Astronomers detect radio signals from atomic hydrogen in extremely distant galaxy

Using the Giant Metrewave Radio Telescope (GMRT) in Pune, a team of international astronomers have detected a radio signal from atomic hydrogen in an extremely distant galaxy.

This is the first time that strong lensing of 21 cm emission from a galaxy has been confirmed, and the astronomical distance over which the signal was picked up is the greatest ever recorded.

Atomic hydrogen is the basic fuel required for star formation in a galaxy. Until now, the most distant galaxy detected using 21 cm emission was at redshift z=0.376. This time, the radio signal was detected at redshift z=1.29.

The researchers, including Arnab Chakraborty, a postdoctoral researcher at the Department of Physics and Trottier Space Institute of McGill University in Canada, and Nirupam Roy, Associate Professor, Department of Physics, at the Indian Institute of Science (IISc) in Bengaluru, detected the atomic hydrogen emission signal by gravitational lensing -  a phenomenon in which the gravity of a massive object, such as a galaxy, bends and distorts the light from a more distant object, such as a quasar, effectively resulting in the magnification of the signal.

"Due to the immense distance to the galaxy, the 21 cm emission line had redshifted to 48 cm by the time the signal travelled from the source to the telescope. The signal detected by the team was emitted from this galaxy when the universe was only 4.9 billion years old; in other words, the look-back time for this source is 8.8 billion years," said Arnab Chakraborty.

Astronomers from @McGillUPhysics & @Physics_at_IISc have detected radio signals from atomic hydrogen in an extremely distant galaxy, using the Giant Metrewave Radio Telescope @NCRA_Outreachhttps://t.co/SuWy07uLbu@ArnabCh88024907 @RAS_JournalsImage: @CuriousArtom #IIScresearch pic.twitter.com/69q78P38f1

— IISc Bangalore (@iiscbangalore) January 16, 2023

According to a press release by IISc, the team found that the atomic hydrogen mass of this galaxy is almost twice as much as its stellar mass. The findings show that it is possible to observe atomic gas from galaxies at cosmological distances with a reasonable amount of observing time. This opens up the potential to use existing and upcoming low-frequency radio telescopes to explore the cosmic evolution of neutral gas in the near future.