Record-breaking detection of radio signal from atomic hydrogen in extremely distant galaxy using GMRT
Astronomers from McGill University, Canada and Indian Institute of Science (IISc), Bengaluru have detected a radio signal originating from atomic hydrogen in an extremely distant galaxy using data from the Giant Metre Wave Radio Telescope (GMRT) in Pune
Astronomers from McGill University, Canada and Indian Institute of Science (IISc), Bengaluru have detected a radio signal originating from atomic hydrogen in an extremely distant galaxy using data from the Giant Metre Wave Radio Telescope (GMRT) in Pune. So far, this is the largest astronomical distance over which such a signal has been picked up. It is also the first confirmed detection of strong lensing of 21 cm emission from a galaxy. The findings have been published in the monthly notices of the Royal Astronomical Society.
Arnab Chakraborty, post-doctoral researcher, department of Physics and Trottier Space Institute, McGill University and Nirupam Roy, associate professor, department of Physics, IISc detected the radio signal from atomic hydrogen in an extremely distant galaxy at redshift z=1.29 using data from the GMRT built and operated by the National Centre for Radio Astrophysics (NCRA) TIFR. The research was funded by McGill University and IISc.
Chakraborty said, “Due to the immense distance of the galaxy, the 21 cm emission line had redshifted to 48 cm by the time the signal travelled from the source to the telescope. Atomic hydrogen is the basic fuel required for star formation in a galaxy. When hot ionised gas from the surrounding medium of a galaxy falls onto the galaxy, the gas cools and forms atomic hydrogen which then becomes molecular hydrogen and eventually leads to the formation of stars. Therefore, understanding the evolution of galaxies over cosmic time requires tracing the evolution of neutral gas at different cosmological epochs.”
The signal detected by the team was emitted by this galaxy when the universe was only 4.9 billion years old; in other words, the look-back time (lapse of time between detecting the signal and its original emission) for this source is 8.8 billion years.
Chakraborty said, “Atomic hydrogen emits radio waves of 21 cm wavelength, which can be detected using low frequency radio telescopes like the GMRT. Thus, 21 cm emission is a direct tracer of the atomic gas content in both nearby and distant galaxies. However, this radio signal is extremely weak and it is nearly impossible to detect the emission from a distant galaxy using current telescopes due to their limited sensitivity. Until now, the most distant galaxy detected using 21 cm emission was at redshift z=0.376, which corresponds to a look-back time – the time elapsed between detecting the signal and its original emission – of 4.1 billion years.”
Roy said, “This detection was made possible by a phenomenon called gravitational lensing in which the light emitted by 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, effectively resulting in the ‘magnification’ of the signal. In this specific case, the magnification of the signal was about a factor of 30, allowing us to see through the high redshift universe.”
The team also observed that the atomic hydrogen mass of this particular galaxy is almost twice as high as its stellar mass. These results demonstrate the feasibility of observing atomic gas from galaxies at cosmological distances in similar lensed systems with a modest amount of observing time. It also opens up exciting new possibilities for probing the cosmic evolution of neutral gas with existing and upcoming low-frequency radio telescopes in the near future.
Yashwant Gupta, centre director, NCRA Pune, said, “Detecting neutral hydrogen in emission from the distant universe is extremely challenging and has been one of the key science goals of GMRT. We are happy with this new pathbreaking result with the GMRT, and hope that the same can be confirmed and improved upon in the future.”
Photo caption - Illustration showing detection of the lensed 21 cm atomic hydrogen emission signal from a distant galaxy.