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Press release Further scientific description Images and captions In depth technical description Scientific team Contact Information The Canada-France-Hawaii Telescope The DESCART project Another form of gravitational lensing Wide-field imaging at CFHT Press releaseKamuela, Hawaii, March 7, 2000
The 13-member team, headed by Dr. Yannick Mellier of the Institut d'Astrophysique de Paris and the Observatoire de Paris, drew on a wide range of expertise, including cosmology, astrophysics, statistics, data analysis and instrument technology by bringing together researchers from France, Germany, Canada and the United States. The nature of dark matter is one of the greatest unsolved mysteries of modern science. While dark matter makes up at least 90% of the mass of the Universe, both its composition and its distribution are unknown. Knowledge of dark matter is, however, critical to understanding the evolution and fate of the Universe. "In cosmology we develop models to try and understand what processes underlie the evolution of the Universe," explains Dr. Ludovic van Waerbeke of the Canadian Institute for Theoretical Astrophysics in Toronto. "We want to know, for example, how galaxies evolved, why we see great voids in space, what is causing galaxies to cluster in large filaments and sheets." Cosmologists also want models that predict the fate of the Universe. At issue is whether the Universe will expand forever, contract and collapse, or oscillate between expansion and contraction. But without a knowledge of dark matter, the major constituent of the Universe, accurate models are difficult to build. "To build cosmological models we need to have an idea of the total matter content of the Universe," says Dr. Yannick Mellier, the team's leader. "Since somewhere around 90% of this matter is invisible, it's hard for us to get a precise reading on this. Also, to test our models, to see if they accurately describe the Universe we need to look at the results of our simulations against what is actually out there, what astronomers really see." But, says Mellier, up until now astronomers could see the distribution of only 10% of the matter in the Universe, making it difficult to judge the accuracy of different models. To determine the distribution of dark matter, Mellier's team used CFHT's wide-field imaging camera CFH12K, one of the largest in the world, to obtain high-resolution images of a two-square-degree section of sky (10 times the surface of the full moon). Using state-of-the-art image analysis software largely developed at the TERAPIX data analysis and processing center in Paris, the team was able to analyze the light from 200,000 very distant and faint galaxies, looking for the minute distortions that, in theory, should occur as the light passes through the gravitational fields of intervening dark matter. Using this information the team has developed the first ``map'' of dark matter in that area of sky, allowing researchers to visualize how it condensed out of the early universe and distributed itself over the course of time. The analysis has revealed the presence of a vast matrix of interconnected dark matter. The result is not only a significant technological feat, but also a major advance in astronomy and cosmology. According to Dr. Greg Fahlman, Director of the Canada-France-Hawaii Telescope, the results are but a preliminary view of what the future is promising: "By 2002 we will have a new wide-field imaging camera on the telescope that will cover, with improved sensitivity, an area of sky 3 times greater than the current camera. This new instrument will greatly enhance our ability to map the cosmic distribution of dark matter." MegaCam, as the camera is called, will provide astronomers with the data they need to develop significantly more accurate models of the universe. "Our goal," Dr. Fahlman adds, "is to help create the first distribution maps of dark matter across the sky, similar to the distribution maps you currently see for galaxies." Further scientific descriptionObservational discovery of cosmic astigmatism caused by Dark Matter in the UniverseAn international team based in France has announced the first direct detection of the dark matter by measuring the cosmic astigmatism caused by the gravitational lensing effect first noted by Albert Einstein some ninety years ago. Light rays from distant galaxies are slightly deflected by gravity as they pass through and near clumps of dark matter on their way to the Earth. Consequently, the appearance of a distant galaxy is slightly distorted. For the first time, this type of distortion has been detected. Using a series of deep images obtained at the Canada-France-Hawaii Telescope over the past two years (Figure 1), the French team analyzed the shapes of some 200,000 faint galaxies spread over two square degrees of the sky (an area approximately 10 times greater than that of the full moon). They have determined that the galaxies appear to be elongated in a coherent manner over large regions of the sky. The measured effect is small, a percent or so deviation from a purely random distribution of shapes, but the accuracy of the results leaves no doubt that the signal is due to the gravitational lensing effect of the dark matter distribution. These results have been partially confirmed by subsequent reports from two teams, one