A&A 487, 539-554 (2008)
DOI: 10.1051/0004-6361:200810157
G. Worseck1 - L. Wisotzki1 - F. Selman2
1 - Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
2 -
European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago, Chile
Received 7 May 2008 / Accepted 10 June 2008
Abstract
We present the results of the ``Quasars near Quasars'' (QNQ) survey, a CCD-based
slitless spectroscopic survey for faint quasars at
on 18
fields centred on bright quasars at
2.76<z<4.69. In total 169 quasar candidates with emission lines were selected
from the extracted flux-calibrated spectra on the basis of well-defined automatic
selection criteria followed by visual inspection and verification. With follow-up
spectroscopy of 81 candidates that were likely to reside at z>1.7 we were able
to confirm 80 new quasars at
on 16 of our fields. 64 of the
newly discovered quasars are located at z>1.7. The overall high success rate
implies that most of the remaining 88 candidates are quasars as well, although
the majority of them likely resides at z<1.7 on the basis of the observed line
shapes and strengths. Due to the insufficient depth of the input source
catalogues needed for extraction of the slitless spectra our survey is not well
defined in terms of limiting magnitude for faint
quasars whose
Ly
emission is detectable well beyond V=22, albeit at a continuum
.
While not useful for characterising the evolving space density of
quasars, our sample provides many new closely spaced quasar sightlines around
intensely studied quasars for further investigations on the three-dimensional
distribution of the intergalactic medium.
Key words: surveys - galaxies: quasars: general - galaxies: intergalactic medium - cosmology: large-scale structure of Universe
Recent large optical surveys, such as the Sloan Digital Sky Survey (SDSS) and
the 2dF QSO Redshift Survey (2QZ), have revealed thousands of previously
unknown quasars selected on the basis of their broadband optical colours
(Croom et al. 2004; Schneider et al. 2007). Colour selection is efficient if quasar
candidates are well separated from normal stars in multidimensional colour
space, most notably at
(UV excess) and at
.
However, even
optical multicolour surveys are systematically incomplete at
,
where the colours of quasars and stars are similar
(e.g. Warren et al. 1991; Richards et al. 2002a). Incompleteness in this redshift range
can be significantly reduced by a better tracing of the spectral energy
distributions with additional filters, e.g. by incorporating mediumband
filters as in the COMBO-17 survey (Wolf et al. 2003).
Alternatively, slitless spectroscopy is a particularly efficient way to
find quasars at redshifts
because of the prominent Ly
emission
line redshifted into the optical wavelength regime. Early surveys
generated hundreds of quasars by visual scanning of objective-prism
photographic plates for emission-line objects
(e.g. Osmer & Smith 1980; Crampton et al. 1985).
Subjecting such plates to digitisation with fast measuring machines
made it possible to employ the automated selection of quasar candidates
(Hewett et al. 1985; Clowes et al. 1984) and to build substantial quasar samples
at redshifts
(Wisotzki et al. 2000; Hewett et al. 1995).
The systematic CCD-based slitless survey for
quasars
by Schneider et al. (1994) was among the first to quantify the declining space
density of high-redshift quasars (Schmidt et al. 1995).
Apparent pairs or close groups of high-redshift quasars are very attractive
targets to study the three-dimensional distribution of the intergalactic
medium (IGM). But high-resolution studies have so far been limited to a small number
of suitable groups of bright quasars (e.g. D'Odorico et al. 2002,2006).
Going fainter than
immediately limits the achievable spectral
resolution and S/N. A possible compromise lies in combining high-resolution
spectra of bright quasars with lower resolution, lower S/N data of fainter
quasars in the surroundings. Pichon et al. (2001) argued that one can significantly
improve the recovery of the 3-dimensional topology of the IGM this way.
Although most known quasars were colour-selected from either SDSS or 2QZ, these
surveys produced relatively few useful quasar groups because of the reduced
selection efficiency at
combined with a bright magnitude limit. In
fact, most well-studied close groups of quasars at z>2 were found by slitless
spectroscopy. Follow-up spectroscopy of candidates by Bohuski & Weedman (1979) revealed
13 z>1.5 quasars on 2.1 deg2 (Jakobsen & Perryman 1992) with two showing
correlated complex intergalactic C IV absorption at
1.48<z<2.15,
indicative of an elongated superstructure extending over
on the sky
(e.g. Jakobsen et al. 1986; Dinshaw & Impey 1996). Another group discovered by
Sramek & Weedman (1978) contains now 6 QSOs at
within a radius of
20
around Q 1623 + 2653, all of which are bright enough for correlation
studies of the IGM (e.g. Crotts & Fang 1998). Williger et al. (1996) reported
25 quasars at
within a
1 deg2 region and used these to
reveal large-scale structure in the IGM (Liske et al. 2000; Williger et al. 2000). At lower
redshifts, slitless surveys revealed large associations of quasars at similar
redshift (Clowes et al. 1999; Crampton et al. 1990).
Groups of quasars, or more generally speaking, active galactic nuclei, have also been discovered by recent deep multi-wavelength surveys in selected fields, such as in the Chandra Deep Fields North (Barger et al. 2003; Cowie et al. 2004) and South (Szokoly et al. 2004; Wolf et al. 2004), the Marano field (Krumpe et al. 2007; Zitelli et al. 1992), or the COSMOS field (Prescott et al. 2006; Trump et al. 2007). However, the majority of the AGN thus found are too faint for follow-up studies at a spectral resolution allowing for meaningful IGM studies.
Complementary to slitless spectroscopy, quasar pairs can be found from
similarities in multi-colour space. Using this approach, Hennawi et al. (2006b)
confirmed 40 new associated and 73 projected quasar pairs with separations
from a sample of faint
quasar pair candidates
selected via SDSS photometry. Follow-up spectra revealed transverse clustering
of optically thick absorption systems near foreground quasars
(Hennawi et al. 2006a; Hennawi & Prochaska 2007).
Targeted deep surveys of sky regions around well-studied high-redshift quasars
are rare. An exception are many of the fields selected for the Lyman-break
galaxy survey by Steidel et al. (2003) which were centred on bright quasars to
correlate the galaxies with the intergalactic absorption along the sightline
(Adelberger et al. 2005).
Here we describe a systematic search for apparent quasar groups at
in the southern hemisphere, targeting fields centred on known bright
z>2.7 quasars that had been observed at high resolution with the UV-Visual
Echelle Spectrograph (UVES) at the VLT. We already reported results for two
special fields (Worseck & Wisotzki 2006; Worseck et al. 2007, hereafter Papers I and II,
respectively). The present paper is devoted to present
the entire survey. In Sect. 2 we describe the slitless
spectroscopic survey observations. Section 3 outlines the
automatic reduction pipeline developed for these data.
Section 4 describes the semi-automatic selection of
quasar candidates. We report on the follow-up slit spectroscopy of candidates
in Sect. 5, followed by a brief discussion of the properties
of confirmed quasars and the remaining candidates (Sect. 6).
In Sect. 7 we present the resulting quasar groups and
discuss the efficiency and completeness of our survey. We conclude in
Sect. 8.
The survey was carried out using the ESO Wide Field Imager (WFI, Baade et al. 1999) at the ESO/MPI 2.2 m Telescope (La Silla) in its slitless spectroscopic mode (Wisotzki et al. 2001). Since this mode has been rarely used we shortly describe its main characteristics.
The WFI is a focal-reducer type camera offering a field of view of
sampled by a mosaic of 8 2k
4k CCDs with
/pixel. In the slitless spectroscopic mode a low-resolution grism
is placed in the converging beam of the telescope in front of the WFI in order
to disperse the light of every object in the field of view. A blue-blazed
grism and a red-blazed grism are available. However, the red-blazed grism
(R50, dispersion
7 Å/pixel, blaze wavelength 6000 Å,
Å FWHM) has a much higher throughput for 1st-order
spectroscopy even in the blue (Wisotzki et al. 2001), rendering the blue-blazed
B50 grism almost obsolete. We only used the R50 grism. As both grisms were
originally constructed for the prime focus of the ESO 3.6 m telescope (long
decommissioned) and only retrofitted into WFI, the size of the grisms does not
fully match that of the WFI field of view. In a
strip on the left
side of the chip mosaic the light passes undispersed, effectively reducing
the usable field of view to 6 of the 8 WFI CCDs, or
.
During two visitor mode runs in October 2002 (5 nights) and February 2003
(3 nights) we observed in total 18 fields centred on bright high-redshift
quasars with available UVES spectra in order to find faint quasars in their
surroundings. We additionally included the Extended Chandra Deep Field South
(ECDFS) to compare our selection with the results of deeper multiwavelength
surveys.
