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 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.[1]

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[2][3][4] — 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.

See also

References

  1. ^ Kellermann, K. I.; Wall, J. V. (1987). "Radio Source Counts and Their Interpretation". Observational Cosmology: Proceedings of the IAU Symposium, Beijing, People's Republic of China, Aug. 25-30, 1986. Vol. 124. Dordrecht: D. Reidel Publishing Co. pp. 545–564. Bibcode:1987IAUS..124..545K. doi:10.1007/978-94-009-3853-3_56. ISBN 978-90-277-2476-2.
  2. ^ "The FIRST log N - log S".
  3. ^ White, Richard L.; Becker, Robert H.; Helfand, David J.; Gregg, Michael D. (1997). "A Catalog of 1.4 GHz Radio Sources from the FIRST Survey". The Astrophysical Journal. 475 (2): 479. Bibcode:1997ApJ...475..479W. doi:10.1086/303564.
  4. ^ Bengaly, Carlos A. P.; Maartens, Roy; Santos, Mario G. (2018). "Probing the Cosmological Principle in the counts of radio galaxies at different frequencies". Journal of Cosmology and Astro-Particle Physics. 2018 (4): 031. arXiv:1710.08804. Bibcode:2018JCAP...04..031B. doi:10.1088/1475-7516/2018/04/031. S2CID 119182940.

Content Disclaimer

Informasi ini disarikan dari Wikipedia dan disajikan kembali untuk tujuan edukasi. Konten tersedia di bawah lisensi CC BY-SA 3.0. Kami tidak bertanggung jawab atas ketidakakuratan data yang bersumber dari kontribusi publik tersebut.

  1. The information displayed on this website is sourced in part or in whole from Wikipedia and has been adapted for the purpose of restating it. We strive to provide accurate and relevant information, however:
  2. There is no guarantee of absolute accuracy. Wikipedia is an open, collaborative project that can be edited by anyone, so information is subject to change.
  3. It is not intended to constitute professional advice. The content displayed is for informational and educational purposes only. For important decisions (e.g., medical, legal, or financial), please consult a professional.
  4. Content copyright. Wikipedia is licensed under the Creative Commons Attribution-ShareAlike License (CC BY-SA). This means that content may be reused with appropriate attribution and shared under a similar license.
  5. Responsible use. Any risk arising from the use of information from this website is entirely the responsibility of the user.