The Second Cambridge Catalogue of Radio Sources (2C) was published in 1955 by John R Shakeshaft and colleagues. It comprised a list of 1936 sources between declinations -38 and +83, giving their right ascension , declination , both in 1950.0 coordinates, and flux density . The observations were made with the Cambridge Interferometer , at 81.5 MHz.
8-522: The data appeared to show a flux/number (' source counts ') trend which precluded some cosmological models (such as the Steady-State ):- For a uniform distribution of radio sources the slope of the cumulative distribution of log(number, N) versus log (power, S) would have been -1.5, but the Cambridge data apparently implied a (log(N),log(S)) slope of nearly -3.0. Unfortunately, this interpretation
16-508: A 'steady-state Euclidean universe,' would produce a slope of −1.5 in the cumulative distribution of log( N ) versus log( S ). Data from the early Cambridge 2C survey (published 1955) apparently implied a (log( N ), log( S )) slope of nearly −3.0. This appeared to invalidate the steady state theory of Fred Hoyle , Hermann Bondi and Thomas Gold . Unfortunately many of these weaker sources were subsequently found to be due to 'confusion' (the blending of several weak sources in
24-424: Is known as the log N – log S plot. It is one of several cosmological tests that were conceived in the 1930s to check the viability of and compare new cosmological models . Early work to catalogue radio sources aimed to determine the source count distribution as a discriminating test of different cosmological models. For example, a uniform distribution of radio sources at low redshift, such as might be found in
32-425: The 'confusion' (see above) in the later survey. This astronomical catalog article is a stub . You can help Misplaced Pages by expanding it . Source counts The source counts distribution of radio-sources from a radio-astronomical survey is the cumulative distribution of the number of sources ( N ) brighter than a given flux density ( S ). As it is usually plotted on a log-log scale its distribution
40-490: The interferometer records later showed some aspects of the initial interpretation to have been broadly correct, with the correct measure of the (log(N),log(S)) slope of nearly -1.8 derived once confusion was taken into account. The survey was superseded by the much more reliable 3C and 3CR surveys. The 3C survey also used the Cambridge Interferometer, but at 159 MHz, which helped significantly reduce
48-405: The side-lobes of the interferometer, producing a stronger response). By contrast, analysis from the contemporaneous Mills Cross data (by Slee and Mills) were consistent with an index of −1.5. Later and more accurate surveys from Cambridge, 3C, 3CR , and 4C , also showed source count slopes steeper than −1.5, though by a smaller margin than 2C. This convinced some cosmologists that
56-465: The steady state theory was wrong, although residual problems with confusion provided some defense for Hoyle and his colleagues. The immediate interest in testing the steady-state theory through source-counts was reduced by the discovery of the 3K microwave background radiation in the mid-1960s, which essentially confirmed the Big-Bang model. Later radio survey data have shown a complex picture —
64-464: Was premature as a significant number of the sources listed were later found to be the product of 'confusion', the blending of several weaker sources in the lobes of the interferometer to produce the apparent effect of a single stronger source. Key data demonstrating this came from the then-recently commissioned Mills Cross Telescope in Australia. However, subsequent statistical analysis by Hewish of
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