3C48 is a

quasar A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...

discovered in 1960; it was the second source conclusively identified as such. 3C48 was the first source in the

Third Cambridge Catalogue of Radio Sources 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. History 3C The catalogue was published in 1959 by members of the ...

for which an optical identification was found by

Allan Sandage Allan Rex Sandage (June 18, 1926 – November 13, 2010) was an American astronomer. He was Staff Member Emeritus with the Carnegie Observatories in Pasadena, California. He determined the first reasonably accurate values for the Hubble const ...

and Thomas A. Matthews in 1960 through

interferometry Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...

. In 1963 Jesse L. Greenstein and Thomas Matthews found that it had a redshift of 0.367, making it one of the highest redshift sources then known. It was not until 1982 that the surrounding faint galactic "nebulosity" was confirmed to have the same redshift as 3C48, cementing its identification as an object in a distant galaxy. This was also the first solid identification of a quasar with a surrounding galaxy at the same redshift. 3C 48 is one of four primary calibrators used by the

Very Large Array The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory in the southwestern United States built in the 1970s. It lies in central New Mexico on the Plains of San Agustin, between the towns of Magdalena, Ne ...

(along with

3C 138 3C 138 is a quasar located in the constellation of Taurus. It has a redshift of (z) 0.76. The radio spectrum of this source appears both compact and steep, making it a compact steep-spectrum radio quasar. It is also one of the few 3C objects sho ...

and 3C 147, and 3C 286). Visibilities of all other sources are calibrated using observed visibilities of one of these four calibrators.

Nomenclature

The name of the object “3C 48” consists of two significant parts. The first part, “3C,” means that the object belongs to the Third Cambridge Catalog of Radio Sources. The second part - “48” - is the serial number in the catalog ordered by

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...

History

3C 48 was the first source in the Third Cambridge Catalog of Radio Sources to be optically identified by Allan Sandage and Thomas Matthews in 1960 using interferometry. Jesse Greenstein and Thomas Matthews found that it had a redshift of 0.367, one of the highest redshifts of any source known at the time. It was not until 1982 that a surrounding faint galactic "nebula" was measured to have the same redshift as 3C 48, confirming its identification as an object in a distant galaxy. This was also the first reliable identification of a quasar with a surrounding galaxy of the same redshift.

References

{{reflist Quasars 048 Astronomical objects discovered in 1960 Triangulum 073991