Scientists have determined the properties of radio-luminous galaxies that formed just 200 million years after the Big Bang, a period known as the Cosmic Dawn, providing insight into the properties of the oldest radio-loud galaxies, which are typically powered by supermassive black holes. In their curiosity about how the early stars and galaxies formed and what they looked like, people have tried to pick up the faint signals emanating from the depths of space through an array of ground-based and space-based telescopes peering into the sky to gain a better understanding. universe.
Measurements of the Background Shaped Antenna Radio Spectrum 3 (SARAS) telescope—originally designed and built at the Raman Research Institute—were deployed over Dandiganahalli Lake and the Sharavati Backwaters, located in northern Karnataka, in early 2020. In the first work of its kind using data from SARAS 3, researchers from the Raman Research Institute (RRI), Bengaluru, Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia, along with collaborators from the University of Cambridge. and the University of Tel-Aviv, estimated the energy output, luminosities and masses of the first generation of galaxies that are bright at radio wavelengths.
Scientists study the properties of very early galaxies by observing radiation from hydrogen atoms in and around galaxies, which is emitted at a frequency of about 1420 MHz. The radiation is expanded by the expansion of space as it travels to us through space and time and arrives on Earth in the lower frequency radio bands of 50-200 MHz, which are also used by FM and TV broadcasts. The cosmic signal is extremely weak, buried in the orders of magnitude brighter radiation from our own Galaxy and man-made terrestrial interference. Therefore, detecting the signal, even with the most powerful existing radio telescopes, has remained a challenge for astronomers.
Results from a paper by RRI’s Saurabh Singh and CSIRO’s Ravi Subrahmanyan published in the journal Nature Astronomy on 28 November 2022 described how even not detecting this line from the early universe can allow astronomers to study the properties of the very first galaxy by achieving exceptional sensitivity. “The SARAS 3 results are the first time that 21-centimeter-diameter radio observations have been able to provide insight into the properties of the oldest radio-loud galaxies, which are typically powered by supermassive black holes,” said Subrahmanyan. , former Director of RRI and currently with Space & Astronomy CSIRO, Australia and author of the paper. “This work takes the results from SARAS 2, which was the first to report on the properties of the oldest stars and galaxies.”
“SARAS 3 improved our understanding of the astrophysics of the Cosmic Dawn, telling us that less than 3 percent of the gaseous mass in early galaxies was converted into stars, and that the earliest galaxies that were bright in radio emission were also bright in X-rays. , which heated the cosmic gas in and around early galaxies,” said Singh, one of the authors of the paper titled “Astrophysical Constraints from the Non-Detection of the SARAS 3 Signal in the 21-cm Cosmic Dawn Sky.”
This March, Singh, along with Subrahmanyan and the SARAS 3 team, used the same data to refute the claim of detecting an anomalous 21cm signal from Cosmic Dawn, taken by the EDGES radio telescope developed by researchers at Arizona State University (ASU). ) and MIT, USA. This rejection helped restore confidence in the concordant model of cosmology, which had been called into question by the claimed detection. In March this year, Singh along with Subrahmanyan’s team and SARAS 3 used the same data to refute claims of detection of a 21 cm signal from Cosmic Dawn by the EDGES radio telescope developed by researchers at Arizona State University (ASU) and MIT, USA.
“We now have constraints on the masses of early galaxies, along with constraints on their energy outputs at radio, X-ray, and ultraviolet wavelengths,” Singh noted. Furthermore, using the phenomenological model, SARAS 3 was able to establish an upper limit on excess radiation at radio wavelengths, lowering the existing limits set by the ARCADE and Long Wavelength Array (LWA) experiments in the US. “The analysis showed that the 21 cm hydrogen signal can inform the population of the first stars and galaxies,” said another author, Dr. Anastasia Fialkov from the Institute of Astronomy, University of Cambridge. “Our analysis constrains some key properties of the first light sources, including the masses of the oldest galaxies and the efficiency with which these galaxies can form stars,” Fialkov said.
Since its last deployment in March 2020, SARAS 3 has undergone a series of upgrades. These improvements are expected to bring even greater sensitivity to the detection of the 21 cm signal. Currently, the SARAS team is evaluating several locations in India for further deployment. “These sites are quite remote and present several logistical challenges for deployment. However, from a scientific point of view, they seem promising, and with the new upgrades, they seem ideal for our experiment,” adds Yash Agrawal, a member of the SARAS team.
