2016MNRAS.458.4512G

We present far-infrared (FIR) 70-500 µm imaging observations obtained with Herschel/Photodetector Array Camera (PACS) and Spectral and Photometric Imaging REceiver (SPIRE) of 33 nearby (median distance of 30 Mpc) Seyfert galaxies from the Revised Shapley-Ames (RSA) catalogue. We obtain the FIR nuclear (r=1 kpc and r=2 kpc) and integrated spectral energy distributions (SEDs). We estimate the unresolved nuclear emission at 70 µm and we fit the nuclear and integrated FIR SEDs with a grey body model. We find that the integrated FIR emission of the RSA Seyferts in our sample is dominated by emission from the host galaxy, with dust properties similar to those of normal galaxies (non-AGN). We use four criteria to select galaxies whose nuclear 70 µm emission has a significant AGN contribution: (1) elevated 70/160 µm flux ratios, (2) spatially resolved, high dust temperature gradient, (3) 70 µm excess emission with respect to the fit of the FIR SEDs with a grey body, and (4) excess of nuclear SFR obtained from 70 µm over SFR from mid-infrared indicators. 16 galaxies (48 per cent of the initial sample) satisfy at least one of these conditions, whereas 10 satisfy half or more. After careful examination of these, we select six bona fide candidates (18 per cent of the initial sample) and estimate that ∼40-70 per cent of their nuclear (r=1-2 kpc) 70 µm emission is contributed by dust heated by the AGN.