When Less Is More: Are Radio Galaxies below the Fanaroff-Riley Break More Polarized on Parsec Scales?

Abstract

We present images showing the first detections of polarization on parsec scales in the nuclei of four Fanaroff-Riley type I (low-luminosity) radio galaxies. Observations with VLBI at lambda = 3.6 cm reveal the presence of ordered magnetic fields within similar to 1650 Schwarzschild radii of the putative central supermassive black hole. The relatively high fractional polarization in the parsec-scale jets of these galaxies is consistent with the standard scheme unifying low-luminosity radio galaxies with BL Lac objects. This result also suggests that these radio galaxies lack the obscuring tori that apparently depolarize the nuclear emission in the more powerful FR II type radio galaxies, and that their supermassive black holes are poorly fed and/or inefficient radiators.