Field | z | ![]() |
![]() |
Night | Filters | Rotations [
![]() |
Exposure [s] | Seeing [
![]() |
Q 0000-263 | 4.125 | 00
![]() ![]() ![]() |
![]() |
03 Oct. 2002 | B, V | 0 | 1800 | 0.7-1.0 |
04 Oct. 2002 | B, V | 10 | 1800 | 0.9-1.4 | ||||
Q 0002-422 | 2.767 | 00
![]() ![]() ![]() |
![]() |
01 Oct. 2002 | B, V | 0, 10 | 3600 | 1.3-1.6 |
Q 0055-269 | 3.665 | 00
![]() ![]() ![]() |
![]() |
02 Oct. 2002 | B, V | 0, 10 | 3600 | 0.9-1.5 |
Q 0302-003 | 3.285 | 03
![]() ![]() ![]() |
![]() |
03 Oct. 2002 | B, V | 0 | 1800 | 0.9 |
03 Oct. 2002 | B | 10 | 1800 | 0.9 | ||||
04 Oct. 2002 | V | 10 | 1800 | 0.9-1.1 | ||||
Q 0347-383 | 3.220 | 03
![]() ![]() ![]() |
![]() |
27 Feb. 2003 | B, V | 10 | 1800 | 1.0 |
27 Feb. 2003 | V | 0 | 1800 | 1.0 | ||||
28 Feb. 2003 | B | 0 | 1800 | 1.9 | ||||
CTQ 0247 | 3.025 | 04
![]() ![]() ![]() |
![]() |
30 Sep. 2002 | B, V | 0 | 1800 | 1.3-1.8 |
01 Oct. 2002 | B, V | 10 | 1800 | 1.4-1.8 | ||||
Q 0420-388 | 3.120 | 04
![]() ![]() ![]() |
![]() |
26 Feb. 2003 | B, V | 0, 10 | 3600 | 0.8 |
PKS 0528-250 | 2.813 | 05
![]() ![]() ![]() |
![]() |
03 Nov. 2002 | V | 10 | 1800 | 1.1 |
04 Nov. 2002 | V | 0 | 1800 | 1.2 | ||||
28 Feb. 2003 | B | 0, 10 | 3600 | 1.2 | ||||
HE 0940-1050 | 3.088 | 09
![]() ![]() ![]() |
![]() |
26 Feb. 2003 | B, V | 0, 10 | 3600 | 0.8 |
CTQ 0460 | 3.139 | 10
![]() ![]() ![]() |
![]() |
27 Feb. 2003 | B, V | 0, 10 | 3600 | 1.0-1.5 |
BR 1117-1329 | 3.958 | 11
![]() ![]() ![]() |
![]() |
28 Feb. 2003 | B, V | 0, 10 | 3600 | >2 |
BR 1202-0725 | 4.690 | 12
![]() ![]() ![]() |
![]() |
26 Feb. 2003 | B, V | 0 | 1800 | 0.8 |
27 Feb. 2003 | V | 10 | 1800 | 1.6 | ||||
Q 1209+093 | 3.291 | 12
![]() ![]() ![]() |
![]() |
27 Feb. 2003 | B, V | 0, 10 | 3600 | 1.6 |
Q 1451+123 | 3.246 | 14
![]() ![]() ![]() |
![]() |
28 Feb. 2003 | B, V | 0, 10 | 3600 | 0.8-2.0 |
PKS 2126-158 | 3.285 | 21
![]() ![]() ![]() |
![]() |
30 Sep. 2002 | B, V | 0, 10 | 3600 | 0.8-1.0 |
Q 2139-4434 | 3.214 | 21
![]() ![]() ![]() |
![]() |
03 Oct. 2002 | B, V | 0, 10 | 3600 | 1.0-1.5 |
HE 2243-6031 | 3.010 | 22
![]() ![]() ![]() |
![]() |
02 Oct. 2002 | B, V | 0, 10 | 3600 | 1.0-1.7 |
HE 2347-4342 | 2.885 | 23
![]() ![]() ![]() |
![]() |
04 Oct. 2002 | B, V | 0, 10 | 3600 | 0.8-1.2 |
The sky transparency during the October 2002 run was variable with some thick
cirrus clouds passing occasionally, but mostly the sky was clear. Conditions
were clear to photometric in the February 2003 run. The seeing varied over a
broad range of values (see Table 1) but was mostly of
the order of 1
.
Since the spectral resolution in slitless spectroscopy
is given by the seeing, this quantity varied by
-50.
We used the broadband B and V filters of the WFI to lower the effectively
undispersed sky background and to reduce the degree of crowding by limiting
the length of the spectra. Crowding was further accounted for by taking the
spectra in two instrument rotations (0
and 10
). For all fields
(except the one centred on BR 1202-0725) three dithered 600 s exposures were
taken per band and rotation, resulting in a total exposure time of 1 h per
band. Figure 1 illustrates the observing pattern. The
dithered exposures produced a contiguous
field of view per rotation angle. The combination of the R50 grism with the
broadband B and V filters resulted in a spectral coverage from the blue
sensitivity cutoff at
4200 Å to 5800 Å. An unfiltered spectrum of
the low-redshift emission-line galaxy HE 1250-0256 provided the input for an
approximate wavelength calibration of the slitless data. The
spectrophotometric standard stars HD 49798, LTT 7987 and GD 108 were observed
in astronomical twilight for relative flux calibration. Blank sky fields
observed during twilight provided flat fields. The V band exposures
of the field centred on PKS 0528-250 were retrieved from the ESO Science
Archive (PI Vanzi). Table 1 summarises the slitless
survey observations.
The nominal surveyed area was 4.39 deg2. However, due to the two
rotation angles of the instrument, the field edges received only
1/2 of
the exposure time. Moreover, spectra located near interchip gaps are affected by
dithering. The net exposure time per field is further decreased for some
objects due to contamination by nearby other sources or spectral orders of
bright stars (see Fig. 3 below). However, the two instrument
rotations ensured that a clean spectrum of almost every object was obtained.
Direct images are necessary for object identification in the slitless data. We
primarily relied on images from the Digitised Sky Survey
(DSS)
available for all our fields. For three fields we also employed direct WFI
images taken in service mode.
The slitless data were reduced with a semi-automatic pipeline running under ESO-MIDAS, but largely consisting of our own dedicated software modules. For several parts of the data reduction we could use the extensive toolbox developed for the slitless spectroscopy reduction pipeline of the Hamburg/ESO Survey (HES, Wisotzki et al. 2000). This was supplemented by new software where necessary. Each exposure was reduced separately before combining the extracted spectra. Briefly, the data reduction comprised the following steps:
The magnitude limit of our survey obviously depends on both the depth of the
input source catalogues and on the obtainable S/N in the slitless spectroscopy
data. We estimated the completeness of the source catalogues as a function of
magnitude by considering the differential source counts.
Figure 5 shows the differential surface densities per
mag obtained from the DSS source catalogues in the 18 fields.
From the breaks in the differential number counts we conclude that the input
catalogues are reasonably complete to
,
with 4 fields being shallower
by
0.5 mag. Similar limiting magnitudes were obtained in the three fields
with direct WFI data.
The limiting magnitude of the slitless survey material was determined by
evaluating the continuum S/N of the extracted spectra. The V magnitude of
each object was calculated by integrating the flux over the V band which is
completely covered by the spectra. We estimate that the V magnitudes of
objects are accurate to
0.1 mag. Fainter sources have larger
uncertainties due to their lower S/N. The S/N is a function of the
wavelength-dependent system sensitivity (Fig. 4) and of
the source spectral energy distribution. We defined the median S/N in the
V band as a characteristic value. Recall that the extraction yielded a noise
array along with each spectrum, so that the S/N can be estimated rather
accurately. In Fig. 6 we plot the median S/N of all extracted
1800 spectra in one particular field,
as a function of V magnitude. One can see that a S/N of 3 is obtained
at
,
and for
a S/N of unity is reached.
Some objects appear to have too low S/N for their V magnitude; these
generally have shorter net exposure times induced by dithering and field
rotation. After excluding these outliers we fitted a simple log-linear
relation for the S/N as a function of magnitude,
We conclude that at a magnitude of
,
our survey should be
reasonably complete in terms of the input catalogues, and that the slitless
spectra at these magnitudes are generally still good enough to search for
emission-line objects. We demonstrate below that the selection of even fainter
z>2.4 quasars with prominent Ly
lines was also possible, in some
fields down to
or beyond (corresponding to a continuum S/N
of 1
in the slitless spectra). However, it is clear that only the most promising
candidates will be selected at these faint levels. Moreover, we have seen that
at
,
already the input catalogues are heavily affected by
approaching to the limits of the DSS itself. We return to a more quantitative
assessment of (in)completeness of the quasar samples in
Sect. 7.2 below.
![]() |
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. |
![]() |
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. |
Quasar candidates were semi-automatically selected from the calibrated slitless spectra on the basis of prominent emission lines. Figure 7 shows the redshift ranges in which major quasar emission lines can be observed in the slitless spectra. The detectability of the various emission lines depends on their equivalent widths and the S/N in the data (Sect. 7.2). Moreover, quasar candidates could not be selected in two narrow low-redshift ranges due to the lack of major emission lines (see Fig. 7).
We first estimated a (pseudo-)continuum for each spectrum by applying a simple
median filter with a window width of 400 Å. The
continuum-subtracted spectra were searched automatically for emission line
objects by cross-correlating them with Gaussian emission line templates. The
fields around Q 0000-263, Q 0302-003 and Q 2139-4434 were chosen for
testing the continuum subtraction and the line detection algorithm, ensuring
that all emission line objects selected by eye were also found automatically.
Finally, we chose two Gaussians with dispersions
Å and
of
Å in order to match emission lines with small and
large widths, respectively. Only features detected with a total line
and an observed equivalent width of
Å were kept.
At our spectral resolution, the continuum subtracted spectra of normal stars
often appeared to show ``emission lines'' that in reality were artefacts of poor
continuum estimation and oversubtraction. The initial samples of emission line
objects contained therefore 1/4 of all extracted spectra. However, it
was quite straightforward to beat down this number significantly. First of
all, the equivalent widths of these features were generally quite small.
Secondly, most of the spuriously selected stars had rather red colours.
We quantified a colour measure by defining a ``hardness ratio''
as
![]() |
(2) |
We finally decided to treat emission line candidates with large equivalent
widths differently from those with weak line detections. A strong-lined
object was defined as one with a line
and
Å. If the line was detected in the B band, the object needed to be
moderately blue,
;
this criterion removed most of the
red stars. If the line was detected in the V band, no further restriction
was applied.
A line detection with small equivalent width,
Å,
needed always to be accompanied by a blue but meaningful spectrum, given by the
conditions
and
.
Essentially all Ly
detected quasars, but also some of the C IV
and [O III] detections have large equivalent widths and therefore fell
into the first set of criteria. Quasars at lower redshifts generally have
weaker lines (C IV, C III], Mg II and [O III]),
but are distinctly blue. Note that our highly conservative colour cuts were
only applied after the emission line object selection; these cuts would
by no means have sufficed to select quasar candidates on the basis of their
colours.
