Arcminute Microkelvin Imager
Encyclopedia
The Arcminute Microkelvin Imager (AMI) consists of a pair of interferometric
radio telescopes
- the Small and Large Arrays - located at the Mullard Radio Astronomy Observatory
near Cambridge
. AMI was designed, built and is operated by the Cavendish Astrophysics Group
. AMI was designed, primarily, for the study of galaxy clusters
by observing secondary anisotropies
in the cosmic microwave background (CMB) arising from the Sunyaev–Zel'dovich (SZ) effect. Both arrays are used to observe radiation
with frequencies
between 12 and 18 GHz
, and have very similar system designs. The telescopes are used to observe both previously known galaxy clusters, in an attempt to determine, for example, their masses
and temperatures
, and to carry out surveys, in order to locate previously undiscovered clusters.
parabolic antennas
, which were previously part of the Ryle Telescope
. The antennas are separated by distances ranging between 18 and 110 m. The telescope has an angular resolution
of approximately 30 arcseconds
. The LA is used to image the radio sources (mainly radio galaxies
) that contaminate the Small Array observations of the CMB. The LA is being used to carry out the Tenth Cambridge Survey of radio sources. The first results from the survey were used to extend the measured 15-GHz source counts
to sub-millijansky
levels; this is an order of magnitude deeper than achieved by the Ninth Cambridge Survey
, which was the first survey of significant sky coverage at a comparable radio frequency.
and anomalous microwave emission
.
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...
radio telescopes
Radio telescope
A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...
- the Small and Large Arrays - located at the Mullard Radio Astronomy Observatory
Mullard Radio Astronomy Observatory
Mullard Radio Astronomy Observatory is home to a number of large aperture synthesis radio telescopes, including the One-Mile Telescope, 5-km Ryle Telescope, and the Arcminute Microkelvin Imager...
near Cambridge
Cambridge
The city of Cambridge is a university town and the administrative centre of the county of Cambridgeshire, England. It lies in East Anglia about north of London. Cambridge is at the heart of the high-technology centre known as Silicon Fen – a play on Silicon Valley and the fens surrounding the...
. AMI was designed, built and is operated by the Cavendish Astrophysics Group
Cavendish Astrophysics Group
The Cavendish Astrophysics Group is based at the Cavendish Laboratory at the University of Cambridge. The group operates all of the telescopes at the Mullard Radio Astronomy Observatory except for the 32m MERLIN telescope, which is operated by Jodrell Bank.The group is the second largest of three...
. AMI was designed, primarily, for the study of galaxy clusters
Galaxy groups and clusters
Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. They form the densest part of the large scale structure of the universe...
by observing secondary anisotropies
Anisotropy
Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
in the cosmic microwave background (CMB) arising from the Sunyaev–Zel'dovich (SZ) effect. Both arrays are used to observe radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
with frequencies
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
between 12 and 18 GHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, and have very similar system designs. The telescopes are used to observe both previously known galaxy clusters, in an attempt to determine, for example, their masses
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
and temperatures
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, and to carry out surveys, in order to locate previously undiscovered clusters.
AMI Large Array
The AMI Large Array (LA) is composed of eight 12.8-metre-diameter, equatorially mountedEquatorial mount
An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras...
parabolic antennas
Parabolic antenna
A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish...
, which were previously part of the Ryle Telescope
Ryle Telescope
The Ryle Telescope was a linear east-west radio telescope array at the Mullard Radio Astronomy Observatory. In 2004 three of the telescopes were moved to create a compact two-dimensional array of telescopes at the east end of the interferometer. The remaining five antennas were switched off on 19...
. The antennas are separated by distances ranging between 18 and 110 m. The telescope has an angular resolution
Angular resolution
Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...
of approximately 30 arcseconds
Minute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....
. The LA is used to image the radio sources (mainly radio galaxies
Radio galaxy
Radio galaxies and their relatives, radio-loud quasars and blazars, are types of active galaxy that are very luminous at radio wavelengths, with luminosities up to 1039 W between 10 MHz and 100 GHz. The radio emission is due to the synchrotron process...
) that contaminate the Small Array observations of the CMB. The LA is being used to carry out the Tenth Cambridge Survey of radio sources. The first results from the survey were used to extend the measured 15-GHz source counts
Source counts
The source counts distribution of radio-sources from a radio-astronomical survey is the cumulative distribution of the number of sources brighter than a given flux density...
to sub-millijansky
Jansky
The flux unit or jansky is a non-SI unit of spectral flux density equivalent to 10−26 watts per square metre per hertz...
levels; this is an order of magnitude deeper than achieved by the Ninth Cambridge Survey
Ninth Cambridge survey at 15GHz
-External links:* on the internet....
, which was the first survey of significant sky coverage at a comparable radio frequency.
AMI Small Array
The AMI Small Array (SA) consists of 10 3.7-m-diameter antennas, similar in design to those of the LA. They are arranged at intervals of between 5 and 20 m. The SA has an angular resolution of approximately 3 arcminutes and is used to image, at high resolution, the galaxy clusters of interest. The SA is being used to search for previously unknown galaxy clusters; results from the first such cluster, detected using AMI, were released in December 2010. In addition to observations of galaxy clusters, the SA has been used to carry out observations, amongst other things, towards supernova remnantsSupernova remnant
A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...
and anomalous microwave emission
Spinning dust
"Spinning dust" or more formally Anomalous Microwave Emission is a galactic emission mechanism proposed to be generated by the electric dipole of very rapidly spinning extremely small dust grains...
.
See also
- South Pole TelescopeSouth Pole TelescopeThe South Pole Telescope is a 10 metre diameter telescope located at the Amundsen-Scott South Pole Station, Antarctica. It is a microwave/millimetre-wave telescope that observes in a frequency range between 70 and 300 GHz...
- Sunyaev-Zel'dovich ArraySunyaev-Zel'dovich ArrayThe Sunyaev–Zel'dovich Array in California is an array of eight 3.5 meter telescopes that is now operating as part of the Combined Array for Research in Millimeter-wave Astronomy . Its initial goals were to survey the Cosmic Microwave Background in order to measure its fine-scale anisotropies...
- Atacama Cosmology TelescopeAtacama Cosmology TelescopeThe Atacama Cosmology Telescope is a six-metre telescope on Cerro Toco in the Atacama Desert in the north of Chile, near the Llano de Chajnantor Observatory. It is designed to make high-resolution, microwave-wavelength surveys of the sky in order to study the cosmic microwave background radiation...