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Up: Optical colour maps

7. Conclusions

Colour maps provide a new, powerful method to reveal star formation and scattering in the nuclear region of Seyfert galaxies. We have detected ring-like or elongated blue structures in the B-I (or V-I) maps of several Seyfert galaxies and found a good agreement with previous spectroscopic and multifrequency studies of these galaxies. In NGC 1068, NGC 3227, NGC 4151, Mrk 3 and Mrk 573, we interpret the clear colour structure as arising from scattering of the nuclear light from electrons or dust. In Mrk 78 and Mrk 348 the structure is less clear, and may indicate that the scattering mirrors are less efficient and/or further away from the nucleus than in the other galaxies. In NGC 7469, there is a good agreement with the integrated molecular CO gas emission and radio continuum structure indicating circumnuclear star formation in a ring or a disk around the Seyfert nucleus.

Colour maps in multiple, emission line-free windows, in UV as well as in the optical, and detailed spectrophotometry would be valuable to confirm the presence of the detected elongations and to probe the physical conditions in more detail. In a forthcoming paper, we shall analyse broad band data of a further, larger sample of candidates of Seyfert 2s with obscured BLRs, obtained recently at the NOT.


We thank Malcolm Bremer for help with the observations of December 1992. This work was started when both authors were at the Institute of Astronomy, Cambridge. JKK thanks ESO for a postdoctoral fellowship, during which most of this work was done.

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