After these cuts we visually inspected the selected objects to cull the quasar
candidates from the remaining sample of slitless spectra, dominated by three
types of spurious detections: (i) M stars with strong TiO absorption bands
that our selection criteria did not catch; these features are always at the
same wavelengths and could be recognised with good confidence after some
training; (ii) low-redshift emission line galaxies with [O III] visible
at ;
at the low resolution of the WFI spectra, the
[O III] doublet is blended, resulting in an asymmetric single line that could be
unambiguously identified in almost all cases (see Fig. 8, for
examples). Since emission line galaxies are interesting in their own right, we
kept them in a separate bin; (iii) defective spectra were overlapping 1st
order spectra of two close objects, or spectra with unrecognised zero order
contamination or spectra with unphysical breaks at
5000 Å resulting
from an imperfect splicing of the two bandpasses. Any remaining spectral
overlaps were easily identified by comparing the spectra obtained at the two
instrument rotation angles. All emission line candidates that passed
the visual check of the one-dimensional spectra were finally verified on the
slitless WFI images to check for any remaining flaws that could result in a
spurious emission line. For objects at the field edges detected in only one
instrument rotation (Fig. 1) this visual examination was
essential. In total, 387 emission line objects were selected from the
29 000 objects detected on the DSS images of the 18 survey fields.
![]() |
Figure 8:
Slitless spectra (black) and corresponding ![]() ![]() |
![]() |
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
(
![]() ![]() ![]() |
Visual inspection of the sky-subtracted slitless images revealed three additional candidates that were missed in the DSS catalogues, mainly due to source blending. These fields were reprocessed with the source catalogues of available direct WFI data. At the higher resolution of the direct WFI data, these candidates were resolved and their spectra were successfully extracted. Figure 9 presents the slitless B band data and the corresponding direct WFI image of a region near HE 0940-1050 where two prime quasar candidates were discovered. On the DSS image of this field, QNQ J09434-1053 could not be resolved from the nearby foreground object. The WFI catalogues did not reveal further undetected candidates, confirming our expectation that the fraction of candidates lost due to blended sources is very small.
In total, our semi-automated search for emission line objects yielded 390 sources on the surveyed 4.39 deg2. Of those, 38 we rejected as dubious due to very low S/N. The remaining sample of 351 objects consists of 37 known quasars (including 15 of the 18 targeted central quasars), 169 quasar candidates, and 145 candidate low-redshift star-forming galaxies. The classification was purely based on the slitless spectra. No morphological selection was made.
Most of the emission line galaxies were identified by their blended
[O III] doublet. However, due to low S/N at this low resolution
,
we could not determine whether the H
lines seen in the
spectra are broad or narrow, so that this sample of low-redshift objects might
still contain low-redshift AGN. At the bright end of our survey (
), the
surface density of
emission line galaxies is
1.1 deg-2,
which compares well with other slitless surveys (Bongiovanni et al. 2005; Salzer et al. 2002).
As most of the deeper surveys for emission line galaxies select
H
emission (e.g. Pascual et al. 2001), a comparison at fainter limits is difficult.
In total, we rediscovered 37 previously known quasars in the survey fields with
detectable emission lines in the observed wavelength range. Three of the central
quasars (Q 0000-263, BR 1117-1329 and BR 1202-0725) reside at too high
redshift to be detected in emission. Excluding the central bright quasars, 10
out of 12 known quasars are rediscovered in the range of high selection
probability (,
1.7<z<3.6, see Sect. 7.2 below).
One of the two missed quasars had been recorded in one WFI rotation only,
whereas the other one was not contained in the shallow DSS source catalogue of
the Q 0302-003 field (Fig. 5). The redshifts of the
rediscovered quasars measured in the slitless data are consistent
(within
)
with the published values
(see Sect. 6.2 and Fig. 11 below).
We estimated redshifts of the 169 quasar candidates from the slitless data,
and the candidates were grouped by redshift confidence. The redshifts were
considered to be almost secure if either two emission lines with a consistent
redshift were present in the spectral range, or if a single line could be
confidently identified due to its shape and/or that of the adjacent
continuum. In particular, Ly emission blended with N V could
often be unambiguously identified (for examples see
Fig. 9). Bright low-redshift candidates displayed lines with
small equivalent widths (likely C III] or Mg II) superimposed on
a blue continuum. Redshift assignments of fainter quasar candidates were less
certain due to the similar equivalent widths of the C IV, C III]
and Mg II emission lines. We decided in all doubtful cases to assign
the highest plausible redshifts to the candidates.
For eight of our fields we retrieved WFI+grism R band data from the
ESO Science Archive (taken in the course of another programme, PI Vanzi). We
reduced the data with our pipeline, yielding calibrated R band spectra of
our candidates in the range 5800 Å
7400 Å. Due to
the much higher sky background, however, the R band spectra are considerably
noisier than the B and V band spectra. Therefore, only emission lines of
brighter objects of our sample were unambiguously detected. Nevertheless, the
R band spectra confirmed the previously adopted low redshift assignments of
8 candidates. No systematic search for further emission line objects was
performed among the R band spectra.
Follow-up spectroscopy of 81 quasar candidates was obtained with the Focal
Reducer/Low Dispersion Spectrograph 2 (FORS2, Appenzeller et al. 1998) on
ESO VLT UT1/Antu in Visitor Mode on November 17-19, 2004 and in Service Mode
between April and July 2005. We restricted the follow-up campaign to candidates
with a high-confidence slitless WFI redshift .
Quasar
candidates likely residing at lower redshifts (C III] or Mg II
seen in the slitless spectra) were not followed up. The field of PKS 0528-250
was not selected for follow-up and also the field of Q 1451+123 was not
included due to the lack of high-quality candidates. Longslit spectra with a
1
slit kept at the parallactic angle were taken either with the
300V grism or the 600B grism, resulting in a spectral resolution of
10 Å FWHM and
4.5 Å FWHM, respectively. Each resolution element is
oversampled by a factor of
3
(300V: 3.36 Å/pixel, 600B: 1.5 Å/pixel). No order separation filter was
employed to maximise the UV coverage in the spectra, leading to possible order
overlap at
Å in the spectra taken with the 300V grism.
Exposure times were adjusted to yield
in the quasar continuum and
ranged between one and 40 min. The sky was clear to photometric during the
Visitor Mode run, but the seeing varied strongly during the nights, resulting
in slit losses for some of the 53 targeted objects. The remaining 28 prime
quasar candidates were observed in Service Mode under variable conditions. The
spectra were calibrated in wavelength against the FORS2 He/Ne/Ar/HgCd arc lamps
and flux-calibrated via spectrophotometric standard stars taken each night.
However, absolute spectrophotometry was not achieved due to the narrow slit and
the sometimes variable or poor sky transparency in the Service Mode
observations. Table 2, available in the online edition
of the Journal, lists the quasars confirmed in the spectroscopic follow-up
observations.
The VLT spectra were reduced with standard IRAF
tasks. The bias value was taken from the overscan regions. Dome flatfields
were used to correct pixel sensitivity variations. After sky subtraction by
fitting both spatial regions close to the target by 2nd-order Chebychev
polynomials, the spectra were extracted with the optimal extraction algorithm
by Horne (1986). The root-mean-square residuals of the wavelength
calibration with low-order Chebychev polynomials were
0.05 Å and
0.2 Å for the 600B and the 300V grism, respectively. The spectra were
corrected for atmospheric extinction assuming average conditions.
In order to approximately correct the spectra for slit losses we carried out
aperture photometry on the FORS2 aquisition images taken in the B filter,
which were calibrated against photometric standard stars (Landolt 1992)
taken each night.
Table 2 provides the airmass-corrected Johnson
B magnitudes and their calculated standard deviations. Apparent magnitudes were
also derived by integrating the flux-calibrated slit spectra.
Slit losses were estimated by calculating the expected loss over the used 1
slit for a
Gaussian PSF with a FWHM equal to the seeing during the observations that we
measured on the aquisition images. Figure 10 presents the
correlation of the integrated and photometric magnitudes. The integrated
magnitudes are consistent with the photometric ones after correcting for slit
losses.
The two outliers are the two quasars QNQ J09425-1048 and QNQ J21294-1521
that were observed in strongly variable clearly non-photometric conditions.
Redshifts of all candidates observed with FORS2 were determined by taking into
account all detectable emission lines. Peak positions of the lines were
measured by eye and errors were estimated by considering the S/N of the
lines, blending with other emission lines and the presence of absorption
lines, sky residuals or line asymmetries. We confirmed that in many objects
high-ionisation lines (Ly,
N V, Si IV+O IV],
C IV) are blueshifted with respect to low-ionisation lines
(Richards et al. 2002b; Gaskell 1982; Tytler & Fan 1992; McIntosh et al. 1999). However, the low-ionisation
lines O I+Si II and C II were often weak and noisy,
resulting in larger individual redshift errors. Mg II could be measured
only for quasars at
(
)
taken with the 300V (600B)
grism. Therefore, we estimated the systemic redshift of each quasar by
weighting the measurements of individual lines, giving a lower weight to
high-ionisation lines or discarding them completely in case of large
blueshifts. The redshift uncertainty of each quasar was estimated from the
redshift scatter between the remaining lines and their centroiding errors. The
adopted quasar redshifts and their estimated errors are listed in
Table 2.
With the follow-up spectroscopy we confirmed that 80 of our 81 candidates are
broad-line AGN in the redshift range
.
Only one of the
candidates turned out to be a low-redshift galaxy with narrow emission lines
(object J03490-3820,
(J2000) = 03
49
00
56,
(J2000) = -38
20
31
9, z=0.2848). 12 of the
confirmed quasars, located in the fields around Q 0302-003 and
HE 2347-4342, were already presented and discussed in Papers I and II. In
Fig. 12 we show the spectra for the quasars in one
additional, particularly rich field. 11 quasars were found in the vicinity of
HE 0940-1050. Appendix A, available in the online edition
of the Journal, lists the spectra of the remaining 57 newly discovered quasars.
In Fig. 11 we compare the redshifts derived from the FORS2 spectra and the slitless WFI spectra, respectively. The slit spectra confirmed the redshifts determined from the slitless WFI spectra for the majority of candidates (54/81). The WFI redshifts of the other 27 objects in the follow-up had been overestimated (note that we had systematically assigned the highest plausible redshifts). 64 of the 80 confirmed quasars are above our low-redshift cutoff z= 1.7 set for inclusion in the follow-up.
The scatter between slit and slitless spectroscopic redshifts for the 54 quasars
correctly placed in z is
.
