The C-Band All Sky Survey (C-BASS) is a

radio astronomy Radio astronomy is a subfield of astronomy that studies Astronomical object, celestial objects using radio waves. It started in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observat ...

project that aims to map the entire sky in the C Band (5 GHz). It has been conducted on two

radio telescope A radio telescope is a specialized antenna (radio), antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the r ...

s, one operating in the

Karoo The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe Khoemana (also known as !Orakobab or Korana) word is a semidesert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its extent is ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

, the other at

Owens Valley Radio Observatory Owens Valley Radio Observatory (OVRO) is a radio astronomy observatory located near Big Pine, California (US) in Owens Valley. It lies east of the Sierra Nevada, approximately north of Los Angeles and southeast of Bishop. It was established in 19 ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

Project description

The survey is a collaboration between the

University of Oxford The University of Oxford is a collegiate university, collegiate research university in Oxford, England. There is evidence of teaching as early as 1096, making it the oldest university in the English-speaking world and the List of oldest un ...

University of Manchester The University of Manchester is a public university, public research university in Manchester, England. The main campus is south of Manchester city centre, Manchester City Centre on Wilmslow Road, Oxford Road. The University of Manchester is c ...

, the

California Institute of Technology The California Institute of Technology (branded as Caltech) is a private research university in Pasadena, California, United States. The university is responsible for many modern scientific advancements and is among a small group of institutes ...

, the

Hartebeesthoek Radio Astronomy Observatory The Hartebeesthoek Radio Astronomy Observatory (HartRAO) is a radio astronomy observatory, located in a natural bowl of hills at Hartebeesthoek just south of the Magaliesberg mountain range, and about 50 km west of Johannesburg, Gauteng, Sout ...

(HartRAO), and the

King Abdulaziz City for Science and Technology King Abdulaziz City for Science and Technology (KACST; ) in Riyadh, Saudi Arabia is a governmental organization established in 1977 as the Saudi Arabian National Center for Science & Technology (SANCST; ); in 1985, it was renamed King Abdulaziz ...

. The initial observations were made with two telescopes; one based at the

(OVRO) in

, United States, and the other near the

Meerkat National Park Meerkat National Park is a large South African National Parks, National Park in the Northern Cape, South Africa, that encompasses the Square Kilometre Array's MeerKAT, Precision Array for Probing the Epoch of Reionization, PAPER and Hydrogen ...

in Klerefontein in the

Karoo desert The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe Khoemana (also known as !Orakobab or Korana) word is a semidesert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its extent is ...

.Square Kilometer Array Media Release
, South Africa. For an all sky survey two ground-based telescopes are required, one in the southern and one in the northern hemisphere. C-BASS North was a 6.1m

Gregorian telescope The Gregorian telescope is a type of reflecting telescope designed by Scottish mathematician and astronomer James Gregory in the 17th century, and first built in 1673 by Robert Hooke. James Gregory was a contemporary of Isaac Newton, and both ...

, the dish was donated to the project by the

Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center (FFRDC) in La Cañada Flintridge, California, Crescenta Valley, United States. Founded in 1936 by Cali ...

. C-BASS South is a 7.6-m

Cassegrain telescope The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to th ...

with two antennae donated by

Telkom (South Africa) Telkom SA SOC Limited is a South African wireline and wireless telecommunications provider, operating in more than 38 countries across the African continent. Telkom is majority State-owned enterprise, state-owned (55.3%) with the South African ...

. One was used for testing at Hartebeesthoek and the other relocated to Klerefontein. It was commissioned at

and began survey observations in 2014 when it was deployed in the Karoo. The secondary mirrors on both telescopes were supported by cones of radio-transparent foam to minimize the contamination from ground pick up and to avoid scattering the incoming polarized radiation. The C-BASS North telescope was retired in April 2015 after the initial observing phase was complete. C-BASS South continues to operate as of 2019.

Scientific goals

The survey has mapped not only the intensity but also the orientation of the incoming electromagnetic waves (

polarization Polarization or polarisation may refer to: Mathematics *Polarization of an Abelian variety, in the mathematics of complex manifolds *Polarization of an algebraic form, a technique for expressing a homogeneous polynomial in a simpler fashion by ...

) at every point on the sky with an

angular resolution Angular resolution describes the ability of any image-forming device such as an Optical telescope, optical or radio telescope, a microscope, a camera, or an Human eye, eye, to distinguish small details of an object, thereby making it a major det ...

of 0.73 degrees. The angular resolution represents the smallest details that can be distinguished in the images. This has been the first survey to map the sky at a frequency of 5 GHz—low enough to be

synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in some types ...

dominated but high enough to be relatively unaffected by

Faraday rotation The Faraday effect or Faraday rotation, sometimes referred to as the magneto-optic Faraday effect (MOFE), is a physical magneto-optical phenomenon. The Faraday effect causes a polarization rotation which is proportional to the projection of the ...

. At this frequency most of the signal comes from emissions from high-energy electrons spiralling around magnetic fields in the galaxy. This radiation is highly polarized and a major foreground distorting the

Cosmic Microwave Background The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dar ...

(CMB) signal. The primary scientific goal of the project is to aid in the subtraction of

foreground radiation Foreground and background or background and foreground may refer to: *Background, foreground, sideground and postground intellectual property, distinct forms of intellectual property assets *Background subtraction, a technique in image processing a ...

, mainly from our own galaxy, from measurements of the CMB in order to improve the exactness of the CMB measurements. The CMB is polarized, this polarization can help shed light on

inflation theory In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the very early universe. Following the inflationary period, the universe continued to expand, but at a slower ...

and

gravity waves In fluid dynamics, gravity waves are waves in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere and the oc ...

in the early universe. Secondary goals include studying the

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

s within the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

, the WMAP Haze and

spinning dust In astronomy, spinning dust emission is a mechanism proposed to explain anomalous microwave emission from the Milky Way. The emission could arise from the electric dipole of very rapidly spinning (10–60 GHz) extremely small (nanometer) dus ...

References

{{Portal bar, Astronomy, Stars, Outer space Radio telescopes Educational institutions in the United States with year of establishment missing Organisations associated with the University of Oxford University of Manchester California Institute of Technology Radio astronomy Karoo Collaborative projects Astronomical surveys