Radio imaging of the Subaru/XMM-NewtonDeep Field- III. Evolution of the radio luminosity function beyond z = 1

Chris Simpson, Steve Rawlings, Rob Ivison, Masayuki Akiyama, Omar Almaini, Emma Bradshaw, Scott Chapman, Rob Chuter, Scott Croom, Jim Dunlop, Sébastien Foucaud, Will Hartley

Research output: Contribution to journalArticlepeer-review

101 Citations (Scopus)


We present spectroscopic and 11-band photometric redshifts for galaxies in the 100-μJy Subaru/XMM-NewtonDeep Field radio source sample. We find good agreement between our redshift distribution and that predicted by the Square Kilometre Array (SKA) Simulated Skies project. We find no correlation between K-band magnitude and radio flux, but show that sources with 1.4-GHz flux densities below ∼1mJy are fainter in the near-infrared than brighter radio sources at the same redshift, and we discuss the implications of this result for spectroscopically incomplete samples where the K-z relation has been used to estimate redshifts. We use the infrared-radio correlation to separate our sample into radio-loud and radio-quiet objects and show that only radio-loud hosts have spectral energy distributions consistent with predominantly old stellar populations, although the fraction of objects displaying such properties is a decreasing function of radio luminosity. We calculate the 1.4-GHz radio luminosity function (RLF) in redshift bins to z= 4 and find that the space density of radio sources increases with lookback time to z≈ 2, with a more rapid increase for more powerful sources. We demonstrate that radio-loud and radio-quiet sources of the same radio luminosity evolve very differently. Radio-quiet sources display strong evolution to z≈ 2 while radio-loud active galactic nuclei below the break in the RLF evolve more modestly and show hints of a decline in their space density at z > 1, with this decline occurring later for lower-luminosity objects. If the radio luminosities of these sources are a function of their black hole spins then slowly rotating black holes must have a plentiful fuel supply for longer, perhaps because they have yet to encounter the major merger that will spin them up and use the remaining gas in a major burst of star formation.

Original languageEnglish
Pages (from-to)3060-3083
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 2012 Apr


  • Galaxies: active
  • Galaxies: distances and redshifts
  • Galaxies: evolution
  • Radio continuum: galaxies
  • Surveys


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