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Astron. Astrophys. 344, 36-42 (1999)

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The circumnuclear gas and dust environment of the ringed Seyfert 2 galaxy Mkn 620

I.M. Yankulova

Department of Astronomy, Faculty of Physics, St Kl. Okhridski University of Sofia, 5 James Bourchier Street, BG-1164 Sofia, Bulgaria

Received 23 July 1998 / Accepted 4 January 1999


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 ] [FORMULA] Å, [O I ] [FORMULA] + [Fe X ] [FORMULA] ÅÅ and [N II ] [FORMULA] Å emission lines and two continuum images at [FORMULA]Å and [FORMULA]Å, and in a broad band Gunn r continuum.

The color map [FORMULA] Å[FORMULA] Å[FORMULA] reveals a dusty ring-like structure around the nucleus of Mkn 620. This ring-like structure has a diameter of about 14 arcsec corresponding to [FORMULA] 1700 pc . Its mean projected thickness is about 500 pc 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 ] [FORMULA] Å contour map. The [N II ] [FORMULA] Å and [O I ] [FORMULA] Å emissions 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 [FORMULA] Å[FORMULA] Å[FORMULA] we have estimated an extinction of [FORMULA]1[FORMULA] 04 which yields [FORMULA][FORMULA] for the mass of the dust in the ring. This dust mass would be able to produce the observed 12 and 25 [FORMULA]m emission if the equilibrium dust temperature [FORMULA] is larger than 110 K. 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 [FORMULA].

A second dusty ring is clearly seen on the color map. Its radius is [FORMULA] arcsec (2.4 kpc) and is approximately placed on the inward side of an ovally distorted disk.

Key words: galaxies: individual: Mkn 620 = NGC 2273 – galaxies: ISM – galaxies: Seyfert – galaxies: structure

© European Southern Observatory (ESO) 1999

Online publication: March 10, 1999