Astronomers using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in Guizhou Province in China have found an abundance of gas-rich galaxies in the distant Universe.

Figure 1: Signals of the new six galaxies discovered by FAST (black lines) and confirmed by optical telescopes (cyan lines). (Credit: NAOC)

Dr XI Hongwei from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), the lead author, together with his colleagues, revealed the properties of six new high-redshift galaxies, the research result of which has been published online in The Astrophysical Journal Letters on May 10.

These remarkable galaxies, whose radio wave emissions have taken almost the age of the Solar System to reach us, contain similar or more atomic hydrogen gas than the tens of thousands of galaxies previously surveyed in the local Universe with other radio telescopes.

The astronomers conclude 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.

"These discoveries are part of the ongoing FAST Ultra Deep Survey, showing the tremendous sensitivity of the world's largest radio telescope," said Prof.PENG Bo from NAOC, one of the corresponding authors.

"The new FAST survey has so far discovered over 100 new galaxies at distances up to 5 billion light years, with the final number expected to reach over 1000."

Finding the optical counterparts to the new radio discoveries turned into a detective story, because galaxies are very faint at such large distances and, because of the wavelength difference, the localisation accuracy of FAST is not as good as that of optical telescopes.

Figure 2: Radio contours (white lines) overlayed on optical images. Their optical counterparts are zoomed in at bottom right corners. Red circles show the FAST resolution. (Credit: NAOC)

However, with the help of experts in our collaborating teams using the largest US and Russian optical telescopes, the counterparts were eventually identified. The counterparts were found to contain 2-3 times more stars than the Milky Way, yet contain about 10 times the mass of hydrogen gas.

"This collaborative workbetween the Chinese and Australia radio astronomers demonstrates the tremendous potential of the new generation of radio telescopes that, later this decade, will also include the international Square Kilometre Array Observatory (SKAO)," added Professor Lister Staveley-Smith from the University of Western Australia node of the International Centre for Radio Astronomy research, the other corresponding author.