Faintest early-universe galaxy ever, detected and confirmed

May 19, 2016 by Steve Jefferson, W. M. Keck Observatory
Color image of the cluster taken with Hubble Space Telescope (images in three different filters were combined to make an RGB image). In the inset we show three spectra of the multiply imaged systems. They have peaks at the same wavelength, hence showing that they belong to the same source. Credit: BRADAC/HST/W. M. KECK OBSERVATORY

An international team of scientists has detected and confirmed the faintest early-Universe galaxy ever using the W. M. Keck Observatory on the summit on Maunakea, Hawaii. In addition to using the world's most powerful telescope, the team relied on gravitational lensing to see the incredibly faint object born just after the Big Bang. The results are being published in The Astrophysical Journal Letters today.

The detected the galaxy as it was 13 billion years ago, or when the Universe was a toddler on a cosmic time scale.

The detection was made using the DEIMOS instrument fitted on the ten-meter Keck II telescope, and was made possible through a phenomenon predicted by Einstein in which an object is magnified by the gravity of another object that is between it and the viewer. In this case, the detected galaxy was behind the galaxy cluster MACS2129.4-0741, which is massive enough to create three different images of the object.

"Keck Observatory's telescopes are simply the best in the world for this work," said Bradac. "Their power, paired with the gravitational force of a massive cluster of galaxies, allows us to truly see where no human has seen before."

"Because you see three of them and the characteristics are exactly the same, that means it was lensed," said Marc Kassis, staff astronomer at Keck Observatory who assists the discovery team at night. "The other thing that is particularly interesting is that it is small. The only way they would have seen it is through lensing. This allowed them to identify it as an ordinary galaxy near the edge of the visible Universe."

"If the light from this galaxy was not magnified by factors of 11, five and two, we would not have been able to see it," said Kuang-Han Huang, a team member from UC Davis and the lead author of the paper. "It lies near the end of the reionization epoch, during which most of the hydrogen gas between galaxies transitioned from being mostly neutral to being mostly ionized (and lit up the stars for the first time). That shows how is important for understanding the faint galaxy population that dominates the reionization photon production."

The galaxy's magnified images were originally seen separately in both Keck Observatory and Hubble Space Telescope data. The team collected and combined all the Keck Observatory/DEIMOS spectra from all three images, confirming they were the same and that this is a triply-lensed system.

"We now have good constraints on when the reionization process ends – at redshift around 6 or 12.5 billion years ago – but we don't yet know a lot of details about how it happened," Huang said. "The galaxy detected in our work is likely a member of the faint galaxy population that drives the reionization process."

"This galaxy is exciting because the team infers a very low stellar mass, or only one percent of one percent of the Milky Way galaxy," Kassis said. "It's a very, very small galaxy and at such a great distance, it's a clue in answering one of the fundamental questions astronomy is trying to understand: What is causing the hydrogen gas at the very beginning of the Universe to go from neutral to ionized about 13 billion years ago. That's when stars turned on and matter became more complex."

The core of the team consisted of Bradac, Huang, Brian Lemaux, and Austin Hoag of UC Davis who are most directly involved with spectroscopic observation and data reduction of galaxies at redshift above seven. Keck Observatory astronomers Luca Rizzi and Carlos Alvarez were instrumental in helping the team collect the DEIMOS data. Tommaso Treu from University of California, Los Angeles and Kasper Schmidt of Leibniz Institute for Astrophysics Potsdam were also part of the team. They lead the effort that obtains and analyzes spectroscopic data from the WFC3/IR grism on Hubble.

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.

DEIMOS (the DEep Imaging and Multi-Object Spectrograph) boasts the largest field of view (16.7 arcmin by 5 arcmin) of any of the Keck instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity.

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

More information: Kuang-Han Huang et al. DETECTION OF LYMAN-ALPHA EMISSION FROM A TRIPLY IMAGED= 6.85 GALAXY BEHIND MACS J2129.4−0741, The Astrophysical Journal (2016). DOI: 10.3847/2041-8205/823/1/L14

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Hyperfuzzy
not rated yet May 25, 2016
Couple of things that don't make any sense. The speed of light is not constant. Any student of algebra can see that the speed of the wavelet is the emitted wavelength divided by the observed period, i.e. CERN no optical connector gives a 2 nanosecond delay and a clear signal, please verify. The expanding universe is expanding given the permittivity of free space and the permeability is not a function of the volume of space. Note. a vacuum holds a few hydrogen molecules per cubic meter. Therefore it is not proven we are expanding, it's a conjecture. I like the idea that nothing is nothing. But does "nothing" exist. Electromagnetic fields are everywhere. Therefore there is a tensor that should describe epsilon and mu. Since we have "mass" as a fundamental unit, suspect this is an error!
Hyperfuzzy
not rated yet May 25, 2016
The effect and the causal effects are two different things, questionable of our correctness. Secondly, if we see to the end of the universe should we see a reflected wave; hence, how would you verify reality? In other words, if space is nothing then the boundary of space will be a discontinuity of nothing. If no reflection then 100% absorption. If absorbed then into what? Or essentially continued transmission and no need to assume anything else but empty space. No room for expansion. Therefore a fundamental property of space, not defined. Makes more sense to explain the signal spread over the volume of space. So the spectrum of many similar objects at various distances should be used to define proper physics without erroneous theory. We must admit, modern physics has too many assumptions without an axiomatic foundation such as a constant speed of light without regard of the differences of the emitter and the receiver.
Hyperfuzzy
not rated yet May 25, 2016
We know the wave is modified by a media, why not "empty" space, which may be considered a media given very large distances. Note: This does not alter Maxwell only our definition of empty space.
Da Schneib
5 / 5 (1) May 26, 2016
The Keck is nice, but it's a bit hyperbolic to claim it's "the world's most powerful telescope" given the VLT at Atacama. Four 8.2 m telescopes form a more powerful array than two 10m telescopes. It's a simple matter of area:

A = πr²

A = 3.14 x 10² = 314 m²
A x 2 = 628 m²

A = 3.14 x 8.2² = 211 m²
A x 4 = 845 m²

The four telescopes of the VLT therefore outperform the Keck pair by a ratio of 4:3 more or less. That's not even taking the variable baseline of the VLT instruments into account.

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