Telescopes help identify most distant galaxy cluster
COSMOS-AzTEC3, the most distant massive proto-cluster known, is also one of the youngest.
January 13, 2011
Astronomers have uncovered a burgeoning galactic metropolis, the most distant known in the early universe. This ancient collection of galaxies presumably grew into a modern galaxy cluster similar to the massive ones seen today.
Astronomers have discovered a massive cluster of young galaxies forming in the distant universe. The growing galactic metropolis, named COSMOS-AzTEC3, is the most distant known massive "proto-cluster" of galaxies, lying about 12.6 billion light-years from Earth. Members of the developing cluster are shown here, circled in white. The other dots in this picture are stars or galaxies that are not members of the cluster — most of them are located closer to us than the cluster, but some are farther away. The two brightest spots are stars. Though they appear bright in this image, they are actually tens of thousands of times fainter than what we can see with our eyes. Subaru/NASA/JPL-Caltech
The developing cluster, named COSMOS-AzTEC3, was discovered and characterized by multi-wavelength telescopes, including NASA's Spitzer, Chandra, and Hubble Space telescopes, and the ground-based W.M. Keck Observatory, and Japan's Subaru Telescope.
"This exciting discovery showcases the exceptional science made possible through collaboration among NASA projects and our international partners," said Jon Morse from NASA headquarters in Washington, D.C.
Scientists refer to this growing lump of galaxies as a proto-cluster. COSMOS-AzTEC3 is the most distant massive proto-cluster known, and also one of the youngest, because it is being seen when the universe itself was young. The cluster is roughly 12.6 billion light-years from Earth. Our universe is estimated to be 13.7 billion years old. Previously, more-mature versions of these clusters had been spotted at 10 billion light-years away.
The astronomers also found that this cluster is buzzing with extreme bursts of star formation and one enormous feeding black hole.
"We think the starbursts and black holes are the seeds of the cluster," said Peter Capak of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena. "These seeds will eventually grow into a giant, central galaxy that will dominate the cluster — a trait found in modern-day galaxy clusters.
Most galaxies in our universe are bound together into clusters that dot the cosmic landscape like urban sprawls, usually centered around one old, monstrous galaxy containing a massive black hole. Astronomers thought that primitive versions of these clusters, still forming and clumping together, should exist in the early universe, but locating one proved difficult — until now.
Capak and his colleagues first used the Chandra X-ray Observatory and the United Kingdom's James Clerk Maxwell Telescope on Mauna Kea, Hawaii, to search for the black holes and bursts of star formation needed to form the massive galaxies at the centers of modern galaxy cities. The astronomers then used Hubble and the Subaru telescopes to estimate the distances to these objects and look for higher densities of galaxies around them. Finally, the Keck telescope was used to confirm that these galaxies were at the same distance and part of the same galactic sprawl.
Once the scientists found this lumping of galaxies, they measured the combined mass with the help of Spitzer. At this distance, the optical light from stars is shifted, or stretched, to infrared wavelengths that can only be observed in outer space by Spitzer. The lump sum of the mass turned out to be a minimum of 400 billion Suns — enough to indicate that the astronomers had uncovered a massive proto-cluster. The Spitzer observations also helped confirm a massive galaxy at the center of the cluster was forming stars at an impressive rate.
Chandra X-ray observations were used to find and characterize the whopping black hole with a mass of more than 30 million Suns. Massive black holes are common in present-day galaxy clusters, but this is the first time a feeding black hole of this heft has been linked to a cluster that is so young.
Finally, the Institut de Radioastronomie Millimetrique's interferometer telescope in France and the 30-meter telescope in Spain, along with the National Radio Astronomy Observatory's Very Large Array telescope in New Mexico, measured the amount of gas, or fuel for future star formation, in the cluster. The results indicate the cluster will keep growing into a modern city of galaxies.
"It really did take a village of telescopes to nail this cluster," said Capak. "Observations across the electromagnetic spectrum, from X-ray to millimeter wavelengths, were all critical in providing a comprehensive view of the cluster's many facets."
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