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arXiv:astro­ph/0403628
v1
26
Mar
2004
Astronomy & Astrophysics manuscript no. vvds—cdfs2 August 2, 2004
(DOI: will be inserted by hand later)
The VIMOS VLT Deep Survey
Public release of 1599 redshifts to I AB # 24 across the Chandra Deep Field
South #
O. Le F‘evre 1 , G. Vettolani 2 , S. Paltani 1 , L. Tresse 1 , G. Zamorani 10 , V. Le Brun 1 , C. Moreau 1 , C. Adami 1 , M.
Arnaboldi 7 , S. Arnouts 1 S. Bardelli 10 , M. Bolzonella 11 , M. Bondi 2 , A. Bongiorno 11 , D. Bottini 3 , G. Busarello 7 , A.
Cappi 10 , P. Ciliegi 10 , T. Contini 4 , S. Charlot 5 , S. Foucaud 3 , P. Franzetti 3 , B. Garilli 3 , I. Gavignaud 4 , L. Guzzo 6 , O.
Ilbert 1 , A. Iovino 6 , D. Maccagni 3 , D. Mancini 7 , B. Marano 11 , C. Marinoni 1 , H.J. McCracken 8 , G. Mathez 4 , A.
Mazure 1 , Y. Mellier 8 , B. Meneux 1 , P. Merluzzi 7 , C. Moreau 1 , R. Pell‘o 4 , J.P. Picat 4 , A. Pollo 6 , L. Pozzetti 10 , M.
Radovich 7 , V. Ripepi 7 , D. Rizzo 4 , R. Scaramella 2 , M. Scodeggio 3 , A. Zanichelli 2 , E. Zucca 10
1 Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS­Universit’e de Provence, Traverse du Siphon­Les trois Lucs,
13012 Marseille, France
email: olivier.lefevre@oamp.fr
2 Istituto di Radio­Astronomia ­ CNR, Bologna, Italy
3 IASF ­ INAF, Milano, Italy
4 Laboratoire d'Astrophysique ­ Observatoire Midi­Pyr’en’ees, Toulouse, France
5 Max Planck Institut fur Astrophysik, 85741 Garching, Germany
6 Osservatorio Astronomico di Brera, via Brera, Milan, Italy
7 Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
8 Institut d'Astrophysique de Paris, UMR 7095, 98 bis Bvd Arago, 75014 Paris, France
9 Observatoire de Paris, LERMA, UMR 8112, 61 Av. de l'Observatoire, 75014 Paris, France
10 Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
11 Universit‘a di Bologna, Departimento di Astronomia, via Ranzani 1, 40127 Bologna, Italy
Received ..., 2004; accepted ..., 2004
Abstract.This paper presents the VIMOS VLT Deep Survey around the Chandra Deep Field South (CDFS). We have measured
1599 new redshifts with VIMOS on the European Observatory Very Large Telescope ­ UT3, in an area 21 â 21.6 arcmin 2 ,
including 784 redshifts in the Hubble Space Telescope ­ Advanced Camera for Surveys GOODS area. 30% of all objects with
I AB = 24 have been observed independently of magnitude, indicating that the sample is purely magnitude limited. We have
reached an unprecedented completeness level of 88% in terms of the ratio of secure measurements vs. observed objects, while
95% of all objects have a redshift measurement. A total of 1452 galaxies, 139 stars, 8 QSOs have a redshift identification, 141
of these being unsecure measurements. The redshift distribution down to I AB = 24 is peaked at a median redshift z=0.73, with
a significant high redshift tail extending up to # 4. Several high density peaks in the distribution of galaxies are identified. In
particular, the strong peak at z=0.735 contains more than 130 galaxies in a velocity range ±2000km/s distributed all across the
transverse #20 h -1 Mpc of the survey. We are releasing all redshifts to the community, along with the cross identification with
HST­ACS GOODS sources on the CENCOS database environment http://cencosw.oamp.fr.
Key words. Cosmology: observations -- Cosmology: deep redshift surveys -- Galaxies: evolution -- -- Cosmology: large scale
structure of universe
1. Introduction
Understanding the major steps in the evolution of galax­
ies still remains a major challenge to modern astrophysics.