The main cause for this
scatter is optical distortions of the grism causing the astrometric
transformation to produce residual variations of the wavelength zeropoint across
the WFI field of view. Of the 27 candidates whose redshifts were overpredicted,
only 5 had been assigned a high confidence redshift. This suggests that the
majority of remaining candidates with high redshift confidence likely reside at
those redshifts. After completion of the follow-up observations we compared the
WFI spectra of quasars whose redshifts had been overestimated to the WFI spectra
of the remaining candidates and adjusted the redshift estimates where applicable.
With 169 candidates in our sample and 81 of them followed up by VLT slit
spectroscopy, 88 further possible quasars remain unconfirmed. For the benefit of
potential future users we list these in Appendix B, available
in the online edition of the Journal. We provide the slitless spectra of these
88 quasar candidates and their celestial coordinates, magnitudes, WFI redshifts,
and our assessment of redshift confidence. For 23 of these we judge the WFI
redshifts to be most likely correct. For 28 candidates we call our redshift
estimate plausible; for 37 they are uncertain and could be identified with any
of the major emission lines, although we hold it unlikely that many
Ly quasars will be hidden among them. As an example we show in
Fig. 13 the slitless spectra of 10 quasar candidates in the
field of PKS 0528-250 that was completely left out of the spectroscopic
follow-up. Three of these candidates have a secure redshift z>2.5. The
remaining candidates on the other fields are either faint with noisy WFI spectra
or they likely reside at redshifts z<1.7.
We summarise the overall redshift distribution of the quasar sample in
Fig. 14. The open histogram shows the redshift distribution of all
detected known quasars, newly discovered quasars and remaining candidates
assuming that the inferred WFI redshifts of the candidates are correct. In
total, 205 quasars and candidates are shown. The gap at
expectedly arises from the lack of visible quasar emission lines in the
observed spectral range (cf. Fig. 7). The very small number
of low-redshift (
)
AGN is also to this effect. For
,
no
clearly preferred redshifts are discernible from this histogram. In
Sect. 7.2 we present an attempt to quantify our redshift-
and magnitude selection function. First we discuss our results in terms of the
main rationale driving this survey, the construction of new apparent groups of
high-redshift quasars.
The main goal of this survey was to reveal new groups of quasars for further studies of the three-dimensional distribution of the intergalactic medium. In the follow-up observations we concentrated on likely high-redshift (z>1.7) quasars, with some success: 80% of the newly established quasars match that condition. In addition to the central quasars, we recovered 85% of all detectable previously known quasars in these fields (22/26).
Including the remaining candidates, the number of quasars with
per
field varies substantially, between 2
(near CTQ 0247, Q 1209+093 and Q 1451+123) and 11 (near Q 0347-383). Some
of our fields are thus almost devoid of high-redshift quasars except the central
object, but other fields we found to be quite richly populated. These fields may
in the future become interesting targets for multiple line of sight absorption
spectroscopy. A list of currently known
quasars in our survey fields
is provided in Table C. 1, available in the online edition of the
Journal. We briefly discuss some of the most prominent cases:
![]() |
Figure 14: Redshift histograms of confirmed previously unknown quasars (cross-hashed), rediscovered quasars (hashed) and remaining quasar candidates (open). |
We have shown above that quasars displaying strong emission lines can be selected from the slitless spectra with very high efficiency; only 1 out of 81 candidates followed up with the VLT turned out not to be a quasar. Although in all parts of the survey we optimised the procedure towards efficiency, also at the expense of completeness, nevertheless it was interesting to see how our emission-line based candidate selection performed with respect to the quasar population displaying broad emission lines. We address this issue in two ways: first we present an estimate of the survey selection function from Monte Carlo simulations. Then we use this selection function to determine quasar surface densities from our sample and compare these numbers with the results of other surveys.
We define the survey selection function as the recovered fraction of the
broad-line quasar population matching a given broad band flux limit. The main
variables governing the detectability of quasars in a survey such as ours are
(i) the continuum magnitudes; and (ii) the equivalent widths of the detectable
emission lines (Gratton & Osmer 1987; Schmidt et al. 1986). Quasar surveys based on emission
lines tend to preferentially select strong-lined quasars, even more so near
their survey limits. In order to quantify this selection effect, we first
generated several template quasar spectra via a Monte Carlo routine.
The quasar emission lines of Ly,
Si IV+O IV], C IV,
C III] and Mg II were modelled as Gaussian profiles with mean
equivalent widths and line dispersions from the quasar template spectrum by
Vanden Berk et al. (2001) superposed on a power law continuum
with a mean spectral index
.
We
incorporated variations in the model parameters by assuming Gaussian
distributions with a standard deviation of 20% around the mean. We then
generated 200 random spectral templates in the quasar rest frame. The neglect of
non-Gaussian line shapes and intrinsic or intervening absorption does not have a
big effect on our low-resolution spectra.
Mock slitless WFI quasar spectra were created by shifting the templates to the
desired redshift, degrading them to the WFI resolution followed by adding
Gaussian noise that varied with wavelength according to the overall throughput
of the spectrograph (Fig. 4). The S/N in the simulated
spectra, related to the V magnitude by Eq. (1), was normalised
in the quasar continuum near the maximum throughput at 5400 Å. We then
performed Monte Carlo simulations of the detection rates of quasars as a
function of redshift (
)
and continuum S/N values
(
). At each considered redshift and S/N, WFI spectra of the
200 quasar templates were generated and subjected to our automated selection
routines (Sect. 4.1). Each quasar template was simulated
100 times in order to quantify the impact of noise on the detection rate per object.
We also performed the subsequent visual screening done for the real candidates
on several hundred simulated spectra to investigate visual selection effects,
finding that
90% of the automatically selected candidates survived the
selection by eye.
Figure 16 presents the resulting selection function,
displayed as a contour map of the median detection probability as a function of
redshift and V magnitude. Overplotted are the quasars and quasar candidates
from our survey. The selection function obviously varies with the visibility of
different emission lines in the spectrum. Due to its high equivalent width
Ly emission is detectable for essentially 100% of quasars brighter
than
,
and still
80% of the simulated spectra are recovered
at
(continuum S/N of
1). At redshifts below
2.5 the
selection function obtains lower values because of the lower equivalent widths
of C IV, C III], and Mg II, and we have already commented
upon the gap at
where no emission line is visible in the
range of our spectra. The selected quasars and quasar candidates fill the full
range of the selection function spanned by the simulated redshifts and
magnitudes (S/N). The known quasars at the field centres are clearly separated
from the other quasars and candidates in magnitude and redshift. Note, however,
that the survey selection function in Fig. 16 assumes that
all quasar spectra were extracted from the slitless data. Due to photometric
incompleteness (Sect. 3.2), the detection probability at
is lower, as we will describe in the following.
With the survey selection function from above we were able to compare our number
counts of quasars with those of other surveys. We consider two surveys reaching
similar or greater depths. The only comparably deep slitless survey is
the Palomar Scan Grism Survey (PSGS, Schneider et al. 1999) which yielded
39 quasars on 1.10 deg2 at .
Disregarding the known bright quasars at
the field centres we detected 102 quasars (known or newly confirmed) and
88 highly promising candidates on 4.39 deg2. Assuming that the candidates are
quasars, the total surface density for our survey is
20% higher. The
wavelength ranges and therefore the redshift ranges are not exactly equal
between the two surveys, so that we simply state that the results are in good
agreement.
A more quantitative comparison is possible by comparing our survey to the
photometric COMBO-17 survey (Wolf et al. 2003). Since COMBO-17 is flux-limited in
the R band whereas our survey is best defined in V, we assumed a mean quasar
colour of V-R=0.2 to convert the COMBO-17 surface densities. After correction
for the selection function, the cumulative surface number density of quasars
found for our survey is 48 deg-2 at V<21, and 89 deg-2 at V<22.
The corresponding values for COMBO-17 are 51.3 deg-2 and 93.5 deg-2,
respectively. Thus again, the numbers are in excellent agreement, even at
magnitudes as faint as .
Looking closer at the differential
number counts we find that they agree very well at
20.5 < V < 21.5(
in our survey vs.
in COMBO-17), but that our survey drops
by a factor of 1.5 in the subsequent magnitude bin at
21.5 < V < 22.5(
vs.
). It is not surprising to find that our survey is
incomplete at these magnitudes, probably as a combination of incompleteness
already in the input catalogues and missing true quasars among the noisy spectra.
As we had included the ECDFS from COMBO-17 in our survey observations, we could
also perform an object by object comparison in this well-studied field. The
slitless spectra confirmed the general trend of the above survey selection
function. We rediscovered 7 out of 10 R<21 COMBO-17 quasars at 1.3<z<3.6located in the common survey area. The three missed quasars are quite faint
(R>20) and reside at ,
where the selection function of our survey
drops (Fig. 16). At z>2.5 only one out of three
21<R<22 quasars was rediscovered, indicating photometric incompleteness at the faint
end of the DSS catalogue.
Slitless spectroscopic surveys are successful in finding closely projected
quasar groups at high redshift, especially in redshift ranges where colour
surveys are less effective. However, previous targeted slitless surveys for
quasar groups were few, always pointed at one individual field only
(e.g. Williger et al. 1996; Jakobsen & Perryman 1992), and also generally shallower than our
survey by 1 mag. Thus, the resulting surface maps of quasars were sparse,
but probed the large-scale distribution of quasars. Our survey significantly
increases the number of high-redshift quasar groups with separations
in the southern hemisphere. The centroiding of our
fields on known bright quasars enables follow-up studies on the
three-dimensional distribution of the IGM. Our faint survey limit
(
-22) results in a high surface density of high-redshift
quasars despite the comparatively small survey area per field.
