Third Cambridge Catalogue of Radio Sources
Encyclopedia
The Third Cambridge Catalogue of Radio Sources (3C) is an astronomical catalogue of celestial radio sources detected originally at 159 MHz, and subsequently at 178 MHz. It was published in 1959 by members of the Radio Astronomy Group
of the University of Cambridge
. References to entries in this catalogue in the scientific literature use the prefix 3C followed by the entry number, with a space, e.g. 3C 273. The catalogue was produced using the Cambridge Interferometer
on the west side of Cambridge
. (The interferometer had previously been used for the 2C survey, published in 1955.)
The catalogue was subsequently revised by Bennett in 1962 using observations at 178 MHz, and for many years '3CR' was considered as the definitive listing of the brighter radio sources in the Northern Hemisphere. The revision resulted in a number of sources being deleted from the catalogue (as being below the flux limit of 9 Jy
or as now-resolved blends of adjacent sources) and others being added. To avoid renumbering the existing sources (which were listed in RA order) these new sources were added using a decimal extension. E.g. 3C 323.1 follows 3C 323 in Right Ascension
and precedes 3C 324.
A further revision by Laing, Riley
and Longair
in 1983, called 3CRR or 3CR², included galaxies which were not detected in the original catalogue due to shortcomings of the original observations, but which otherwise meet the flux and declination limits. This new catalogue, which includes all extragalactic radio sources
with 178-MHz flux density > 10.9 Jy (on the scale of Baars et al.), declination greater than 10 degrees, and Galactic latitude greater than 10 degrees or less than -10 degrees, is formally a complete sample of radio galaxies and radio loud quasar
s. It excludes a number of well known 3C/3CR objects, including, of course, all the supernova remnants from 3C, but also some well-known radio galaxies that fall foul of the declination, flux density or galactic latitude constraints. Objects that had been discovered to consist of multiple components associated with different objects were given an alphabetical suffix (A, B...) to make it clear which component was part of the sample: e.g. the radio galaxy 3C 66B is part of the sample, but the BL Lac object
3C 66A
is not.
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...
of the University of Cambridge
University of Cambridge
The University of Cambridge is a public research university located in Cambridge, United Kingdom. It is the second-oldest university in both the United Kingdom and the English-speaking world , and the seventh-oldest globally...
. References to entries in this catalogue in the scientific literature use the prefix 3C followed by the entry number, with a space, e.g. 3C 273. The catalogue was produced using the Cambridge Interferometer
Cambridge Interferometer
The Cambridge Interferometer was a radio telescope interferometer built by Martin Ryle and Antony Hewish in the early 1950s to the west of Cambridge . The interferometer consisted of an array of 4 fixed elements to survey the sky...
on the west side of 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...
. (The interferometer had previously been used for the 2C survey, published in 1955.)
The catalogue was subsequently revised by Bennett in 1962 using observations at 178 MHz, and for many years '3CR' was considered as the definitive listing of the brighter radio sources in the Northern Hemisphere. The revision resulted in a number of sources being deleted from the catalogue (as being below the flux limit of 9 Jy
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...
or as now-resolved blends of adjacent sources) and others being added. To avoid renumbering the existing sources (which were listed in RA order) these new sources were added using a decimal extension. E.g. 3C 323.1 follows 3C 323 in Right Ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
and precedes 3C 324.
A further revision by Laing, Riley
Julia Riley
Julia M. Riley a Fellow of Girton College, works at the Cavendish Astrophysics Group, University of Cambridge in the area of radio astronomy. In 1974, along with Fanaroff, she wrote a famous paper classifying radio galaxies into two types based on their morphology . These became known as...
and Longair
Malcolm Longair
-External links:...
in 1983, called 3CRR or 3CR², included galaxies which were not detected in the original catalogue due to shortcomings of the original observations, but which otherwise meet the flux and declination limits. This new catalogue, which includes all extragalactic radio sources
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...
with 178-MHz flux density > 10.9 Jy (on the scale of Baars et al.), declination greater than 10 degrees, and Galactic latitude greater than 10 degrees or less than -10 degrees, is formally a complete sample of radio galaxies and radio loud quasar
Quasar
A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
s. It excludes a number of well known 3C/3CR objects, including, of course, all the supernova remnants from 3C, but also some well-known radio galaxies that fall foul of the declination, flux density or galactic latitude constraints. Objects that had been discovered to consist of multiple components associated with different objects were given an alphabetical suffix (A, B...) to make it clear which component was part of the sample: e.g. the radio galaxy 3C 66B is part of the sample, but the BL Lac object
BL Lac object
A BL Lacertae object or BL Lac object is a type of active galaxy with an active galactic nucleus and is named after its prototype, BL Lacertae. In contrast to other types of active galactic nuclei, BL Lacs are characterized by rapid and large-amplitude flux variability and significant optical...
3C 66A
3C 66A
3C 66A is a Blazar located in the constellation Andromeda.The "distance" of a far away galaxy depends on what distance measurement you use. With a redshift of 0.444, light from this active galaxy is estimated to have taken around 4.5 billion years to reach us...
is not.