text:
A New Window of Exploration in the Mass Spectrum: Strong Lensing by Galaxy Groups in the SL2S
ABSTRACT The existence of strong lensing systems with Einstein radii (Re) covering the full mass spectrum, from ~1-2" (produced by galaxy scale dark matter haloes) to >10" (produced by galaxy cluster scale haloes) have long been predicted. Many lenses with Re around 1-2" and above 10" have been reported but very few in between. In this article, we present a sample of 13 strong lensing systems with Re in the range 3"- 8", i.e. systems produced by galaxy group scale dark matter haloes, spanning a redshift range from 0.3 to 0.8. This opens a new window of exploration in the mass spectrum, around 10^{13}- 10^{14} M_{sun}, which is a crucial range for understanding the transition between galaxies and galaxy clusters. Our analysis is based on multi-colour CFHTLS images complemented with HST imaging and ground based spectroscopy. Large scale properties are derived from both the light distribution of the elliptical galaxies group members and weak lensing of the faint background galaxy population. On small scales, the strong lensing analysis yields Einstein radii between 2.5" and 8". On larger scales, the strong lenses coincide with the peak of the light distribution, suggesting that mass is traced by light. Most of the luminosity maps have complicated shapes, indicating that these intermediate mass structures are dynamically young. Fitting the reduced shear with a Singular Isothermal Sphere, we find sigma ~ 500 km/s and an upper limit of ~900 km/s for the whole sample. The mass to light ratio for the sample is found to be M/L_i ~ 250 (solar units, corrected for evolution), with an upper limit of 500. This can be compared to mass to light ratios of small groups (with sigma ~ 300 km/s and galaxy clusters with sigma > 1000 km/s, thus bridging the gap between these mass scales. Comment: A&A Accepted. Draft with Appendix images can be found at http://www.dark-cosmology.dk/~marceau/groups_sl2s.pdf
- SourceAvailable from: Marceau Limousin
Article: Strong Lensing as a Probe of the Mass Distribution Beyond the Einstein Radius. Mass & Light in SL2S J08544-0121, a Galaxy Group at z=0.35[Show abstract] [Hide abstract]
ABSTRACT: Precise modelling of strong lensing systems can be affected by external mass distributions, e.g. the group or cluster within which the lens is embedded. In this article, we propose to turn this limitation to our advantage and to use precise strong lensing modelling to probe external mass distributions surrounding the lens. We consider SL2S J08544-0121, a galaxy group at z=0.35 that contains a strong lensing system. A simple elliptical isothermal potential cannot reproduce satisfactorily the strong lensing constraints. We include an external mass perturbation corresponding to the group within which the lens is embedded. The lensing properties of this perturbation are parametrised by its total mass M and a smoothing scale s that quantifies the characteristic scale over which M is distributed. For a range of these parameters, we are able to reproduce accurately the observations. This suggests that light is a good tracer of mass. Interestingly, this also shows that a localised strong lensing analysis (on scales of ~10") allows us to constrain global properties of the group as a whole (on scales of ~100). Indeed, we constrain the group mass-to-light ratio to be M/L=98+-27 (i band, solar units, not corrected for evolution) and s=20" +- 9 (2sigma confidence level). We demonstrate that these strong lensing only constraints are due to the perturbed strong lensing configuration, where the main arc is located at ~5" from the galaxy, whereas its counter-image is found at ~8". To test independently our resulting strong lensing model, we pursue an independent weak lensing analysis of the group and find a mass-to-light ratio in the range 66-146 (1sigma confidence level). Comment: accepted for publication in AandA06/2009;
Article: The final candidate from the JVAS/CLASS search for 6 arcsec to 15 arcsec image separation lensing[Show abstract] [Hide abstract]