More recently, Hennawi et al. (2006b) selected faint
quasar candidates in
the vicinity of confirmed SDSS quasars using the SDSS photometry. Their survey
was dedicated to find close quasar pairs with separations
,
especially binary quasars at the same redshift. They
confirmed 40 new binary quasars and 73 projected quasar pairs. However, 89 of
their candidates turned out to be stars, most likely due to broadband colour
similarities between stars and quasars in certain redshift ranges. In
comparison, our high success rate of almost 100% shows that slitless
spectroscopy is highly efficient in finding high-redshift quasars. A smooth
selection function (Fig. 16) is essential to discover
high-redshift quasar groups in selected fields. However, given the small
surface density of high-redshift quasars, we were unlikely to find quasars at
very small separations to the central quasars in our fields.
We performed the ``Quasars near Quasars'' (QNQ) survey, a CCD-based slitless
spectroscopic survey for faint
quasars at
around 18 well-studied bright quasars at
2.76<z<4.69, covering a total area of
4.39 deg2. In order to analyse the slitless data we developed a data
reduction pipeline that performs an optimal extraction of the spectra and that
is able to cope with contaminating spectral orders of slitless grism data. From
the
29 000 extracted flux-calibrated spectra we selected 169 previously
unknown quasar candidates and >100 likely low-redshift emission line galaxy
candidates on the basis of emission features that fall in the covered wavelength
range 4200 Å
5800 Å. A semi-automatic selection routine
limited potential biases of purely visual selection and allowed to quantify
selection effects.
Follow-up spectroscopy confirmed 80 out of 81 selected quasar candidates on 16 fields. 64 of these newly established quasars reside at z>1.7. The highest redshift quasar is QNQ J22484-6002 at z=3.586. The brightest newly discovered high-redshift quasar is QNQ J11197-1340 (z=2.220, B=18.3). Given the high success rate of the follow-up, the vast majority of the remaining 88 candidates will be quasars as well, although most of them likely reside at lower redshifts.
The primary aim of this survey was to provide new groups of quasars for
medium-resolution spectroscopy in the vicinity of well-studied known quasars.
Originally, we had not expected to reach as faint as
in the survey
observations. At these faint magnitudes our survey is not well defined because
of photometric incompleteness in the source catalogues needed for automatic
extraction of the slitless spectra. Together with the fact that not all selected
quasar candidates could be included in the spectroscopic follow-up, our survey
probably is of limited use for constraining quasar evolution. However, focusing
on survey efficiency rather than on completeness at the faint end was justified
in order to accomplish the main goal of this survey. In fact, the faintest
quasars discovered will for now remain beyond the limits for obtaining
high-quality spectra. But at least the
quasars are well suited for
follow-up studies with current (e.g. ESI at Keck) or upcoming
(e.g. X-shooter at VLT) high-throughput spectrographs at 8-10 m-class telescopes.
Together with the central quasars in the fields already observed at high
resolution, these quasar groups can be used to perform a tomography of the
intergalactic medium. Large-scale clustering of the Ly forest or
correlations of metal line systems can be investigated as well
(Williger et al. 2000; D'Odorico et al. 2002,2006). Some of the discovered quasars reside
at similar redshifts or approximately at the same redshift of the central quasar
in the field, giving potentially insights to quasar clustering along overdense
filaments in the plane of the sky. We have identified two quasars coinciding
with a damped Ly
absorber on one central line of sight, as well as a
large-scale group of quasars at z=2.70-2.78. Moreover, our study provides
new foreground quasars to investigate the transverse proximity effect of quasars
(Papers I and II). In combination with the already available high-resolution
spectra of the central quasars, medium-resolution spectra of these quasar groups
will offer great opportunities to study the large-scale cosmic web in three
dimensions.
Acknowledgements
We thank the staff of the ESO observatories La Silla and Paranal for their professional assistance in obtaining the data presented in this paper. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. G.W. was partly supported by a HWP grant from the state of Brandenburg, Germany. G.W. and L.W. acknowledge support by the Deutsche Forschungsgemeinschaft under Wi 1369/21-1.
Field | QSO | ![]() |
![]() |
z | B | Night | Grism |
![]() |
Seeing | Transparency |
Q 0000-263 | QNQ J00025-2558 | 00
![]() ![]() ![]() |
-25
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 300V | 300 | 0
![]() |
clear |
QNQ J00040-2603 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 600B | 1000 | 1
![]() |
clear | |
QNQ J00035-2610 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 600B | 1800 | 1
![]() |
clear | |
QNQ J00028-2547 | 00
![]() ![]() ![]() |
-25
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 600B | 400 | 0
![]() |
clear | |
QNQ J00035-2551 | 00
![]() ![]() ![]() |
-25
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 600B | 1600 | 1
![]() |
clear | |
QNQ J00038-2617 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 300V | 1200 | 1
![]() |
clear | |
Q 0002-422 | QNQ J00043-4151 | 00
![]() ![]() ![]() |
-41
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 300 | 1
![]() |
photometric |
QNQ J00041-4158 | 00
![]() ![]() ![]() |
-41
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 400 | 1
![]() |
photometric | |
QNQ J00045-4201 | 00
![]() ![]() ![]() |
-42
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 400 | 1
![]() |
photometric | |
Q 0055-269 | QNQ J00576-2626 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 300V | 300 | 1
![]() |
clear |
QNQ J00582-2649 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 300V | 1800 | 0
![]() |
clear | |
QNQ J00583-2626 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 300V | 300 | 1
![]() |
clear | |
Q 0302-003 | QNQ J03052-0016 | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 300 | 0
![]() |
clear |
QNQ J03052+0000a | 03
![]() ![]() ![]() |
+00
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 600 | 0
![]() |
clear | |
Q 0347-383 | QNQ J03494-3814 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 60 | 0
![]() |
clear |
QNQ J03500-3820 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 120 | 0
![]() |
clear | |
QNQ J03490-3812 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 600 | 0
![]() |
clear | |
QNQ J03496-3821 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 300 | 0
![]() |
clear | |
QNQ J03496-3810 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 1800 | 0
![]() |
clear | |
QNQ J03495-3806 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 1800 | 0
![]() |
clear | |
QNQ J03508-3812 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 360 | 0
![]() |
clear | |
QNQ J03503-3800 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 900 | 0
![]() |
clear | |
QNQ J03490-3825 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 1000 | 0
![]() |
clear | |
QNQ J03494-3826 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 1800 | 0
![]() |
clear | |
CTQ 0247 | QNQ J04061-4401 | 04
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 600B | 900 | 1
![]() |
photometric |
QNQ J04075-4416 | 04
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 600B | 2000 | 1
![]() |
photometric | |
QNQ J04084-4420 | 04
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 1800 | 1
![]() |
photometric | |
Q 0420-388 | QNQ J04217-3847 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 600B | 800 | 0
![]() |
clear |
QNQ J04229-3831 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 600B | 400 | 0
![]() |
clear | |
QNQ J04222-3829 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 300V | 300 | 0
![]() |
clear | |
QNQ J04215-3857 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 300V | 1400 | 1
![]() |
clear | |
QNQ J04215-3854 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 600B | 200 | 0
![]() |
clear | |
QNQ J04212-3853 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 600B | 1000 | 0
![]() |
clear | |
QNQ J04230-3853 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
![]() |
![]() |
18 Nov. 2004 | 300V | 1800 | 0
![]() |
clear | |
HE 0940-1050 | QNQ J09422-1117 | 09
![]() ![]() ![]() |
-11
![]() ![]() ![]() |
![]() |
![]() |
06 Apr. 2005 | 600B | 420 | 0
![]() |
thin cirrus |
QNQ J09437-1109 | 09
![]() ![]() ![]() |
-11
![]() ![]() ![]() |
![]() |
![]() |
06 Apr. 2005 | 300V | 600 | 0
![]() |
thin cirrus | |
QNQ J09427-1108 | 09
![]() ![]() ![]() |
-11
![]() ![]() ![]() |
![]() |
![]() |
12 May 2005 | 600B | 300 | 1
![]() |
photometric | |
QNQ J09430-1108 | 09
![]() ![]() ![]() |
-11
![]() ![]() ![]() |
![]() |
![]() |
10 May 2005 | 300V | 1800 | 0
![]() |
clear | |
