Radio galaxies and their magnetic fields out to z <= 3

Abstract

We present polarisation properties at $1.4$GHz of two separate extragalactic source populations: passive quiescent galaxies and luminous quasar-like galaxies. We use data from the {\it Wide-Field Infrared Survey Explorer} data to determine the host galaxy population of the polarised extragalactic radio sources. The quiescent galaxies have higher percentage polarisation, smaller radio linear size, and $1.4$GHz luminosity of $6\times 10^{21}<L_{1.4}<7\times 10^{25}$W Hz${}^{-1}$, while the quasar-like galaxies have smaller percentage polarisation, larger radio linear size at radio wavelengths, and a $1.4$GHz luminosity of $9\times 10^{23}<L_{1.4}<7\times 10^{28}$W Hz${}^{-1}$, suggesting that the environment of the quasar-like galaxies is responsible for the lower percentage polarisation. Our results confirm previous studies that found an inverse correlation between percentage polarisation and total flux density at $1.4$GHz. We suggest that the population change between the polarised extragalactic radio sources is the origin of this inverse correlation and suggest a cosmic evolution of the space density of quiescent galaxies. Finally, we find that the extragalactic contributions to the rotation measures (RMs) of the nearby passive galaxies and the distant quasar-like galaxies are different. After accounting for the RM contributions by cosmological large-scale structure and intervening Mg\,{II} absorbers we show that the distribution of intrinsic RMs of the distant quasar-like sources is at most four times as wide as the RM distribution of the nearby quiescent galaxies, if the distribution of intrinsic RMs of the WISE-Star sources itself is at least several rad m${}^{-2}$ wide.

12 pages, 8 figures, accepted for publication into MNRAS

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• S-PASS/ATCA: a window on the magnetic universe in the southern hemisphere
• The Magnetic Field and Polarization Properties of Radio Galaxies in Different Accretion States
• A low frequency study of linear polarization in radio galaxies
• Evidence for strong intracluster magnetic fields in the early Universe