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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 is known as the log N – log S plot. It is one of several that were conceived in the 1930s to check the viability of and compare new cosmological models. By contrast, analysis from the contemporaneous Mills Cross data (by Slee and Mills) were consistent with an index of −1.5.

Attributes	Values
rdf:type	software
rdfs:label	Source counts (en)
rdfs:comment	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 is known as the log N – log S plot. It is one of several that were conceived in the 1930s to check the viability of and compare new cosmological models. By contrast, analysis from the contemporaneous Mills Cross data (by Slee and Mills) were consistent with an index of −1.5. (en)
dcterms:subject	Physical cosmology
Wikipage page ID	1602252 (xsd:integer)
Wikipage revision ID	987283143 (xsd:integer)
Link from a Wikipage to another Wikipage	Cosmological models Big Bang Tolman surface brightness test Fred Hoyle Thomas Gold Cumulative distribution function Hermann Bondi Radio astronomy Physical cosmology Steady State theory Second Cambridge Catalogue of Radio Sources Third Cambridge Catalogue of Radio Sources Microwave background radiation Fourth Cambridge Catalogue of Radio Sources Mills Cross dbr:Cosmological_test
sameAs	Source counts Source counts Source counts
dbp:wikiPageUsesTemplate	dbt:Reflist
has abstract	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 is known as the log N – log S plot. It is one of several 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 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 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 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 — the 3C and 4C claims appear to hold up, while at fainter levels the source counts flatten substantially below a slope of −1.5. This is now understood to reflect the effects of both density and luminosity evolution of the principal radio sources over cosmic timescales. (en)
gold:hypernym	Distribution
prov:wasDerivedFrom	wikipedia-en:Source_counts?oldid=987283143&ns=0
page length (characters) of wiki page	4059 (xsd:nonNegativeInteger)
foaf:isPrimaryTopicOf	wikipedia-en:Source_counts
is rdfs:seeAlso of	Steady-state model
is Link from a Wikipage to another Wikipage of	Big Bang Arcminute Microkelvin Imager List of space telescopes Index of physics articles (S) Tolman surface brightness test Timeline of telescopes, observatories, and observing technology Cosmic infrared background Second Cambridge Catalogue of Radio Sources Steady-state model Source count Number count
is Wikipage redirect of	Source count Number count
is foaf:primaryTopic of	wikipedia-en:Source_counts

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