A massive project to map a distant region of the Universe in multiple wavelengths--from x-rays through ultraviolet, visible, infrared, and radio waves--is releasing its data this week to both fellow scientists and the general public. It is the first data release from the AEGIS survey and the first release of multiwavelength data to take advantage of the capabilities of Google Sky, a new feature of Google Earth.
AEGIS--the All-wavelength Extended Groth Strip International Survey--combines the efforts of nearly 100 researchers from around the world observing the same small region of sky in all available wavelengths of the electromagnetic spectrum. The target area, called the Extended Groth Strip, covers an area the width of four full moons that is a hop, skip and jump from the end of the Big Dipper's handle. The AEGIS region has now been surveyed more intensively and with more telescopes than any other region of the sky.
"We are still sorting through this treasure trove to discover the many gems of information it contains," said Sandra Faber, University Professor and chair of astronomy and astrophysics at the University of California, Santa Cruz. Faber worked with Jeffrey Newman of the University of Pittsburgh, Shui Kwok of the W. M. Keck Observatory in Hawaii, UCSC graduate student Genevieve Graves, and many other members of the AEGIS team to coordinate the data release through Google Sky.
"It is clear that serving astronomical data through Google Sky is going to revolutionize the way astronomers communicate, both among themselves and with the public," Faber said. "AEGIS is proud and pleased to be the pathfinder dataset for Google Sky's new multiwavelength capabilities."
Featured in this week's release are color images from four different satellite telescopes, as well as numerous data catalogs, from x-ray to radio wavelengths, giving brightnesses and distances of tens of thousands of galaxies. Google Earth's new Sky feature provides a fast and powerful access tool for astronomical data similar to what the popular Google Earth software has provided for terrestrial data.
"AEGIS images projected onto the celestial sphere show how it would look with infrared, ultraviolet, or x-ray eyes," Faber said. "Some galaxies look brighter at certain wavelengths than others, which carries important information about their composition and the processes occurring within them."
The rapid browsing abilities of Google Sky provide a new way to compare many views of a single galaxy or a set of galaxies instantly. For researchers, it is a powerful tool for exploring AEGIS's massive data sets. The AEGIS collaboration is also making all of its data available this week on its web site, so that researchers can download it directly.
Of the four color images in the first AEGIS data release, the most detailed is a visible-light image stitched together from 63 separate pointings of the Hubble Space Telescope. This image forms the base map in Google Sky. Stretching twice the width of the full Moon, it is the largest unbroken color mosaic ever made with Hubble and contains images of approximately 50,000 faraway galaxies. Light has traveled for more than 10 billion years from the most distant ones, giving us pictures of them as they looked long ago, more than three-quarters of the way back to the Big Bang. The exquisite detail of the Hubble images shows infant and adolescent galaxies as they began to form.
The second image shows the same galaxies through the ultraviolet eyes of NASA's Galaxy Evolution Explorer (GALEX) satellite. Ultraviolet wavelengths are shorter and bluer than those of visible light. Massive, hot young stars that are just forming produce ultraviolet light in abundance. Brightness in the GALEX image therefore provides a measure of the rate at which each galaxy is forming stars. Galaxies that contain relatively few hot, young stars or that are obscured by either their own dust or diffuse gas along our line of sight will appear redder in the GALEX image.
The third view is a mosaic of images taken with the Infrared Array Camera on NASA's Spitzer Space Telescope, the last mission in NASA's Great Observatory series. Near-infrared brightness is closely related to the total number of stars in a galaxy, while the colors of a galaxy as seen through infrared eyes reveal information on both its contents (stars and dust) and its distance from us.
The fourth image was produced with data from NASA's Chandra X-ray Observatory. In the objects seen by Chandra, highly energetic x-ray radiation has been produced when gas is spiralling into a supermassive black hole, like those believed to lie at the center of almost every galaxy. Many of the x-ray-emitting objects lie buried within otherwise normal-looking galaxies. In the x-ray images, the bluest objects are the ones most obscured by gas within their host galaxies.
In combination, these images simultaneously measure the sizes and shapes of galaxies, their current rates of star formation, the total number of stars each galaxy has already formed, and the rate at which a black hole at its center is actively accreting matter. All of this information provides separate clues to help scientists understand the evolution of galaxies over the past 10 billion years.
These images from space-based telescopes are tied together by the spectra of nearly 15,000 AEGIS galaxies taken with the Keck II Telescope in Hawaii as part of the DEEP2 Galaxy Redshift Survey, led by Faber and Marc Davis of UC Berkeley. Among other information, these spectra enable astronomers to determine distances to these objects, which is crucial for distinguishing small galaxies in the foreground from giant galaxies that appear faint because they are so far away. Once they have determined the distance to a galaxy, astronomers know how far back in time light left it. The most distant galaxies in the AEGIS survey are seen as they looked only a few billion years after the Big Bang.
With the Sky feature in Google Earth, users can pan and zoom around all of these pictures of the sky to select individual galaxies for closer inspection. By adjusting the transparency of each image, the user can focus on only one of the AEGIS images at a time, or look at a combination (e.g., the GALEX image superimposed on Hubble). Clicking on galaxies in AEGIS catalogs brings up their distances and intrinsic properties. A further mouse click links the user to the Keck spectrum and additional information being used for AEGIS science studies.
"The simple interface of Google Sky provides great power for exploring astronomical images, for scientists as well as the public," Newman said.
The AEGIS data release is featured this week on the Google Earth Gallery. To use the Sky feature, users must have the most recent version of Google Earth (v. 4.2). From the gallery site, click on "Learn more" to find the link to the AEGIS KML file. The KML file and instructions for viewing the AEGIS images are also available on the AEGIS web site.
This first data release from AEGIS is only the first step. Later releases will feature images taken at far-infrared and radio wavelengths. A master catalog is being prepared that combines information from all of AEGIS's many views of the sky. As future images are prepared, they and the growing data catalogs will all be linked through Google Sky.
The AEGIS web site gives more information about the survey, science results to date, and links to additional images and data that can be downloaded. The many windows on the universe provided by AEGIS have already produced a variety of new results on the evolution of galaxies, and many more new findings from the AEGIS team will appear soon, according to Newman.
"With this public release of both interactive images and the underlying data catalogs, the full astronomical community will now be able to take advantage of this powerful new dataset," he said.
The AEGIS teams that contributed images and data for this release include the Hubble team led by Marc Davis of UC Berkeley; the Chandra team lead by Kirpal Nandra of Imperial College, London; the Spitzer team led by Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics; and the GALEX team led by Chris Martin of the California Institute of Technology. Funding for the AEGIS collaboration was provided by the National Science Foundation and NASA.
Note to reporters: You may contact Faber at 831-459-2944 or faber@ucolick.org; and Newman at janewman@pitt.edu or (after October 8) at 412-592-3853.
