High-resolution optical observations compared to radio structure of the jet in M87

Abstract

THE jet in the nearby elliptical galaxy NGC4486 (M87) is a prototype of this kind of nuclear activity¹. High-resolution observations over a wide wavelength range have been used to investigate the propagation of energy along the jet and the radiation mechanism, but these studies have been hampered by the much lower resolution available at optical compared with radio wavelengths. Here we present high-resolution multi-colour images of the jet, obtained using image reconstruction techniques. Morphological features in the jet known from radio observations are seen in our optical images. In particular, we find that the radio-bright 'knots' are spatially extended, and that there is significant emission in the regions between the knots. There is also evidence for limb-brightening at a number of positions along the jet. Taken together, our observations suggest that the jet propagates essentially free of losses, generating radio and optical emission at its edges, where interstellar material may be encountered.