While the general theoretical framework of the hierarchi­
cal growth of structures in the universe including the build
Send o#print requests to: O. Le F‘evre
# The data presented in this paper has been obtained with the
European Southern Observatory Very Large Telescope, Paranal, Chile
up of galaxies is well in place (e.g. Peacock et al., 2004),
at high redshifts this picture remains largely unconstrained
by observations. The detailed properties of the main popu­
lation of galaxies from large samples representative of the
universe at various epochs remain to be established across
most of the life of the universe beyond the large local vol­
umes explored by the 2dFGRS (Colless et al., 2001 and the
SDSS (Schneider, et al., 2003), and expanding from smaller

2 Le F‘evre, O., Vettolani, G., et al.: VVDS: public release of redshifts in CDFS
exploratory surveys (Lilly et al., 1995, Le F‘evre et al., 1995,
Steidel et al., 2003, Cimatti, et al., 2002).
The VIMOS VLT Deep Survey (VVDS) is a deep redshift
survey aimed at studying the evolution of galaxies, large scale
structures and AGNs over more than 90% of the current age
of the universe. The unique feature of the VVDS is the simple
magnitude selection applied to define a complete magnitude
limited sample of distant galaxies, with a goal of more than
100000 objects observed in multi­object spectroscopy. The
VVDS rests on the observations of 5 di#erent fields to smooth
out the e#ects of cosmic variance when building the statistical
properties of the galaxy population (Le F‘evre et al., 2004).
This paper presents the redshift survey observations of
1599 objects with I AB # 24 conducted by the VVDS team
around the Chandra Deep Field South, including the HST­
GOODS area (Giavalisco et al., 2004). The observations have
been carried out with the VIsible Multi­Object Spectrograph
(VIMOS) on the 8.2m Melipal telescope of the European
Southern Observatory Very Large Telescope. We are describ­
ing the processing steps and redshift measurements, and the
associated quality control we have applied to these data. The
content of the final catalog is detailed, as well as the cross iden­
tification with the Hubble Space Telescope Advanced Camera
for Surveys GOODS images, and we present the main entries
available from our interactive database. The main properties of
the sample are briefly presented, including the redshift distri­
bution of the sample.
2. Observations
2.1. Multi­Object Spectroscopy with VIMOS
Spectroscopic observations have been conducted with VIMOS
on the VLT­UT3 Melipal (Le F‘evre et al., 2003). The low res­
olution red grism LRRED has been used with slits of 1 arcsec
width. The spectral resolution in this mode is 34åat 7500åor
R # 220. The spectral length has been limited by the red band­
pass filter to 5500 - 9500 å. Slits placed on objects have a
typical length # 10 arcsec each.
2.2. VIMOS pointings
A complete VIMOS pointing is a combination of observations
with the 4 quadrants of the instrument, each separated by a
cross about 2 arcminutes wide. With the above setup and the
projected sky density of objects down to I AB = 24, one VIMOS
pointing allows to observe # 500 - 575 targets in one single
observation (Le F‘evre et al., 2003).
We have set a total of 5 pointings around the Chandra Deep
Field South, the positions are listed in Table 1. Together, they
cover a total area of # 453 #2 including the complete HST­
GOODS survey field (Giavalisco et al., 2004). The layout of
observed galaxies is presented in Figure 1.
2.3. Mask preparation
The preparation of slit masks for VIMOS observations has
been done using the photometric catalog produced by the ESO
Imaging Survey (EIS, Arnouts et al., 2001), and short images
taken with VIMOS. The VIMOS images are used to produce
a catalog of source positions in the VIMOS instrument coordi­
nate system, which are then cross­correlated with the EIS cat­
alog to compute the transformation matrix from the EIS cat­
alog astrometric system to the VIMOS focal plane where slit
masks are located. The VMMPS code was then run on the EIS
catalog for all sources brighter than I AB = 24 to optimize the
number and positions of slits for each of the 4 masks per point­
ing. Masks have been cut by ESO Paranal Sta# using the Mask
Manufacturing Unit (Conti et al., 2001).
2.4. VIMOS observations
Observations with VIMOS have been obtained between
October 31 and December 6, 2002. Observing conditions were
photometric with an image quality between 0.6 and 1.2 arcsec
FWHM. We have moved the telescope, hence the objects along
the slits, in a sequence of 5 positions with o#sets ­0.7, ­0.3,
0, +0.3, +0.7 arcsec from the reference pointing position. This
is necessary to compute the fringing pattern produced above
8300å by the thinned EEV CCDs used in VIMOS, and remove
it during processing.
Wavelength calibrations have been obtained during the day,
observing Helium and Argon arc lamps through the observed
masks. The spectrophotometric standard star LTT3218 has
been used to derive the absolute flux calibration.
