University of Hertfordshire

From the same journal

From the same journal

By the same authors


  • Leah K. Morabito
  • W. L. Williams
  • Kenneth J. Duncan
  • H.~J.~A. Röttgering
  • George Miley
  • Aayush Saxena
  • Peter Barthel
  • Philip N. Best
  • M. Bruggen
  • G. Brunetti
  • K. T. Chyży
  • D. Engels
  • M. J. Hardcastle
  • J. J. Harwood
  • Matt J. Jarvis
  • E. K. Mahony
  • I. Prandoni
  • Timothy W. Shimwell
  • Alexander Shulevski
  • C. Tasse
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Original languageEnglish
Pages (from-to)1883-1896
JournalMonthly Notices of the Royal Astronomical Society
Journal publication date1 Aug 2017
Early online date21 Apr 2017
StatePublished - 1 Aug 2017


Low radio frequency surveys are important for testing unified models of radio-loud quasars and radio galaxies. Intrinsically similar sources that are randomly oriented on the sky will have different projected linear sizes. Measuring the projected linear sizes of these sources provides an indication of their orientation. Steep-spectrum isotropic radio emission allows for orientation-free sample selection at low radio frequencies. We use a new radio survey of the Bo\"otes field at 150 MHz made with the Low Frequency Array (LOFAR) to select a sample of radio sources. We identify 44 radio galaxies and 16 quasars with powers $P>10^{25.5}$ W Hz$^{-1}$ at 150 MHz using cross-matched multi-wavelength information from the AGN and Galaxy Evolution Survey (AGES), which provides spectroscopic redshifts. We find that LOFAR-detected radio sources with steep spectra have projected linear sizes that are on average 4.4$\pm$1.4 larger than those with flat spectra. The projected linear sizes of radio galaxies are on average 3.1$\pm$1.0 larger than those of quasars (2.0$\pm$0.3 after correcting for redshift evolution). Combining these results with three previous surveys, we find that the projected linear sizes of radio galaxies and quasars depend on redshift but not on power. The projected linear size ratio does not correlate with either parameter. The LOFAR data is consistent within the uncertainties with theoretical predictions of the correlation between the quasar fraction and linear size ratio, based on an orientation-based unification scheme.


This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©:2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


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