2014MNRAS.441..630S

The mid-infrared (MIR) spectra observed with Gemini/Michelle have been used to study the nuclear region of the Compton-thick type 2 Seyfert galaxy, Markarian 3 (Mrk 3), at a spatial resolution of ∼ 200 pc. No polycyclic aromatic hydrocarbon emission bands were detected in the N-band spectrum of Mrk 3. However, intense [Ar iii] 8.99 µm, [S iv] 10.5 µm and [Ne ii] 12.8 µm ionic emission lines, as well as a silicate absorption feature at 9.7 µm, have been found in the nuclear extraction ( ∼ 200 pc). We also present a subarcsecond-resolution Michelle N-band image of Mrk 3, which resolves its circumnuclear region. This diffuse MIR emission shows up as a wing towards the east-west direction, closely aligned with the S-shape of the narrow-line region observed in the optical [O iii] λ5007Å image from the Faint Object Camera onboard the Hubble Space Telescope. The nuclear continuum spectrum can be well represented by a theoretical torus spectral energy distribution, suggesting that the nucleus of Mrk 3 might host a dusty toroidal structure, as predicted by the unified model of an active galactic nucleus (AGN). In addition, the hydrogen column density (N_H= 4.8^+3.3_-3.1×10^23/cm2) estimated with a torus model for Mrk 3 is consistent with the value derived from X-ray spectroscopy. The torus model geometry of Mrk 3 is similar to that of NGC 3281 (both are Compton-thick galaxies), confirmed through fitting the 9.7-µm silicate band profile. These results might provide further evidence that silicate-rich dust can be associated with the AGN torus and might also be responsible for the absorption observed at X-ray wavelengths in those galaxies.