Resolving the nuclear dust distribution of the Seyfert 2 galaxy NGC 3081

Abstract

We report far-infrared (FIR) imaging of the Seyfert 2 galaxy NGC 3081 in the range 70–500 µm, obtained with an unprecedented angular resolution, using the Herschel Space Observatory instruments PACS and SPIRE. The 11 kpc (∼70 arcsec) diameter star-forming ring of the galaxy appears resolved up to 250 µm. We extracted IR (1.6–500 µm) nuclear fluxes, that is active nucleus-dominated fluxes, and fitted them with clumpy torus models, which successfully reproduce the FIR emission with small torus sizes. Adding the FIR data to the near- and mid-IR spectral energy distribution (SED) results in a torus radial extent of Ro= 4+2− 1 pc, as well as in a flat radial distribution of the clouds (i.e. the q parameter). At wavelengths beyond 200 µm, cold dust emission at T= 28 ± 1 K from the circumnuclear star-forming ring of 2.3 kpc (∼15 arcsec) in diameter starts making a contribution to the nuclear emission. The dust in the outer parts of the galaxy is heated by the interstellar radiation field (19 ± 3 K).