The depolarisation properties of powerful radio sources: breaking the radio-power vs. redshift degeneracy

Abstract

We define 3 samples of extragalactic radio sources of type FRII, containing 26 objects in total. The control sample consists of 6C and 7C sources with radio powers of around 10e27 W\Hz at 151 MHz and redshifts of around z=1. The other samples contain 3CRR sources with either comparable redshifts but radio powers about a decade larger or with comparable radio powers but redshifts around z = 0.4. We use these samples to investigate the possible evolution of their depolarisation and rotation measure properties with redshift and radio power independently. We used VLA data for all sources at 4800 MHz and two frequencies within the 1400 MHz band, either from our own observations or from the archive. We present maps of the total intensity flux, polarised flux, depolarisation, spectral index, rotation measure and magnetic field direction where not previously published. Radio cores were detected in twelve of the twenty-six radio sources. Fourteen of the sources show a strong Laing-Garrington effect but almost all of the sources show some depolarisation asymmetry. All sources show evidence for an external Faraday screen being responsible for the observed depolarisation. We find that sources at higher redshift are more strongly depolarised. Rotation measure shows no trend with either redshift or radio power, however variations in the rotation measure across individual sources increase with the redshift of the sources but do not depend on their radio power.

21 pages, very low resolution version 33 figures. Accepted to MNRAS. High resolution paper at http://www.astro.soton.ac.uk/~jag/paper.html

References in corpus (12)

• A first sample of faint radio sources with virtually complete redshifts: I. Infrared images, the Hubble diagram, and the alignment effect
• VLA radio continuum observations of a new sample of high redshift radio galaxies
• Quasars in the 2MASS Second Incremental Data Release
• The cluster environments of the z~1 3CR radio galaxies
• A sample of 6C radio sources with virtually complete redshifts. II - optical spectroscopy
• Optical spectroscopy of two overlapping, flux-density-limited samples of radio sources in the North Ecliptic Cap, selected at 38 MHz and 151 MHz
• Radio-quiet quasar environments at 0.5 < z < 0.8
• Deep radio observations of 3C324 and 3C368: evidence for jet-cloud interactions
• Studies of a sample of 6C radio galaxies at redshift one, I -- Deep multi-frequency radio observations
• The Clustering of K\sim 20 Galaxies on 17 Radio Galaxy Fields
• Dust in 3C324
• A Polarization Study of Radio Galaxies and Quasars selected from the Molonglo Complete Sample

Cited by in corpus (11)

• Observed properties of FRII quasars and radio galaxies at z < 1.0
• Parent population of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies
• A Study of 13 Powerful Classical Double Radio Galaxies
• The new sample of giant radio sources III. Statistical trends and correlations
• Dominance of outflowing electric currents on decaparsec to kiloparsec scales in extragalactic jets
• The depolarisation properties of powerful extragalactic radio sources as a function of cosmic epoch
• Evidence for strong intracluster magnetic fields in the early Universe
• A Detailed Study of the Lobes of Eleven Powerful Radio Galaxies
• A Spectropolarimetric Study of Pictor A Radio Galaxy with MeerKAT
• On The Depolarization Asymmetry Seen in Giant Radio Lobes
• Simulations and Observations of the Microwave Universe