All Figures

$\begin{figure} \par\includegraphics[width=16.4cm,clip]{6692f01CMJN.eps} % \end{figure}$ Figure 1: Composite image of the NGC 5291 system in pseudo-colours: 8.0 $\mu$ m IRAC (red channel), H $\alpha$ (green channel) and near ultraviolet GALEX (blue channel). The overplotted red and green contours represent respectively the 8.0 $\mu$ m and the H $\alpha$ fields of view. The blue contours represent the HI emission from the VLA HI map. The levels represent HI column densities of: $5.0\times 10^{20}$ , $1.1\times 10^{21}$ , $1.7\times 10^{21}$ , $2.3\times 10^{21}$ , $2.9\times 10^{21}$ , $3.5\times 10^{21}$ cm^-2.
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In the text

$\begin{figure} \par\includegraphics[width=16.4cm,clip]{6692f02.ps} \end{figure}$ Figure 2: The different tracers of star formation towards NGC 5291: VLA HI map ( top left), GALEX near-ultraviolet ( top right), Fabry-Perot H $\alpha$ ( bottom left), and Spitzer 8.0 $\mu$ m ( bottom right) maps, all at the same spatial scale. The scaled 3.6 $\mu$ m emission was subtracted from the 8.0 $\mu$ m map to remove contaminating stellar light from the mid-infrared emission (see for instance Pahre et al. 2004) and thus mainly shows dust emission.
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In the text

$\begin{figure} \par\includegraphics[width=17.7cm,clip]{6692f03CMJN.eps} \end{figure}$ Figure 3: Ultraviolet image of NGC 5291 with a mosaic of the selected regions. The individual regions and the main galaxies in the group are labelled. The thumbnails are zoomed images of each selected region using pseudo-colours (red representing 8.0 $\mu$ m emission, green H $\alpha$ and blue ultraviolet), with the corresponding polygonal aperture overplotted in white. Note that for region 14 only the UV emission is available and shown (see Fig. 1).
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In the text

$\begin{figure} \par\includegraphics[width=7.9cm,clip]{6692f04.eps} \end{figure}$ Figure 4: Ratio of $\left [{\rm H}\alpha \right ]/\left [{\rm NUV}\right ]$ versus SFR(UV).
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In the text

$\begin{figure} \par\includegraphics[width=7.9cm,clip]{6692f05.eps} \end{figure}$ Figure 5: Ratio of $\left [8.0\right ]/\left [{\rm NUV}\right ]$ versus SFR(UV).
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{6692f06.ps} \end{figure}$ Figure 6: Ratio of the mid-infrared fluxes ${F_{\rm IR8.0}/(F_{\rm IR4.5}-\alpha F_{\rm IR3.6}})$ versus the monochromatic luminosity at 8.0 $\mu$ m of SINGS galaxies (Dale et al. 2007, open circles), of the dwarf galaxies in the Rosenberg et al. sample (triangles), of Engelbracht et al. sample (squares) and the HII regions in NGC 5291 (filled circles with error bars). The large filled black circle represents the sum over all NGC 5291 regions.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{6692f07.eps} \end{figure}$ Figure 7: Star formation rate estimated from the IRAC 8.0 $\mu$ m band as a function of SFR(UV) for the NGC 5291 intergalactic SF regions (filled circles) and for the galaxies of the SINGS sample (Dale et al. 2007, open circles).
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In the text

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{6692f08.ps} \end{figure}$ Figure 8: Ratio of the mid-infrared fluxes ${F_{\rm IR8.0}/(F_{\rm IR4.5}-\alpha F_{\rm IR3.6}})$ versus the monochromatic luminosity at 8.0 $\mu$ m of M 81 (Pérez-González et al. 2006, purple diamonds), Arp 82 (Hancock et al. 2007, red squares; filled squares represent star forming regions in tidal features) and NGC 5291 (filled circles with error bars) HII regions. The large filled circled represents the integration of all NGC 5291 regions.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{6692f09CMJN.eps} \end{figure}$ Figure 9: Star formation rate estimated from the IRAC 8.0 $\mu$ m band as a function of SFR(UV) for the NGC 5291 intergalactic SF regions (filled circles), for samples of HII regions in two spiral disks: M 51 (Calzetti et al. 2005, blue triangles; filled triangles represent inner regions where Pa $\alpha$ flux is available) and M 81 (Pérez-González et al. 2006, purple diamonds), and for the interacting system Arp 82 (Hancock et al. 2007, red squares; filled squares represent star forming regions in tidal features).
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{6692f010CMJN.eps} \end{figure}$ Figure 10: Star formation rate estimated from the $\left [{\rm H}\alpha \right ]$ luminosity as a function of SFR(UV) for the NGC 5291 intergalactic SF regions (filled circles), for samples of galactic HII regions in two spiral disks: M 51 (Calzetti et al. 2005) (blue triangles; filled triangles represent HII regions near centre of M 51 where Pa $\alpha$ flux is available) and M 81 (Pérez-González et al. 2006, purple diamonds), and for the interacting system Arp 82 (Hancock et al. 2007, red squares; filled squares represent star forming regions in tidal features).
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{6692f11.ps} \end{figure}$ Figure 11: Ratio of the mid-infrared fluxes ${F_{\rm IR8.0}/(F_{\rm IR4.5}-\alpha F_{\rm IR3.6}})$ (with $\alpha =0.57$ ) versus the metallicity of dwarf galaxies from the Rosenberg et al. sample (triangles), Engelbracht galaxies (open squares) and HII regions in NGC 5291 (filled circles).
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In the text

