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 at which the signal was picked up was “the largest so far by a wide margin”.
The findings are published in Monthly Notices of the Royal Astronomical Society.
While detection of 21 cm wavelength radio waves emitted by atomic hydrogen is possible with low-frequency radio telescopes such as GMRT, the “extremely weak” nature of the radio signal makes it nearly impossible to detect emission from a distant galaxy.
The most distant galaxy detected by the 21 cm beam so far was at redshift z=0.376.
The value indicates the lookback time, or the time elapsed between detection and initial broadcast; in this case 4.1 billion years.
Arnab Chakraborty, postdoctoral researcher in McGill University’s Department of Physics and Trottier Space Institute, and Nirupam Roy, Associate Professor, Department of Physics, IISc, used GMRT data 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, giving a look-back time of 8.8 billion years.
Atomic hydrogen – formed when hot ionized gas from the galactic environment falls on the galaxy and cools – and its subsequent conversion to molecular hydrogen leads to star formation. Therefore, studying the evolution of the neutral gas becomes critical to understanding the evolution of galaxies.
The GMRT was built and operated by the National Center for Radio Astrophysics – Tata Institute of Fundamental Research, Pune. The research was funded by McGill and IISc.
The astronomers traced the discovery to a phenomenon called gravitational lensing, which causes the light emitted by the source to be bent by the presence of another massive body, “like an early-type elliptical galaxy,” between the observer and the target galaxy, resulting in a signal that is increased. “In this particular case, the signal boost was about a factor of 30, which allowed us to see through the high-redshift universe,” Roy said.
The discovery greatly increases the possibilities for observing atomic gas from galaxies at cosmological distances and studying the cosmic evolution of neutral gas with low-frequency radio telescopes.
Yashwant Gupta, director of the center at NCRA, called the detection of neutral hydrogen in emissions from the distant universe one of GMRT’s “key scientific goals.”
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