English and the other American, who have studied different patches of the sky. The measurement of cosmic astigmatism has been the object of a lively international competition. The long term goal is to obtain a detailed map of the large-scale distribution of dark matter. With such a map, our understanding of the evolution of structure in the Universe, which arises from the clumping due to the attractive force of gravity, can be greatly refined. Gravity causes matter to aggregate into long, intersecting filaments surrounded by vast, nearly empty voids (Figures 2 & 3). The precise characterization of these structures by analyzing cosmic astigmatism will reveal the initial conditions that prevailed at the origin of the Universe. Cosmic astigmatism has been studied extensively over the past decade. The predicted signal is so weak that the prospects of a successful detection seemed very poor but the importance of the measurement was too great to simply abandon the effort. In order to mount a comprehensive attack on the problem, a research team assembled by the IAP has put in place a program to fully exploit the new wide-field CCD camera at CFHT. The data analysis was performed at the TERAPIX center for high-capacity data analysis at the IAP, where the statistical methodology has been under development for the past five years. This first observation of the gravitational distortion produced by dark matter is a significant achievement. The result immediately provides some constraints on the amplitude of the dark matter density fluctuations in the early universe but, perhaps more importantly, it demonstrates the feasibility of mapping the dark matter distribution across large areas of the sky. A new instrument for the CFHT known as MegaCam is under construction by the astrophysics group at CEA, HIA in Canada and the CFHT. This camera has a field of view three times larger than the present camera and will be able to map vast regions of the sky. Cosmologists will soon have a tool, unique in world, with which to map the dark matter in the Universe and to understand its evolution. A new window for studying the Universe has been opened. Images and captionsYou can save the images by opening them within the Browser and then using the ``Save As...'' command in the ``File'' menu at the top of the window; or access directly the ``Save Image As...'' function by clicking on the right button while having the mouse cursor positionned on the image. ``[Low res.]'' images are small size (800x800 pixels) high quality JPEG format images while ``[High res.]'' images are large size (2,500x2000 pixels) high quality JPEG format images.
Contact about images: Dr. Jean-Charles Cuillandre Canada-France-Hawaii Telescope Corporation Phone number: 808 885 7944 E-mail: jcc@cfht.hawaii.edu In depth technical descriptionThe following link will take you to the electronic archive and distribution server for research papers (``astro-ph'') where the technical article has been placed. Title: Detection of correlated galaxy ellipticities on CFHT data: first evidence for gravitational lensing by large-scale structures Authors: L. Van Waerbeke (CITA), Y. Mellier (IAP, Obs Paris), T. Erben (MPA), J.-C. Cuillandre (CFHT), F. Bernardeau (CEA Saclay), R. Maoli (IAP), E. Bertin (IAP, Obs Paris), H.J. Mc Cracken (LAS), O. Le Fevre (LAS), B. Fort (IAP), M. Dantel-Fort (Obs Paris), B. Jain (JHU), P. Schneider (MPA) Comments: 18 pages, submitted to ``Astronomy and Astrophysics'' on the 27th Feb. 2000. Accepted for publication 11th April 2000. Scientific TeamThe team responsible for this work consists of: Ludovic Van Waerbeke (1), Yannick Mellier (2,3), Thomas Erben (4), Jean-Charles Cuillandre (5), Francis Bernardeau (6), Roberto Maoli (2), Emmanuel Bertin (2,3), Henry J. Mc Cracken (7), Olivier Le Fevre (7), Bernard Fort (2), Mireille Dantel-Fort (3), Bhuvnesh Jain (8), Peter Schneider (4) 1: Canadian Institute for Theoretical Astrophysics, Toronto, Canada 2: Institut d'Astrophysique de Paris, Paris, France 3: Observatoire de Paris, DEMIRM, Paris, France 4: Max Planck Institut fur Astrophysik, Garching, Germany 5: Canada-France-Hawaii Telescope Corporation, Kamuela, USA 6: Service de Physique Theorique. C.E.A. de Saclay, France 7: Laboratoire d'Astronomie Spatiale, Marseille, France 8: Dept. of Physics, Johns Hopkins University, Baltimore, USA Contact Information
Contact about this web page and images: Dr. Jean-Charles Cuillandre Canada-France-Hawaii Telescope Corporation Phone number: 808 885 7944 E-mail: jcc@cfht.hawaii.edu The Canada-France-Hawaii TelescopeThe Canada-France-Hawaii Telescope is funded through the National Research Council of Canada (NRC), the Centre National de la Reserche Scientifique (CNRS) in France, and the University of Hawaii.The DESCART projectThe Descart project is supported par the Institut National des Sciences de l'Univers of the CNRS and the Programme National de Cosmologie. It has also received support from the Region Ile-de-France through the Centre de Traitement d'Information et de Simulation based at IAP.Another form of gravitational lensingThis recent document featured in ``CFHT's Image of the Week'' introduces to a stronger form of gravitational lensing discovered in the mid 80's: lensing caused by massive clusters of galaxies.Wide-field imaging at CFHTVisit the CFH12K CCD mosaic camera web page to find out more about CFHT's most recent instrument. |