Radio observations of the S0 galaxy NGC 1218 (3C 78)

Abstract

We present VLA observations of the S0 galaxy NGC 1218 at λ20 and 6 cm with both the A and D arrays, at λ20 cm with the B array and at λ2 and 1.3 cm with the A array. They also present VLBI observations at λ6 cm with the European Network. The high-resolution radio observations reveal a flat-spectrum core and a one-sided jet whose width increases with distance from the nucleus. Assuming Faraday rotation to be small at λ6 cm, the magnetic field lines in the outer region of the jet are inclined to its axis and appear to diverge. The large-scale structure does not exhibit well-defined lobes but forms an extended halo with a largely circumferential magnetic field. The authors suggest that the observed one-sidedness of the jet could perhaps be due to a difference in the collimation of the jets on opposite sides of the nucleus, in addition to any possible effects of relativistic beaming.