VLA OBSERVATIONS OF THE RADIO GALAXY HYDRA-A (3C 218)

We present multiconfiguration, multifrequency observations of the radio galaxy Hydra A (3C 218) using the VLA. The radio emission of Hydra A consists of two components: (1) a pair of well-collimated, curved jets possessing "S" symmetry, each of which makes a turn through ∼40° between the core and the lobe, and (2) diffuse radio lobes, also rotation-symmetric, although straighter, which extend north out to 5′ (420 kpc) and south out to 3′ (250 kpc). The overall morphology of Hydra A is similar to that of wide-angle tail sources. By combining data taken with the VLA in its A-, B-, C-, and D-configurations, we have made 6 and 2 cm maps with a resolution of 0″.6, allowing for the first time a detailed mapping of the Faraday rotation measure (RM) structure. We find RMs ranging from -1000 to +3300 radians m-2 in the northern lobe with gradients in the RM of up to 1000 radians m-2 arcsec-1. In the southern lobe the gradients in RM are so large that the 6 cm data have been beamwidth-depolarized to less than 2%. This, and the presence of nπ ambiguities in the remaining polarization-angle data, suggest RMs in excess of ±3750 radians m-2, the maximum value that we can unambiguously determine.