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1st of December 2022
Constraints on the cosmic dawn
by Bevins et al.
Understanding the early Universe, when the first stars and galaxies formed (the "Cosmic Dawn"), is one of the major science goals of a number of new observatories. The James Webb Space Telescope (JWST), for example, will directly image these early galaxies in deep near-infrared surveys. Observations of the redshifted 21-cm line of atomic hydrogen have provided several upper limits on the 21-cm power spectrum. A tentative detection of the sky-averaged signal at redshift z≈17, made with the Experiment to Detect the Global EoR Signature (EDGES) low-band antenna, was reeported in 2018. However, this is yet to be confirmed.

SARAS 3 is a radiometer based on a monocone antenna that has made observations of the sky from a location in Southern India. The experiment is the first global 21-cm experiment of its kind to take observations while floating on a body of water, which is expected to improve the total efficiency of the antenna. Fifteen hours of observations were integrated in the frequency range 55–85 MHz (z≈15–25), reduced after radio frequency interference filtering, with corrections made for emission from the water beneath the antenna and receiver noise temperature. No evidence for an EDGES-like signal was seen, and the data were used to constrain a population of radio-luminous galaxies ~200 million years after the Big Bang. The results are presented in this week's issue of Nature Astronomy. (Image credit: https://arxiv.org/pdf/2104.03522.pdf)

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