3. Data Processing
Data processing has been conducted under the VIPGI environ­
ment developed by our team (Franzetti, et al., 2004). VIPGI
has been used to organize the multiple files and process all
data from the raw 2D images and calibration to the production
of sky subtracted, wavelength and flux calibrated 1D spectra.
Because of instrument flexures not yet minimized at the time
of these observations, the fringing pattern has been occasion­
ally hard to remove. The quality control performed on these
steps is described in Le F‘evre et al., 2004. The wavelength ac­
curacy is better than # 1å rms all over the wavelength range,
and the spectrophotometry is accurate to about 10%.
4. Redshift Measurements
Measuring redshifts for a complete magnitude limited sam­
ple down to I AB = 24 had never been attempted before our
observations. The challenge is to measure redshifts within a
possible range 0 # z ## 5, without any a priori indica­
tion to preserve the complete magnitude selected sample ap­
proach. The approach we have followed involves an itera­
tive build up of galaxy templates as observed with VIMOS,
coupled to the powerful redshift measuring machine KBRED
(Scaramella et al., 2004), based on cross correlation and prin­
cipal component analysis methods. This approach has been ap­
plied and tuned on the more than 20000 spectra obtained for
the VVDS in the fall of 2002, and remained until recently very
manpower intensive. On this critical step, we have enforced a
very strict quality control.

Le F‘evre, O., Vettolani, G., et al.: VVDS: public release of redshifts in CDFS 3
Table 1. Observed VIMOS pointings.
Pointing # 2000 # 2000 Date Number T exp
VVDS (2000) (2000) Observed o f slits minutes
CDFS001 03h32m28.0s -27 # 48 # 30 ## 31 - Oct - 02 447 10x27
1, 2, 4 - Nov - 02
CDFS002 03h32m37.04s -27 # 50 # 30 ## 5, 6 - Nov - 02 331 a 8x27
CDFS003 03h32m18.95s -27 # 50 # 30 ## 9, 10, 11, 12 - Nov - 02 447 9x27
CDFS004 03h32m37.04s -27 # 46 # 30 ## 27, 28, 29 - Nov - 02 436 12x27
1, 2 - Dec - 02
CDFS005 03h32m18.95s -27 # 46 # 30 ## 2, 4, 5, 6 - Dec - 02 448 10x27
a Quadrant 2 not observed
Fig. 1. Objects observed with VIMOS­VLT around the Chandra Deep Field South. Black circles are objects in the HST­ACS
GOODS area.
Each spectrum has been measured independently by 2
VVDS team members, and then compared. A final check has
been done by a third team member prior to release into the
database. Each spectrum is assigned a redshift, and a flag in­
dicating the reliability level of the measurement, as defined in
Le F‘evre et al., 1995 and described in Section 6. Flags 2,3,4
are the most secure, flag 1 is an indicative measurement based
on continuum and few supporting features, and flag 0 indicates
a measurement failure with no features identified. Flag 9 in­
dicates that there is only one secure emission line tentatively
assigned to the listed redshift (e.g. [OII]3727å or H#).
4.1. Redshift accuracy
The redshift accuracy can be estimated from a sample of 160
galaxies which have been observed twice with VIMOS within
the 5 CDFS pointings. These galaxies have been included in
two or more di#erent mask sets, and observed independently
at di#erent times. The distribution of measured redshift di#er­

4 Le F‘evre, O., Vettolani, G., et al.: VVDS: public release of redshifts in CDFS
ences is presented in Figure 2. The redshift dispersion of the
distribution is # = 0.0012, or 360km/s.
We have compared our redshift measurements with the
measurements of the K20 survey (Cimatti, et al., 2002) and
VLT­FORS2 measurements conducted by the ESO­GOODS
team (www.eso.org/science/goods). A total of 70 objects have
been observed both by the VVDS and the K20. For the 63
VVDS objects with flags # 1, the redshifts agree for # 87%
of the sample with a #z = -0.0004 and # z = 0.0017, with
the main disagreement concentrated on flag 1, as expected. The
comparison with the FORS2 data yields 46 objects in common,
of which 42 have a VVDS flag # 1. The VVDS vs. FORS2
redshift agree for 66% of the sample with #z = -0.0006 and
# z = 0.0013. The detailed comparison of VVDS redshift mea­
surements with the measurements from these other teams will
be presented in Le F‘evre et al., 2004.
