Astronomers make first accurate measurement of oxygen in distant galaxy

August 3, 2016, University of California, Los Angeles
Galaxy COSMOS-1908 is in the center of this Hubble Space Telescope image, indicated by the arrow. Nearly everything in the image is a galaxy; many of these galaxies are much closer to the Earth than COSMOS-1908. Credit: Ryan Sanders and the CANDELS team

UCLA astronomers have made the first accurate measurement of the abundance of oxygen in a distant galaxy. 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 research is published online in the Astrophysical Journal Letters, and is based on data collected at the W. M. Keck Observatory on Mauna Kea, in Hawaii.

"This is by far the most for which the oxygen abundance has actually been measured," said Alice Shapley, a UCLA professor of astronomy, and co-author of the study. "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 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, UCLA researchers used a direct measurement, said Ryan Sanders, astronomy graduate student and the study's lead author.

"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 . "We hope this will be the first of many," he said.

Shapley said that prior to Sanders' discovery researchers didn't know if they could measure how much oxygen there was in these distant galaxies.

"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 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—a ubiquitous phenomenon in the early universe, when the rate of stellar births was dramatically higher than the rate in the universe today; how much of that oxygen gets ejected from the galaxy by so-called "super winds," which propel oxygen and other interstellar gases out of galaxies at hundreds of thousands of miles per hour; and how much pristine gas enters the galaxy from the intergalactic medium, which doesn't contain much oxygen.

"If we can measure how much oxygen is in a galaxy, it will tell us about all these processes," said Shapley, who, along with Sanders, is interested in learning how galaxies form and evolve, why galaxies have different structures, and how galaxies exchange material with their intergalactic environments.

Shapley expects the measurements of oxygen will reveal that super winds are very important in how galaxies evolved. "Measuring the 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 ," she said.

The researchers used an extremely advanced and sophisticated instrument called MOSFIRE (Multi-Object Spectrometer for Infra-Red Exploration) installed on the Keck I telescope at the Keck Observatory. This five-ton instrument was designed to study the most distant, faintest galaxies, said UCLA physics and astronomy professor Ian McLean, project leader on MOSFIRE and director of UCLA's Infrared Laboratory for Astrophysics. McLean built the instrument with colleagues from UCLA, the California Institute of Technology and UC Santa Cruz and industrial sub-contractors.

MOSFIRE collects visible-light photons from objects billions of light years away whose wavelengths have been stretched or "redshifted" to the infrared by the expansion of the universe. Due to the finite speed of light, MOSFIRE is providing a view of these galaxies as they existed billions of years ago, when the light first started traveling to Earth.

MOSFIRE is a type of instrument known as a "spectrograph," which spreads the light from astronomical objects out into a spectrum of separate wavelengths (colors), indicating the specific amount of energy emitted at each wavelength. Spectrographs enable astronomers to determine the chemical contents of galaxies, because different chemical elements—such as oxygen, carbon, iron or hydrogen—each provide a unique spectral fingerprint, emitting light at specific wavelengths.

To characterize the chemical contents of COSMOS-1908, Sanders analyzed a particular wavelength in the MOSFIRE spectrum of this galaxy that is sensitive to the amount of . "MOSFIRE made Ryan's measurement possible," said Shapley, who described it as an "amazing instrument."

Explore further: Metal content in early galaxies challenges star forming theory

More information: "The MOSDEF Survey: Detection of [OIII]4363 and the Direct-Method Oxygen Abundance of a Star-Forming Galaxy at z=3.08," Ryan L. Sanders, Alice E. Shapley et al., 2016, Astrophysical Journal Letters iopscience.iop.org/article/10. … /2041-8205/825/2/L23 , On Arxiv: arxiv.org/abs/1606.04107

Related Stories

Image: Hubble gets in on a galactic gathering

May 30, 2016

Nearly as deep as the Hubble Ultra Deep Field, which contains approximately 10,000 galaxies, this incredible image from the Hubble Space Telescope reveals thousands of colorful galaxies in the constellation of Leo (The Lion). ...

Recommended for you

HESS J1943+213 is an extreme blazar, study finds

June 21, 2018

An international group of astronomers have carried out multi-wavelength observations of HESS J1943+213 and found evidence supporting the hypothesis that this gamma-ray source is an extreme blazar. The finding is reported ...

The Rosetta stone of active galactic nuclei deciphered

June 21, 2018

A galaxy with at least one active supermassive black hole – named OJ 287 – has caused many irritations and questions in the past. The emitted radiation of this object spans a wide range – from the radio up to the highest ...

'Red nuggets' are galactic gold for astronomers

June 21, 2018

About a decade ago, astronomers discovered a population of small, but massive galaxies called "red nuggets." A new study using NASA's Chandra X-ray Observatory indicates that black holes have squelched star formation in these ...

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

wduckss
1 / 5 (4) Aug 04, 2016
"Oxygen, the third-most abundant chemical element in the universe, is created inside stars and released into interstellar gas when stars die."

In our system (real-world) is not so. Oxygen other than in the sun (0.77%) has, and on other bodies that are not stars and they're not dead. (Rhea O2 / CO2 5/2), Europe, 67P / Churyumov-Gerasimenko, ...).
Other important is that the country has 20.95% oxygen (O2), which undoubtedly shows that geological and other processes giving rise occurs O2 are several times higher than on Earth of Sun.
The process of creating elements going up to 89% H 2, He 11%, O2 less than 1%, etc.
ElectricBoobVerses
Aug 04, 2016
This comment has been removed by a moderator.
wduckss
1 / 5 (1) Aug 05, 2016
The winners are those who talk and make money on lies. Truth, therefore, belong to the losers.
This is science?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.