China Focus: China's FAST telescope discovers distant gas-rich galaxies

BEIJING, May 10 (Xinhua) -- Chinese scientists have discovered an abundance of gas-rich galaxies in the distant universe, using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in southwest China's Guizhou Province.

The research result has been published online in The Astrophysical Journal Letters on Friday.

According to the study, the newly discovered galaxies, whose radio wave emissions have taken almost the age of the solar system to reach the earth, contain similar or more atomic hydrogen gas than the tens of thousands of galaxies previously surveyed with other radio telescopes.

Xi Hongwei from the National Astronomical Observatories under the Chinese Academy of Sciences (NAOC), the lead author, together with his colleagues from Australia, the United States and Russia, revealed the properties of six new high-redshift galaxies in the study.

The new high-redshift galaxy sample provides the opportunity to better investigate the evolution of cool gas in galaxies, said the paper. "A larger sample size in the future will allow us to refine our knowledge of the formation and evolution of galaxies."

Hydrogen is the most common element in the universe. In its neutral form, it is abundant in spiral galaxies such as the Milky Way. Neutral hydrogen is the primary component of the cool interstellar medium (ISM) and is the reservoir of fuel for star formation. However, owing to the sensitivity of existing radio telescopes, the understanding of the evolution of the ISM in galaxies remains limited.

"We have carried out a blind neutral hydrogen search, or the FAST Ultra-Deep Survey. These discoveries are part of the ongoing survey, showing the tremendous sensitivity of the world's largest radio telescope," said Peng Bo, a scientist at the NAOC.

"The new FAST survey has so far discovered over 100 new galaxies at distances of up to 5 billion light years, with the final number expected to reach over 1,000," Peng added.

The researchers concluded that galaxies 4 billion years ago had much more star-forming gas than current-day galaxies, and that distant galaxies have much greater gas reservoirs than previously believed.

Meanwhile, because the newly discovered galaxies are very faint at such large distances and have different wavelengths, FAST was not able to locate the optical counterparts with the same accuracy as optical telescopes. With the help of experts using the largest optical telescopes in the United States and Russia, the counterpart galaxies were eventually identified.

It was found that these counterparts contain 2-3 times as many stars as the Milky Way, but contain 10 times the mass of hydrogen gas, Peng said.

"This successful collaborative program between Chinese and Australian radio astronomers demonstrates the tremendous potential of the new generation of radio telescopes," said Lister Staveley-Smith, a professor from the University of Western Australia.

FAST is the world's largest single-dish radio telescope, with a reception area equal to 30 standard football fields. Located in a deep and round karst depression in Guizhou Province, FAST started formal operation in January 2020 and officially opened to the world on March 31, 2021.