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$\begin{figure} \par\includegraphics[width=7cm,clip]{5493fig1.eps} \end{figure}$ Figure 1: Schematic diagram of filter positioning for the four observational approaches described in Sect. 2.3 the text. Narrowband filters (on-line, black) have widths of 2% their central wavelengths and broadband filters (continuum, grey) have widths of 20% $\lambda _{\rm c}$ . Wavelength indications represent central wavelength of the filters and are marked in the restframe of the SED. I.e. observation-frame filters are centred at $(1+z) \cdot \lambda _{\rm c}$ . (This figure is available in color in electronic form.)
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.0cm,height=4.0cm]{5493fig2a.ep... ...m} \includegraphics[width=8.0cm,height=4.0cm]{5493fig2h.eps} } \par \end{figure}$ Figure 2: Histograms showing the distribution of detected Ly $\alpha$ flux ( left) and equivalent width ( right) for a population of 10 000 galaxies at a redshift of z=5.7. The descending pairs of plots represent distributions as computed by observational techniques #1, #2, #3, #4. The vertical dashed red lines indicate the true line flux and equivalent width (i.e. that added to the restframe SED). The vertical green line shows the mean values computed for the whole sample of 10 000 objects, while the blue line shows the mean value of these quantities for all objects with $W_{{\rm Ly}\alpha }$ > 20 Å (refined mean). The dotted black line in the uppermost equivalent width plot shows the fraction of galaxies in the sample with observed $W_{{\rm Ly}\alpha }$ greater than the value on the abscissa axis (i.e. for that value of $W_{{\rm Ly}\alpha }$ , the fraction of galaxies that have $W_{{\rm Ly}\alpha }$ greater than this value). (This figure is available in color in electronic form.)
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.3cm,clip]{5493fig3a.eps}\hspace{0.8cm} \includegraphics[width=8.3cm,clip]{5493fig3b.eps} }\end{figure}$ Figure 3: The evolution of $F_{{\rm Ly}\alpha }$ and $W_{{\rm Ly}\alpha }$ as function of redshift. The left plot shows the recovered $F_{{\rm Ly}\alpha }$ , normalised by the predicted flux at the observatory, calculated from the intrinsic line luminosity added in the restframe (i.e. the fractional deviation from the true value). The right plot shows the evolution of $W_{{\rm Ly}\alpha }$ . Colour blue represents technique #1, green: technique #2, red: technique #3 and black: technique #4. Dotted lines represent total mean values, dashed lines represent median values, and solid lines show the refined means. (This figure is available in color in electronic form.)
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.0cm,height=4.0cm]{5493fig4a.ep... ...0.3cm} \includegraphics[width=8.0cm,height=4.0cm]{5493fig4d.eps} }\end{figure}$ Figure 4: Histogram showing the detected $W_{{\rm Ly}\alpha }$ of 10 000 galaxies at z=5.7. These are the same objects as plotted in Fig. 2 but fluxes have been regenerated within assumed observational errors from a simple assumed noise model. Dotted line and vertical dashed lines as in Fig. 2. (This figure is available in color in electronic form.)
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=6.2cm,height=4.5cm]{5493fig5a.ep... ...ps}\includegraphics[width=5.7cm,height=4.5cm]{5493fig5c.eps} } \par \end{figure}$ Figure 5: Recovered $W_{{\rm Ly}\alpha }$ as a function of internal reddening using the starburst extinction laws. The abscissa shows the internal reddening E_B-V, using a known extinction law. The ordinate shows the recovered value of $W_{{\rm Ly}\alpha }$ using an an extinction law assumed by the observer. Left: true dust: SMC-law; assumed dust: LMC. Centre: true dust: Calzetti-law; extinction law free parameter in SED fitting routine Right: as for centre but with noise model applied. Colours represent observational strategies as in Fig. 3. The filter setup is as described in Sect. 2.3 (solid lines). The dashed lines show the same results but with the nearest off-line filter (restframe 1500 Å) shifted to 1400 Å. (This figure is available in color in electronic form.)
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{5493fig6.eps} \end{figure}$ Figure 6: The effect of varying n₄₅₀₀ on the recovered values of $W_{{\rm Ly}\alpha }$ as determined by the various techniques. n₄₅₀₀ is defined in Sect. 3.3. The error bars on the black line show the standard deviation in recovered $W_{{\rm Ly}\alpha }$ when 1000 objects are generated using the noise model described in the text. (This figure is available in color in electronic form.)
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In the text

$\begin{figure} \par\mbox{\includegraphics[width=8.0cm,height=4.0cm]{5493fig4a.ep... ...0.3cm} \includegraphics[width=8.0cm,height=4.0cm]{5493fig4d.eps} }\end{figure}$	Figure 4: Histogram showing the detected $W_{{\rm Ly}\alpha }$ of 10 000 galaxies at z=5.7. These are the same objects as plotted in Fig. 2 but fluxes have been regenerated within assumed observational errors from a simple assumed noise model. Dotted line and vertical dashed lines as in Fig. 2. (This figure is available in color in electronic form.)
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