QNQ J09424-1047 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
![]() |
![]() |
12 May 2005 | 300V | 240 | 0
![]() |
photometric | |
QNQ J09437-1057 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
![]() |
![]() |
09 Jun. 2005 | 300V | 240 | 0
![]() |
clear | |
QNQ J09435-1049 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
![]() |
![]() |
06 Apr. 2005 | 600B | 720 | 0
![]() |
thin cirrus | |
QNQ J09425-1048 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
![]() |
19.80 | 02 May 2005 | 600B | 720 | 1
![]() |
thick cirrus | |
QNQ J09434-1053 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
![]() |
![]() |
12 May 2005 | 300V | 1400 | 1
![]() |
photometric | |
QNQ J09427-1121 | 09
![]() ![]() ![]() |
-11
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 600B | 1200 | 1
![]() |
photometric | |
05 Apr. 2005 | 600B | 600 | 0
![]() |
thick cirrus | ||||||
QNQ J09437-1052 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 600B | 1200 | 1
![]() |
photometric | |
06 Apr. 2005 | 600B | 1200 | 0
![]() |
thick cirrus | ||||||
CTQ 0460 | QNQ J10399-2321 | 10
![]() ![]() ![]() |
-23
![]() ![]() ![]() |
![]() |
![]() |
07 May 2005 | 600B | 900 | 0
![]() |
thin cirrus |
QNQ J10388-2258 | 10
![]() ![]() ![]() |
-22
![]() ![]() ![]() |
![]() |
![]() |
28 Jun. 2005 | 600B | 420 | 0
![]() |
thin cirrus | |
QNQ J10385-2317 | 10
![]() ![]() ![]() |
-23
![]() ![]() ![]() |
![]() |
![]() |
09 Jun. 2005 | 600B | 1800 | 0
![]() |
clear | |
BR 1117-1329 | QNQ J11208-1345 | 11
![]() ![]() ![]() |
-13
![]() ![]() ![]() |
![]() |
![]() |
27 Jun. 2005 | 300V | 180 | 0
![]() |
thin cirrus |
QNQ J11205-1343 | 11
![]() ![]() ![]() |
-13
![]() ![]() ![]() |
![]() |
![]() |
27 Jun. 2005 | 300V | 180 | 0
![]() |
thin cirrus | |
QNQ J11197-1340 | 11
![]() ![]() ![]() |
-13
![]() ![]() ![]() |
![]() |
![]() |
27 Jun. 2005 | 600B | 420 | 0
![]() |
thin cirrus | |
QNQ J11192-1334 | 11
![]() ![]() ![]() |
-13
![]() ![]() ![]() |
![]() |
![]() |
27 Jun. 2005 | 300V | 1600 | 0
![]() |
thin cirrus | |
BR 1202-0725 | QNQ J12059-0754 | 12
![]() ![]() ![]() |
-07
![]() ![]() ![]() |
![]() |
![]() |
06 May 2005 | 600B | 900 | 1
![]() |
clear |
QNQ J12062-0727 | 12
![]() ![]() ![]() |
-07
![]() ![]() ![]() |
![]() |
![]() |
29 Jun. 2005 | 300V | 180 | 0
![]() |
thin cirrus | |
QNQ J12061-0745 | 12
![]() ![]() ![]() |
-07
![]() ![]() ![]() |
![]() |
![]() |
06 May 2005 | 600B | 600 | 1
![]() |
clear | |
Q 1209+093 | QNQ J12124+0851 | 12
![]() ![]() ![]() |
+08
![]() ![]() ![]() |
![]() |
![]() |
28 Jun. 2005 | 600B | 300 | 0
![]() |
thin cirrus |
QNQ J12111+0906 | 12
![]() ![]() ![]() |
+09
![]() ![]() ![]() |
![]() |
![]() |
29 Jun. 2005 | 600B | 2400 | 0
![]() |
thin cirrus | |
PKS 2126-158 | QNQ J21294-1521 | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
![]() |
18.38 | 04 May 2005 | 600B | 180 | 0
![]() |
thin cirrus |
QNQ J21291-1524A | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
![]() |
![]() |
04 May 2005 | 300V | 2400 | 0
![]() |
thin cirrus | |
QNQ J21297-1536 | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
![]() |
![]() |
06 May 2005 | 300V | 180 | 1
![]() |
clear | |
QNQ J21286-1528 | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
![]() |
![]() |
06 May 2005 | 300V | 120 | 1
![]() |
clear | |
QNQ J21291-1524B | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
![]() |
![]() |
04 May 2005 | 600B | 720 | 1
![]() |
thin cirrus | |
QNQ J21301-1533 | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
![]() |
![]() |
05 May 2005 | 600B | 2200 | 0
![]() |
clear | |
Q 2139-4434 | QNQ J21434-4432 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
![]() |
![]() |
05 May 2005 | 600B | 540 | 1
![]() |
clear |
HE 2243-6031 | QNQ J22454-6020 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 300 | 1
![]() |
photometric |
QNQ J22455-6015 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 800 | 1
![]() |
photometric | |
QNQ J22460-6024 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 1800 | 1
![]() |
photometric | |
QNQ J22454-6011 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 300 | 0
![]() |
clear | |
QNQ J22463-6009 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 500 | 1
![]() |
clear | |
QNQ J22484-6002 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 600 | 1
![]() |
clear | |
19 Nov. 2004 | 600B | 600 | 1
![]() |
photometric | ||||||
HE 2347-4342 | QNQ J23510-4336 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 1200 | 1
![]() |
photometric |
QNQ J23507-4319 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 360 | 0
![]() |
clear | |
QNQ J23507-4326 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 200 | 1
![]() |
clear | |
QNQ J23509-4330 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 300 | 0
![]() |
clear | |
QNQ J23502-4334 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 60 | 0
![]() |
clear | |
QNQ J23503-4328 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 400 | 0
![]() |
clear | |
QNQ J23495-4338 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 360 | 1
![]() |
photometric | |
QNQ J23511-4319 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 600B | 1000 | 1
![]() |
clear | |
QNQ J23514-4339 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
17 Nov. 2004 | 300V | 1400 | 1
![]() |
clear | |
QNQ J23503-4317 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
![]() |
![]() |
19 Nov. 2004 | 300V | 1800 | 1
![]() |
photometric | |
19 Nov. 2004 | 600B | 1800 | 1
![]() |
photometric |
![]() |
Figure A.1:
VLT/FORS2 spectra (black) and ![]() |
Field | Object | V | z | z confidence | Field | Object | V | z | z confidence |
Q 0000-263 | J000239.4-261139 | 22.0 | 0.68 | uncertain | HE 0940-1050 | J094223.0-110952 | 19.1 | 0.67 | plausible |
Q 0000-263 | J000256.4-260956 | 21.2 | 1.77 | plausible | HE 0940-1050 | J094228.1-111403 | 20.5 | 1.38 | plausible |
Q 0000-263 | J000256.8-254703 | 21.4 | 0.91 | plausible | HE 0940-1050 | J094228.1-104719 | 21.5 | 2.70 | uncertain |
Q 0000-263 | J000257.9-255750 | 21.1 | 1.79 | secure | HE 0940-1050 | J094233.4-112119 | 20.5 | 1.24 | uncertain |
Q 0000-263 | J000404.9-254841 | 22.5 | 0.68 | uncertain | HE 0940-1050 | J094324.7-111526 | 17.6 | 0.99 | secure |
Q 0000-263 | J000408.5-255024 | 21.5 | 0.71 | uncertain | HE 0940-1050 | J094336.0-110129 | 19.5 | 1.70 | plausible |
Q 0000-263 | J000422.1-255830 | 20.6 | 0.91 | plausible | HE 0940-1050 | J094342.5-111730 | 19.0 | 0.90 | secure |
Q 0002-422 | J000531.8-415410 | 20.6 | 1.07 | secure | CTQ 0460 | J103833.6-232642 | 19.9 | 1.93 | uncertain |
Q 0055-269 | J005709.5-265900 | 20.8 | 0.70 | uncertain | CTQ 0460 | J103836.2-231020 | 21.9 | 2.36 | plausible |
Q 0055-269 | J005750.3-263910 | 20.6 | 1.41 | secure | CTQ 0460 | J103903.6-225625 | 19.9 | 1.92 | plausible |
Q 0055-269 | J005805.6-265755 | 23.0 | 2.88 | uncertain | BR 1117-1329 | J111910.3-133139 | 21.4 | 1.55 | uncertain |
Q 0055-269 | J005840.0-263314 | 19.5 | 2.55 | plausible | BR 1117-1329 | J111924.7-135152 | 20.8 | 1.29 | uncertain |
Q 0055-269 | J005847.4-264308 | 21.0 | 0.75 | uncertain | BR 1117-1329 | J111946.1-134157 | 20.0 | 0.84 | plausible |
Q 0347-383 | J034856.4-380847 | 21.2 | 1.83 | uncertain | BR 1117-1329 | J112028.1-133612 | 20.5 | 1.30 | uncertain |
Q 0347-383 | J034905.8-380146 | 21.9 | 1.84 | secure | BR 1117-1329 | J112037.2-133603 | 18.6 | 0.15 | secure |
Q 0347-383 | J034933.3-381618 | 19.5 | 0.94 | secure | BR 1117-1329 | J112049.4-133422 | 21.2 | 2.84 | plausible |
Q 0347-383 | J034945.9-380150 | 20.9 | 1.85 | secure | BR 1202-0725 | J120506.0-075537 | 18.6 | 1.58 | secure |
Q 0347-383 | J035003.7-375855 | 22.0 | 2.08 | uncertain | BR 1202-0725 | J120512.7-075926 | 20.5 | 3.32 | uncertain |
Q 0347-383 | J035008.5-375359 | 20.8 | 1.84 | secure | BR 1202-0725 | J120601.9-073433 | 21.6 | 2.11 | uncertain |
Q 0347-383 | J035039.4-382425 | 19.4 | 1.38 | plausible | BR 1202-0725 | J120602.2-074358 | 20.0 | 0.84 | plausible |
CTQ 0247 | J040634.9-440757 | 19.6 | 1.37 | plausible | BR 1202-0725 | J120612.2-072814 | 20.4 | 0.71 | uncertain |
CTQ 0247 | J040637.7-442152 | 21.1 | 1.68 | uncertain | Q 1209+093 | J121108.4+085707 | 20.6 | 0.86 | uncertain |
CTQ 0247 | J040706.6-442223 | 20.5 | 1.68 | uncertain | Q 1209+093 | J121234.8+085701 | 20.5 | 2.17 | uncertain |
CTQ 0247 | J040735.1-440020 | 18.8 | 1.47 | plausible | Q 1451+123 | J145508.6+121245 | 20.5 | 1.68 | uncertain |
CTQ 0247 | J040744.2-440050 | 19.8 | 0.59 | plausible | Q 1451+123 | J145514.6+115655 | 21.5 | 2.04 | uncertain |
CTQ 0247 | J040816.1-442158 | 20.5 | 0.91 | uncertain | PKS 2126-158 | J212924.5-154820 | 18.5 | 1.57 | secure |
CTQ 0247 | J040822.8-441814 | 21.5 | 1.76 | plausible | PKS 2126-158 | J213009.8-153633 | 22.0 | 2.41 | plausible |
Q 0420-388 | J042116.9-384010 | 22.0 | 2.41 | uncertain | PKS 2126-158 | J213016.1-154153 | 20.2 | 0.77 | uncertain |
Q 0420-388 | J042145.7-385720 | 21.6 | 1.79 | secure | PKS 2126-158 | J213017.3-154324 | 18.5 | 1.41 | secure |
Q 0420-388 | J042153.2-383256 | 20.5 | 0.86 | plausible | Q 2139-4434 | J214119.4-441256 | 21.6 | 1.57 | uncertain |
