In a first, oxygen accurately measured in galaxy far, far away

A team of astronomers has made the first accurate measurement of the abundance of oxygen in a distant galaxy.

This UCLA research is based on data collected at the W. M. Keck Observatory on Mauna Kea, in Hawaii.

"This is by far the most distant galaxy for which the oxygen abundance has actually been measured," said co-author Alice Shapley. "We're looking back in time at this galaxy as it appeared 12 billion years ago."

Knowing the abundance of oxygen in the galaxy called COSMOS-1908 is an important stepping stone toward 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 approximately 1 billion stars. In contrast, the Milky Way contains approximately 100 billion stars; some galaxies in the universe contain many more, while others contain many fewer. Furthermore, COSMOS-1908 contains approximately only 20 percent 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. But in this case, researchers used a direct measurement, said lead author Ryan Sanders.

"Close galaxies are much brighter, and we have a very good method of determining the amount of oxygen in nearby galaxies," Sanders said. In faint, distant galaxies, the task is dramatically more difficult, but COSMOS-1908 was one case for which Sanders was able to apply the "robust" method commonly applied to nearby galaxies. "We hope this will be the first of many," he said.

"Ryan's discovery shows we can measure the oxygen and compare these observations with models of how galaxies form and what their history of star formation is," Shapley said.

The study is published online in the Astrophysical Journal Letters.