First accurate measurement of oxygen in distant galaxy

Astronomers have made the first accurate measurement of the abundance of oxygen in a distant galaxy, an advance that may help better understand evolution of galaxies.
Oxygen, the third-most abundant chemical element in the universe, is created inside stars and released into interstellar gas when stars die.
Quantifying the amount of oxygen is key to understanding how matter cycles in and out of galaxies.
"This is by far the most distant galaxy for which the oxygen abundance has actually been measured. We're looking back in time at this galaxy as it appeared 12 billion years ago," said Alice Shapley, a professor at the University of California, Los Angeles.

Knowing the abundance of oxygen in the galaxy called COSMOS-1908 is an important stepping stone towards allowing astronomers to better understand the population of faint, distant galaxies observed when the universe was only a few billion years old and galaxy evolution, Shapley said.
COSMOS-1908, contains about a billion stars. In contrast, the Milky Way hosts about 100 billion stars. COSMOS-1908 contains approximately only 20 per cent the abundance of oxygen that is observed in the Sun.

Typically, astronomers rely on extremely indirect and imprecise techniques for estimating oxygen abundance for the vast majority of distant galaxies.
However, in this case researchers used a direct measurement, said Ryan Sanders, graduate student at UCLA.

Prior to the discovery, researchers did not know if they could measure how much oxygen there was in these distant galaxies, Shapley said.
The amount of oxygen in a galaxy is determined primarily by three factors: how much oxygen comes from large stars that end their lives violently in supernova explosions, how much of that oxygen gets ejected from the galaxy by so-called "super winds," and how much pristine gas enters the galaxy from the intergalactic medium, which does not contain much oxygen.
Supernova explosions are ubiquitous phenomena in the early universe, when the rate of stellar births was dramatically higher than the rate in the universe today.

On the other hand, "super winds" propel oxygen and other interstellar gases out of galaxies at hundreds of thousands of miles per hour.
"If we can measure how much oxygen is in a galaxy, it will tell us about all these processes," said Shapley.
Shapley expects the measurements of oxygen will unveil that super winds are very important in how galaxies evolved.
"Measuring the oxygen content of galaxies over cosmic time is one of the key methods we have for understanding how galaxies grow, as well as how they spew out gas into the intergalactic medium," she said.
The research was published in the Astrophysical Journal Letters.