Rotation Measures in the parsec scale jets of the radio galaxies M 87 , 3 C 111 , and 3 C 120

Parsec scale Faraday rotation measure maps are presented for the radio galaxies M87, 3C 111, and 3C 120. These VLBA observations were made at 8, 12, and 15 GHz. M87 has an extreme RM distribution which varies from −4000 rad m −2 to more than 9000 rad m −2 across a projected distance of 0.3 parsecs in its jet. M87 has no polarized flux closer than 17 mas from the core. 3C 111 and 3C 120 both show polarized emission in their cores which is consistent with the expectations of unified schemes for these broad line radio galaxies. 3C 111 has an RM gradient which increases from ∼ −200 rad m −2 4 mas from the core to ∼ −750 rad m −2 on the side of the jet closest to the core. 3C 120 has a more moderate RM distribution in the jet of approximately 100 rad m −2 but this increases by an order of magnitude in the core.