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

Abstract

We present polarization properties at 1.4 GHz of two separate extragalactic source populations: passive quiescent galaxies and luminous quasar-like galaxies. We use data from the Wide-Field Infrared Survey Explorer to determine the host galaxy population of the polarized extragalactic radio sources. The quiescent galaxies have higher percentage polarization, smaller radio linear size, and 1.4 GHz luminosity of 6 × 1021 < L1.4 < 7 × 1025 W Hz−1, while the quasar-like galaxies have smaller percentage polarization, larger radio linear size at radio wavelengths, and a 1.4 GHz luminosity of 9 × 1023 < L1.4 < 7 × 1028 W Hz−1, suggesting that the environment of the quasar-like galaxies is responsible for the lower percentage polarization. Our results confirm previous studies that found an inverse correlation between percentage polarization and total flux density at 1.4 GHz. We suggest that the population change between the polarized 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. Show more