5 Conclusions

This NIR study on 15 active (starburst and/or Seyfert) objects leads us to these morphological results:

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4 galaxies are double-barred systems: NGC3393 (already known), ESO215-G031, ESO320-G030, ESO443-G017 (new ones). These objects confirm previous studies which concluded that embedded bars are dynamically decoupled;

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4 galaxies have nested feature inside the primary bar: three present a triaxial bulge (ESO508-G005, ESO323-G077, NGC6221), one (NGC5135) harbours a nuclear spiral structure;

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We suggest to classify NGC5643 and ESO320-G030 as SB rather than SAB;

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Among the 2 unbarred galaxies (NGC4939, NGC4941), one (NGC4941) harbours a nuclear bar (like e.g. NGC7702, Paper I);

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The Seyfert or starburst activity is not directly linked to the presence of embedded structures: galaxies with embedded structures span a wide range of starburst activity and are found in Seyferts and non-Seyferts (see Fig. 3 and Table 4).

A careful examination has been applied to $\mu _{J}-\mu _{K'}$, and has lead us to the following considerations:

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The outer $\mu _{J}-\mu _{K'}$ profiles are roughly constant ( $\approx\!0.8-1.2\,{\rm mag}\,\hbox{$^{\prime\prime}$ }^{-2}$);

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For the whole sample, the $\mu _{J}-\mu _{K'}$ profiles increases toward the center or at least is constant at higher value than the disc;

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We have characterized these inner $\mu _{J}-\mu _{K'}$profiles behaviour by the $\Delta$(J-K') parameter which seems to be:

i)

independent of the Seyfert activity;

ii)

linked to the starburst indicator $\log(S_{60}/S_{100})$. Starburst galaxies tend to have a central J-K' value 0.3 - 1.5 mag higher than the disc one. This trend links up the nuclear NIR colour to the integrated FIR colour;

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A young nuclear starburst naturally tends to increase $\Delta$(J-K'), and could be partially responsible for the trend mentioned above;

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Classical starburst models are unable to reproduce a  mag, so that other factors or components have to be considered (e.g. dust extinction, the metallicity or the stellar population gradient, warm gaz). Their quantitative incidence on $\Delta$(J-K'), requires additional data.

Acknowledgements

This project is supported by the Swiss National Science Foundation (FNS). This research have made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contact with the U.S. Aeronautics and Space Administration. Partially based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. We warmly thank Almudena Alonso-Herrero for its NIR data.