Far, far away: A galaxy

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  • Published: Nov 1, 2013
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: Far, far away: A galaxy

Working the night shift

An artist's rendition of the newly discovered most distant galaxy z8-GND-5296. (The galaxy looks red in the actual Hubble Space Telescope image because the collective blue light from stars get shifted toward redder colors due to the expansion of the universe and its large distance from Earth.) Image credit: V. Tilvi, S.L. Finkelstein, C. Papovich, and the Hubble Heritage Team.

Near infra-red has revealed the presence of the most distant galaxy to astronomers at the University of California, Riverside. The light from the galaxy set off on its outward journey a mere 700 million years after the Big Bang, when the universe was just 5 percent of its current age of approximately 13.8 billion years.

Writing in the journal Nature, Keely Finkelstein and Mimi Song of the University of Texas at Austin, Bahram Mobasher and Naveen Reddy of the University of California Riverside and Mark Dickinson of the National Optical Astronomy Observatory, Vithal Tilvi of Texas A&M University, explain how they have identified this ancient galaxy using deep optical and infrared images obtained by the Hubble Space Telescope. The distance to this galaxy was confirmed using observations the terrestrial Keck Telescope in Hawaii.

To spot this ancient galaxy, the astronomers had selected several candidates based on their observed colours, which is indicative of the red shift of the light from those galaxies and as such hints at their age and distance. The team used magnified images from stacks of optical and infrared images taken by the Advanced Camera for Survey (ACS) and Wide-Field Camera 3 (WFC3) on board the Hubble telescope.

Telescopic scanning

They scanned approximately 100,000 galaxies identified in the Hubble Space Telescope images taken as a part of the CANDELS survey. Segregating the distant objects based on colour alone from those nearby objects that might have similar colours for other physical reasons is difficult. Nevertheless, the team found a distinctly red galaxy, currently known as z8-GND-5296, which they suspected would be extremely distant and thus existed at a very early time in the universe's lifetime.

Spectroscopic measurements of the galaxy's red shift provide definitive evidence of its great distance based on hydrogen's Lyman alpha transition. This latest discovery was possible because of a new sensitive, infrared instrument, MOSFIRE, on the Keck Telescope. The instrument can target several objects in the night sky simultaneously, which let the researchers observe 43 galaxy candidates over the course of just two nights and get better data than had been possible in other studies.

"What makes this galaxy unique, compared to other such discoveries, is the spectroscopic confirmation of its distance," explains Mobasher. "By observing a galaxy that far back in time, we can study the earliest formation of galaxies," he explains. "By comparing properties of galaxies at different distances, we can explore the evolution of galaxies throughout the age of the universe."

Star maker

Of the 43 galaxies observed with MOSFIRE, the research team saw the Lyman alpha transition only in one galaxy, z8-GND-5296, which had a red shift of 7.5. The team suggests that this galaxy may have existed at a time 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, the Era of Re-ionization.

The new observations suggest that z8-GND-5296 was forming new stars very rapidly, pulling together about three-hundred times the mass of our own star, the Sun every Earth year. In contrast, the Milky Way generates just two or three new stars annually. This new red shift record holder lies in the same part of the sky as the previous record-holder, which had a red shift of 7.2 but was also a fast star maker.

Austin's Steven Finkelstein led the project and suggests that, "There are many more regions of very high star formation than we previously thought. There must be a decent number of them if we happen to find two in the same area of the sky." The new larger ground-based telescopes, including the Thirty Meter Telescope in Hawaii and the Giant Magellan Telescope in Chile as well as the 6.5-metre James Webb Space Telescope should allow astronomers to find many more as these instruments come online during the next few years. They might even reveal galaxy formation itself if we can look even farther back in time, Mobasher adds.

"The next step is to obtain more spectroscopic observations to confirm more galaxies," Finkelstein told SpectroscopyNOW.

Related Links

Nature, 2013, 502,524-527: "A galaxy rapidly forming stars 700 million years after the Big Bang at redshift 7.51"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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