All Figures

$\begin{figure} \par\includegraphics[scale=0.80]{0157f1.eps} \end{figure}$ Figure 1: Schematic view of the WFI dither pattern. The full lines denote the edges of the $25\hbox {$.\mkern -4mu^\prime $ }1\times 32\hbox {$.\mkern -4mu^\prime $ }7$ field of view in the dithered 600 s exposures. Dashed lines mark the 6 2k $\times$ 4k chips with the inter-chip gaps. After rotating the instrument by $10\hbox {$^\circ $ }$ about its origin in the focal plane (cross) three further 600 s exposures were taken.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{0157f2.eps} \end{figure}$ Figure 2: Flat-fielded sky-subtracted and combined slitless spectroscopic WFI field in the vicinity of HE 0940-1050. The spectra were taken with the B filter and without rotation (i.e. north is up and east is left on the image). The dispersion runs horizontally from left to right. The three dithered 600 s exposures were combined to fill the inter-chip gaps. The (linear) intensity of each pixel is weighted by its effective exposure time. The total dimension of the combined image is $26\hbox {$.\mkern -4mu^\prime $ }16\times 33\hbox {$.\mkern -4mu^\prime $ }53$ .
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[scale=1]{0157f3.eps} \end{figure}$ Figure 3: Masking of unwanted spectral orders. The upper panel shows a $850\hbox {$^{\prime \prime }$ }\times 45\hbox {$^{\prime \prime }$ }$ region of a sky-subtracted 600 s B band exposure of the field around HE 0940-1050. A bright star in this region generates the indicated different spectral orders in the slitless exposure that may contaminate 1st-order spectra of nearby sources. The white stripe marks a vertical inter-chip gap. The lower panel displays the corresponding region of the variance image. Black rectangles show masked spectral orders of the bright star and other objects. Dark vertical stripes correspond to masked bad columns on the chips.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f4.eps}} \end{figure}$ Figure 4: Sensitivity curves of the WFI B and V filters derived from the spectrophotometric standard HD 49798. At $\sim$ 4700 Å one triggered photoelectron per second per $\simeq$ 6.7 Å pixel corresponds to a flux density of $10^{-16}~{\rm erg}~{\rm cm}^{-2}~{\rm s}^{-1}~{\rm \AA}^{-1}$ . Dotted lines mark the considered wavelength range.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f5.eps}} \end{figure}$ Figure 5: Differential source density of the survey fields in $\Delta V=0.5$ mag bins derived from the DSS plates. The colours indicate different estimated limiting magnitudes ( $V_{\rm lim}\simeq 20.5$ : CTQ 0460, Q 0302-003, Q 1209+093, PKS 2126-158, $V_{\rm lim}\simeq 21.0$ : BR 1117-1329, BR 1202-0725, HE 0940-1050, HE 2243-6031, PKS 0528-250, Q 0420-388, Q 1451+123, Q 2139-4434, $V_{\rm lim}\simeq 21.5$ : CTQ 0247, Q 0055-269, HE 2347-4342, Q 0000-263, Q 0002-422, Q 0347-383).
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[angle=270]{0157f6.eps}} \end{figure}$ Figure 6: Integrated WFI V magnitude vs. median S/N in the WFI spectra in the field of HE 0940-1050 (dots). The line shows the fitted log-linear relation of the magnitude and the S/N for this field.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f7.eps}} \end{figure}$ Figure 7: Visibility of strong emission lines over the covered wavelength range. Dashed lines mark gaps without major emission lines where quasar candidates are missed.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f8.eps}} \end{figure}$ Figure 8: Slitless spectra (black) and corresponding $1\sigma$ noise arrays (green/grey) of four emission line galaxies showing blended [O III] emission. H $\beta$ can be recognised as well.
Open with DEXTER

