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 distant galaxy 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 galaxies observed when the universe was only a few billion years old and galaxy evolution, Shapley said.

COSMOS-1908 shown above, 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 nearby galaxies. "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 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 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 oxygen. "MOSFIRE made Ryan's measurement possible," said Shapley, who described it as an "amazing instrument."

The galaxy NGC 1291 shown at the top of the page is about 12 billion years. So what's it doing with a ring of newborn stars around it? In this newly released image from NASA's Spitzer Space Telescope, trapped gas at the galaxy's outskirts have triggered star birth.

The Daily Galaxy via UCLA

Related articles

"The Galaxy at the Beginning of the Universe" --Only 670 Million Years After Big Bang

Image of the Day: Galaxies in Collision --Preview of the Milky Way/Andromeda Destiny

NASA's Rebooted K2 Mission Yields 104 New Exoplanets --"A Brilliant Second Life!" - The Daily Galaxy --Great Discoveries Channel

Is Jupiter's Moon Io Poised to Top Its Titanic Surt Volcano Eruption? --"The Most Powerful Ever Observed in Our Solar System" - The Daily Galaxy --Great Discoveries Channel

The Milky Way's Massive Spinning Halo --New Insights

Colossal Void, a Dead Zone Discovered in Heart of the Milky Way --"Requires a Major Revision in Our Thinking"

"Are We Entering the Danger Zone?" The Solar System's 250-Million-Year Orbit Through the Milky Way - The Daily Galaxy --Great Discoveries Channel

Is anybody out there? How would we know? And what happens if there is? In this episode of StarTalk All-Stars,  host Carolyn Porco,  a planetary scientist and imaging team leader for the Cassini mission at Saturn, and her guest Dan Werthimer, principal investigator of the Breakthrough Listen Initiative, answer Cosmic Queries about the search for ET, chosen by co-host Chuck Nice. You'll learn why Breakthrough Listen is the most comprehensive search for extraterrestrial intelligence ever, a new leap forward able to scan 10 times more of the sky and 5 times more of the radio spectrum, with 50 times greater sensitivity than any previous SETI project.

You'll hear about the search for life on the moons of exoplanets, as well as the possibility of microbial life here in our solar system. Explore the difficulties with the Drake Equation, which predicts the likelihood of intelligent alien civilizations, as well as the difficulties of designing instruments and spacecraft to detect life forms that could be quite different from us. Find out what a “second genesis” in our solar system could tell us about the chances for life in the rest of the universe.

Carolyn and Dan discuss the protocols that are in place for responding to an alien signal and ponder an even bigger question: who should speak for Earth if we do make contact? Finally, dive into one of the most controversial issues being debated today: should humanity be broadcasting our existence to the galaxy at large, or is that a recipe for disaster that could end up with humanity's enslavement…or worse?

Listening for Aliens Radio Program

Related articles

"6EQUJ5" --The Signal from Cosmic Depths That Might Have Changed Human Civilization (Best of 2014)

Today's 'Galaxy' Insight --"The Dominant Intelligence in the Universe May Be Non-Biological"

Scientists Shift Search for Alien Technological Civilizations to Ancient Red-Dwarf Stars --"Twice Age of Earth"

Search for Transmissions from Advanced Civilizations --"The Next Ten Years" (Weekend Feature)