A Young Mammoth Cluster of Galaxies Sighted in the Early Universe

The newly discovered protocluster of galaxies located in the Bootes field of the NOAO Deep Wide-field Survey.. Green circles identify the confirmed cluster members. Density contours (white lines) emphasize the concentration of member galaxies toward the center of the image. The patch of sky shown is roughly 20 arcminutes x 17 arcminutes in size. The cluster galaxies are typically very faint, about 10 million times fainter than the faintest stars visible to the naked eye on a dark night. The inset images highlight two example members that glow in the Ly-alpha line of atomic hydrogen. The protocluster is massive, with its core weighing as much as a quadrillion suns. The protocluster is likely to evolve, over 12 billion years, into a system much like the nearby Coma cluster of galaxies, shown in the image below. Credit: Dr. Rui Xue, Purdue University. Hi-res image

Coma Cluster image from the Sloan Digital Sky Survey
Credit: Dustin Lang and SDSS Collaboration 

Hi-res image

Astronomers have uncovered evidence for a vast collection of young galaxies 12 billion light years away. The newly discovered “proto-cluster” of galaxies, observed when the universe was only 1.7 billion years old (12% of its present age), is one of the most massive structures known at that distance. The discovery, made using telescopes at Kitt Peak National Observatory in Arizona and the W. M. Keck Observatory on Mauna Kea, has been reported in the Astrophysical Journal.

“The protocluster will very likely grow into a massive cluster of galaxies like the Coma cluster, which weighs more than a quadrillion suns,” said Purdue University astrophysicist Dr. Kyoung-Soo Lee, who initially spotted the protocluster and is one of the authors in this study. Clusters this massive are extremely rare: only a handful of candidates are known at such early times. The new system is the first to be confirmed using extensive spectroscopy to establish cluster membership.

The team, led by Dr. Lee (Purdue University) and Dr. Arjun Dey of the National Optical Astronomy Observatory, used the Mayall telescope on Kitt Peak to obtain very deep images of a small patch of sky, about the size of two full moons, in the constellation of Bootes. The team then used the Keck II Telescope on Mauna Kea to measure distances to faint galaxies in this patch, which revealed the large grouping. “Many of the faint galaxies in this patch lie at the same distance,” say Dr. Dey. “They are clumped together due to gravity and the evidence suggests that the cluster is in the process of forming.”

Matter in the universe organizes itself into large structures through the action of gravity. Most stars are in galaxies, which in turn collect in groups and clusters. Galaxy clusters are commonly observed in the present-day universe and contain some of the oldest and most massive galaxies known. The formation and early history of these clusters is not well understood. The discovery of young proto-clusters allows scientists to directly witness and study their formation. The prevalence of massive clusters in the young universe can help constrain the size and expansion history of the universe.

The team is now searching larger areas of sky to uncover more examples of such young and massive protoclusters. “The discovery and confirmation of one distant and very massive protocluster is very exciting,” said Dr. Naveen Reddy, an astrophysicist at the University of California at Riverside and a coauthor of the study, “but it is important to find a large sample of these so we can understand the possibly varied formation history of the population as a whole.”

The other members of the team are Dr. Michael Cooper (University of California, Irvine), Dr. Hanae Inami (Observatoire de Lyon), Dr. Sungryong Hong (University of Texas, Austin), Dr. Anthony Gonzalez (University of Florida), and Dr. Buell Jannuzi (University of Arizona).

Reference: “Spectroscopic Confirmation of a Protocluster at z=3.786,” Arjun Dey, Kyoung-Soo Lee, Naveen Reddy et al., 2016 May 20, Astrophysical Journal

preprint: http://arxiv.org/abs/1604.08627

Kitt Peak National Observatory and the National Optical Astronomy Observatory are operated by the Association of Universities for Research in Astronomy under a Cooperative Agreement with the National Science Foundation. The W. M. Keck Observatory is a scientific partnership between the National Aeronautics and Space Administration, the California Institute of Technology and the University of California, and made possible by the generous financial support of the W. M. Keck Foundation. The research was funded by the National Aeronautics and Space Administration and by NOAO.