4.2. Completeness
We have defined the completeness of the measurements as the
ratio between the actual redshifts measurements and the ob­
served spectra. We have removed from the list of observed
spectra those which have a clearly identified instrumental or
data processing problem a#ecting the measurement, like e.g.
the slit is behind the guide probe of the VLT­UT3, or the data
processing with VIPGI failed to properly detect the object be­
cause of strong residual features from the sky / fringing correc­
tions. This will be described in details in Le F‘evre et al., 2004.
We are presenting in Figure 3 the completeness vs. I AB
magnitude of all objects (galaxies, stars, QSOs) with flags
2,3,4,9 and 12,13,14,19 (the most secure) and the completeness
level adding the flags 1 and 11 to the above.
The overall redshift measurement completeness reaches
88% excluding flags 0 and 1; it reaches 95% including objects
with flags 1 and excluding objects with flags 0.
5. Cross identification with HST­ACS GOODS
sources
The cross identification of the objects observed from the EIS
catalog and the objects detected by HST­ACS has been per­
formed running a cross correlation of our target list with the list
of objects published in the version r1.0, December 22 2003, of
the GOODS survey multi­band catalog. The relative astrometry
of the EIS vs. GOODS catalogs has been found to be extremely
good, to within 0.1 arcsecond over our survey field. A search
circle with radius 0.3 arcsecond has been used to search for
HST sources corresponding to the ground based sources. This
produced a matched list with only one to one identifications,
and no double identifications.
6. Basic properties of the sample
6.1. Magnitude distribution
The magnitude distribution of objects observed in our survey is
shown in Figure 4 compared to the distribution of all objects in
the EIS photometric catalog over the same area. We have ob­
served 30% of all objects with I AB # 24 in the area covered by
the survey, independently of magnitude, as shown in Figure 4.
This demonstrates that there is no magnitude ­ dependent bias
in our object selection and that our sample is purely magnitude
selected even after the complex target selection in the making
of the VIMOS multi­slit masks.
6.2. Redshift Distribution
The redshift distribution of the full sample of galaxies and
QSOs is presented in Figure 5. The median of the redshift dis­
tribution is < z >= 0.73. Galaxies are identified up to z = 4.63.
As described in Le F‘evre et al., 2004 and Paltani et al., 2004,
we have been successful in breaking into the ``redshift desert''
artificially produced by the di#culty to identify redshifts in the
range 1.5 # z # 3 due to our instrumental set­up, through ex­
tensive work on galaxy templates based on the high redshift
galaxies measured in the VVDS (Paltani et al., 2004). We ex­
tensively discuss the incompleteness of the VVDS sample vs.
redshift in Le F‘evre et al., 2004.
The strongest peaks in the distribution are at redshifts z =
0.667, and z = 0.735. A total of 149 galaxies are measured in
the z = 0.667 peak and 116 galaxies z = 0.735 peak. These
structures are extending all across transverse # 16 Mpc of this
survey (z # 0.7 #CDM with H 0 =
70,# m =
0.3,# Lambda =
0.7) in a wall­like pattern rather than in clusters.
6.3. Absolute Magnitude and B­I distributions vs.
redshift
The absolute magnitude M B vs. redshift distribution is pre­
sented in Figure 6. The absolute magnitudes have been com­
puted based on k(z) corrections derived from the fitting of the
broad band photometry using rest frame galaxy templates (see
Ilbert et al., 2004). The B AB -I AB vs. redshift distribution is pre­
sented in Figure 7
7. The CDFS catalog
Our catalog contains 1599 spectra including 1452 galaxies, 139
stars, and 8 QSOs, with 141 of these having an uncertain red­
shift identification. We have listed for each observed object:
-- the ESO Imaging Survey identification number, equatorial
coordinates # 2000 , # 2000 , I AB magnitudes and associated errors
(Arnouts et al., 2001)
-- the HST­GOODS identification number and BVIz magni­
tudes and associated errors (Giavalisco et al., 2004)
-- the redshift measured by the VVDS team
-- the redshift quality flag (see Le F‘evre et al., 2004 for a de­
tailed description). The flags definition from the Canada France
Redshift Survey (Le F‘evre et al., 1995) is as follows:
0: no redshift could be measured
1: some spectral features like e.g. weak line(s) or continuum
break give a possible indication of the redshift (more than
# 50% confidence in the measurement)
2: a few secure features are identified in support of the redshift

Le F‘evre, O., Vettolani, G., et al.: VVDS: public release of redshifts in CDFS 5
Fig. 2. Redshift di#erence between objects observed twice or more in independent VIMOS observations. The distribution has a
velocity dispersion # z = 0.0012 or 360km/s.
