Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the UK) and with the participation of ISAS and NASA.

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We also detect a weak and unknown emission feature between 9.3 and 9.9 $\mu$ m, which seems brighter, relatively to UIBs, in disks than in central regions. However, the very poor signal to noise ratio of disk spectra does not allow us to be conclusive. It cannot be an artefact due to the change of filter since that change occurs after the feature is observed. It is too narrow to be emitted by silicates. The identification with ionized PAHs (see e.g. Allamandola et al. 1999) would be inconsistent with the fact that the flux ratio of this feature to classical UIBs seems higher in regions of low radiation density and excitation than in central regions. It is also unlikely that it corresponds to the H₂ rotational line at 9.66 $\mu$ m since this is characteristic of warm and excited molecular clouds in starburst nuclei (e.g. Spoon et al. 2000). Finally, we mention that it also matches in wavelength a feature from the CH₃functional group at 9.6 $\mu$ m (Duley & Williams 1981).

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...4102

This galaxy shows a peculiar structure, with a central lens-like body or fat oval of moderate length ( $D_{\rm bar} / D_{25} \approx 0.2$ ) surrounded by an external pseudo-ring probably associated with a Lindblad resonance. NGC4102 is thus a genuine weakly barred galaxy, and not a SB. However, such a dynamical structure is still efficient to drive inward mass transfer. We also point to the very strong concentration of its mid-infrared emission (see Table 2), a property common to early-type barred spirals (Fig. 6).

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... active

Far-infrared diagnostics of nuclear activity are ambiguous for NGC4388: its infrared to radio flux ratio as defined by Condon et al. (1991) is q = 2.27, and its spectral index between 25 and 60 $\mu$ m (de Grijp et al. 1987) is $\alpha = 1.23$ . Both values indicate that stellar and non-stellar excitations may contribute in comparable amounts to the infrared energy output. Concerning VCC1326, its spectral index between 25 and 60 $\mu$ m, $\alpha = 1.67$ , is rather typical of starbursts.

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...profiles

In NGC1530, the scales of the molecular gas and infrared concentrations are of the same order. In NGC1022, the source HPBW is estimated to be $\approx$ $17\hbox{$^{\prime\prime}$ }$ , which is $\approx$ 2.9 times that of the innermost infrared regions. However, these are clearly more extended than a central Gaussian and not representative of normal CNRs, since likely gathered by a merger. For this and other galaxies whose central regions are clearly structured (i.e. NGC1097 and NGC4691), detailed CO maps where the source is resolved were used. It is also the case for NGC1530, 5236 and 6946.

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... $T_{\rm R}^*$ scale

Which includes corrections for atmospheric attenuation and all instrumental effects except antenna to source coupling.

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... emission

Note that it is however conceivable that a fraction of UIB carriers are destroyed, which would cause such a deficit.

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... fit

We give this name to a fit where the quantity to be minimized is the sum of absolute values of the distances between the data points and the line. This method is less sensitive to outliers than the least squares fit.

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