Evidence for a BL Lac nucleus in Centaurus A⋆

Abstract

We present a detailed ionization map ([OIII]λ;5007/Hα) of the prominent emission- line filaments in the nearby radio galaxy Centaurus A. The map reveals striking ionization structure which, we argue, is best explained by ionizing photons arriving from the direction of the nucleus. This new evidence adds direct support to the conclusion of a recent study that the filaments are photoionized by a powerful radiation beam originating in the nucleus. We suggest that Centaurus A may harbour a misdirected BL Lac object, as predicted by unified schemes relating these objects to a parent population of FR I radio galaxies.