Galaxies Gather at Great Distances
Credit: NASA/JPL-Caltech/ M. Brodwin (JPL)
Credit: NASA/JPL-Caltech/ M. Brodwin (JPL)Across the cosmos, galaxies rarely stand alone. Instead, they are grouped into large, densely populated communities containing thousands of galactic residents, called galaxy clusters.
"Previously, we only knew of a handful of galaxy clusters that existed when our universe was in its first few billion years. Now, thanks to Spitzer's superb sensitivity, we've identified over a hundred," says Dr. Mark Brodwin, of the National Optical Astronomy Observatory, in Tucson, Ariz.
Using Spitzer's substantial sample of distant galaxy clusters, Brodwin and his colleagues were able to conduct a statistical analysis showing that distant galaxy clusters tend to huddle together -- like cosmic urban sprawl with neighborhoods growing together into a larger and larger community.
"The clustering of clusters indicates that these ancient galactic cities are not randomly distributed across space," says Brodwin.
Astronomers have long suspected that the first galaxy clusters grew in very special regions of space, where pockets of hot gas began collecting hundreds of thousands of years after the big bang. The fact that ancient galaxy clusters clump together could be evidence that they formed in such dense regions in the early universe.
Brodwin notes that this observed clumping matches current astronomical theories about galaxy cluster formation. Theory predicted the density of these cosmic cities in the distant past, and the recent measurements of his team have confirmed these predictions.
"This analysis is helping us understand how the largest structures in the universe came to be," says Brodwin.
Brodwin's paper was published in the December 20, 2007 issue of Astrophysical Journal Letters. Co-authors on this paper are Leonidas Moustakas, Peter Eisenhardt, and Daniel Stern, of NASA's Jet Propulsion Laboratory in Pasadena, Calif.; Anthony Gonzalez, of the University of Florida, Gainsville, Fla.; Adam Stanford, of the University of California at Santa Cruz; and Michael Brown of Monash University in Clayton, Australia.
Written by Linda Vu, Spitzer Science Center
*Kitt Peak National Observatory is part of the
National Optical Astronomy Observatory in Tuscon, Ariz.
About this image: Astronomers have discovered nearly 300 galaxy clusters and groups, including almost 100 located 8 to 10 billion light-years away, using the space-based Spitzer Space Telescope and the ground-based Mayall 4-meter telescope at *Kitt Peak National Observatory in Tucson, Ariz. The new sample represents a six-fold increase in the number of known galaxy clusters and groups at such extreme distances, and will allow astronomers to systematically study massive galaxies two-thirds of the way back to the Big Bang.
A mosaic portraying a bird's eye view of the field in which the distant clusters were found is shown at upper left. It spans a region of sky 40 times larger than that covered by the full moon as seen from Earth. Thousands of individual images from Spitzer's infrared array camera instrument were stitched together to create this mosaic. The distant clusters are marked with orange dots.
Close-up images of three of the distant galaxy clusters are shown in the adjoining panels. The clusters appear as a concentration of red dots near the center of each image. These images reveal the galaxies as they were over 8 billion years ago, since that's how long their light took to reach Earth and Spitzer's infrared eyes.
These pictures are false-color composites, combining ground-based optical images captured by the Mosaic-I camera on the Mayall 4-meter telescope at Kitt Peak, with infrared pictures taken by Spitzer's infrared array camera. Blue and green represent visible light at wavelengths of 0.4 microns and 0.8 microns, respectively, while red indicates infrared light at 4.5 microns.
A mosaic portraying a bird's eye view of the field in which the distant clusters were found is shown at upper left. It spans a region of sky 40 times larger than that covered by the full moon as seen from Earth. Thousands of individual images from Spitzer's infrared array camera instrument were stitched together to create this mosaic. The distant clusters are marked with orange dots.
Close-up images of three of the distant galaxy clusters are shown in the adjoining panels. The clusters appear as a concentration of red dots near the center of each image. These images reveal the galaxies as they were over 8 billion years ago, since that's how long their light took to reach Earth and Spitzer's infrared eyes.
These pictures are false-color composites, combining ground-based optical images captured by the Mosaic-I camera on the Mayall 4-meter telescope at Kitt Peak, with infrared pictures taken by Spitzer's infrared array camera. Blue and green represent visible light at wavelengths of 0.4 microns and 0.8 microns, respectively, while red indicates infrared light at 4.5 microns.
*Kitt Peak National Observatory is part of the
National Optical Astronomy Observatory in Tuscon, Ariz.