Q 0420-388 | J042222.0-385755 | 21.5 | 2.92 | plausible | Q 2139-4434 | J214124.0-443301 | 21.0 | 1.96 | uncertain |
Q 0420-388 | J042258.9-384749 | 20.8 | 0.89 | plausible | Q 2139-4434 | J214326.2-442036 | 18.2 | 0.60 | uncertain |
PKS 0528-250 | J052916.6-245655 | 21.1 | 2.34 | plausible | HE 2243-6031 | J224542.2-600645 | 20.0 | 1.53 | secure |
PKS 0528-250 | J052920.1-251337 | 20.5 | 2.20 | uncertain | HE 2243-6031 | J224543.0-603049 | 19.4 | 1.56 | secure |
PKS 0528-250 | J052930.5-245305 | 18.5 | 0.86 | secure | HE 2243-6031 | J224553.3-600659 | 20.2 | 1.36 | secure |
PKS 0528-250 | J052939.1-250148 | 20.2 | 2.85 | secure | HE 2243-6031 | J224602.9-603115 | 21.0 | 0.66 | uncertain |
PKS 0528-250 | J052940.7-245927 | 21.5 | 1.72 | plausible | HE 2243-6031 | J224612.7-600355 | 21.9 | 2.91 | uncertain |
PKS 0528-250 | J052947.4-250426 | 20.0 | 2.88 | secure | HE 2243-6031 | J224653.0-603046 | 20.5 | 0.62 | uncertain |
PKS 0528-250 | J053015.5-250307 | 21.1 | 2.52 | secure | HE 2243-6031 | J224729.0-601443 | 20.8 | 0.93 | secure |
PKS 0528-250 | J053039.7-245306 | 21.9 | 1.53 | uncertain | HE 2243-6031 | J224750.4-602117 | 19.5 | 1.02 | plausible |
PKS 0528-250 | J053043.2-250840 | 21.4 | 1.84 | plausible | HE 2243-6031 | J224837.7-601431 | 21.4 | 3.08 | uncertain |
PKS 0528-250 | J053048.2-250435 | 20.6 | 2.95 | plausible | HE 2347-4342 | J235001.9-431229 | 18.6 | 0.92 | secure |
PKS 0528-250 | J053115.3-251311 | 21.0 | 1.41 | uncertain | HE 2347-4342 | J235107.0-432246 | 19.0 | 1.48 | plausible |
HE 0940-1050 | J094219.2-105019 | 20.9 | 0.94 | plausible | HE 2347-4342 | J235140.8-431615 | 20.9 | 1.26 | uncertain |
![]() |
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. |
![]() |
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. |
![]() |
Figure C.1: As Fig. 15 for the field centred near Q 0000-263. |
![]() |
Figure C.2: As Fig. 15 for the field centred near Q 0002-422. |
![]() |
Figure C.3: As Fig. 15 for the field centred near Q 0055-269. |
![]() |
Figure C.4: As Fig. 15 for the field centred near Q 0302-003. |
![]() |
Figure C.5: As Fig. 15 for the field centred near Q 0347-383. |
![]() |
Figure C.6: As Fig. 15 for the field centred near CTQ 0247. |
![]() |
Figure C.7: As Fig. 15 for the field centred near Q 0420-388. |
![]() |
Figure C.8: As Fig. 15 for the field centred near PKS 0528-250. |
![]() |
Figure C.9: As Fig. 15 for the field centred near CTQ 0460. |
![]() |
Figure C.10: As Fig. 15 for the field centred near BR 1117-1329. |
![]() |
Figure C.11: As Fig. 15 for the field centred near BR 1202-0725. |
![]() |
Figure C.12: As Fig. 15 for the field centred near Q 1209+093. |
![]() |
Figure C.13: As Fig. 15 for the field centred near Q 1451+123. |
![]() |
Figure C.14: As Fig. 15 for the field centred near PKS 2126-158. |
![]() |
Figure C.15: As Fig. 15 for the field centred near HE 2347-4342. |
Field | QSO | ![]() |
![]() |
z | Magnitude | Filter | ![]() ![]() |
Discovery paper |
Q 0000-263 | QNQ J00040-2603 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
2.002 | 20.54 | B | 9.54 | this paper |
QNQ J00035-2610 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
2.771 | 21.61 | B | 7.90 | this paper | |
QNQ J00028-2547 | 00
![]() ![]() ![]() |
-25
![]() ![]() ![]() |
2.812 | 19.84 | B | 16.87 | this paper | |
QNQ J00035-2551 | 00
![]() ![]() ![]() |
-25
![]() ![]() ![]() |
2.875 | 20.99 | B | 11.70 | this paper | |
Q 0000-C14 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
3.057 | 25.33 | g | 2.56 | Steidel et al. (2003) | |
QNQ J00038-2617 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
3.073 | 22.09 | B | 15.72 | this paper | |
Q 0000-C7 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
3.426 | 24.28 | g | 1.47 | Steidel et al. (2003) | |
Q 0000-C5 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
3.791 | 24.70 | g | 2.55 | Steidel et al. (2003) | |
Q 0000-263 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
4.125 | 17.53 | R | 0.00 | Shaver (1987) | |
Q 0002-422 | QNQ J00041-4158 | 00
![]() ![]() ![]() |
-41
![]() ![]() ![]() |
1.720 | 20.36 | B | 7.34 | this paper |
QNQ J00045-4201 | 00
![]() ![]() ![]() |
-42
![]() ![]() ![]() |
2.157 | 20.35 | B | 4.98 | this paper | |
Q 0000-4239 | 00
![]() ![]() ![]() |
-42
![]() ![]() ![]() |
2.190 | 21.10 | V | 29.01 | Osmer (1980) | |
Q 0001-4227 | 00
![]() ![]() ![]() |
-42
![]() ![]() ![]() |
2.260 | 19.80 | B | 17.29 | Osmer (1980) | |
Q 0002-422 | 00
![]() ![]() ![]() |
-41
![]() ![]() ![]() |
2.767 | 17.20 | V | 0.00 | Osmer & Smith (1976) | |
Q 0055-269 | Q 0053-2656 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
1.882 | 19.67 | V | 29.83 | La Franca et al. (1999) |
QNQ J00576-2626 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
1.942 | 20.73 | B | 16.99 | this paper | |
Q 0056-2700 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
2.294 | 20.55 | B | 14.08 | La Franca et al. (1999) | |
Q 0055-2654 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
2.389 | 20.46 | B | 6.00 | La Franca et al. (1999) | |
QNQ J00582-2649 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
2.572 | 22.02 | B | 7.06 | this paper | |
QNQ J00583-2626 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
2.720 | 21.00 | B | 17.69 | this paper | |
Q 0055-269 | 00
![]() ![]() ![]() |
-26
![]() ![]() ![]() |
3.665 | 17.50 | V | 0.00 | Hazard & McMahon (1985) | |
Q 0302-003 | SDSS J0305+0007 | 03
![]() ![]() ![]() |
+00
![]() ![]() ![]() |
1.758 | 20.71 | r | 17.58 | Schneider et al. (2007) |
QSO 03022-0023 | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
2.142 | 22.46 | V | 3.55 | Jakobsen et al. (2003) | |
QNQ J03052-0016 | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
2.290 | 20.05 | B | 10.28 | Worseck & Wisotzki (2006) | |
SDSS J0303-0020B | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
2.718 | 19.67 | r | 22.03 | Hennawi et al. (2006a) | |
QNQ J03052+0000 | 03
![]() ![]() ![]() |
+00
![]() ![]() ![]() |
2.808 | 21.79 | B | 11.22 | Worseck & Wisotzki (2006) | |
Q 0302-D113 | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
2.920 | 24.68 | g | 4.88 | Steidel et al. (2003) | |
QSO 03020-0014 | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
3.050 | 20.44 | V | 6.48 | Jakobsen et al. (2003) | |
Q 0301-005 | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
3.231 | 17.64 | r | 22.92 | Barbieri & Cristiani (1986) | |
Q 0302-003 | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
3.285 | 18.76 | B | 0.00 | Barbieri & Cristiani (1986) | |
SDSS J0305-0006 | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
3.450 | 20.80 | r | 4.46 | Schneider et al. (2007) | |
SDSS J0303-0019 | 03
![]() ![]() ![]() |
-00
![]() ![]() ![]() |
6.070 | 23.92 | i | 22.48 | Jiang et al. (2008) | |
Q 0347-383 | QNQ J03500-3820 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
1.819 | 20.03 | B | 11.09 | this paper |
QNQ J03490-3812 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
1.945 | 21.66 | B | 8.14 | this paper | |
QNQ J03496-3821 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.351 | 19.43 | B | 11.08 | this paper | |
QNQ J03496-3810 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.433 | 20.87 | B | 1.53 | this paper | |
QNQ J03495-3806 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.475 | 20.86 | B | 4.35 | this paper | |
QNQ J03508-3812 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.705 | 20.86 | B | 13.34 | this paper | |
QNQ J03503-3800 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.734 | 20.67 | B | 12.67 | this paper | |
QNQ J03490-3825 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.777 | 20.52 | B | 16.89 | this paper | |
QNQ J03494-3826 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.782 | 20.97 | B | 15.96 | this paper | |
Q 0347-383 | 03
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
3.220 | 18.66 | B | 0.00 | Osmer & Smith (1980) | |
CTQ 0247 | QNQ J04061-4401 | 04
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.410 | 19.35 | B | 15.25 | this paper |
CTQ 0247 | 04
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
3.025 | 17.40 | V | 0.00 | Maza et al. (1993) | |
QNQ J04075-4416 | 04
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
3.034 | 21.75 | B | 6.62 | this paper | |
QNQ J04084-4420 | 04
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
3.080 | 22.88 | B | 16.19 | this paper | |
Q 0420-388 | MS 0420-3838B | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
1.931 | 20.61 | B | 14.48 | Ciliegi et al. (1994) |
QNQ J04229-3831 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
1.990 | 19.98 | B | 15.93 | this paper | |
QNQ J04222-3829 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.168 | 20.91 | B | 15.33 | this paper | |
QNQ J04215-3857 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.235 | 22.23 | B | 14.45 | this paper | |
QNQ J04215-3854 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.270 | 19.49 | B | 12.97 | this paper | |
PKS 0422-389 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.346 | 18.00 | V | 27.36 | Hook et al. (2003) | |
Q 0420-3850 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.410 | 21.01 | B | 2.13 | Hewitt & Burbidge (1993) | |
