All Figures

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig1.eps} \end{figure}$ Figure 1: $45'\times 45'$ ( $540 \times 540$ kpc at the cluster distance) image of the Hydra I cluster centred on NGC 3311, extracted from the Digital Sky Survey. The small squares are the fields observed with LDSS2. The large square marks the VIMOS-pointing. The circle indicates the cluster core radius $r_{{\rm c}}=170~h^{-1}$ kpc (Girardi et al. 1995), adopting h=0.75.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig2.eps} \end{figure}$ Figure 2: Colour-magnitude diagram of all observed objects in the seven LDSS2 fields (the dwarf galaxy sample). Dots (open triangles) mark unresolved (resolved) sources, according to SExtractor star-galaxy classifier (Bertin & Arnouts 1996). The photometry is taken from VLT/FORS1 images (see Sect. 3.1).
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig3.eps} \end{figure}$ Figure 3: Colour-magnitude diagram of all photometrically selected objects in the VIMOS-pointing (the UCD sample). Dots are unresolved sources and open triangles are dwarf galaxy candidates. Green open circles mark objects for which a slit could be allocated on the masks.
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In the text

$\begin{figure} \par\includegraphics[width=4.4cm]{0014fi4a.eps}\includegraphics[w... ...dth=4.4cm]{0014fi4c.eps}\includegraphics[width=4.4cm]{0014fi4d.eps} \end{figure}$ Figure 4: Thumbnails of four cluster dwarf galaxy candidates that fulfil the selection criteria. The thumbnail sizes are $40''\times 40''$ ( $8\times 8$ kpc at the cluster distance).
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig5.eps} \end{figure}$ Figure 5: Coordinate map of the cluster dwarf galaxy candidates, confirmed cluster members, background galaxies and major cluster galaxies with their corresponding NGC number. The seven observed VLT/FORS1 fields are marked by large open squares, the field number is indicated.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig6.eps} \end{figure}$ Figure 6: Radial velocity distribution of all successfully measured objects with $v_{{\rm rad}}<30~000$ km s^-1 (black histogram). The grey histogram shows the data from CZ03. Vertical dashed lines mark the velocity range assumed for cluster membership. Note also the overdensity at $v_{{\rm rad}} \sim 11~000$ km s^-1 from which we identify five members.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig7.eps} \end{figure}$ Figure 7: Coordinates of the 494 objects that were selected for spectroscopy (small dots). Small open circles mark the 365 observed objects, small filled circles are the 126 objects for which a reliable radial velocity could be determined. Red filled circles are cluster members, green open squares mark the 8 newly confirmed cluster members.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig8.eps} \end{figure}$ Figure 8: Properties of all successfully observed objects in our dwarf galaxy sample. Filled red circles are confirmed cluster members, grey triangles represent resolved background objects. Small black dots are foreground stars, asterisks are unresolved cluster members (red) or background objects (grey). a) Coordinate map of all foreground stars, background sources and cluster members. The observed fields are indicated by large open squares. b) Colour-magnitude diagram of all objects. c) Magnitude velocity diagram of all objects, except for background objects with $v_{{\rm rad}}>13~000$ km s^-1. d) Colour velocity diagram of all objects, except for background objects with $v_{{\rm rad}}>13~000$ km s^-1.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig9.eps} \end{figure}$ Figure 9: Properties of all successfully observed objects in the UCD sample. The symbols are as in Fig. 8. a) Coordinate map. The four quadrants (q1-q4) of the VIMOS pointing are indicated by large open squares. Note the low number of successfully observed objects in q2 due to the mask misalignment. b) Colour-magnitude diagram of all objects. c) Magnitude velocity diagram of all objects, except for background objects with $v_{{\rm rad}}>9000$ km s^-1. d) Colour velocity diagram of all objects, except for background objects with $v_{{\rm rad}}>9000$ km s^-1.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fi10.eps} \end{figure}$ Figure 10: Colour-magnitude diagram of early-type galaxies in the Hydra I cluster in comparison with Local Group dEs and dSphs. Black filled circles are probable cluster galaxies, selected by their morphology. Red open hexagons mark cluster members, confirmed by radial velocity measurements. Blue open circles are presumable background galaxies (see text for futher explanations). Grey triangles are confirmed background elliptical galaxies with R^1/4 surface brightness profiles. Typical errorbars are indicated. The solid line is a linear fit to dwarf galaxies with M_V>-17 mag (Eq. (1)). Dotted lines are the $2\sigma$ deviations from the fit. Green asterisks represent the Local Group dEs and dSphs (data from Grebel et al. 2003) projected to the Hydra I distance. Mean errors for the LG dwarfs are indicated in the upper left corner.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fi11.eps} \end{figure}$ Figure 11: Magnitude-surface brightness diagram of all early-type dwarf galaxies (M_V>-17 mag) in our sample in comparison with Local Group dEs and dSphs. The symbols are as in Fig. 10. Typical errorbars are indicated. The solid line is a linear fit to the data (Eq. (2)). Dotted lines are the $2\sigma$ deviations from the fit. The dash-dotted line is a fit to the same data, but using a higher distance modulus (see text for details). Green asterisks represent Local Group dEs and dSphs (data from Grebel et al. 2003) projected to the Hydra I distance. The green dashed line is the LG magnitude-surface brightness relation. Mean errors for the LG dwarfs are indicated in the lower left corner. The blue long-dashed line indicates a scale length of $0.7\hbox {$^{\prime \prime }$ }$ for an exponential profile, representing the resolution limit of our images.