In the text

$\begin{figure} \includegraphics[width=18cm]{0157f9.eps} \end{figure}$ Figure 9: Slitless WFI spectra of two newly discovered quasars near HE 0940-1050. The upper left panel shows a close-up of the combined slitless B-filtered exposures in the field of HE 0940-1050 taken without rotation (Fig. 2). The dispersion runs horizontally from left to right. The lower left panel shows a direct WFI B band image of the corresponding sky region north-east of HE 0940-1050 ( $6\hbox {$.\mkern -4mu^\prime $ }10\times 1\hbox {$.\mkern -4mu^\prime $ }19$ ). The indicated objects display prominent emission lines in the slitless data. The right panels show the automatically reduced and calibrated one-dimensional B band spectra of the two quasars (black) and their $1\sigma$ noise arrays (green/grey). Both of them display Ly $\alpha$ emission blended with N V at the indicated redshifts.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f10.eps}} \end{figure}$ Figure 10: Blue magnitudes of the quasar candidates observed with the VLT. The abscissa shows the photometric B magnitudes obtained from the aquisition images, the ordinate the difference to the magnitudes integrated from the slit spectra. Full (open) circles correspond to measurements with (without) correction for slit losses. The line marks a perfect 1:1 relation between $B_{\rm phot}$ and $B_{\rm spec}$ .
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f11.eps}} \end{figure}$ Figure 11: Comparison of the redshifts obtained with FORS2 and WFI. Circles (+ signs) denote quasar candidates with almost secure (uncertain) WFI redshifts. Previously known quasars in the fields have been added with their published redshift in comparison to the redshift measured in the slitless spectra ( $\times$ signs). The line marks a 1:1 relation.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=18cm]{0157f12.eps} \end{figure}$ Figure 12: VLT/FORS2 spectra of the 11 discovered quasars in the vicinity of HE 0940-1050. The spectra are shown in black together with their $1\sigma$ noise arrays (green/grey). The spectra have been scaled to yield the measured photometric B magnitudes. Major emission lines are labelled. The small inserts show the corresponding slitless WFI spectra in the same units.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f13.eps}} \end{figure}$ Figure 13: Slitless spectra (black) and corresponding $1\sigma$ noise arrays (green/grey) of 10 quasar candidates in the field of PKS 0528-250 with indicated coordinates, approximate V magnitudes and estimated redshifts with confidence level (! = secure, + = plausible, : = uncertain). Major emission lines are labelled.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,scale=1.04]{0157f14.eps} \end{figure}$ Figure 14: Redshift histograms of confirmed previously unknown quasars (cross-hashed), rediscovered quasars (hashed) and remaining quasar candidates (open).
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=18.0cm]{0157f15.eps} \end{figure}$ Figure 15: Distributions of quasars in three of the survey fields (upper panels: HE 0940-1050, middle panels: Q 2139-4434, lower panels: HE 2243-6031). Left panels: angular separation distribution of quasars and quasar candidates with respect to the central quasar as a function of redshift. Asterisks and star symbols mark known quasars and newly discovered confirmed quasars, respectively. Crosses show remaining WFI quasar candidates. Symbol size indicates apparent optical magnitude. Right panels: quasar distribution on the sky centred on the targeted known quasar in the field with indicated redshifts. Objects at $z\ge 1.7$ (z<1.7) are shown in black (red/grey). The rectangle marks the nominal contiguous slitless WFI field of view ( $26\hbox {$.\mkern -4mu^\prime $ }2\times 33\hbox {$.\mkern -4mu^\prime $ }5$ ) without rotating the instrument, for simplicity centred on the central quasar. New quasars located slightly outside the nominal field of view are due to field rotation and small offsets of the actual field centre.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[angle=270]{0157f16.eps}} \end{figure}$ Figure 16: Survey selection function as a function of redshift and apparent V magnitude. Contours correspond to median simulated detection probabilities $p\in\left\lbrace0.2,0.4,0.6,0.8,0.99\right\rbrace$ . Full and open circles mark newly discovered confirmed quasars and known quasars, respectively. Crosses denote remaining candidates.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=18.0cm]{0157af1a.eps} \end{figure}$ Figure A.1: VLT/FORS2 spectra (black) and $1\sigma$ noise arrays (green) of 57 quasars discovered in the QNQ survey. Spectra presented in Worseck & Wisotzki (2006), Worseck et al. (2007) and in Fig. 12 of this paper are not shown. The spectra have been scaled to yield the measured photometric B magnitudes. The small inserts show the corresponding slitless WFI spectra in the same units. The spectra are ordered columnwise by right ascension of the field and redshift of the quasar.
Open with DEXTER

In the text

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=18cm]{0157af1b.eps} \end{figure}$ Figure A.1: continued.
Open with DEXTER

In the text

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=18cm]{0157af1c.eps} \end{figure}$ Figure A.1: continued.
Open with DEXTER

