Non-detection of key signal helps determine what first galaxies were and were not like

The non-detection key signal is crucial in determining what the first galaxies looked like.

By Staff Writers

Cambridge UK (SPX) Nov 29, 2022

Illustration taken from stock

In one of the earliest astrophysical studies of the time in the early Universe when first stars and galaxies formed (known as the cosmic dawn), researchers have made some important discoveries about the first galaxies that actually existed.

Researchers at the University of Cambridge used data from India’s SARAS3 radio telescope to examine the very beginning of the Universe, just 200 million years after its Big Bang. They were able also to place limits on the energy and mass of the first galaxies and stars.

In a surprising twist, the researchers were able put these limits on galaxies earliest than they were by not finding the signal, known as 21-centimetre hydrogen lines.

The researchers were able to make other determinations about cosmic dawn. They placed restraints upon the first galaxies to prevent them from ruling out possible scenarios such as galaxies that were inefficient producers of radio emission and heaters of cosmic gases.

Although we can’t yet observe these galaxies in their earliest stages, the Nature Astronomy journal report shows that it is a significant step towards understanding how the Universe changed from being mostly empty to full of stars.

One of the main goals of new observatories is to understand the early Universe. This is when the first stars and galaxies were formed. These results, which were obtained with the SARAS3 data, are a proof of concept study that opens the door to understanding this period in evolution.

SKA Project – which involves two next-generation telescopes, due to be finished by the end the decade – will likely allow for images of early Universe. Current telescopes have to detect the cosmological signals of first stars re-radiated in thick hydrogen clouds.

This signal is called the 21-centimetre signal – it’s a radio signal that was produced in the early Universe by hydrogen atoms. The JWST will not be able to image individual galaxies within the early Universe. Instead, the 21-centimetre-long line can be studied using radio telescopes like the Cambridge-led REACH (Radio Experiment for the Analysis of Cosmic Hydrogen). REACH is expected to release its first results in 2023.

Astronomers search for the radio signal that is produced by hydrogenatoms in the early Universe. This signal can be affected by the light from the first star and radiation behind the hydrogen fog. These same researchers also developed a method earlier this year that they claim will enable them see through the fog of early universe and detect light from first stars. These techniques were already used in the current study.

Another research group that operated the EDGES experiment published a 2018 result that suggested a possibility of detecting this earliest light. The signal reported was strong in comparison to what can be expected in the simplest Astrophysical picture of the early Universe. Recent SARAS3 data disputed the detection. Independent observations are still needed to confirm the EDGES result.

Cambridge-led team tested a range of astrophysical scenarios to explain the EDGES result. But they failed to find a corresponding signal. The team was able instead to set limits on the properties of first stars and galaxies.

SARAS3’s analysis provides the first insight into the properties of first galaxies through radio observations at the average 21-centimetre distance.

With collaborators in India and Australia, the Cambridge team used data taken from the SARAS3 telescope to find signals from cosmic Dawn, the time when the first galaxies emerged. The researchers failed to detect any signal in the SARAS3 data using statistical modelling techniques.

Harry Bevins (a Cambridge Cavendish Laboratory student and the paper’s author) said that “we were looking for a signal of a certain magnitude.” “But, by not finding that signal we can limit its depth. This, in turn allows us to learn about the brightness of the first galaxies.

“Our analysis proved that the hydrogen signals can provide information about the population of galaxies and first stars,” co-lead author Dr Anastasia Fialkov of Cambridge’s Institute of Astronomy. “Our analysis limits some of the most important properties of the first sources light, including the masses and efficiency of galaxies that can form stars. We also discuss the question of whether these sources emit radio, X-ray and ultraviolet radiation.

“This is a first step in what we hope to be a decade full of discoveries about the Universe’s transition from darkness and emptiness into the complex realms of stars, galaxies, and other celestial objects that we can see from Earth,” stated Dr Eloy De Lera Acedo, a researcher at Cambridge’s Cavendish Laboratory.

The observational study, which is the first in its kind, excludes situations in which the earliest galaxies emitted radio-band emission more than 1000 times brighter than present galaxies and were poor heaters to hydrogen gas.

“Our data also suggests something that was hinted at before: that the first stars, galaxies, could have made a measurable contribution, which has been travelling towards you ever since the Big Bang,” said de Lera Acedo. “We also are establishing a limit on that contribution.”

Bevins stated, “It’s incredible to be able look so far back in history – to just 200million years after the Big Bang – and be capable of learning about the early Universe.”

Research Report:Astrophysical limitations from the SARAS 3 nondetection cosmic dawn sky-averaged 21 cm signal

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“The brightest part of the intragroup light is 50 times fainter then the darkest night skies on Earth. It is extremely… continue reading

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