QNQ J04212-3853 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
2.723 | 20.08 | B | 14.87 | this paper | |
QNQ J04230-3853 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
3.042 | 21.95 | B | 12.30 | this paper | |
Q 0420-388 | 04
![]() ![]() ![]() |
-38
![]() ![]() ![]() |
3.120 | 16.90 | V | 0.00 | Osmer & Smith (1980) | |
PKS 0528-250 | PKS 0528-250 | 05
![]() ![]() ![]() |
-25
![]() ![]() ![]() |
2.813 | 17.50 | V | 0.00 | Wright et al. (1977) |
HE 0940-1050 | QNQ J09430-1108 | 09
![]() ![]() ![]() |
-11
![]() ![]() ![]() |
1.730 | 21.03 | B | 4.05 | this paper |
QNQ J09424-1047 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
1.971 | 20.61 | B | 17.94 | this paper | |
QNQ J09437-1057 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
2.023 | 20.64 | B | 14.24 | this paper | |
QNQ J09435-1049 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
2.216 | 20.79 | B | 17.01 | this paper | |
QNQ J09425-1048 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
2.325 | 19.80 | B | 16.55 | this paper | |
QNQ J09434-1053 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
2.760 | 21.16 | B | 13.24 | this paper | |
QNQ J09427-1121 | 09
![]() ![]() ![]() |
-11
![]() ![]() ![]() |
2.963 | 20.99 | B | 17.37 | this paper | |
QNQ J09437-1052 | 09
![]() ![]() ![]() |
-10
![]() ![]() ![]() |
3.018 | 20.78 | B | 17.01 | this paper | |
HE 0940-1050 | 09
![]() ![]() ![]() |
-11
![]() ![]() ![]() |
3.088 | 16.96 | BJ | 0.00 | Reimers et al. (1995) | |
CTQ 0460 | QNQ J10399-2321 | 10
![]() ![]() ![]() |
-23
![]() ![]() ![]() |
2.216 | 20.73 | B | 14.00 | this paper |
QNQ J10388-2258 | 10
![]() ![]() ![]() |
-22
![]() ![]() ![]() |
2.326 | 19.63 | B | 15.92 | this paper | |
QNQ J10385-2317 | 10
![]() ![]() ![]() |
-23
![]() ![]() ![]() |
3.099 | 21.28 | B | 9.81 | this paper | |
CTQ 0460 | 10
![]() ![]() ![]() |
-23
![]() ![]() ![]() |
3.139 | 17.50 | V | 0.00 | Maza et al. (1995) | |
BR 1117-1329 | QNQ J11208-1345 | 11
![]() ![]() ![]() |
-13
![]() ![]() ![]() |
1.893 | 20.10 | B | 9.31 | this paper |
QNQ J11205-1343 | 11
![]() ![]() ![]() |
-13
![]() ![]() ![]() |
1.910 | 19.84 | B | 6.48 | this paper | |
QNQ J11197-1340 | 11
![]() ![]() ![]() |
-13
![]() ![]() ![]() |
2.220 | 18.32 | B | 8.03 | this paper | |
QNQ J11192-1334 | 11
![]() ![]() ![]() |
-13
![]() ![]() ![]() |
3.252 | 22.55 | B | 18.71 | this paper | |
BR 1117-1329 | 11
![]() ![]() ![]() |
-13
![]() ![]() ![]() |
3.958 | 18.00 | R | 0.00 | Storrie-Lombardi et al. (1996) | |
BR 1202-0725 | QNQ J12061-0745 | 12
![]() ![]() ![]() |
-07
![]() ![]() ![]() |
1.730 | 19.15 | B | 11.81 | this paper |
CIRSI 05 | 12
![]() ![]() ![]() |
-07
![]() ![]() ![]() |
2.661 | 19.39 | B | 3.08 | Sharp et al. (2002) | |
BR 1202-0725 | 12
![]() ![]() ![]() |
-07
![]() ![]() ![]() |
4.690 | 18.70 | R | 0.00 | McMahon et al. (1994) | |
Q 1209+093 | QNQ J12111+0906 | 12
![]() ![]() ![]() |
+09
![]() ![]() ![]() |
2.534 | 21.17 | B | 8.26 | this paper |
Q 1209+093 | 12
![]() ![]() ![]() |
+09
![]() ![]() ![]() |
3.291 | 19.04 | g | 0.00 | Hazard et al. (1987) | |
Q 1451+123 | SDSS J1455+1216 | 14
![]() ![]() ![]() |
+12
![]() ![]() ![]() |
1.901 | 19.29 | g | 16.08 | Schneider et al. (2007) |
Q 1451+123 | 14
![]() ![]() ![]() |
+12
![]() ![]() ![]() |
3.249 | 18.80 | V | 0.00 | Hazard et al. (1986) | |
SDSS J1452+1156 | 14
![]() ![]() ![]() |
+11
![]() ![]() ![]() |
4.026 | 21.44 | g | 26.58 | Schneider et al. (2007) | |
PKS 2126-158 | QNQ J21286-1528 | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
1.925 | 19.79 | B | 12.93 | this paper |
QNQ J21291-1524B | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
2.480 | 20.33 | B | 14.29 | this paper | |
PKS 2126-158 | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
3.285 | 17.00 | V | 0.00 | Jauncey et al. (1978) | |
QNQ J21301-1533 | 21
![]() ![]() ![]() |
-15
![]() ![]() ![]() |
3.487 | 21.94 | B | 14.34 | this paper | |
Q 2139-4434 | Q 2138-4416 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
1.732 | 19.38 | B | 17.42 | Hawkins (2000) |
QSO J2142-4406 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
1.736 | 21.10 | B | 13.83 | Francis et al. (2004) | |
QSO J2143-4410 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
1.768 | 21.71 | B | 15.24 | Francis et al. (2004) | |
QSO J2142-4430 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
1.795 | 20.26 | B | 11.40 | Francis et al. (2004) | |
QSO J2142-4432 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
1.849 | 21.44 | B | 12.97 | Francis et al. (2004) | |
QSO J2142-4358 | 21
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
1.853 | 21.96 | B | 21.65 | Francis et al. (2004) | |
QSO J2140-4432 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
1.863 | 20.69 | B | 25.62 | Francis et al. (2004) | |
QSO J2142-4431 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.036 | 22.79 | B | 11.23 | Francis et al. (2004) | |
Q 2137-4422 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.045 | 20.78 | B | 26.11 | Hawkins (2000) | |
QSO J2140-4403 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.097 | 20.31 | B | 25.70 | Francis et al. (2004) | |
Q 2138-4420 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.107 | 20.28 | B | 17.56 | Hawkins (2000) | |
QSO J2144-4412 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.140 | 22.86 | B | 23.55 | Francis et al. (2004) | |
QSO J2144-4423 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.162 | 20.49 | B | 20.87 | Francis et al. (2004) | |
QSO J2143-4408 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.166 | 22.02 | B | 17.78 | Francis et al. (2004) | |
QSO J2141-4356 | 21
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
2.202 | 21.51 | B | 27.36 | Francis et al. (2004) | |
QSO J2143-4356 | 21
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
2.223 | 21.82 | B | 25.81 | Francis et al. (2004) | |
QSO J2141-4442 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.224 | 21.89 | B | 22.41 | Francis et al. (2004) | |
Q 2139-4444 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.372 | 21.19 | B | 10.04 | Hawkins (2000) | |
QSO J2142-4359 | 21
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
2.458 | 21.59 | B | 20.97 | Francis et al. (2004) | |
QNQ J21434-4432 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.709 | 19.33 | B | 15.94 | this paper | |
QSO J2144-4407 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.725 | 21.04 | B | 24.01 | Francis et al. (2004) | |
QSO J2143-4435 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
2.725 | 22.02 | B | 18.27 | Francis et al. (2004) | |
Q 2138-4427 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
3.120 | 18.13 | V | 8.29 | Morris et al. (1991) | |
Q 2140-4406 | 21
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
3.180 | 20.64 | V | 28.52 | Véron & Hawkins (1995) | |
Q 2139-4434 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
3.214 | 17.70 | V | 0.00 | Morris et al. (1991) | |
Q 2139-4433 | 21
![]() ![]() ![]() |
-44
![]() ![]() ![]() |
3.228 | 21.63 | B | 1.02 | Véron & Hawkins (1995) | |
HE 2243-6031 | QNQ J22454-6020 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
1.984 | 20.94 | B | 13.46 | this paper |
QNQ J22455-6015 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
2.036 | 21.74 | B | 11.71 | this paper | |
QNQ J22460-6024 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
2.041 | 21.25 | B | 12.46 | this paper | |
QNQ J22454-6011 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
2.324 | 19.36 | B | 13.16 | this paper | |
QNQ J22463-6009 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
2.329 | 19.71 | B | 9.20 | this paper | |
HE 2243-6031a | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
3.010 | 16.40 | V | 0.00 | ||
QNQ J22484-6002 | 22
![]() ![]() ![]() |
-60
![]() ![]() ![]() |
3.586 | 20.97 | B | 16.72 | this paper | |
HE 2347-4342 | QNQ J23509-4330 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
1.762 | 18.23 | B | 6.01 | Worseck et al. (2007) |
QNQ J23502-4334 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
1.763 | 18.95 | B | 8.88 | Worseck et al. (2007) | |
QSO J23508-4335 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
1.778 | 22.01 | V | 9.73 | Worseck et al. (2007) | |
QNQ J23503-4328 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
2.282 | 20.66 | B | 3.57 | Worseck et al. (2007) | |
QSO J23500-4319 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
2.302 | 22.61 | V | 8.76 | Worseck et al. (2007) | |
QNQ J23495-4338 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
2.690 | 20.21 | B | 16.27 | Worseck et al. (2007) | |
HE 2347-4342 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
2.885 | 17.18 | B | 0.00 | Reimers et al. (1997) | |
QNQ J23511-4319 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
3.020 | 21.00 | B | 8.98 | Worseck et al. (2007) | |
QNQ J23514-4339 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
3.240 | 21.57 | B | 16.03 | Worseck et al. (2007) | |
QNQ J23503-4317 | 23
![]() ![]() ![]() |
-43
![]() ![]() ![]() |
3.542 | 21.94 | B | 8.78 | Worseck et al. (2007) |