Clear detection of dusty torus signatures in a weak-line radio galaxy: the case of PKS 0043−42.

We report the clearest detection to date of dusty torus signatures in a weak-line radio galaxy (WLRG). The deep Spitzer InfraRed Spectrograph (IRS) rest-frame mid-infrared (MIR) spectrum of the WLRG PKS 42 () shows a clear spectral turnover at s suggestive of warm dust, as well as a 9.7-μm silicate absorption feature. In addition, the hard X-ray results, based on Chandra data, strongly support a picture in which PKS 42 has a torus and accretion disc more typical of strong-line radio galaxies (SLRGs). The MIR and X-ray spectra are markedly different from those of other WLRGs at similar redshifts, and here we show that the former can be successfully fitted with clumpy torus models with parameters characteristic of Type-2 AGN tori: close to edge-on () and relatively broad (), with an outer radius of 2 pc, , and AGN bolometric luminosity . The presence of a compact torus in PKS 42 provides evidence that this WLRG is fuelled by cold, rather than hot, gas accretion. We suggest that WLRGs are a diverse population, and PKS 42 may represent a type of radio galaxy in which the AGN activity has been recently re-triggered as a consequence of intermittent gas supply, or in which the covering factor of the narrow-line region (NLR) clouds is relatively low. [ABSTRACT FROM AUTHOR]