1999A&A...344...36Y

We present here new flux-calibrated narrow-band images of the circumnuclear region of the Seyfert 2 galaxy Mkn 620 = NGC 2273 in the light of [O III]λ4959Å, [O I]λ6364+[Fe X]λ6374ÅÅ and [N II] λ6548Å emission lines and two continuum images at λ6300Å and λ4260Å, and in a broad band Gunn r continuum. The color map F_λ(6300Å)/F_λ(4260Å) reveals a dusty ring-like structure around the nucleus of Mkn 620. This ring-like structure has a diameter of about 14arcsec corresponding to ≃1700pc. Its mean projected thickness is about 500pc and it is much more prominent in the north-west direction from the nucleus. The dusty ring-like structure surrounds a zone of high ionization which is represented by the [O III]λ4959Åcontour map. The [N II] λ6548Åand [O I]λ6364Åemissions are visible both in the inner high ionized zone and in the outer partially ionized zone (PIZ), which coincides with the dusty ring. Based on the color map F_λ(6300Å)/F_λ(4260Å) we have estimated an extinction of A_V=1.04mag which yields 10⁵M_☉ for the mass of the dust in the ring. This dust mass would be able to produce the observed 12 and 25µm emission if the equilibrium dust temperature T_d is larger than 110K. This value is determined by the equilibrium between the absorbed and emitted energy, assuming thermal dust reemission of the nonthermal AGN continuum. Both larger nonthermal ionizing flux and star formation events in the innermost circumnuclear region could result in higher equilibrium dust temperature T_d . A second dusty ring is clearly seen on the color map. Its radius is ≃20arcsec (2.4kpc) and is approximately placed on the inward side of an ovally distorted disk.