Canadian and IISc astronomers detect radio signal in distant galaxy using Giant Metrewave Radio Telescope 

Images of detection of radio signal originating from atomic hydrogen in an extremely distant galaxy.

Images of detection of radio signal originating from atomic hydrogen in an extremely distant galaxy.
| Photo Credit: Special Arrangement

Astronomers from McGill University in Canada and the Indian Institute of Science (IISc) in Bengaluru have used data from the Giant Metrewave Radio Telescope (GMRT) in Pune to detect a radio signal originating from atomic hydrogen in an extremely distant galaxy.

“The astronomical distance over which such a signal has been picked up is the largest so far. This is also the first confirmed detection of strong lensing of 21 cm emission from a galaxy, “IISc said. The findings have been published in the Monthly Notices of the Royal Astronomical Society.

Distant galaxy

Using GMRT data, Arnab Chakraborty, postdoctoral researcher at the Department of Physics and Trottier Space Institute of McGill University, and Nirupam Roy, Associate Professor, Department of Physics, IISc have detected a radio signal from atomic hydrogen in a distant galaxy at redshift z=1.29.

“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,” said Chakraborty.

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.

Gravitational lensing

“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,” said Prof Roy.

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.

Challenging task

Yashwant Gupta, Center Director at NCRA, 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 path breaking result with the GMRT, and hope that the same can be confirmed and improved upon in the future.”

The Giant Metrewave Radio Telescope was built and is operated by NCRA-TIFR. The research was funded by McGill and IISc.

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