Cosmic Dawn, and the subsequent Epoch of Reionization. In 2018, the EDGES experiment caught the attention of the cosmology community with a potential detection of an absorption feature in the sky-averaged radio spectrum centred at 78 MHz. The feature is deeper than expected, and, if confirmed, would call for new physics. However, different groups have re-analyzed the EDGES data and questioned the reliability of the signal. The Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) is a sky-averaged 21-cm experiment aiming at improving the current observations by tackling the issues faced by current instruments related to residual systematic signals in the data. The novel experimental approach focuses on detecting and jointly explaining these systematics together with the foregrounds and the cosmological signal using Bayesian statistics. To achieve this, REACH features simultaneous observations with two different antennas, an ultra wideband system (redshift range 7.5 to 28), and a receiver calibrator based on in-field measurements. Simulated observations forecast percent-level constraints on astrophysical parameters, potentially opening up a new window to the infant Universe.
Forward citations
Cited by 8 Pith papers
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Impact of numerical stability in Bayesian noise wave calibration on global 21-cm experiments
Near-collinearity of noise-source and load design-matrix columns makes REACH’s five-parameter Bayesian calibration non-reproducible; a four-parameter Chebyshev fit with hot-load T_NS(ν) recovery and spike masking stab...
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Cosmological constraints on TeV-scale dark matter subcomponents decaying between recombination and reionisation
Future global 21-cm observations could beat CMB limits on TeV-scale decaying dark matter for lifetimes ≳10^15 s, especially for decays into neutrinos.
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Global 21cm Measurement Calibration Methodology
Three-way Dicke switching is inadequate for broadband global 21cm work; five independent calibrators plus the classical four noise parameters yield the correct absolute temperature, and Rogers & Bowman (2012) missed |...
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Cosmological constraints on TeV-scale dark matter subcomponents decaying between recombination and reionisation
Future 21-cm observations may constrain TeV-scale decaying dark matter subcomponents more tightly than CMB data for lifetimes above 10^15 s, with strongest sensitivity for neutrino decay channels due to differences in...
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Dark ages bounds on non-accreting massive compact halo objects
Upper bounds on the dark matter fraction in MACHOs of 10^3 to 10^7 solar masses are derived from limits on distortions to the global 21-cm signal at z~17, z~89, and z>300.
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Imprints of energy injection by compact dark stars in the 21-cm signal
Compact dark stars from asymmetric dark matter may inject energy that significantly deviates the 21-cm brightness temperature evolution from standard cosmology, offering a new probe for particle dark matter.
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Mitigating gain calibration errors from EoR observations with SKA1-Low AA*
Simulations show hybrid foreground mitigation (GPR + PCA combined with avoidance) recovers the HI 21cm signal within 2σ for gain calibration errors ≤1% in SKA1-Low AA* observations over 0.05-0.5 Mpc^{-1} scales.
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Axion-Photon Conversion in FLRW with Primordial Magnetic Fields: Explaining the Radio Excess
Resonant conversion of axion-like particles into photons in nanogauss primordial magnetic fields is claimed to explain both the ARCADE2 radio excess and the EDGES 21-cm trough for axion masses near 10^-14 to 10^-12 eV.
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