The Atacama Desert in Chile is considered by scientists to be nearly as arid and lifeless as Mars. One of the driest and least hospitable places on Earth, it is chiefly populated by salt lakes, dormant volcanoes and rocks. Within the next five years, however, it will also be home to one of the most powerful astronomical facilities in the world: the Cornell-Caltech Atacama Telescope.
CCAT, a 25-meter class telescope, will give astronomers “a first-hand view of the genesis of structure in the universe,” according to Prof. Riccardo Giovanelli, astronomy,
CCAT will be sensitive to light in the submillimeter, or far-infrared, part of the electromagnetic spectrum, which is generally considered an “unfriendly spectral range” because it is easily affected by water absorption. This makes the high and dry Atacama region ideal for submillimeter astronomy: parts of the desert have gone for centuries without ever seeing rainfall.
“[It] delivers the best skies of all the driest, high-altitude sites on Earth,” Giovanelli said.
CCAT will be built at an altitude of about 18,000 feet, 200 feet below the peak of Cerro Chajnator, a dormant volcano. This is 5,000 feet higher than observatories on Mauna Kea, Hawaii, which currently have the distinction of being the highest telescopes on Earth.
“We’re going higher than anyone else has gone,” Giovanelli said. “Basically, we want to go as high up as you can go by driving a truck.” Why do scientists want to study such an unfriendly part of the spectral domain? According to Giovanelli, CCAT will allow astronomers to see objects up to 13 billion light years away; in other words, objects that started forming only 1 billion years after the Big Bang.
These early objects, the beginnings of what we consider galaxies, formed in regions with a lot of dust. The radiation emitted by the infant galaxies was absorbed by the dust and then reemitted at a longer wavelength. This radiation shifted to longer wavelengths by the expansion of the universe; because these galaxies are moving away from us, the wavelength of the light we see is longer than the original wavelength, in much the same way as a car horn falls in pitch as the car drives away from you. By the time the radiation from these early objects reaches Earth, most of it is in the submillimeter range.
“We have models of how the evolution of galaxies occurred,” Giovanelli said. “This telescope will allow us to see lots of galaxies when they were very young, in the early stages of the universe,” and thereby test the models.
Another advantage that the Atacama Desert will hold for CCAT is the planned presence of a neighboring telescope array, the Atacama Large Millimeter Array (ALMA). CCAT will be an excellent survey instrument, able to scan large portions of the sky and find interesting objects quickly. ALMA will use its 64 telescopes to see the fine structure and details of these and other objects.
“CCAT will be the finder, ALMA will be the refiner,” Giovanelli said. “Having the products of CCAT will give us a very strong leverage arm at ALMA. This is a two-for-one deal.”
According to Prof. Gordon Stacey, astronomy, who heads CCAT’s instrumentation development team, CCAT will be about 15 times more sensitive than the current leaders in submillimeter astronomy. Right now, the best submillimeter telescopes in the world are the Caltech Submillimeter Observatory and the James Clerk Maxwell Telescope, which share space on top of Mauna Kea. The Submillimeter Common User Bolometer Array, the first camera used at the JCMT, only worked at one wavelength: 850 micrometers.
“Working at 850 micrometers is good because you can detect galaxies at all redshifts equally well, but it’s limited because you don’t know what the redshift of each source is,” Stacey said.
CCAT will have two cameras, one which can see in the 200-650 micrometer range and one that can see in the 740 micrometer-2 millimeter range. This will allow astronomers using CCAT to determine the number of galaxies in an area based on their distance from the Earth, and from there, determine how many galaxies existed at a given point in the history of the universe.
“CCAT will go deeper than SCUBA,” Stacey said. “It will go to redshifts at which galaxies are first assembling from protogalaxies.”
Cornell and the California Institute of Technology decided to team up and share responsibility for the $100 million telescope about three years ago. Since then, several other institutions have expressed interest in joining the project, including the University of Colorado, the Consortium of Canadian Universities and the Royal Observatory of Edinburgh. These institutions are expected to sign an agreement with Cornell and Caltech later this month, making CCAT an international endeavor. Giovanelli expects construction on the telescope to begin in about a year.
“If all goes well, by spring 2008, we should expect our institutions to give us a go,” he said.