All Figures

$\begin{figure} \par\includegraphics[width=17.5cm,clip]{1955fig01.eps} \end{figure}$ Figure 1: Examples of the radial distribution of Visual-Near IR colours, derived from 2MASS frames and published V-images or profiles. Abscissae: $\log r$ . Ordinates from top to bottom, J-H, J-K, V-J and V-K colours. V data are from OHP frames, either before background adjustment (dots) or after (stars), and from Gal94 profiles (circles). In NGC 1700 and 4278 note the large effects of "differential seeing'' on V-J and V-K gradients, specially for the Gal94 profiles derived from sharper images. For the very large objects NGC 3379 and 4472, background corrections are needed to compensate small truncatures of the galaxy light in the 2MASS mosaics: these corrections are small, i.e. 0.4% in J and 0.15% in K in the difficult case of NGC 4472.
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In the text

$\begin{figure} \par\includegraphics[width=15cm,clip]{1955fig02.eps} \end{figure}$ Figure 2: Histograms of the distributions of the gradients of "optical'' colours.
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In the text

$\begin{figure} \par\includegraphics[width=17cm,clip]{1955fig03.eps} \end{figure}$ Figure 3: Correlation diagrams between $\Delta _{BV}$ and gradients in other colours, with calculated regressions (Table 5) and indications of the estimated average errors (Table 4). See comments in text.
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In the text

$\begin{figure} \par\includegraphics[width=8.3cm,clip]{1955fig04.eps} \end{figure}$ Figure 4: Correlation diagram between the $\Delta _{UV}$ gradient and the central velocity dispersion $\log \sigma{_0}$ . There is an uncertain trend for this gradient to decrease for objects with $\log \sigma{_0}>2.4$ . Other colours lead to similar diagrams.
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In the text

$\begin{figure} \par\includegraphics[width=16cm,clip]{1955fig05.eps} \end{figure}$ Figure 5: Correlation diagrams between the IRAS 100 $\mu$ flux and gradients in various colours. The fluxes are reduced to the Virgo distance and plotted in a logarithmic scale, after applying a bias of 10 units of the Knapp et al. (1989) scale. Average errors are plotted for two ranges of IRAS flux: they were estimated from a number of individual $\sigma$ values in the quoted catalogue.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{1955fig06.eps} \end{figure}$ Figure 6: Correlation diagrams for the pairs of gradients $\Delta _{VK}$ against $\Delta _{UB}$ or against $\Delta _{BV}$ , and $\Delta _{VJ}$ against $\Delta _{UB}$ . Stars: dataset of 53 dummy objects with gradients mimicking the results of the hierarchical scenario. Open circles: subsample of 43 dustless objects affected by noise. Filled circles: subsample of 10 objects with gradients affected by diffuse dust with $\tau _V=2$ in models by Wal92 (Tau(V) in their notation) and noise. Line: objects mimicking the monolithic scenario. The dummies are built from SSP in BC03. These correlation diagrams show a significant segregation, often larger than noise, between dustless and dusty objects.
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In the text

$\begin{figure} \par\includegraphics[width=12.5cm,clip]{1955fig07.eps} \end{figure}$ Figure 7: Correlation diagrams for the pairs of gradients $\Delta _{VK}$ against $\Delta _{UB}$ or against $\Delta _{BV}$ , and $\Delta _{VJ}$ against $\Delta _{UB}$ . Open circles: observed galaxies with no evidence for a significant amount of dust. Filled circles: subsample of objects with gradients possibly affected by diffuse dust. Average observational errors (Table 4) are indicated. The correlation diagram $\Delta _{VK}$ against $\Delta _{UB}$ gives evidence of the expected bimodality between dusty and dustless objects, an evidence which is supported by the other two diagrams. Our estimates of dust content, in terms of models in Wal92, are collected in Table 10. Average obsevational errors are from Table 4.
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In the text

$\begin{figure} \par\includegraphics[width=15cm,clip]{1955fig02.eps} \end{figure}$	Figure 2: Histograms of the distributions of the gradients of "optical'' colours.
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$\begin{figure} \par\includegraphics[width=17cm,clip]{1955fig03.eps} \end{figure}$	Figure 3: Correlation diagrams between $\Delta _{BV}$ and gradients in other colours, with calculated regressions (Table 5) and indications of the estimated average errors (Table 4). See comments in text.
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$\begin{figure} \par\includegraphics[width=8.3cm,clip]{1955fig04.eps} \end{figure}$	Figure 4: Correlation diagram between the $\Delta _{UV}$ gradient and the central velocity dispersion $\log \sigma{_0}$ . There is an uncertain trend for this gradient to decrease for objects with $\log \sigma{_0}>2.4$ . Other colours lead to similar diagrams.
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$\begin{figure} \par\includegraphics[width=16cm,clip]{1955fig05.eps} \end{figure}$	Figure 5: Correlation diagrams between the IRAS 100 $\mu$ flux and gradients in various colours. The fluxes are reduced to the Virgo distance and plotted in a logarithmic scale, after applying a bias of 10 units of the Knapp et al. (1989) scale. Average errors are plotted for two ranges of IRAS flux: they were estimated from a number of individual $\sigma$ values in the quoted catalogue.
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