Wednesday, December 21, 2011

Keck & Subaru Telescopes Find Rare Galaxy at Dawn of Time

Images showing the location of GN-108036 in Hubble and Spitzer space telescope images. Credit: NASA / JPL-Caltech / STScI-ESA / Y. Ono (Univ. of Tokyo) and B. Weiner (Univ. of Arizona)

A portion of the Keck DEIMOS spectrum of GN-108036. The red arrow points to what the researchers interpret as a Lyman Alpha emission line at 9985 Angstroms. Since hydrogen actually emits this at 1216 Angstroms, the line in the distant galaxy's spectrum has been shifted far to the red end of the spectrum due to the Doppler shift of light in an expanding universe. The "redshift" of the galaxy is calculated to be 7.2, making it one of the most distant objects ever discovered. Credit: Y. Ono, et al.

Kamuela, HI – Astronomers have spotted one of the most distant galaxies known, churning out stars at a shockingly high rate. The blob-like galaxy, called GN-108036, is located 12.9 billion light-years away from Earth, and is the most luminous galaxy known at that great distance.

The galaxy was first identified by the Subaru telescope and its extreme distance was then carefully confirmed with the Keck II telescope and its DEIMOS instrument (Deep Extragalactic Multi-Object Spectrograph). Both observatories are located on the summit of Mauna Kea, Hawaii. NASA’s Spitzer and Hubble space telescopes were used to measure the galaxy’s high star production rate, equivalent to about 100 suns per year. For comparison, our Milky Way galaxy is about five times larger and a hundred times more massive than GN-108036, but makes new stars roughly 30 times more slowly.

“We’re really surprised to know that GN-108036 is quite luminous in ultraviolet and harbors a powerful star formation,” said astronomer Yoshiaki Ono of the University of Tokyo, Japan. “We had never seen such a vigorously star-forming galaxy at a comparable distance until the discovery of GN-108036.” Ono is the lead author on a paper on the results that is accepted for publication in The Astrophysical Journal. The principal investigator is Masami Ouchi, also at the University of Tokyo.

“The discovery is surprising because previous surveys had not found galaxies this bright that early in the history of the universe,” agreed Mark Dickinson of the National Optical Astronomy Observatory in Tucson. “Perhaps those surveys were just too small to find galaxies like GN-108036. It may be a special, rare object that we just happened to catch during an extreme burst of star formation.”

GN-108036 lies near the very beginning of time itself, a mere 750 million years after our universe was created in an explosive “big bang.” Its light has taken 12.9 billion years to reach us, so we are seeing it as it was in the very distant past.

Astronomers refer to the object’s distance by a number called its “redshift,” which relates to how much its light has stretched to longer, redder wavelengths due to the expansion of the universe. Objects with larger redshifts are farther away and are seen further back in time. GN-108036 has a redshift of 7.2, making it one of only a handful of galaxies have confirmed redshifts greater than 7. Only two others have been reported to be more distant than GN-108036.

During this epoch, as the universe expanded and cooled after its explosive start, hydrogen atoms permeating the cosmos formed a thick fog that was opaque to ultraviolet light. This period, before the first stars and galaxies had formed and illuminated the universe, was known as the “dark ages.” The dark ages came to an end when light from the earliest galaxies burned through, or “ionized”, the opaque gas, causing it to become transparent. Galaxies similar to GN-108036 may have played an important role in this event. The question to be answered now is how many of these galaxies existed back then.

“The high rate of star formation found for GN-108036 implies that it was rapidly building up its mass some 750 million years after the Big Bang, when the universe was only five percent of its present age,” said Bahram Mobasher, a member of the team from the University of California, Riverside. “This was therefore a likely ancestor of massive and evolved galaxies seen today.”

The W. M. Keck Observatory operates two 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Big Island of Hawaii. The twin telescopes feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system which cancels out much of the interference caused by Earth’s turbulent atmosphere. The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.