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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{6300fig1.eps} \end{figure}$ Figure 1: Central surface brightness $\mu _{\rm V,0}$ plotted vs. V₀ of the candidate dEs from Hilker et al. (2003, Paper II), based on WFCCD data. The solid line indicates the 50% completeness limit. The two large red asterisks indicate two candidate dEs found in a background WFCCD field. Small black asterisks indicate galaxies with confirmed cluster membership from radial velocity (Drinkwater et al. 2001; Mieske et al. 2004; Hilker et al. 1999a). Coloured circles indicate objects re-observed with the higher resolution IMACS data presented in this paper. See Fig. 2 for a map of the imaged Fornax cluster region. Green filled circles indicate galaxies with cluster membership confirmed from SBF (Sect. 3). Blue filled circles indicate galaxies with probable cluster membership based on revised morphology assessment (Sect. 4). Red filled circles indicate probable background galaxies based on revised morphological assessment (Sect. 4). Grey filled circles indicate unclear classifications (Sect. 4). The dotted line is a fit to the $M_{\rm V} - \mu _{\rm V,0}$ values of Local Group dEs (Grebel et al. 2003). The lower dashed line indicates the location of an exponential galaxy light profile with ${\it FWHM}=3.5''$ , which is twice the seeing for the Paper II data. The upper dashed line indicates an exponential profile with ${\it FWHM}=1.5''$ , which is about twice the seeing in the IMACS data presented in this paper.
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In the text

$\begin{figure} \includegraphics[width=12cm,clip]{6300fig2.eps} \end{figure}$ Figure 2: Map of the central Fornax cluster. Small dots are cluster member candidates from Hilker et al. (2003, Paper II). Large dots are cluster members previously confirmed by radial velocity (Drinkwater et al. 2001; Mieske et al. 2004; Hilker et al. 1999a). Squares indicate the IMACS pointings from this paper. The two dashed squares indicate the two central IMACS pointings with lower integration times (see text). The coloured circles mark objects observed within those pointings. Green circles are cluster members confirmed by SBF (Sect. 3). Blue circles are probable members based on a morphological analysis (Sect. 4). Red circles are probable background galaxies based on a morphological analysis (Sect. 4). Grey filled circles are unclear classifications (Sect. 4). Golden circles without a dot inside indicate the new dE candidates detected with the IMACS imaging (Sect. 5). Those candidates from Paper II that were not observed were either outside the vignetted field of view or fell in the gaps between chips. Crosses mark the giant Fornax galaxies with their corresponding NGC numbers indicated.
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In the text

$\begin{figure} \par\mbox{\epsfig{figure=6300fig3a.ps,width=2.75cm}\hspace{0.2cm}... ...t]{2.75cm}{\vspace{-2.5cm}\hspace{0.5cm}\Large \bf FCC 191} } \par\end{figure}$ Figure 3: Thumbnails of SBF-confirmed Fornax cluster members (Sect. 3), i.e. those with flag = 1 in Table 1. Top: WFCCD images. The PSF FWHM is about 1.8''. Bottom: IMACS images. The PSF FWHM is about 0.8''. The thumbnail sizes are from left to right $77\times 50''$ ( $7\times 4.6$ kpc at the Fornax cluster distance), $38 \times 25''$ ( $3.5 \times 2.3$ kpc), and $19 \times 12''$ ( $1.8 \times 1.1$ kpc).
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In the text

$\begin{figure} \par\mbox{ \epsfig{figure=6300fig4a.ps,width=2.75cm}\hspace{0.2cm... ...]{2.75cm}{\vspace{-2.5cm}\hspace{0.1cm}\Large \bf WFLSB2-1} } \par\end{figure}$ Figure 4: Thumbnails of morphologically-confirmed Fornax cluster members (Sect. 4), i.e. those with flag = 2 in Table 1. Top: WFCCD images. Bottom: IMACS images. The thumbnail sizes are $38 \times 25''$ ( $3.5 \times 2.3$ kpc at the Fornax cluster distance).
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In the text

