Cosmic star-formation history, as traced by radio source evolution.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract / Description of output

I briefly review our current knowledge of the cosmological evolution of radio sources, and show that the redshift distributions of new complete samples of radio sources confirm the existence of the high-redshift decline in comoving number density (or 'cutoff') beyond z similar or equal to 2.5 first deduced by Dunlop & Peacock (1990). Taken at face value these new data favour a luminosity dependent 'cutoff', in which the decline is least drastic for the most luminous radio sources. I demonstrate, however, that regardless of the precise form of radio source evolution, the evolution of radio luminosity density is well determined, and appears essentially identical to the evolution of ultra-violet luminosity density from star-forming galaxies in the universe (e.g. Madau 1997). I convert radio luminosity density into an estimate of black hole fueling rate per Mpc(3), and conclude that radio source evolution is a good tracer of the star-formation history of the Universe; at any epoch, for every 10(7) M-. of material converted into stars, approximately 1 M-. appears to be consumed by radio-loud active galactic nuclei. If this is indeed true at all epochs, then this would imply that star-formation activity in the Universe peaked at z similar or equal to 2 - 2.5, and that the values of star-formation rate density currently derived from Lyman-iimit galaxies at z similar or equal to 2.8 and z similar or equal to 4 are under-estimates by a factor similar or equal to 4. Finally I briefly speculate as to why radio source evolution might trace global star-formation activity as manifested primarily in the disc/spiral population, whereas the hosts of the radio sources themselves generally appear to be well-evolved elliptical galaxies.

Original languageEnglish
Title of host publicationOBSERVATIONAL COSMOLOGY
EditorsMN Bremer, N Jackson, I PerezFournon
Place of PublicationDORDRECHT
Number of pages8
ISBN (Print)0-7923-4885-0
Publication statusPublished - 1998
EventWorkshop on Observational Cosmology with the New Radio Surveys - PUERTO LA CRUZ
Duration: 13 Jan 199715 Jan 1997


ConferenceWorkshop on Observational Cosmology with the New Radio Surveys


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