HST and Spitzer point source and dust lane detection in powerful narrow-line radio galaxies

 

Edgar Ramirez (IAG)

 

I will present the analysis of infrared HST and Spitzer data for a sample of 13 FRII powerful radio galaxies at 0.03<z<0.11 that are optically classified as narrow-line radio galaxies (NLRG), under the context of the unified schemes for active galactic nuclei (AGN). Our high resolution infrared observations  provide new information about the degree of extinction induced by the torus, and the incidence of obscured AGN and kpc-scale dust lanes in NLRG.

 

The extinction produced by the obscuring structures has been estimated by five different methods. All the extinction estimates  are consistent, with the exception of those derived from measurements of the 9.7um silicate absorption feature, which are consistently lower. This discrepancy challenges the assumption that all the mid-infrared emission of NLRG is produced by warm, AGN-heated dust in the inner parts of the torus, and that this emission is extinguished by a simple screen of dust at larger radii. In my talk I will give three possible explanations to the disagreement.

 

Furthermore, the higher point-like nucleus detection rate at longer infrared wavelengths that we find in this work supports the idea that a large proportion of NLRG host an obscured AGN in their centre. On the other hand, at 1.025um, we detect kpc-scale dust lanes perpendicular to the inner kpc radio jet axis. Assuming that the torus is perpendicular to the radio jet, this suggests a continuity from the parsec-scale tori to the kpc-scale dust lanes.