An international team of researchers has detected gas containing oxygen in a galaxy 13.1 billion light years from Earth, providing a glimpse into what the universe was like in ancient times.
The universe we know today is abundant with different chemical elements. But at the beginning of the universe, there was only hot, ionised gas filled with electrons and ions of hydrogen and helium buzzing around. After 400,000 years, the universe cooled, and electrons and hydrogen ions combined to form neutral hydrogen atoms. Nothing more happened for several hundreds of millions of years until the first generation of stars were formed, emitting strong radiation that ionised hydrogen once again, also synthesising other heavier elements such as carbon and oxygen.
Studying these heavy elements from this era provides clues about what triggered reionisation, the nature of the first stars, and how galaxies were born. But studying these elements is extremely difficult because it requires astronomers to find objects as far away as possible, something only possible using the best telescopes available today.
One of these includes the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile. In June 2015, a team of researchers including Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Project Professor Naoki Yoshida, and lead by Osaka Sangyo University Associate Professor Akio Inoue, University of Tokyo Assistant Professor Yoichi Tamura and National Astronomical Observatory of Japan Associate Professor Hiroshi Matsuo, targeted SXDF-NB1006-2, a galaxy discovered in 2012 and confirmed by other telescopes as being the most distant galaxy discovered at the time.
Earlier in 2014, the team had run large-scale numerical simulations of galaxy formation to conclude that the ALMA telescope would be capable of detecting light from ionised oxygen in SXDF-NB1006-2.
As a result, ALMA detected radiation coming from doubly ionised oxygen. From the light’s strength the team also calculated the amount of oxygen in the galaxy is much smaller than that of the Sun.
“Our results showed this galaxy contains one tenth of oxygen found in our Sun. But the small abundance is expected because the universe was still young and had a short history of star formation at that time,” says Yoshida.
The team’s leader Inoue has suggested the lack of dust could be an indication that almost all the gas in the galaxy is highly ionised.
“SXDF-NB1006-2 would be a prototype of the light sources responsible for the cosmic reionisation,” says Inoue.
“This is the first step to understanding what kind of objects caused cosmic reionisation,” adds Tamura.
Work is already underway for another observation using the ALMA telescope, and this time the team hopes to capture a higher resolution image that will reveal details of ionised oxygen gas distribution within the galaxy, and the high-speed motion of the gas.