$\begin{figure} \par\includegraphics[width=5.7cm,clip]{6692f12.ps} \end{figure}$ Figure 12: $\left [{\rm H}\alpha \right ]/\left [{\rm NUV}\right ]$ as a function of $\left [8.0\right ]/\left [{\rm NUV}\right ]$ for HII knots with an uncorrected ultraviolet star formation rate greater than 0.02 $M_{\hbox {$\odot $ }}$ yr^-1. Filled circles are uncorrected for extinction while empty ones are.
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{6692f13.ps} \end{figure}$ Figure 13: Plot of the variation of the equivalent width of H $\beta$ in Å, as a function of ages for different types of starbursts. The black line shows an instantaneous starburst whereas the red one corresponds to an exponentially decreasing starburst with a timescale $\tau =40\times 10^6$ years. Lines for all intermediate $\tau$ with intervals of $1\times 10^6$ years are also shown. The light grey zone indicates the range of observed values of the H $\beta$ equivalent width for the few regions where this was measured (Duc & Mirabel 1998).
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{6692f14.ps} \end{figure}$ Figure 14: Plot of the variation of the $\left [{\rm H}\alpha \right ]/\left [{\rm NUV}\right ]$ ratio as a function of age for different types of starbursts. The black line shows an instantaneous starburst whereas the red one corresponds to an exponentially decreasing starburst with a timescale $\tau =40\times 10^6$ years. Lines for all intermediate $\tau$ with intervals of $1\times 10^6$ years are also shown. The light grey zone indicates the range of observed values of $\left [{\rm H}\alpha \right ]/\left [{\rm NUV}\right ]$ after correction for extinction.
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{6692f15.ps} \end{figure}$ Figure 15: Plot of the variation of $\left [{\rm H}\alpha \right ]$ (it is to say the star formation rate that would give the Kennicutt estimator) over the actual star formation rate as a function of age for different types of starbursts. The black line shows an instantaneous starburst whereas the red one corresponds to an exponentially decreasing starburst with a timescale $\tau =40\times 10^6$ years. Lines for all intermediate $\tau$ with intervals of $1\times 10^6$ years are also shown.
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In the text

$\begin{figure} \par\includegraphics[width=7.3cm,clip]{6692f16.ps} \end{figure}$ Figure 16: Plot of the variation of the $\left [{\rm NUV}\right ]$ (it is to say the star formation rate that would give the Kennicutt estimator) over the actual star formation rate as a function of age for different types of starbursts. The black line shows an instantaneous starburst whereas the red one corresponds to an exponentially decreasing starburst with a timescale $\tau =40\times 10^6$ years. Lines for all intermediate $\tau$ with intervals of $1\times 10^6$ years are also shown.
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In the text

$\begin{figure} \par\includegraphics[width=7.9cm,clip]{6692f04.eps} \end{figure}$	Figure 4: Ratio of $\left [{\rm H}\alpha \right ]/\left [{\rm NUV}\right ]$ versus SFR(UV).
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$\begin{figure} \par\includegraphics[width=7.9cm,clip]{6692f05.eps} \end{figure}$	Figure 5: Ratio of $\left [8.0\right ]/\left [{\rm NUV}\right ]$ versus SFR(UV).
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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{6692f07.eps} \end{figure}$	Figure 7: Star formation rate estimated from the IRAC 8.0 $\mu$ m band as a function of SFR(UV) for the NGC 5291 intergalactic SF regions (filled circles) and for the galaxies of the SINGS sample (Dale et al. 2007, open circles).
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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{6692f11.ps} \end{figure}$	Figure 11: Ratio of the mid-infrared fluxes ${F_{\rm IR8.0}/(F_{\rm IR4.5}-\alpha F_{\rm IR3.6}})$ (with $\alpha =0.57$ ) versus the metallicity of dwarf galaxies from the Rosenberg et al. sample (triangles), Engelbracht galaxies (open squares) and HII regions in NGC 5291 (filled circles).
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$\begin{figure} \par\includegraphics[width=5.7cm,clip]{6692f12.ps} \end{figure}$	Figure 12: $\left [{\rm H}\alpha \right ]/\left [{\rm NUV}\right ]$ as a function of $\left [8.0\right ]/\left [{\rm NUV}\right ]$ for HII knots with an uncorrected ultraviolet star formation rate greater than 0.02 $M_{\hbox {$\odot $ }}$ yr^-1. Filled circles are uncorrected for extinction while empty ones are.
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