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Cavendish Astrophysics



How did the first luminous objects in the sky form?

How did they shape the Universe?


These are some of the questions REACH will try to answer. The first stars and galaxies formed some time after the epoch of cosmic recombination (when the Cosmic Microwave Background formed ~378,000 years after the Big Bang at a redshift (z) of ~1100) and before the current 'realm of the galaxies' that we can see today (~1 to 13.7 billion years after the Big Bang). The radiation from these first luminous sources heated and re-ionized the neutral hydrogen that pervaded the primordial Cosmos. Probing these epochs, the 'Dark Ages' before the first galaxies, through cosmic re-ionization and first new light in the Universe, represents the frontier in studies of cosmic structure formation. Neutral hydrogen has a rest wavelength of 21 cm and by observing at low radio frequencies we can study directly its red-shifted radio emission (and absorption) from the gas clouds that were the raw material that formed the first luminous cosmic structures at these early epochs. While the future SKA telescope will aim to do full tomography of the hydrogen emission from the Cosmic Dawn (CD) and the Epoch of Re-ionization (EoR), an in principle simpler way to attempt the detection and study of this signal aims to observe the monopole emission (averaged from all directions in the sky, i.e. global, see Fig. 1) through cosmological time, red-shifted from 21-cm to a few meters due to the expansion of the Universe, with a stand alone radiometer system.

REACH is the Radio Experiment for the Analysis of Cosmic Hydrogen. It is a single antenna radiometer aiming to detect and analyse the redshifted radio emission (and absorption) from the 21-cm line. 

Figure 1. Model of the Global 21-cm signal


The team has conceived the basics of the proposed system over the last 2 years and is now committed to its construction, deployment and operation over the period 2019-2020. We are also finalising the site selection.

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