AMiBA

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.

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]

Observations

The 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]

Collaboration

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. 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]

References