Scientists have discovered gases containing oxygen in one of the most distant galaxies in the universe, and their discovery – reported this week in the journal Science – could provide new insight into the nature of the first stars and the birth of the first-ever galaxies.
Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, an international team of researchers led by Osaka Sangyo University associate professor Akio Inoue, University of Tokyo assistant professor Youichi Tamura and National Astronomical Observatory of Japan (NAOJ) associate professor Hiroshi Matsuo began their analysis in June 2015.
Their target was SXDF-NB1006-2, a galaxy discovered in 2012 and later confirmed to be the most distant galaxy detected at the time of its discovery, and their work began following a series of large-scale numerical simulations of galaxy formation where they were able to discover the ALMA telescope could detect light from ionized oxygen there.
A color composite image of a portion of the Subaru XMM-Newton Deep Survey Field. The red galaxy at the center of the image is the most distant galaxy, SXDF-NB1006-2. Credit: NAOJ
While the modern universe has an abundance of different chemical elements, during the earliest stages of the universe, only hot ionized gas filled with electrons and ions of hydrogen and helium existed until the universe started to cool approximately 400,000 years after the Big Bang. At that point, electrons and hydrogen ions combined, forming neutral hydrogen atoms.
Several hundred million years later, the first generation of stars formed, emitting radiation that was strong enough to once again cause hydrogen to be ionized and synthesizing heavier elements such as oxygen and carbon, the study authors explained. Analyzing heavy elements from this era can provide researchers with insight into what caused reionization and led to the formation of the first stars and galaxies, but historically, they have been extremely difficult to study.
Findings could open the door to find the cause of cosmic reionization
Analysis of very young heavy elements, the researchers explained in a statement, requires that astronomers discover objects as far away from Earth as possible. Only the most powerful types of telescopes are capable of such feats; fortunately, ALMA happens to be one such telescope.
In 2014, prior to the official start of their analysis, Inoue, Tamura, Matsuo and their colleagues conducted a series of simulations that confirmed that ALMA would be able to detect light from ionized oxygen in SXDF-NB1006-2, which is 13.1 billion light years from Earth. This indicated that the telescope array was detecting oxygen from doubly-ionized oxygen, and enabled the team to calculate that the galaxy contained just a fraction of the oxygen found in our sun.
“Our results showed this galaxy contains one tenth of oxygen found in our Sun,” co-author and Kavli Institute for the Physics and Mathematics of the Universe professor Naoki Yoshida said in a statement. “But the small abundance is expected because the universe was still young and had a short history of star formation at that time.”
The lack of dust discovered around SXDF-NB1006-2 suggests that the overwhelming majority of the gas located there is highly ionized, and that the galaxy could be “a prototype of the light sources responsible for the cosmic,” said Inoue. Tamur added that the findings are “the first step to understanding what kind of objects caused cosmic reionization.”
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Image credit: NAOJ
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