ABSTRACT: A search for 6 arcsec to 15 arcsec image separation lensing in the Jodrell Bank-Very Large Array Astrometric Survey (JVAS) and the Cosmic Lens All-Sky Survey (CLASS) by Phillips et al. found thirteen group and cluster gravitational lens candidates. Through radio and optical imaging and spectroscopy, Phillips et al. ruled out the lensing hypothesis for twelve of the candidates. In this paper, new optical imaging and spectroscopy of J0122+427, the final lens candidate from the JVAS/CLASS 6 arcsec to 15 arcsec image separation lens search, are presented. This system is found not to be a gravitational lens, but is just two radio-loud active galactic nuclei that are separated by ~10 arcsec on the sky and are at different redshifts. Therefore, it is concluded that there are no gravitational lenses in the JVAS and CLASS surveys with image separations between 6 arcsec to 15 arcsec. This result is consistent with the expectation that group- and cluster-scale dark matter haloes are inefficient lenses due to their relatively flat inner density profiles. Comment: 5 pages, 3 figures, 2 tables, accepted for publication in MNRASMonthly Notices of the Royal Astronomical Society 10/2010; · 5.52 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: We have discovered a strong lensing fossil group (J0454) at z=0.26, projected near the well-studied cluster MS0451-0305. Using multicolour Subaru/Suprime-Cam and CFHT/Megaprime imaging together with Keck spectroscopy we identify member galaxies. A VLT/FORS2 spectrum was taken to determine the redshifts of the brightest elliptical and the lensed arc. Using HST/ACS images we determine the group's weak lensing signal and model the strong lens system. This is the first time that a fossil group is analysed with lensing methods. The X-ray luminosity and temperature are derived from XMM-Newton data. We find two filaments extending over 4 Mpc, and within the virial radius we identify 31 members spectroscopically and 33 via the red sequence with i<22 mag. They segregate into spirals and a dynamically cooler central concentration of ellipticals with a velocity dispersion of 480 km/s. Weak lensing and cluster richness relations yield r200 = 830 kpc and M200 = 0.85 x 10^14 Msun. The brightest group galaxy (BGG) is inconsistent with the dynamic centre of J0454. It strongly lenses a galaxy at z~2.1, and we model the lens with a pseudo-isothermal elliptical mass distribution. A large external shear requires that the BGG must be offset from J0454's dark halo centre by at least 90-130 kpc. The X-ray halo is offset by 24 kpc from the BGG, shows no signs of a cooling flow and is well described by a beta-model. With L = 1.4 x 10^43 erg/s J0454 falls well onto standard X-ray cluster scaling relations, but appears cooler (1.1 keV) than expected (2 keV). We conclude that J0454 consists of two systems, a sparse cluster and an infalling fossil group, the latter seeding the BCG. An alternative explanation is that galaxies in a filament, projected along the line of sight, stream towards the denser fossil group.Astronomy and Astrophysics 02/2010; 514. · 5.08 Impact Factor
Page 1
Astronomy & Astrophysics manuscript no. 11473
June 2, 2009
c ? ESO 2009
A New Window of Exploration in the Mass Spectrum:
Strong Lensing by Galaxy Groups in the SL2S
M. Limousin1,2,3, R. Cabanac1, R. Gavazzi4,5, J.-P. Kneib2, V. Motta6, J. Richard7,8, K. Thanjavur9, G. Foex10,
R. Pello10, D. Crampton11, C. Faure12, B. Fort4,5, E. Jullo2, P. Marshall13, Y. Mellier4,5, A. More2, G. Soucail10,
S. Suyu14, M. Swinbank15, J.-F. Sygnet4,5, H. Tu16,4,5, D. Valls-Gabaud17, T. Verdugo6& J. Willis9 ?
1Laboratoire d'Astrophysique de Toulouse-Tarbes, Universit´ e de Toulouse, CNRS, 57 avenue d'Azereix, 65000 Tarbes, France
2Laboratoire d'Astrophysique de Marseille, UMR6110, CNRS-Universit´ e de Provence, 38 rue Fr´ ed´ eric Joliot-Curie, 13388
Marseille Cedex 13, France
3Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
4CNRS, UMR7095, Institut d'Astrophysique de Paris, F-75014, Paris, France
5UPMC Universit´ e Paris 06, UMR7095, Institut d'Astrophysique de Paris, F-75014, Paris, France
6Universidad de Valpara´ ıso, Departamento de F´ ısica y Astronomia, Avenida Gran Breta˜ na 1111, Valpara´ ıso, Chile
7Durham University, Physics and Astronomy Department, South Road, Durham DH3 1LE, UK
8Department of Astronomy, California Institute of Technology, 105-24, Pasadena, CA91125, USA
9Department of Physics and Astronomy, University of Victoria, Victoria, BC, Canada, V8W 3P6
10Laboratoire d'Astrophysique de Toulouse-Tarbes, Universit´ e de Toulouse, CNRS, 14 avenue Edouard Belin, 31400 Toulouse,
11Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
12Laboratoire d'Astrophysique, Ecole Polytechnique F´ ed´ erale de Lausanne (EPFL), Observatoire de Sauverny, CH-1290 Versoix,
13Department of Physics, University of California, Santa Barbara, CA 93106, USA
14Argelander-Institut f¨ ur Astronomie, Universit¨ at Bonn, Auf dem H¨ ugel 71, 53121 Bonn, Germany
15Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
