Exciting recent discoveries in observational and theoretical cosmology have given us a glimpse of new fundamental physics. Our conception of the contents and fate of the Universe is clearer and dramatically different than it was just five years ago. We now believe the Universe is geometrically flat and comprised of ~5% baryons, ~30% dark matter, and ~65% a new form of dark energy. Through a highly interlocking program of observations, sophisticated data analysis, and theory, the researchers involved in this collaborative project expect to expand our knowledge well beyond the capabilities of the current generation of investigations.
A revolution in detector technology, namely thousand-element bolometric arrays, has opened the door to new discoveries about the physical Universe. This group will couple a three-color millimeter camera based on these field-tested arrays to a specialized, 6-meter diameter telescope to be located at an altitude above 5000 m in Chile. Observations with this instrument can map out the formation of cosmic structure from the high-redshift (z > 1000) linear regime through the low-redshift (z < 5) non-linear regime when structures form. Optical spectroscopy with 10-meter class telescopes and measurements with modern X-ray satellites will enable the determination of the redshifts and masses of hundreds of galaxy clusters, the latest stage of cosmic evolution. Through a combination of observations - Cosmic Micowave Background (CMB), optical, X-ray - the researchers will probe the picture of the Universe to greater depths than have yet been plumbed.
Goals of the Atacama Cosmology Telescope (ACT) project are to: 1. Map the CMB temperature anisotropy over 100 square deg, beyond the resolution limits of the WMAP (operating) and Planck (launch 2007) satellites. The primary anisotropy constrains the fundamental physics of the infant Universe and provides the initial conditions for structure formation; the secondary anisotropies reflect the emergence of structure. 2. Find and study galaxy clusters in the CMB map region through the Sunyaev-Zel'dovich effect and determine the spectroscopic redshifts of over 400 of them. The masses of these clusters will be measured with X-ray observations and with galaxy velocity dispersions. 3. Combine the high fidelity CMB map data and the cluster measurements to find the equation of state, w = p/p of the "quintessence" or "dark energy" to +0.1. 4. Limit or determine the mass of the neutrino to +0.1 eV from the combined CMB map and cluster measurements. 5. Use the CMB maps to construct gravitational lensing displacement maps at 0.2 degree resolution, which will probe the total mass distribution directly on length scales of 1 Mpc at z ~ 1 to 2. This technique is independent of and complementary to lower redshift galaxy surveys (which involve bias). 6. Detect reionization of the Universe from the formation of the first stars at z ~ 10 through the Ostriker-Vishniac effect in the CMB.
This research team will conduct a range of activities in education, outreach, and technology transfer in conjunction with the ACT project. One program of special note gives research experience to minority students at City University of New York. Undergraduate and graduate students as well as postdocs will receive advance training through participation in all aspects of the ACT project. Cosmology research captures the public imagination, and the results of this project are expected to generate considerable media attention. Within NSF, the funding partners for the ACT project are the Division of Astronomical Sciences, the Division of Physics, and the Office of Multidisciplinary Activities in the Directorate for Mathematical and Physical Sciences. ***
The Atacama Cosmology Telescope (ACT) is a special purpose instrument designed to measure tiny temperature variations in the thermal afterglow of the Big Bang. From this afterglow, called the cosmic microwave background (CMB), one can determine the composition and evolution of the universe. Through precise measurements it is even possible to probe the physics of the universe back to an age less than 0.0000000000000000000001 seconds. ACT has made significant contributions on all of these fronts, with record sensitivity on a number of the cosmological parameters. ACT is advancing our knowledge of the birth and evolution of the universe. The CMB is most sensitively detected at wavelengths near 1 mm. Water vapor too emits and absorbs radiation at these wavelengths. To separate cosmic from atmospheric contributions to the signal, observations are made from dry locales, balloons, or even satellites. ACT is located at 17,000 feet on the slopes of Cerro Toco in the Atacama Desert in northern Chile. This is one of the highest and driest sites in the world. In addition to measuring the CMB, ACT can detect clusters of galaxies, the largest gravitationally bound objects in the universe. Because of the wavelengths at which the observations are made, ACT can detect clusters to vast distances. We have already discovered over a dozen previously unknown clusters. After the clusters are found, they are followed up with a host of optical and X-ray telescopes to determine their distances and masses. From these combined observations, we are determining how structure in the universe evolved. The ACT project has over seventy team members in over twenty institutes in half a dozen countries. It is a large and vibrant group with specialists in many fields. Education is a core goal of collaboration. Over the past five years we have trained over fifty undergraduates, over thirty graduate students, and over thirty postdocs. A number of postdocs have gone on to faculty positions. We are united by the opportunity to do exciting science.
