The Giant Meter Wave Radio Telescope has completed the measurement of the mass of atomic hydrogen in galaxies 9 billion years ago
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A galaxy is mainly composed of gas and stars. During the life of a galaxy, new stars are formed from the existing gas. When the universe was young, stars formed much more frequently than today. For more than two decades, astronomers have known that the star formation activity in the galaxy reached its peak about 8-10 billion years ago and has continued to decline since then.
Until recently, the reason for this decline was unknown, mainly because we had no information about the amount of atomic hydrogen in these early galaxies, and atomic hydrogen was the main fuel for star formation. This situation changed last year. A team of astronomers from NCRA and RRI, including some authors of this study, used the upgraded GMRT to measure the atomic hydrogen content of galaxies about 8 billion years ago for the first time, when the stars formed in the universe. Activity began to decline. They found that the possible reason for the decline in star formation in the galaxy is that the galaxy is running out of fuel.
NCRA-TIFR PhD student Aditya Chowdhury is the lead author of this new study and the 2020 study. He said: “Our new results are for galaxies in earlier periods, but are still close to maximum star formation. At the end of the active age. We found that galaxies 9 billion years ago were rich in atomic gas, and the mass of atomic gas was almost three times the mass of stars! This is completely different from the situation of galaxies. This is completely different from galaxies like the Milky Way today. The gas mass of the latter is almost ten times the mass of stars.”
The measurement of the quality of atomic hydrogen is accomplished by using GMRT to search for a spectral line in atomic hydrogen, which can only be detected by radio telescopes. Unfortunately, this “21 cm” signal is very weak, so it is almost impossible to detect from a single galaxy about 30 billion light years away, even with powerful telescopes like GMRT. Therefore, the research team used a technique called “stacking” to increase sensitivity. This allowed them to measure the average gas content of nearly 3,000 galaxies by combining signals of 21 cm.
“The observations we studied were conducted about 5 years ago, when the GMRT was upgraded in 2018. We used the original receiver and electronic chain before the GMRT upgrade, and its bandwidth is very narrow. Therefore, we can only cover a limited number of galaxies; this is why our current research covers 3000 galaxies, and our 2020 research covers 8000 galaxies under the wider bandwidth of the upgraded GMRT, “NCRA-TIFR” Nissim Kanekar said he is a co-author of the study.
Barnali Das, another doctoral student of NCRA-TIFR, added: “Although we have fewer galaxies, we have improved our sensitivity by longer observation time, which is close to 400 hours. A lot. The data means that it takes a long time to analyze. The star formation of these early galaxies is so intense that they will consume their atomic gas in just 2 billion years. Moreover, if these galaxies cannot get more gas, Their star formation activity will decline and eventually cease. Therefore, the reason for the decline in star formation in the universe seems likely to be that galaxies cannot replenish their gas reservoirs after a certain epoch, perhaps because there is not enough gas available in their environment. ”
“Repeatability is the basis of science. Last year, we reported the first measurement of the atomic gas content in this distant galaxy. With the current results, a completely different set of Receivers and electronics, we now have two independent measurements of the atomic gas mass of these early galaxies. Even a few years ago, this was unbelievable!” Kanekar said.
S. Dwarakanath of K. RRI is the co-author of this study. He mentioned: “Detecting 21 cm signals from distant galaxies is the main original goal of GMRT and continues to be a more powerful telescope. (Such as the square kilometer array) key scientific drivers. These results are extremely important for us to understand the evolution of galaxies.”