$\begin{figure} \par\mbox{\epsfig{figure=6300fig5a.ps,width=2.75cm}\hspace{0.2cm}... ...t]{2.75cm}{\vspace{-2.5cm}\hspace{0.1cm}\Large \bf WFLSB 1-4} } \par\end{figure}$ Figure 5: Left two thumbnails: two morphologically re-classified background galaxies (Sect. 4), i.e. those with flag = 3 in Table 1. Right thumbnail: a source with unclear classification, i.e. those with flag = 4 in Table 1. Top: WFCCD images. Bottom: IMACS images. The thumbnail sizes are $38 \times 25''$ ( $3.5 \times 2.3$ kpc at the Fornax cluster distance).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{6300fig6.eps} \end{figure}$ Figure 6: Magnitude-surface brightness plot as in Fig. 1, now using the new photometry of the IMACS data and plotting only probable cluster members from SBF memberships and morphology (Sects. 3 and 4). Typical error bars are indicated. The magnitudes were redenning-corrected using Schlegel et al. (1998). The golden dots indicate newly found dE candidates in the IMACS data (Sect. 5). The solid line is a fit to the data points applying a 3 $\sigma$ clipping. The dotted line shows the fit from the WFCCD photometry of all dE candidates from Hilker et al. (2003, Paper II), also applying a 3 $\sigma$ clipping. The red asterisks indicate Local Group dEs (Grebel et al. 2003).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{6300fig7.eps} \end{figure}$ Figure 7: This plot shows the normalised distribution of central surface brightnesses of the Fornax sample (solid histogram) and Local Group sample (dashed histogram) relative to the surface-brightness magnitude relation in Fornax (Eq. (1)). By definition, the Fornax distribution is centred on 0. This plot shows that the overall shift in surface brightness between Fornax and Local Group is due to both a lack of small and overabundance of large galaxies in Fornax. According to a KS test, both distributions share the same parent distribution at only 0.08% probability. When shifting the Local Group distribution such that the mean of both distributions agree, the KS probability is 99.9%.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{6300fig8.eps} \end{figure}$ Figure 8: Top two rows: example thumbnails for six of the 12 new Fornax dE candidates detected from our IMACS photometry (Sect. 5), see also Table 1. Thumbnails are $82 \times 72''$ large ( $7.5 \times 6.6$ kpc at the Fornax cluster distance). They are ordered from left to right and top to bottom by decreasing galaxy luminosity. Bottom row: the left thumbnail shows four simulated dE galaxies in the magnitude range $-10.8>M_{\rm V}>-11$ mag that have sizes corresponding to the LG dEs (simulated seeing FWHM was 0.9''). The middle thumbnail shows three simulated dEs in the same absolute magnitude range, but with only 60% the size of LG dEs. They are still clearly resolved. The right thumbnail shows two SExtractor detections that were not accepted as new dE candidates, one since it was part of a ghost image, another one because it was a blend of several very small sources.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{6300fig9.eps} \end{figure}$ Figure 9: Colour-magnitude diagram (CMD) of the sources from Fig. 6. Typical error bars are indicated. The magnitudes and colours were redenning corrected using Schlegel et al. (1998). The V magnitude is from the IMACS data, while (V-I) is adopted as the mean of the WFCCD and IMACS values. Adopting this mean reduces the colour scatter by about 35% as compared to the single IMACS colour: the colour scatter for the IMACS values is 0.15 mag, while that of the mean (and also the WFCCD colour) is about 0.11 mag. The solid line is a fit to the data points applying a 3 $\sigma$ clipping. The dotted line - which is practically on top of the solid line - indicates the colour-magnitude relation derived from the WFCCD photometry of all dE candidates (Hilker et al. 2003, Paper II). The (red) Local Group data points for $M_{\rm V}<-13$ mag are proper (V-I) measurements from Mateo et al. (1998), while for $M_{\rm V}>-13$ mag the (V-I) values are estimated from their [Fe/H] values (Grebel et al. 2003). For this transformation we applied equation (4) from Kissler-Patig et al. (1998), and adopted an additional zero point shift of -0.055 mag. This shift was the difference between the transformed and measured (V-I) values for the five Local Group dEs with $M_{\rm V}<-13$ mag that do have a measured (V-I).
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{6300fig10.eps} \end{figure}$ Figure 10: This figure shows how the Fornax cluster galaxy luminosity function from Hilker et al. (2003, Paper II) is re-assessed in the present paper. The vertical (green) line indicates the 50% detection limit from Paper II, which is also the faint limit for fitting the faint end slope $\alpha$ . Top panel: the solid (red) line indicates a smoothed representation of the Fornax GLF from Paper II. The solid histogram gives the fraction of correct cluster member candidate identifications determined in Sects. 3 to 4, augmented by the inclusion of the new candidate cluster members from Sect. 5. Note that this inclusion of members that were undetected in Paper II makes the fraction larger than 1 in some bins. The (green) dotted line is a smoothed representation of the histogram. The dashed red line indicates the corrected Fornax GLF, i.e. the product of the Paper II LF with the dotted line. See Sect. 6.3 for more details. Bottom panel: solid line: 1-component fit to the Fornax-GLF from Paper II. Dashed line: 1-component fit to the corrected Fornax GLF. The respective faint end slopes are $\alpha =-1.10$ for the Paper II LF and $\alpha =-1.09$ for the corrected LF.
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In the text

$\begin{figure} \par\mbox{ \epsfig{figure=6300fig4a.ps,width=2.75cm}\hspace{0.2cm... ...]{2.75cm}{\vspace{-2.5cm}\hspace{0.1cm}\Large \bf WFLSB2-1} } \par\end{figure}$	Figure 4: Thumbnails of morphologically-confirmed Fornax cluster members (Sect. 4), i.e. those with flag = 2 in Table 1. Top: WFCCD images. Bottom: IMACS images. The thumbnail sizes are $38 \times 25''$ ( $3.5 \times 2.3$ kpc at the Fornax cluster distance).
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$\begin{figure} \par\mbox{\epsfig{figure=6300fig5a.ps,width=2.75cm}\hspace{0.2cm}... ...t]{2.75cm}{\vspace{-2.5cm}\hspace{0.1cm}\Large \bf WFLSB 1-4} } \par\end{figure}$	Figure 5: Left two thumbnails: two morphologically re-classified background galaxies (Sect. 4), i.e. those with flag = 3 in Table 1. Right thumbnail: a source with unclear classification, i.e. those with flag = 4 in Table 1. Top: WFCCD images. Bottom: IMACS images. The thumbnail sizes are $38 \times 25''$ ( $3.5 \times 2.3$ kpc at the Fornax cluster distance).
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