In a groundbreaking achievement, an international team of astronomers, led by Suraj Dhiwar, a research scholar at the Inter-University Centre for Astronomy and Astrophysics (IUCAA) Pune, successfully detected ionising photons from a rare type of galaxies known as ‘Lyman Continuum Leakers.’ This milestone was achieved through the use of the Ultraviolet Imaging Telescope (UVIT) onboard the Astro Sat, showcasing the unique capabilities and high sensitivity of the UVIT.
Unveiling the Cosmic Reionisation Era:
The research, published in ‘The Astrophysical Journal Letters,’ sheds light on the cosmic reionisation process that occurred in the first billion years after the Big Bang. During this period, neutral hydrogen atoms underwent a transition, dissociating into protons and electrons due to high-energy UV radiation below wavelengths of 912 Å, known as Lyman Continuum emission. Understanding the sources responsible for this critical cosmic event has been a major challenge in astronomy.
Technical Marvel of UVIT:
The Lyman Continuum emission, crucial for understanding cosmic reionisation, faces absorption or scattering by the interstellar and circumgalactic mediums within host galaxies. Detecting escaping ionising photons from these galaxies proves exceptionally challenging. The UVIT’s resolution and sensitivity played a pivotal role, allowing the creation of a UV deep field in the far ultraviolet filter, making the discovery of Lyman Continuum leakers a rare event in astrophysics.
Key Findings and Significance:
The astronomers discovered ten Lyman Continuum emitting galaxies from the peak era of cosmic star formation history, providing the first coherent sample of Lyman Continuum leakers at this epoch. These galaxies, located approximately eight to nine billion light years away from Earth, exhibit intense star formation rates, with some forming massive young stars at a rate 100 times higher than the Milky Way Galaxy.
Future Implications and Niche in Astrophysics:
Professor Rogier Windhorst emphasized the importance of the discovery, stating, “The discovery would fill an important niche in understanding the evolution of these rare objects, which are at an epoch when the star formation was at its peak in the cosmic star formation history.”
Collaborative Effort and Funding:
Apart from the UV observations from Astro Sat, the Hubble Space Telescope contributed to obtaining optical/infrared imaging and spectroscopy for these galaxies. The research, utilizing deep ultraviolet observations made by Professor Kanak Saha in 2018 using the UVIT onboard the Astro Sat, was funded by the Indian Space Research Organisation (ISRO).