In the text

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=18cm]{0157af1d.eps} \end{figure}$ Figure A.1: continued.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=16cm]{0157bf1a.eps} \end{figure}$ Figure B.1: RA-ordered list of slitless WFI spectra of 88 unknown quasar candidates without follow-up spectra. The spectra are shown in black together with their $1\sigma$ noise arrays (green/grey) if the S/N is low. The (approximate) flux densities are given in $10^{-17}~{\rm erg}~{\rm cm}^{-2}~{\rm s}^{-1}~{\rm \AA}^{-1}$ . Labelled are the celestial coordinates (format: HHMMSS.SDDMMSS, J2000), the integrated V magnitude and the estimated redshift. Ambiguous redshifts guessed from a single emission line are marked by a colon. Plus signs mark plausible redshift estimates. Exclamation marks stand for almost secure redshifts based on the shape of a single line or the detection of two lines either in the principal spectral range 4200 Å $\le$ $\lambda$ $\le$ 5800 Å or the R band spectra if available. J005840.0-263314 is a prominent BAL QSO.
Open with DEXTER

In the text

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=16cm]{0157bf1b.eps} \end{figure}$ Figure B.1: continued. Note that the field of PKS 0528-250 with 7 bona fide quasar candidates was not included in the follow-up campaign with FORS2.
Open with DEXTER

In the text

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=16cm]{0157bf1c.eps} \end{figure}$ Figure B.1: continued.
Open with DEXTER

In the text

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=16cm]{0157bf1d.eps} \end{figure}$ Figure B.1: continued. The spectrum of J214326.2-442036 might be contaminated by a nearby galaxy. Francis et al. (2004) list J214124.0-443301 as a quasar candidate with uncertain redshift, whereas they identified J214119.4-441256 as a galaxy at z=0.062 which is not supported by the slitless WFI spectrum.
Open with DEXTER

In the text

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=15cm]{0157bf1e.eps} \end{figure}$ Figure B.1: continued.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=17.5cm]{0157cf1.eps} \end{figure}$ Figure C.1: As Fig. 15 for the field centred near Q 0000-263.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=17.5cm]{0157cf2.eps} \end{figure}$ Figure C.2: As Fig. 15 for the field centred near Q 0002-422.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=17.5cm]{0157cf3.eps} \end{figure}$ Figure C.3: As Fig. 15 for the field centred near Q 0055-269.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf4.eps} \end{figure}$ Figure C.4: As Fig. 15 for the field centred near Q 0302-003.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf5.eps} \end{figure}$ Figure C.5: As Fig. 15 for the field centred near Q 0347-383.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf6.eps} \end{figure}$ Figure C.6: As Fig. 15 for the field centred near CTQ 0247.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf7.eps} \end{figure}$ Figure C.7: As Fig. 15 for the field centred near Q 0420-388.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf8.eps} \end{figure}$ Figure C.8: As Fig. 15 for the field centred near PKS 0528-250.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf9.eps} \end{figure}$ Figure C.9: As Fig. 15 for the field centred near CTQ 0460.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf10.eps} \end{figure}$ Figure C.10: As Fig. 15 for the field centred near BR 1117-1329.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf11.eps} \end{figure}$ Figure C.11: As Fig. 15 for the field centred near BR 1202-0725.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf12.eps} \end{figure}$ Figure C.12: As Fig. 15 for the field centred near Q 1209+093.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf13.eps} \end{figure}$ Figure C.13: As Fig. 15 for the field centred near Q 1451+123.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf14.eps} \end{figure}$ Figure C.14: As Fig. 15 for the field centred near PKS 2126-158.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf15.eps} \end{figure}$ Figure C.15: As Fig. 15 for the field centred near HE 2347-4342.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f4.eps}} \end{figure}$	Figure 4: Sensitivity curves of the WFI B and V filters derived from the spectrophotometric standard HD 49798. At $\sim$ 4700 Å one triggered photoelectron per second per $\simeq$ 6.7 Å pixel corresponds to a flux density of $10^{-16}~{\rm erg}~{\rm cm}^{-2}~{\rm s}^{-1}~{\rm \AA}^{-1}$ . Dotted lines mark the considered wavelength range.
Open with DEXTER

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[angle=270]{0157f6.eps}} \end{figure}$	Figure 6: Integrated WFI V magnitude vs. median S/N in the WFI spectra in the field of HE 0940-1050 (dots). The line shows the fitted log-linear relation of the magnitude and the S/N for this field.
Open with DEXTER

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f7.eps}} \end{figure}$	Figure 7: Visibility of strong emission lines over the covered wavelength range. Dashed lines mark gaps without major emission lines where quasar candidates are missed.
Open with DEXTER

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f8.eps}} \end{figure}$	Figure 8: Slitless spectra (black) and corresponding $1\sigma$ noise arrays (green/grey) of four emission line galaxies showing blended [O III] emission. H $\beta$ can be recognised as well.
Open with DEXTER

