Abstract
The Dark Ages and Cosmic Dawn are largely unexplored windows on the infant Universe (z ~ 200–10). Observations of the redshifted 21-cm line of neutral hydrogen can provide valuable new insight into fundamental physics and astrophysics during these eras that no other probe can provide, and drives the design of many future ground-based instruments such as the Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Array (HERA). We review progress in the field of high-redshift 21-cm Cosmology, in particular focussing on what questions can be addressed by probing the Dark Ages at z > 30. We conclude that only a space- or lunar-based radio telescope, shielded from the Earth’s radio-frequency interference (RFI) signals and its ionosphere, enable the 21-cm signal from the Dark Ages to be detected. We suggest a generic mission design concept, CoDEX, that will enable this in the coming decades.
Highlights
The first billion years of the Universe is one of the least explored and understood eras in the Universe, despite enormous observational progress in recent years with optical/uv, infrared, and sub-mm ground- and space-based instruments
To push beyond the current z ~ 25 frontier, though, and measure both the global and spatial fluctuations of the 21-cm signal, low-frequency (1100 MHz; Bandwidth~50 MHz; z > 13) space-based interferometers with vast scalable collecting areas (1–10-100 km2), large filling factors (~1) and large fields-of-view (4π sr.) are needed over a mission lifetime of more than five years. In this ESA White Paper, we argue for the development of new technologies enabling interferometers to be deployed, in space (e.g. Earth-Sun L2) or in the lunar vicinity, to target this 21-cm signal. This places them in a stable environment beyond the reach of most radio-frequency interference (RFI) from Earth and its ionospheric corruptions, enabling them to probe the Dark Ages as well as the Cosmic Dawn, and allowing one to investigate newphysics that is inaccessible in any other way in the coming decades
In this White Paper, we have argued for the development of space-based technology that enables the detection of the 21-cm signal from neutral hydrogen at redshift up to z ~ 50, during the peak of the Dark Ages
Summary
The first billion years of the Universe (its ‘infancy’) is one of the least explored and understood eras in the Universe, despite enormous observational progress in recent years with optical/uv, infrared, and sub-mm ground- and space-based instruments. To push beyond the current z ~ 25 frontier, though, and measure both the global and spatial fluctuations (power-spectra/tomography) of the 21-cm signal, low-frequency (1100 MHz; Bandwidth~50 MHz; z > 13) space-based interferometers with vast scalable collecting areas (1–10-100 km2), large filling factors (~1) and large fields-of-view (4π sr.) are needed over a mission lifetime of more than five years. In this ESA White Paper, we argue for the development of new technologies enabling interferometers to be deployed, in space (e.g. Earth-Sun L2) or in the lunar vicinity (e.g. surface, orbit, or Earth-Moon L2), to target this 21-cm signal. This places them in a stable environment beyond the reach of most RFI from Earth and its ionospheric corruptions, enabling them to probe the Dark Ages as well as the Cosmic Dawn, and allowing one to investigate new (astro)physics that is inaccessible in any other way in the coming decades
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