Astronomers from Canada, IISc detect signal from distant galaxy

Astronomers from McGill University in Canada and the Indian Institute of Science (IISc) 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 IISc said on Monday that the astronomical distance over which the signal has been picked up is “the largest so far by a large margin”.

The findings have been published in the Monthly Notices of the Royal Astronomical Society.

While detection of radio waves with 21 cm wavelength, emitted by atomic hydrogen, is possible through low-frequency radio telescopes like GMRT, the “extremely weak” nature of the radio signal makes it nearly impossible to detect emissions from a distant galaxy.

The most distant galaxy detected through the 21-cm emission, so far, was at redshift z=0.376.

The value denotes the look-back time, or the time elapsed between the detection and the original emission; in this case, 4.1 billion years.

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, used data from GMRT to detect a radio signal from atomic hydrogen in a distant galaxy at redshift z=1.29.

IISc said in an official statement that the signal was emitted when the universe was only 4.9 billion years old, which translated to a look-back time of 8.8 billion
years.

Atomic hydrogen – formed when hot ionised gas from the surrounding medium of a galaxy falls onto the galaxy, and cools – and its subsequent change into molecular hydrogen leads to the formation of stars. Studying the evolution of neutral gas, therefore, becomes critical in understanding the evolution of galaxies.

The GMRT was built and is operated by National Centre for Radio Astrophysics – Tata Institute of Fundamental Research, Pune. The research was funded by McGill and IISc.

The astronomers traced the detection to a phenomenon called gravitational lensing, which causes the light emitted by the source to bend due to the presence of another massive body, “such as an early type elliptical galaxy,” between the observer and the target galaxy, resulting in a signal that is magnified. “In this specific case, the magnification of the signal was about a factor of 30, allowing us to see through the high redshift universe,” Roy said.

The detection significantly increases possibilities in observing atomic gas from galaxies at cosmological distances and studying the cosmic evolution of neutral gas with low-frequency radio telescopes.

Yashwant Gupta, Centre Director at NCRA, called detection of neutral hydrogen in emission from the distant universe one of GMRT’s “key science goals”.