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Science Contacts

Dr. Kyoung-Soo Lee
Purdue University
Tel: 765-494-3047
email: soolee@purdue.edu

Dr. Arjun Dey
National Optical Astronomy Observatory
Tel: 520-318-8429
email: dey@noao.edu

Source: National Optical Astronomy Observatory (NOAO)

NASA's Spitzer Sees Light of Lonesome Stars

New research from scientists using NASA's Spitzer Space Telescope suggests that a mysterious infrared glow across our whole sky is coming from stray stars torn from galaxies. When galaxies grow, they merge and become gravitationally tangled in a violent process that results in streams of stars being ripped away from the galaxies. Such streams, called tidal tails, can be seen in this artist's concept. Scientists say that Spitzer is picking up the collective glow of stars such as these, which linger in the spaces between galaxies. Image credit: NASA/JPL-Caltech/UC Irvine .  Full image and caption

The image on the left shows a portion of our sky, called the Boötes field, in infrared light, while the image on the right shows a mysterious, background infrared glow captured by NASA's Spitzer Space Telescope in the same region of sky. Using Spitzer, researchers were able to detect this background glow, which spreads across the whole sky, by masking out light from galaxies and other known sources of light (the masks are the gray, blotchy marks). Image credit: NASA/JPL-Caltech.

Full image and caption -  enlarge image

PASADENA, Calif. - A new study using data from NASA's Spitzer Space Telescope suggests a cause for the mysterious glow of infrared light seen across the entire sky. It comes from isolated stars beyond the edges of galaxies. These stars are thought to have once belonged to the galaxies before violent galaxy mergers stripped them away into the relatively empty space outside of their former homes.

 "The infrared background glow in our sky has been a huge mystery," said Asantha Cooray of the University of California at Irvine, lead author of the new research published in the journal Nature. "We have new evidence this light is from the stars that linger between galaxies. Individually, the stars are too faint to be seen, but we think we are seeing their collective glow."

 The findings disagree with another theory explaining the same background infrared light observed by Spitzer. A group led by Alexander "Sasha" Kashlinsky of NASA's Goddard Space Flight Center in Greenbelt, Md., proposed in June this light, which appears in Spitzer images as a blotchy pattern, is coming from the very first stars and galaxies.

 In the new study, Cooray and colleagues looked at data from a larger portion of the sky, called the Bootes field, covering an arc equivalent to 50 full Earth moons. These observations were not as sensitive as those from the Kashlinsky group's studies, but the larger scale allowed researchers to analyze better the pattern of the background infrared light.

 "We looked at the Bootes field with Spitzer for 250 hours," said co-author Daniel Stern of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Studying the faint infrared background was one of the core goals of our survey, and we carefully designed the observations in order to directly address the important, challenging question of what causes the background glow."

 The team concluded the light pattern of the infrared glow is not consistent with theories and computer simulations of the first stars and galaxies. Researchers say the glow is too bright to be from the first galaxies, which are thought not to have been as large or as numerous as the galaxies we see around us today. Instead, the scientists propose a new theory to explain the blotchy light, based on theories of "intracluster" or "intrahalo" starlight.

 Theories predict a diffuse smattering of stars beyond the halos, or outer reaches, of galaxies, and in the spaces between clusters of galaxies. The presence of these stars can be attributed to two phenomena. Early in the history of our universe as galaxies grew in size, they collided with other galaxies and gained mass. As the colliding galaxies became tangled gravitationally, strips of stars were shredded and tossed into space. Galaxies also grow by swallowing smaller dwarf galaxies, a messy process that also results in stray stars.

 "A light bulb went off when reading some research papers predicting the existence of diffuse stars," Cooray said. "They could explain what we are seeing with Spitzer."

 More research is needed to confirm this sprinkling of stars makes up a significant fraction of the background infrared light. For instance, it would be necessary to find a similar pattern in follow-up observations in visible light. NASA's upcoming James Webb Space Telescope (JWST) might finally settle the matter for good.

 "The keen infrared vision of the James Webb Telescope will be able to see some of the earliest stars and galaxies directly, as well as the stray stars lurking between the outskirts of nearby galaxies," said Eric Smith, JWST's deputy program manager at NASA Headquarters in Washington. "The mystery objects making up the background infrared light may finally be exposed."

 Other authors include Joseph Smidt, Francesco De Bernardis, Yan Gong and Christopher C. Frazer of UC Irvine; Matthew L. N. Ashby of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass; Peter R. Eisenhardt of JPL; Anthony H. Gonzalez of the University of Florida in Gainesville; Christopher S. Kochanek of Ohio State University in Columbus; Szymon Koz?owski of Ohio State and the Warsaw University Observatory in Poland; and Edward L. Wright of the University of California, Los Angeles.

 JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

 For more information about Spitzer, visit: http://www.nasa.gov/spitzer .

Alan Buis 
818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

J.D. Harrington
202-358-5241
NASA Headquarters, Washington
j.d.harrington@nasa.gov