Finding opens up exciting new possibilities for probing the cosmic evolution of neutral gas with low-frequency radio telescopes
A radio signal originating from atomic hydrogen in an extremely distant galaxy was detected by the Giant Metrewave Radio Telescope (GMRT) located in Pune. This is the largest astronomical distance over which such a signal has been picked up.
The findings have been published in the scientific journal Monthly Notices of the Royal Astronomical Society. Astronomers from McGill University in Canada and the Indian Institute of Science (IISc) in Bengaluru have used data from the telescope to detect atomic hydrogen.
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GMRT is a low-frequency radio telescope that helps investigate various radio astrophysical problems ranging from nearby solar systems to the edge of the observable universe.
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 universe, the gas cools and forms atomic hydrogen. This then becomes molecular hydrogen and eventually leads to the formation of stars.
Understanding the evolution of galaxies over cosmic time requires tracing the evolution of neutral gas at different cosmological periods.
Atomic hydrogen emits radio waves of 21 cm wavelength, meaning the wavelength is a direct tracer of the atomic gas content in nearby and distant galaxies. However, this radio signal is feeble and 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, corresponding to a look-back time – the time elapsed between detecting the signal and its original emission – of 4.1 billion years.
Redshift represents the signal’s wavelength change depending on the object’s location and movement; a greater value of z indicates a farther object.
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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.
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.
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.
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