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f11.eps}} \end{figure}$	Figure 11: Comparison of the redshifts obtained with FORS2 and WFI. Circles (+ signs) denote quasar candidates with almost secure (uncertain) WFI redshifts. Previously known quasars in the fields have been added with their published redshift in comparison to the redshift measured in the slitless spectra ( $\times$ signs). The line marks a 1:1 relation.
Open with DEXTER

$\begin{figure} \par\includegraphics[width=18cm]{0157f12.eps} \end{figure}$	Figure 12: VLT/FORS2 spectra of the 11 discovered quasars in the vicinity of HE 0940-1050. The spectra are shown in black together with their $1\sigma$ noise arrays (green/grey). The spectra have been scaled to yield the measured photometric B magnitudes. Major emission lines are labelled. The small inserts show the corresponding slitless WFI spectra in the same units.
Open with DEXTER

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{0157f13.eps}} \end{figure}$	Figure 13: Slitless spectra (black) and corresponding $1\sigma$ noise arrays (green/grey) of 10 quasar candidates in the field of PKS 0528-250 with indicated coordinates, approximate V magnitudes and estimated redshifts with confidence level (! = secure, + = plausible, : = uncertain). Major emission lines are labelled.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,scale=1.04]{0157f14.eps} \end{figure}$	Figure 14: Redshift histograms of confirmed previously unknown quasars (cross-hashed), rediscovered quasars (hashed) and remaining quasar candidates (open).
Open with DEXTER

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics[angle=270]{0157f16.eps}} \end{figure}$	Figure 16: Survey selection function as a function of redshift and apparent V magnitude. Contours correspond to median simulated detection probabilities $p\in\left\lbrace0.2,0.4,0.6,0.8,0.99\right\rbrace$ . Full and open circles mark newly discovered confirmed quasars and known quasars, respectively. Crosses denote remaining candidates.
Open with DEXTER

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=18cm]{0157af1b.eps} \end{figure}$	Figure A.1: continued.
Open with DEXTER

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=16cm]{0157bf1b.eps} \end{figure}$	Figure B.1: continued. Note that the field of PKS 0528-250 with 7 bona fide quasar candidates was not included in the follow-up campaign with FORS2.
Open with DEXTER

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=16cm]{0157bf1c.eps} \end{figure}$	Figure B.1: continued.
Open with DEXTER

$\begin{figure} \addtocounter{figure}{-1} \includegraphics[width=16cm]{0157bf1d.eps} \end{figure}$	Figure B.1: continued. The spectrum of J214326.2-442036 might be contaminated by a nearby galaxy. Francis et al. (2004) list J214124.0-443301 as a quasar candidate with uncertain redshift, whereas they identified J214119.4-441256 as a galaxy at z=0.062 which is not supported by the slitless WFI spectrum.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=17.5cm]{0157cf1.eps} \end{figure}$	Figure C.1: As Fig. 15 for the field centred near Q 0000-263.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=17.5cm]{0157cf2.eps} \end{figure}$	Figure C.2: As Fig. 15 for the field centred near Q 0002-422.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=17.5cm]{0157cf3.eps} \end{figure}$	Figure C.3: As Fig. 15 for the field centred near Q 0055-269.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf4.eps} \end{figure}$	Figure C.4: As Fig. 15 for the field centred near Q 0302-003.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf5.eps} \end{figure}$	Figure C.5: As Fig. 15 for the field centred near Q 0347-383.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf6.eps} \end{figure}$	Figure C.6: As Fig. 15 for the field centred near CTQ 0247.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf7.eps} \end{figure}$	Figure C.7: As Fig. 15 for the field centred near Q 0420-388.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf8.eps} \end{figure}$	Figure C.8: As Fig. 15 for the field centred near PKS 0528-250.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf9.eps} \end{figure}$	Figure C.9: As Fig. 15 for the field centred near CTQ 0460.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf10.eps} \end{figure}$	Figure C.10: As Fig. 15 for the field centred near BR 1117-1329.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf11.eps} \end{figure}$	Figure C.11: As Fig. 15 for the field centred near BR 1202-0725.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf12.eps} \end{figure}$	Figure C.12: As Fig. 15 for the field centred near Q 1209+093.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf13.eps} \end{figure}$	Figure C.13: As Fig. 15 for the field centred near Q 1451+123.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf14.eps} \end{figure}$	Figure C.14: As Fig. 15 for the field centred near PKS 2126-158.
Open with DEXTER

$\begin{figure} \par\includegraphics[angle=270,width=18.0cm]{0157cf15.eps} \end{figure}$	Figure C.15: As Fig. 15 for the field centred near HE 2347-4342.
Open with DEXTER