| Abstract: Nearly 4,00,000 years after the Big Bang, the universe contained predominantly neutral hydrogen, and this period is known as the “cosmic dark ages”. 21-cm signal redshifts with the expansion of the Universe, and is expected to be detected in the frequency range of 5-45 MHz during the dark ages. The brightness of the redshifted line is predicted to be ~ 42 mK peaking at ~ 16MHz. The signal from the Dark Ages acts as a sensitive thermometer, potentially capable of constraining the exotic processes involved in explaining the physics of the period before star formation. It offers a unique probe to the standard cosmological model without the uncertainty of the first stars and galaxies. However, at these low frequencies, the foregrounds are extremely bright, T ~ 10,000 K at frequency ~ 30 MHz. The systematics introduced by the instrument itself pose a major challenge, making detection very difficult. Additionally, low-frequency radio astronomy is limited by severe ionospheric distortions below 50 MHz and complete reflection of radio waves below 10–30 MHz. Due to these cut-offs imposed by the ionosphere itself, Earth-based measurements are not possible. The far side of the Moon acts as a physical shield that isolates the lunar surface from radio interference/noises from Earth-based sources, the ionosphere, Earth-orbiting satellites, and the Sun’s radio noise during the lunar night. We investigate a range of instrument models, and assess their suitability for the dark ages signal. In particular, the instrument models include realistic performance in the presence of lunar regolith. The simulated foregrounds as seen by these instruments are then modeled using a Bayesian pipeline, leading to signal detection prospects using Bayesian Evidence. We finally compare the results of extracting the dark ages signal from a range of realistic telescopes and contrast these with elemental telescopes. |
