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The Yuan-Tseh Lee Array for Microwave Background Anisotropy, also known as the Array for Microwave Background Anisotropy (AMiBA), is a radio telescope designed to observe the cosmic microwave background and the Sunyaev-Zel'dovich effect in clusters of galaxies. It is located on Mauna Loa in Hawaii, at 3,396 m above sea level. AMiBA is currently configured as a 7-element interferometer atop a hexapod mount. Observations at a wavelength of 3 mm (86–102 GHz) started in October 2006, and the detections of six clusters by the Sunyaev-Zel'dovich effect were announced in 2008. The telescope will be upgraded to 13 elements by early 2009 and is expandable up to 19 elements. AMiBA is the result of a collaboration between the Academia Sinica Institute of Astronomy and Astrophysics, the National Taiwan University and the Australia Telescope National Facility, and also involves researchers from other universities. [edit] Design AMiBA is currently configured as a 7-element interferometer, using 0.576 m Cassegrain dishes mounted on a 6 m carbon fibre hexapod mount. It is located on Mauna Loa, Hawaii, and observes at 3 mm (86–102 GHz) to minimize foregrounds. The telescope has a retractable shelter, made from seven steel trusses and PVC fabric.[1] The receivers are based on Monolithic Microwave Integrated Circuit (MMIC) technology, with low noise amplifiers cooled to 15 K, which have 20 GHz bandwidths[1] and provide 46 dB of amplification.[2] The signals are mixed with a local oscillator to reduce their frequency, prior to correlation with an analog correlator. The system temperatures are between 55 and 75 K.[1] AMiBA started in 2000, with funding for 4 years from the Cosmology and Particle Astrophysics Project of the Taiwan Ministry of Education.[3] A 2-element prototype was set up on Mauna Loa in 2002.[2] Further funding for a second 4 years was provided by the National Science Council.[3] The mount arrived on site in 2004, and the platform was installed in 2005. The first 7 elements were then installed ("AMiBA7"), and the telescope's first light was in September 2006, observing Jupiter. The telescope was dedicated in October 2006 to Yuan-Tseh Lee. The array will be upgraded to have thirteen 1.2 m dishes by early 2009 ("AMiBA13").[1] It is expandable up to 19 elements.[2] [edit] ObservationsThe primary goal of AMiBA is to observe both the temperature and polarization anisotropies in the Cosmic Microwave Background at multipoles between 800 and 8,000 (corresponding to between 2 and 20 arcminutes on the sky), as well as observing the thermal Sunyaev-Zel'dovich effect in clusters of galaxies,[1] which has a maximum decrement around 100 GHz.[2] In its initial configuration, it measures up to multipoles of 3,000[1] with a resolution of around 6 arcminutes.[4] The telescope only observes at night during good weather, using planets for calibration.[2] Six clusters were imaged in 2007: the Abell clusters 1689, 1995, 2142, 2163, 2261 and 2390,[1] which have redshifts between 0.091 and 0.322.[2] For the largest and brightest four of these—Abell 1689, 2261, 2142 and 2390—comparisons were made with X-ray and Subaru weak lensing data to study the cluster layout and radial properties, specifically of the mass profiles and baryon content.[4] It is predicted that AMiBA with either 13 or 19 elements will be able to detect around 80 clusters per year via the SZ effect.[3] [edit] CollaborationAMiBA is the result of a collaboration between the Academia Sinica Institute of Astronomy and Astrophysics, the National Taiwan University and the Australia Telescope National Facility. It also involves researchers from the Harvard-Smithsonian Center for Astrophysics, the National Radio Astronomy Observatory, the University of Hawaii, the University of Bristol, Nottingham Trent University, the Canadian Institute for Theoretical Astrophysics and the Carnegie-Mellon University.[1] [edit] References
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