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 coming 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.
Although the detection of radio waves with a wavelength of 21 cm, emitted by atomic hydrogen, is possible using low-frequency radio telescopes such as the GMRT, the “extremely weak” nature of the radio signal means that it is almost 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 indicates the lookback time, or the time elapsed between the detection and the original emission; in this case, 4.1 billion years.
Arnab Chakraborty, postdoctoral researcher in the Department of Physics and Trottier Space Institute, McGill University, and Nirupam Roy, associate professor in the Department of Physics, IISc, used GMRT data to detect a radio signal from atomic hydrogen in a galaxy distant 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, resulting in a lookback time of 8.8 billion years.
Atomic hydrogen, formed when hot ionized gas from a galaxy’s surrounding medium falls into the galaxy and cools, and its subsequent change to molecular hydrogen leads to star formation. Studying the evolution of neutral gas, therefore, becomes fundamental 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 detection 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 broadened signal. “In this particular case, the signal magnification was a factor of 30, allowing us to see across the high-redshift universe,” Roy said.
The detection significantly increases the possibilities of observing atomic gas from galaxies at cosmological distances and studying the cosmic evolution of neutral gas with low-frequency radio telescopes.
NCRA center director Yashwant Gupta said the detection of neutral hydrogen in emission from the distant universe was one of the GMRT’s “key science goals.”