Bibcode
Ramos-Almeida, C.; Dicken, D.; Tadhunter, C.; Asensio-Ramos, A.; Inskip, K. J.; Hardcastle, M. J.; Mingo, B.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 413, Issue 4, pp. 2358-2364.
Advertised on:
6
2011
Citations
13
Refereed citations
12
Description
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 0043-42 (z=
0.116) shows a clear spectral turnover at λ≳ 20 μs
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 0043-42 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 (i= 74°) and
relatively broad (σ= 60°), with an outer radius of 2 pc,
NH= 1.6 ±0.20.1×
1023 cm-2, and AGN bolometric luminosity
LAGNbol= 1.6
±0.20.1× 1044 erg
s-1. The presence of a compact torus in PKS 0043-42 provides
evidence that this WLRG is fuelled by cold, rather than hot, gas
accretion. We suggest that WLRGs are a diverse population, and PKS
0043-42 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.
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