measurement (more than # 75% confidence in the measure­
ment)
3: many secure features are identified (more than # 95% confi­
dence in the measurement)
4: strong secure features with high S/N are identified (100%
confidence in the measurement)
8. Public data release
We are publicly releasing all redshift measurements through
the CENCOS (CENtre de COSmologie) database environ­
ment on our web site http://cencosw.oamp.fr with access to
the database built under the Oracle environment. The catalog
can be searched by coordinates, redshift interval, identification
number in the EIS or GOODS catalogs, in combination with
the spectra quality flags. Upon query, the database engine re­
turns a list of targets, each of them can be examined in one
single summary panel with all the VVDS spectroscopy infor­
mation including the spectra, as well as the EIS and B,V,I,z
HST­GOODS images, and associated photometry as shown in
Figure 8.
9. Summary
In the framework of the VIMOS VLT Deep Survey (VVDS),
we have observed a large sample of galaxies around the
Chandra Deep Field South, and are releasing the redshift data
to the community. A total of 1599 objects with I AB # 24 have a
measured redshift. The completeness in redshift measurement
for the targeted objects is high, above 88%. We find that the
redshift distribution has a median of z = 0.73, with strong high
density peaks observed across the field.
The combination of this redshift survey and the HST­ACS
GOODS survey enables detailed studies of the evolution of
galaxies in the Chandra Deep Field South.
Acknowledgements. We are grateful to A. Cimatti and the K20 team
for releasing their redshift measurements to us for comparison. The
VLT­VIMOS observations have been carried out on garanteed ob­
serving time (GTO) allocated by the European Southern Observatory
as a compensation for the manpower invested by the VIRMOS con­
sortium in the design, manufacturing and testing of VIMOS under a
contractual agreement between the Centre National de la Recherche
Scientifique of France, and the European Southern Observatory.
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6 Le F‘evre, O., Vettolani, G., et al.: VVDS: public release of redshifts in CDFS
Fig. 3. Completeness of the I AB # 24 sample. (Bottom panel) The magnitude distribution of galaxies with secure redshift mea­
surements (flags 2,3,4,9; open histogram), uncertain and failed measurements (flags 0 and 1, dashed histogram), and failed
measurements alone (flags 0, filled histogram). (Top panel) the ratio of secure redshift measurements (flags 2,3,4,9 continuous
line histogram), and of all measurements (flags 1,2,3,4,9 dashed line histogram). The overall redshift measurement completeness
is 88% (flags 2,3,4,9) and redshifts are measured for 95% of the sample.
Peacock, J., 2002 Tenerife Winter School, ''Dark matter and dark en­
ergy in the universe'', astro­ph/0309240
Scaramella, R., and the VVDS team, 2004, in preparation.
Steidel, C.C., Adelberger, K.L., Shapley, A.E., Pettini, M., Dickinson,
M., Giavalisco, M., 2003, Ap.J., 592, 728
Schneider, D.P., et al., 2003, AJ 126:2579

Le F‘evre, O., Vettolani, G., et al.: VVDS: public release of redshifts in CDFS 7
Fig. 4. (Top panel) I AB magnitude distribution of objects observed with VIMOS in the Chandra Deep Field South (shaded his­
togram), compared to the distribution of all objects in the area in the EIS photometric catalog (open histogram). (Bottom panel)
The ratio of observed vs. all objects is 0.3.

8 Le F‘evre, O., Vettolani, G., et al.: VVDS: public release of redshifts in CDFS
Fig. 5. Redshift distribution of galaxies with I AB # 24 observed with VIMOS in the Chandra Deep Field South. The redshift bin
is dz=0.005. There are 42 objects identified with z # 2 not included in this figure.

Le F‘evre, O., Vettolani, G., et al.: VVDS: public release of redshifts in CDFS 9
Fig. 6. Absolute M B AB magnitude ­ Redshift distribution for the full VVDS--CDFS sample
Fig. 7. B AB - I AB vs. Redshift distribution for the full VVDS--CDFS sample

10 Le F‘evre, O., Vettolani, G., et al.: VVDS: public release of redshifts in CDFS
Fig. 8. VVDS database output panel for one single object. All information is presented, including the EIS and HST­GOODS
identifiers, the ground based and HST­ACS magnitudes, the VVDS redshift and quality flag, and the HST­GOODS images and
VVDS spectrum are displayed.