Dr. XI Hongwei from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), and his collaborators have revealed the properties of six new high-redshift galaxies, using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China’s Guizhou Province. The study was 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 amounts of atomic hydrogen gas similar to or more than that of the tens of thousands of galaxies previously surveyed in the local universe using other radio telescopes.  

The researchers concluded that galaxies four billion years ago had much more star-forming gas than current day galaxies, and 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, a corresponding author. "The new FAST survey has so far discovered over 100 new galaxies at distances up to five billion light-years, with the final number expected to reach over 1000."

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

However, using the largest optical telescopes in the U.S. and Russia, the counterparts were eventually identified by experts from the collaborative team. 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 work between Chinese and Australian 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)," said Prof. Lister Staveley-Smith from the University of Western Australia node of the International Centre for Radio Astronomy research, the other corresponding author.   

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

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. (Image by NAOC)