Using information from the Giant Metrewave Radio Telescope (GMRT) in Pune, astronomers from McGill University in Canada and the Indian Institute of Science (IISc) in Bengaluru have discovered a radio signal coming from atomic hydrogen in a very far-off galaxy.
“By a wide margin, the astronomical distance over which such a signal has been detected is the largest yet. Additionally, this is the first independently verified discovery of strong lensing of a galaxy’s 21 cm emission “according to a statement from IISc.
The fundamental fuel needed for star formation in a galaxy is atomic hydrogen. It was explained that when hot, ionised gas from a galaxy’s surrounding medium falls onto the galaxy, the gas cools and forms atomic hydrogen, which then transforms into molecular hydrogen and ultimately results in the formation of stars.
Therefore, tracing the evolution of neutral gas at various cosmological epochs is necessary to comprehend the evolution of galaxies over cosmic time, according to the statement.
Low frequency radio telescopes like the GMRT can detect the 21 cm wavelength radio waves that atomic hydrogen emits. Therefore, the atomic gas content of both nearby and far-off galaxies can be directly measured using the 21 cm emission.
However, due to the current telescopes’ poor sensitivity and the radio signal’s extreme weakness, it is almost impossible to detect the emission from a distant galaxy.
According to the statement, “Up to this point, the most distant galaxy detected using 21 cm emission was at redshift z=0.376, which corresponds to a look-back time of 4.1 billion years (Redshift represents the change in wavelength of the signal depending on the object’s location and movement; a greater value of z indicates a farther object).”
Arnab Chakraborty, a post-doctoral researcher at McGill University’s Department of Physics and Trottier Space Institute, and Nirupam Roy, an associate professor at the Indian Institute of Science, have discovered a radio signal from atomic hydrogen in a far-off galaxy at redshift z=1.29.
Chakraborty explains that by the time the signal arrived at the telescope from the source, the 21 cm emission line had redshifted to 48 cm because of the galaxy’s enormous distance. The signal the team discovered has a look-back time of 8.8 billion years because it was produced by this galaxy when the universe was only 4.9 billion years old.
This discovery was made possible by a phenomenon known as gravitational lensing, in which the light from the source is bent due to the presence of another massive body, such as an early type elliptical galaxy, between the target galaxy and the observer, essentially “magnifying” the signal.
According to Roy, “in this particular instance, the signal’s magnification was about a factor of 30, allowing us to see through the high redshift universe.”
The team also noticed that this particular galaxy’s atomic hydrogen mass is nearly twice as high as its stellar mass. These findings show that atomic gas from galaxies at cosmological distances can be observed in similar lensed systems with only a small amount of observing time. The statement added that it also opens up fascinating new opportunities for studying the cosmic evolution of neutral gas in the near future with existing and upcoming low-frequency radio telescopes.
NCRA’s (National Centre for Radio Astrophysics) Center Director, Yashwant Gupta, stated, “One of the main scientific objectives of GMRT has been to detect neutral hydrogen, which is extremely difficult to do in emission from the far side of the Universe. We are pleased with the GMRT’s recent ground-breaking result and anticipate that it will be confirmed and enhanced in the future.”