All Figures

$\begin{figure} \par\includegraphics[clip,angle=270,width=8.8cm,clip]{Wolff1.ps} \end{figure}$ Figure 1: COMBO-17 filter set: total system efficiencies are shown in the COMBO-17 passbands, including two telescope mirrors, camera, CCD detector and average La Silla atmosphere. Combining all observations provides a low-resolution spectrum for all objects in the field.
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In the text

$\begin{figure} \par\includegraphics[clip,angle=270,width=11cm,clip]{Wolff2.ps} \end{figure}$ Figure 2: Filter spectra of example quasars: the three panels show quasars at different redshifts across the range addressed in this paper. The filter spectra are plotted with horizontal bars resembling the filter width and vertical bars for 1 $\sigma$ flux errors. Due to variability repeated observations in B and R filters can show different flux levels for the same object. Variability is compensated for the construction of SEDs using R-band images which are available for every observing run. The best-fitting template spectra at indicated redshifts are plotted as grey lines.
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In the text

$\begin{figure} \par\includegraphics[clip,angle=270,width=8.8cm,clip]{Wolff3.ps} \end{figure}$ Figure 3: The present sample of 192 quasars: distribution of redshifts over observed R-band magnitude. Notice that the sample has been truncated at z=1.2 and R=24.
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In the text

$\begin{figure} \par\includegraphics[clip,width=8.8cm,clip]{Wolff4.ps} \end{figure}$ Figure 4: Completeness map for quasar selection and redshift estimation: Grey-scale and contour maps demonstrating how the fraction of quasars having successful redshift measurements depends on magnitude and redshift. Completeness levels are shown as a greyscale from 0% (light grey) to 120% (black). Contour lines are drawn for 90% (white) and 50% completeness (black). Values above 100% occur when redshift aliasing creates local overdensities in the estimated z-distribution based on a flat underlying simulated distribution. See Sect. 3.3 for a more detailed discussion of the completeness correction.
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In the text

$\begin{figure} \par\includegraphics[clip,angle=270,width=14cm,clip]{Wolff5.ps} \end{figure}$ Figure 5: Spectroscopic vs. multi-colour redshifts: 22 QSOs from the COMBO-17 sample at R<24 have spectroscopic identifications. 21 of them were found to be QSOs at redshifts within $\pm 0.05$ of the multi-colour estimate, one of them is a White Dwarf/M dwarf-pair estimated at z<1.
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In the text

$\begin{figure} \par\includegraphics[clip,width=8.8cm,clip]{Wolff6.ps} \end{figure}$ Figure 6: Cumulative surface density of AGN as a function of R band magnitude, corrected for Galactic extinction.
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In the text

$\begin{figure} \par\includegraphics[clip,width=8.8cm,clip]{Wolff7.ps} \end{figure}$ Figure 7: Derivation of the internal K correction used in this paper: each point corresponds to one individual AGN measurement based on the SED fits within COMBO-17. The horizontal line is a linear fit, allowing to predict luminosities at 145 nm with an accuracy of 0.24 mag.
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In the text

$\begin{figure} \par\includegraphics[clip,width=8.8cm,clip]{Wolff8.ps} \end{figure}$ Figure 8: Distribution of the input sample over absolute magnitudes and redshifts: the dashed lines indicate the imposed sample limits of z>1.2 and R<24.
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In the text

$\begin{figure} \par\includegraphics[clip,width=16cm,clip]{Wolff9a.ps}\\ [2ex] \includegraphics[clip,width=16cm,clip]{Wolff9b.ps} \end{figure}$ Figure 9: a) Binned differential luminosity functions for six non-overlapping redshift shells. Only luminosity bins completely covered by the sample are shown. In addition to the data with Poissonian error bars, each panel features the 1.8 < z < 2.4luminosity function as reference. b) Cumulative luminosity functions for the same redshift shells.
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In the text

$\begin{figure} \par\includegraphics[clip,width=17cm,clip]{Wolff10.ps} \end{figure}$ Figure 10: Best-fit parametric representations of the evolving luminosity function, plotted against the binned LF data from Fig. 9a. The density evolution model is shown by the solid, the luminosity evolution model by the dashed lines.
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In the text

$\begin{figure} \par\includegraphics[clip,width=14cm,clip]{Wolff11.ps} \end{figure}$ Figure 11: Evolution of comoving AGN space density with redshift, for different lower luminosity limits, and for two cosmological models. Filled circles: M₁₄₅ < -24; open circles: M₁₄₅ < -25; filled squares: M₁₄₅ < -26; open triangles: M₁₄₅ < -27. The corresponding curves are integrated from the best-fit PDE models.
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In the text

$\begin{figure} \par\includegraphics[clip,width=8.8cm,clip]{Wolff12.ps} \end{figure}$ Figure 12: Integrated UV luminosity density $\varrho _{\rm L(145)}$ as a function of redshift, estimated from the cumulative LF (data points) and for both PDE (solid) and PLE (dashed) models. Below z = 1.2 the relations are extrapolated (dotted lines). The discrepancy between PLE and PDE around the maximum is entirely due to the differences in the bright-end slope of the luminosity function.
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In the text

