Metal content in early galaxies challenges star forming theory

May 11, 2016, W. M. Keck Observatory
Metal content in early galaxies challenges star forming theory
A galaxy observed in this study (surrounded by a blue rectangle). The light we received from the galaxy in the distant Universe tells us - from hydrogen, oxygen, and neon emission lines - that they followed a different rule to produce the heavy elements. Credit: 3D-HST / NASA / ESA / STSCI

An International team led by scientists at ETH Zurich in Switzerland used the W. M. Keck Observatory to study the role of star formation rates in metal contents of distant galaxies. What they discovered is the amount of metals are very similar, irrespective of galaxies' star formation activity, raising new questions about star-forming theory. Their findings were recently published in the Astrophysical Journal.

Using the MOSFIRE instrument installed on the Keck I telescope – one of the two world's largest optical telescopes at Keck Observatory – the scientists gathered data on 41 normal, star-forming galaxies that were 11 billion light years away.

The team found typical galaxies forming stars in the Universe two billion years after the Big Bang have only twenty percent of metals (elements heavier than Helium) compared with those in the present day Universe. They also discovered the metal content is independent of the strength of the activity – in stark contrast with what is known for recently formed, or .

"The galaxies we studied are very faint because they are so far away that light needs more than 11 billion years to reach us," said Masato Onodera, the lead author of the paper. "Therefore, the superb light-gathering ability of the 10 meter Keck Observatory telescope was crucial to accomplish this study."

Gathering the photons is only part of the job, breaking it down into data that could be analyzed by the team was the job of Keck Observatory's latest instrument, MOSFIRE.

"MOSFIRE allowed us to observe multiple objects simultaneously with an exquisite sensitivity, enabling us to collect spectra of many galaxies very efficiently," he said. "We saw number of spectral features emitted by ionized atoms in the galaxies such as hydrogen, oxygen, and neon, which allowed us to determine the metal content of the galaxies."

A diagram showing the star formation rate (SFR) of distant galaxies (11 billion years ago) and today's galaxies (present) versus their metallicity. The former does not show any distinction in the metallicities with respect to the SFRs, while the latter is divided into two distinct metal contents according to their SFRs. Horizontal axis is the weight of the galaxy in the unit of solar mass. Credit: NAOJ

In addition to the telescope time awarded to them through the California Institute of Technology, the team exchanged valuable time on the 8-meter Subaru Telescope, also on Maunakea, for enough time on Keck Observatory to complete the research.

Metal content in star-forming galaxies is the result of a complex interplay between gas coming into the galaxy, star formation in the galaxy, and gas outflowing from the galaxy in the cosmological context. How much metal is in the system and whether the correlation between the and star formation activity exists provide important clues how galaxy evolve in a distant Universe.

"If you extrapolate what is known in the local Universe, you would have expected a higher metallicity in less active star-forming galaxies than they found," said Hien Tran, staff astronomer at Keck Observatory who was not part of the finding. "It's part of the normal stellar and galaxy evolution. Onodera's team realized the role of star formation is not as strong at great distances as it is at zero. Understanding the interplay between metallicity, star formation rates and the mass of star forming galaxies will help us better understand galaxy evolution."

Because the team did not see any influence of the strength of star formation in the metal enrichment in distant galaxies, it is telling that the physical condition regulating star formation in galaxies in the early Universe is possibly different from that seen in the present-day Universe. This could be related to the fact that cannot keep up with the gas accretion rate from the cosmic web.

The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes near the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrographs and world-leading laser guide star adaptive optics systems.

MOSFIRE (Multi-Object Spectrograph for Infrared Exploration) is a highly efficient instrument that can take images or up to 46 simultaneous spectra. Using a sensitive state-of-the-art detector and electronics system, MOSFIRE obtains observations fainter than any other near infrared spectrograph. MOSFIRE is an excellent tool for studying complex star or galaxy fields, including distant in the early Universe, as well as star clusters in our own Galaxy.

Explore further: Tracing star formation rates in distant galaxies

More information: M. Onodera et al. ISM EXCITATION AND METALLICITY OF STAR-FORMING GALAXIES AT ≃ 3.3 FROM NEAR-IR SPECTROSCOPY , The Astrophysical Journal (2016). DOI: 10.3847/0004-637X/822/1/42 , On Arxiv:

Related Stories

Star formation in distant galaxy clusters

February 15, 2016

The first stars appeared about one hundred million years after the big bang, and ever since then stars and star formation processes have lit up the cosmos, producing heavy elements, planets, black holes, and arguably all ...

Hubble peers at a distinctly disorganized dwarf galaxy

April 4, 2016

Despite being less famous than their elliptical and spiral galactic cousins, irregular dwarf galaxies, such as the one captured in this NASA/ESA Hubble Space Telescope image, are actually one of the most common types of galaxy ...

Neutral hydrogen gas in galaxy clusters

September 9, 2015

Most galaxies are members of a cluster, a grouping of several to thousands of galaxies. Our Milky Way, for example, is a member of the "Local Group," a set of about fifty galaxies whose other large member is the Andromeda ...

Recommended for you

Magnetized inflow accreting to center of Milky Way galaxy

August 17, 2018

Are magnetic fields an important guiding force for gas accreting to a supermassive black hole (SMBH) like the one that our Milky Way galaxy hosts? The role of magnetic fields in gas accretion is little understood, and trying ...

First science with ALMA's highest-frequency capabilities

August 17, 2018

The ALMA telescope in Chile has transformed how we see the universe, showing us otherwise invisible parts of the cosmos. This array of incredibly precise antennas studies a comparatively high-frequency sliver of radio light: ...

Six things about Opportunity's recovery efforts

August 17, 2018

NASA's Opportunity rover has been silent since June 10, when a planet-encircling dust storm cut off solar power for the nearly-15-year-old rover. Now that scientists think the global dust storm is "decaying"—meaning more ...

Another way for stellar-mass black holes to grow larger

August 17, 2018

A trio of researchers with The University of Hong Kong, Academia Sinica Institute of Astronomy and Astrophysics in Taiwan and Northwestern University in the U.S., has come up with an alternative theory to explain how some ...

Sprawling galaxy cluster found hiding in plain sight

August 16, 2018

MIT scientists have uncovered a sprawling new galaxy cluster hiding in plain sight. The cluster, which sits a mere 2.4 billion light years from Earth, is made up of hundreds of individual galaxies and surrounds an extremely ...

Hubble paints picture of the evolving universe

August 16, 2018

Astronomers using the ultraviolet vision of NASA's Hubble Space Telescope have captured one of the largest panoramic views of the fire and fury of star birth in the distant universe. The field features approximately 15,000 ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (7) May 11, 2016
Hopefully this requires another look at O Manuel's Iron Sun theory.

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.