Thursday, October 24, 2013

Most distant galaxy discovered: 30 billion light years away

October 24, 2013
This image from the Hubble Space Telescope CANDELS survey highlights the most distant galaxy in the universe with a measured distance, dubbed z8_GND_5296 (credit: V. Tilvi, Texas A&M University; S.L. Finkelstein, University of Texas at Austin; C. Papovich, Texas A&M University; CANDELS Team and Hubble Space Telescope/NASA.)
The most distant spectroscopically confirmed galaxy ever found — one created at about 700 million years after the Big Bang — has been detected by astronomers at Texas A&M University and the University of Texas at Austin
“It’s exciting to know we’re the first people in the world to see this,” said Vithal Tilvi, a Texas A&M postdoctoral research associate and co-author of the paper now available online. “It raises interesting questions about the origins and the evolution of the universe.”
Our home galaxy, the Milky Way, creates about one or two Sun-like stars every year or so. But this newly discovered galaxy, known by its catalog name z8_GND_5296, forms around 300 a year. It was observed by the researchers as it was 13 billion years ago. Because the universe has been expanding the whole time, the researchers estimate the galaxy’s present distance to be roughly 30 billion light years away.
“Because of its distance we get a glimpse of conditions when the universe was only about 700 million years old — only 5 percent of its current age of 13.8 billion years,” said Texas A&M astrophysicist Casey Papovich, an associate professor in the Department of Physics and Astronomy and a member of the George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy.
Spectroscopic analysis and red shift to gauge distance
The Nature paper is the result of raw data gleaned from a powerful Hubble Space Telescope imaging survey of the distant universe called CANDELS, or Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. Using that data, the team was armed with 43 potential distant galaxies and set out to confirm their distances.
It was at a redshift 7.51 — or created about 13 billion years ago. Because the universe is expanding, the space between galaxies also is increasing. And as objects move away, they become redder. In essence, the higher the redshift, the farther away the object. Only five other galaxies have ever been confirmed to have a redshift greater than 7, with the previous high being 7.215.
Papovich notes that researchers are also able to accurately gauge the distances of galaxies by measuring a feature from the ubiquitous element hydrogen called the Lyman alpha transition, which emits brightly in distant galaxies. It’s detected in nearly all galaxies that are seen from a time more than one billion years from the Big Bang, but getting closer than that, the hydrogen emission line, for some reason, becomes increasingly difficult to see.
“We were thrilled to see this galaxy,” said the Nature paper’s lead author, Steven Finkelstein, an assistant professor at the University of Texas at Austin and 2011 Hubble Fellow. “And then our next thought was, ‘Why did we not see anything else? We’re using the best instrument on the best telescope with the best galaxy sample. We had the best weather — it was gorgeous. And still, we only saw this emission line from one of our sample of 43 observed galaxies, when we expected to see around six. What’s going on?’”
Two major effects that conceal the rest of the universe
The researchers suspect they may have zeroed in on the era when the universe made its transition from an opaque state in which most of the hydrogen is neutral to a translucent state in which most of the hydrogen is ionized. So it’s not necessarily that the distant galaxies aren’t there. It could be that they’re hidden from detection behind a wall of neutral hydrogen fog, which blocks the hydrogen emission signal.
Tilvi notes this is one of two major changes in the fundamental essence of the universe since its beginning — the other being a transition from a plasma state to a neutral state. He is leading the effort on a follow-up paper that will use a sophisticated statistical analysis to explore that transition further.
“Everything seems to have changed since then,” Tilvi said. “If it was neutral everywhere today, the night sky that we see wouldn’t be as beautiful. What I’m working on is studying exactly why and exactly where this happened. Was this transition sudden, or was it gradual?”
Finkelstein credits technological advancements in recent years for allowing astronomers to probe deeper into space and closer to the Big Bang. For instance, a powerful new spectrometer called MOSFIRE (Multi-Object Spectrometer For Infra-Red Exploration) that is 25 times more light-sensitive than others of its kind was installed at Keck in 2012. And the Hubble Space Telescope is powered by a new near-infrared camera installed by astronauts aboard the Space Shuttle in 2009 that sees farther into the universe.
Ten other international institutions collaborated on the effort, from California to Massachusetts and Italy to Israel.
To learn more about this research, which is supported by NASA through the Hubble Space Telescope Science Institute (STScI), and Texas A&M astronomy, visit

Abstract of Nature paper
Of several dozen galaxies observed spectroscopically that are candidates for having a redshift (z) in excess of seven, only five have had their redshifts confirmed via Lyman α emission, at z = 7.008, 7.045, 7.109, 7.213 and 7.215. The small fraction of confirmed galaxies may indicate that the neutral fraction in the intergalactic medium rises quickly at z > 6.5, given that Lyman α is resonantly scattered by neutral gas. The small samples and limited depth of previous observations, however, makes these conclusions tentative. Here we report a deep near-infrared spectroscopic survey of 43 photometrically-selected galaxies with z > 6.5. We detect a near-infrared emission line from only a single galaxy, confirming that some process is making Lyman α difficult to detect. The detected emission line at a wavelength of 1.0343 micrometres is likely to be Lyman α emission, placing this galaxy at a redshift z = 7.51, an epoch 700 million years after the Big Bang. This galaxy’s colours are consistent with significant metal content, implying that galaxies become enriched rapidly. We calculate a surprisingly high star-formation rate of about 330 solar masses per year, which is more than a factor of 100 greater than that seen in the Milky Way. Such a galaxy is unexpected in a survey of our size9, suggesting that the early Universe may harbour a larger number of intense sites of star formation than expected.

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