$\begin{figure} \par\includegraphics[clip,angle=270,width=13.5cm,clip]{Wolff13.ps} \end{figure}$ Figure 13: Best-fitting parametric models of quasar space density in comparison: solid lines are constrained by respective surveys and dashed lines are extrapolations to fainter luminosities. Left: COMBO-17 with 2QZ and SDSS (Fan et al.), at luminosities of $M_{145} < [-28 \ldots -24]$ . The apparent disagreement of COMBO-17 with 2QZ at brightest luminosities should not be taken seriously as the curves show the best-fitting model and not actual LF data. Right: COMBO-17 with WHO and SSG, at luminosities of M₁₄₅ < [-28,-27,-26].
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In the text

$\begin{figure} \par\includegraphics[clip,angle=270,width=10.5cm,clip]{Wolff14.ps} \end{figure}$ Figure 14: Filter spectra of the three z>4.5 COMBO-17 quasars in the present sample. See Fig. 2 for interpretation of the symbols.
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In the text

$\begin{figure} \par\includegraphics[clip,angle=270,width=8.8cm,clip]{Wolff1.ps} \end{figure}$	Figure 1: COMBO-17 filter set: total system efficiencies are shown in the COMBO-17 passbands, including two telescope mirrors, camera, CCD detector and average La Silla atmosphere. Combining all observations provides a low-resolution spectrum for all objects in the field.
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$\begin{figure} \par\includegraphics[clip,angle=270,width=8.8cm,clip]{Wolff3.ps} \end{figure}$	Figure 3: The present sample of 192 quasars: distribution of redshifts over observed R-band magnitude. Notice that the sample has been truncated at z=1.2 and R=24.
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$\begin{figure} \par\includegraphics[clip,angle=270,width=14cm,clip]{Wolff5.ps} \end{figure}$	Figure 5: Spectroscopic vs. multi-colour redshifts: 22 QSOs from the COMBO-17 sample at R<24 have spectroscopic identifications. 21 of them were found to be QSOs at redshifts within $\pm 0.05$ of the multi-colour estimate, one of them is a White Dwarf/M dwarf-pair estimated at z<1.
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$\begin{figure} \par\includegraphics[clip,width=8.8cm,clip]{Wolff6.ps} \end{figure}$	Figure 6: Cumulative surface density of AGN as a function of R band magnitude, corrected for Galactic extinction.
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$\begin{figure} \par\includegraphics[clip,width=8.8cm,clip]{Wolff7.ps} \end{figure}$	Figure 7: Derivation of the internal K correction used in this paper: each point corresponds to one individual AGN measurement based on the SED fits within COMBO-17. The horizontal line is a linear fit, allowing to predict luminosities at 145 nm with an accuracy of 0.24 mag.
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$\begin{figure} \par\includegraphics[clip,width=8.8cm,clip]{Wolff8.ps} \end{figure}$	Figure 8: Distribution of the input sample over absolute magnitudes and redshifts: the dashed lines indicate the imposed sample limits of z>1.2 and R<24.
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$\begin{figure} \par\includegraphics[clip,width=16cm,clip]{Wolff9a.ps}\\ [2ex] \includegraphics[clip,width=16cm,clip]{Wolff9b.ps} \end{figure}$	Figure 9: a) Binned differential luminosity functions for six non-overlapping redshift shells. Only luminosity bins completely covered by the sample are shown. In addition to the data with Poissonian error bars, each panel features the 1.8 < z < 2.4luminosity function as reference. b) Cumulative luminosity functions for the same redshift shells.
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$\begin{figure} \par\includegraphics[clip,width=17cm,clip]{Wolff10.ps} \end{figure}$	Figure 10: Best-fit parametric representations of the evolving luminosity function, plotted against the binned LF data from Fig. 9a. The density evolution model is shown by the solid, the luminosity evolution model by the dashed lines.
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$\begin{figure} \par\includegraphics[clip,width=14cm,clip]{Wolff11.ps} \end{figure}$	Figure 11: Evolution of comoving AGN space density with redshift, for different lower luminosity limits, and for two cosmological models. Filled circles: M₁₄₅ < -24; open circles: M₁₄₅ < -25; filled squares: M₁₄₅ < -26; open triangles: M₁₄₅ < -27. The corresponding curves are integrated from the best-fit PDE models.
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$\begin{figure} \par\includegraphics[clip,width=8.8cm,clip]{Wolff12.ps} \end{figure}$	Figure 12: Integrated UV luminosity density $\varrho _{\rm L(145)}$ as a function of redshift, estimated from the cumulative LF (data points) and for both PDE (solid) and PLE (dashed) models. Below z = 1.2 the relations are extrapolated (dotted lines). The discrepancy between PLE and PDE around the maximum is entirely due to the differences in the bright-end slope of the luminosity function.
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$\begin{figure} \par\includegraphics[clip,angle=270,width=10.5cm,clip]{Wolff14.ps} \end{figure}$	Figure 14: Filter spectra of the three z>4.5 COMBO-17 quasars in the present sample. See Fig. 2 for interpretation of the symbols.
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