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Scientists detect most distant oxygen in ancient galaxy

ALMA has observed the most distant oxygen yet detected in a primordial galaxy.

Astronomers have spotted the furthest known evidence of oxygen in the universe.

According to EurekAlert, an international team of scientists used the Atacama Large Millimeter/submillimeter Array (ALMA) to make the observation.  The oxygen was found in a galaxy called SXDF-NB1006-2, which is one of the most distant known galaxies.  It’s a great distance means that scientists are collecting data on the galaxy as it was only 700 million years after the Big Bang.

The researchers set out to look into the presence of heavy chemical elements that reveal the level of star formation in the galaxy.  Study of such an old galaxy yields insight into the state of the universe during the period known as cosmic reionization.

“Seeking heavy elements in the early universe is an essential approach to explore the star formation activity in that period,” lead author Akio Inoue of Osaka Sangyo University said. “Studying heavy elements also gives us a hint to understand how the galaxies were formed and what caused the cosmic reionization,” he added.

The reionization occurred when the first space objects began to shine, ionizing the previously neutral gas filling the universe.  Exactly what sort of objects kick started the reionization is a mystery, and studies of extremely distant galaxies may offer some clues.

The discovery of ionized oxygen in SXDF-NB1006-2 makes the case that oxygen existed in the universe within 700 million years of its birth.  The amount of oxygen, however, is lower in the distant galaxy than in our own sun.

“The small abundance is expected because the universe was still young and had a short history of star formation at that time,” Naoki Yoshida of the University of Tokyo said. “Our simulation actually predicted an abundance ten times smaller than the Sun. But we have another, unexpected, result: a very small amount of dust.”

The ionized oxygen indicates that many gigantic, bright stars populated the galaxy.  The relative lack of dust allows for the stars’ ultraviolet light to escape and ionize large amounts of gas well beyond the galaxy’s borders.

“Something unusual may be happening in this galaxy,” said Inoue. “I suspect that almost all the gas is highly ionized.”

“This is an important step towards understanding what kind of objects caused cosmic reionization,” Yoichi Tamura of the University of Tokyo said. “Our next observations with ALMA have already started. Higher resolution observations will allow us to see the distribution and motion of ionized oxygen in the galaxy and provide vital information to help us understand the properties of the galaxy.”

The study will appear in the journal Science.