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fi12.eps} \end{figure}$ Figure 12: Results of the Sérsic fits: effective surface brightness $\mu _{{\rm e}}$ ( top panel), central surface brightness $\mu _0$ ( middle panel) and profile shape index n ( bottom panel) plotted vs. magnitude for all early-type galaxies in our sample. The dashed line in the upper panel indicates an effective radius of 4'' (0.8 kpc at the cluster distance). The solid line in the middle panel is a linear fit to the data (Eq. (3)) with its $2\sigma$ deviations (dotted lines). Red open hexagons mark spectroscopically confirmed cluster members. Typical errorbars are indicated.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fi13.eps} \end{figure}$ Figure 13: Plot of the input-parameter range of the artificial dwarf galaxies (small grey dots). Black dots are the simulated galaxies recovered by SExtractor after applying several cuts (see text for further explanation). The objects from Fig. 11 are plotted as green squares. Equation (2) with its $2\sigma$ deviations is plotted as in Fig. 11. The blue dashed line indicates a scale length of $0.7\hbox {$^{\prime \prime }$ }$ for an exponential profile, representing the resolution limit of our images.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fi14.eps} \end{figure}$ Figure 14: SExtractor output-parameters of the artificial galaxies below the resolution limit (blue dots). The upper left panel shows the input-parameters M_V and $\mu _V$ . The SExtractor output-parameter magbest is plotted against mupeak ( upper right), area ( lower left) and fwhm ( lower right). Green squares are the objects from Fig. 11. Dash-dotted lines indicate the global cuts on magbest, fwhm and area.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fi15.eps} \end{figure}$ Figure 15: Completeness as a function of magnitude for the seven observed fields. The low completeness in field 2 is due to the high geometrical incompleteness.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fi16.eps} \end{figure}$ Figure 16: Luminosity function of the Hydra I dwarf galaxies. The vertical lines mark the 80% and 50% completeness limits. Upper panel: the uncorrected galaxy number counts are displayed by the shaded histogram. The thin grey curve gives a binning independent representation for the counts (Epanechnikov kernel with 0.5 mag width). The completeness corrected number counts are given by the open histogram. The thick black curve represents the completeness corrected number counts with the $1\sigma$ uncertainties (dashed lines). Lower panel: completeness corrected number counts in logarithmic representation. The best fitting single Schechter function (solid red curve) is overlaid. A power-law slope of $\alpha =-1.4$ is indicated by the dashed line.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig1.eps} \end{figure}$	Figure 1: $45'\times 45'$ ( $540 \times 540$ kpc at the cluster distance) image of the Hydra I cluster centred on NGC 3311, extracted from the Digital Sky Survey. The small squares are the fields observed with LDSS2. The large square marks the VIMOS-pointing. The circle indicates the cluster core radius $r_{{\rm c}}=170~h^{-1}$ kpc (Girardi et al. 1995), adopting h=0.75.
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig2.eps} \end{figure}$	Figure 2: Colour-magnitude diagram of all observed objects in the seven LDSS2 fields (the dwarf galaxy sample). Dots (open triangles) mark unresolved (resolved) sources, according to SExtractor star-galaxy classifier (Bertin & Arnouts 1996). The photometry is taken from VLT/FORS1 images (see Sect. 3.1).
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig3.eps} \end{figure}$	Figure 3: Colour-magnitude diagram of all photometrically selected objects in the VIMOS-pointing (the UCD sample). Dots are unresolved sources and open triangles are dwarf galaxy candidates. Green open circles mark objects for which a slit could be allocated on the masks.
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$\begin{figure} \par\includegraphics[width=4.4cm]{0014fi4a.eps}\includegraphics[w... ...dth=4.4cm]{0014fi4c.eps}\includegraphics[width=4.4cm]{0014fi4d.eps} \end{figure}$	Figure 4: Thumbnails of four cluster dwarf galaxy candidates that fulfil the selection criteria. The thumbnail sizes are $40''\times 40''$ ( $8\times 8$ kpc at the cluster distance).
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig5.eps} \end{figure}$	Figure 5: Coordinate map of the cluster dwarf galaxy candidates, confirmed cluster members, background galaxies and major cluster galaxies with their corresponding NGC number. The seven observed VLT/FORS1 fields are marked by large open squares, the field number is indicated.
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig6.eps} \end{figure}$	Figure 6: Radial velocity distribution of all successfully measured objects with $v_{{\rm rad}}<30~000$ km s^-1 (black histogram). The grey histogram shows the data from CZ03. Vertical dashed lines mark the velocity range assumed for cluster membership. Note also the overdensity at $v_{{\rm rad}} \sim 11~000$ km s^-1 from which we identify five members.
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fig7.eps} \end{figure}$	Figure 7: Coordinates of the 494 objects that were selected for spectroscopy (small dots). Small open circles mark the 365 observed objects, small filled circles are the 126 objects for which a reliable radial velocity could be determined. Red filled circles are cluster members, green open squares mark the 8 newly confirmed cluster members.
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{0014fi15.eps} \end{figure}$	Figure 15: Completeness as a function of magnitude for the seven observed fields. The low completeness in field 2 is due to the high geometrical incompleteness.
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