Optical colour maps of Seyfert galaxies

¹ Tuorla Observatory, University of Turku, Väisäläntie 20, FIN–21500 Piikkiö, Finland
² International School for Advanced Studies (ISAS/SISSA), via Beirut 2-4, I-34014 Trieste, Italy e-mail: jkotilai@sissa.it
³ Astrophysics, Nuclear Physics Building, Keble Road, Oxford OX1 3RH, UK e-mail: m.ward1@physics.oxford.ac.uk

Send offprint request to: J.K. Kotilainen (SISSA address)

Received: 24 January 1996
Accepted: 20 May 1996

Abstract

We present optical broad band colour maps of nine Seyfert galaxies. In the bands used, the contribution from emission lines to the total flux is relatively small, and hence the images predominantly trace the continuum distribution. The ratios of these images are sensitive to gradients in the stellar populations, and to reddening by dust. We detect ringlike, clumpy or elongated morphological features in several galaxies, which are blue in the index ( for NGC 7469). For NGC 7469 there is good spatial agreement with the molecular millimeter CO and radio continuum structure indicating the presence of star forming regions around its Seyfert nucleus. The blue elongations and/or double structures seen in the colour maps of NGC 1068, NGC 3227, NGC 4151, Mrk 3 and Mrk 573 are roughly parallel to their extended radio and NLR emission and probably arise from scattering of nuclear light by extranuclear “mirrors”. In Mrk 78 and Mrk 348, the structure is not well resolved, possibly because the scattering mirrors are either less efficient and/or further away from the nucleus than in the previous galaxies. In NGC 1667, we detect double red maxima, again possibly related to obscuring material. The colours of the blue maxima are not well determined due to contamination from the underlying bulge, but they are generally consistent with those expected from scattering off dust or electrons. Our findings thus give further support to the current unified models of AGN.