CHronOS

The goal of this lifelong project is to detect cosmic neutral hydrogen (H I) from the dark ages and the cosmic dawn — the first 400 million years of the Universe. Neutral hydrogen emits a signal at a rest wavelength of 21 cm (1420 MHz) that can be used to build a three-dimensional tomographic map of the Universe, the third dimension being time.

No radio telescope today can yet detect the cosmological 21-cm signal, though several are closing in on its power spectrum — mapping H I this way is a central motivation for building the Square Kilometre Array (SKA). To recover the signal, the systematic effects of the instrument and the contamination by Galactic and extragalactic foregrounds must be known with high precision, and the residual must match the emission predicted by theoretical models. All four aspects of science — simulation, instrumentation, theory and observation (SITO) — are therefore essential.

One such effect, polarization leakage, was measured and constrained in a series of CASSA studies and in a PhD thesis on Polarization Leakage in Epoch of Reionization Windows. In 2024 a BSc thesis, On the Power of Cosmic Hydrogen, began the simulation side of the project — modelling the 21-cm signal with 21cmFAST, now run on CASSA’s Timaeus HPC. CHronOS remains closely tied to the instrumental project PrimaBERA.