16Physics Department & Shanghai Key Lab for Astrophysics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234,
17Observatoire de Paris, GEPI, CNRS-UMR8111, 5 place Jules Janssen, 92195 Meudon Cedex, France
Preprint online version: June 2, 2009
The existence of strong lensing systems with Einstein radii covering the full mass spectrum, from ∼ 1 − 2??(produced by galaxy
scale dark matter haloes) to > 10??(produced by galaxy cluster scale haloes) have long been predicted. Many lenses with Einstein
radii around 1 − 2??and above 10??have been reported but very few in between. In this article, we present a sample of 13 strong
lensing systems with Einstein radii in the range 3??− 8??(or image separations in the range 6??− 16??), i.e. systems produced
by galaxy group scale dark matter haloes. This group sample spans a redshift range from 0.3 to 0.8. This opens a new window
of exploration in the mass spectrum, around 1013-1014M?, a crucial range for understanding the transition between galaxies and
galaxy clusters, and a range that have not been extensively probed with lensing techniques. These systems constitute a subsample of
the Strong Lensing Legacy Survey (SL2S), which aims to discover strong lensing systems in the Canada France Hawaii Telescope
Legacy Survey (CFHTLS). The sample is based on a search over 100 square degrees, implying a number density of ∼0.13 groups
per square degree. Our analysis is based on multi-colour CFHTLS images complemented with Hubble Space Telescope imaging and
ground based spectroscopy. Large scale properties are derived from both the light distribution of elliptical galaxies group members
and weak lensing of the faint background galaxy population. On small scales, the strong lensing analysis yields Einstein radii between
2.5??and 8??. On larger scales, strong lens centres coincide with peaks of light distribution, suggesting that light traces mass. Most of
the luminosity maps have complicated shapes, implying that these intermediate mass structures may be dynamically young. A weak
lensing signal is detected for 6 groups and upper limits are provided for 6 others. Fitting the reduced shear with a Singular Isothermal
Sphere, we find σSIS ∼ 500kms−1with large error bars and an upper limit of ∼900kms−1for the whole sample (except for the
highest redshift structure whose velocity dispersion is consistent with that of a galaxy cluster). The mass-to-light ratio for the sample
is found to be M/Li∼ 250 (solar units, corrected for evolution), with an upper limit of 500. This compares with mass-to-light ratios
of small groups (with σSIS∼ 300 kms−1) and galaxy clusters (with σSIS> 1000 kms−1), thus bridging the gap between these mass
scales. The group sample released in this paper will be complemented with other observations, providing a unique sample to study
this important intermediate mass range in further detail.
Key words. Gravitational lensing: strong lensing – Galaxies: groups –
Send offprint requests to: email@example.com
?Based on observations obtained with MegaPrime/MegaCam, a joint
project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii
Telescope (CFHT) which is operated by the National Research Council
(NRC) of Canada, the Institut National des Sciences de l'Univers of the
Centre National de la Recherche Scientifique (CNRS) of France, and
arXiv:0812.1033v3 [astro-ph] 2 Jun 2009
Page 2
2 Limousin et al.: Strong Lensing by Galaxy Groups
1. Introduction
1.1. Galaxy Groups & Cosmology
Galaxy groups are believed to play a key role in the formation
and evolution of structures in the Universe. They contain the ma-
jority of the galaxies in the Universe, and within a hierarchi-
cal framework, they span the regime between individual galax-
ies and massive galaxy clusters, making them cosmologically
significant. They are also more varied in their properties than
galaxy clusters, as demonstrated by comparisons between vari-
ous scaling relations in galaxy groups to those in galaxy clus-
ters. This indicates that galaxy groups are probably not a homo-
geneous class of objects, e.g. they cannot be considered simple
scaled-down versions of galaxy clusters. Detailed studies of this
intermediate regime of the mass spectrum (∼1013-1014M?) are
needed to understand better the physical processes behind for-
mation of galaxy groups and how galaxy groups participate to
structure formation and evolution.
Properties of low and intermediate redshift galaxy groups
(z < 0.5) have been studied using X-ray and optical tracers
(e.g. Helsdon & Ponman 2000, 2003; Osmond & Ponman 2004;
2007; Mamon 2007; Faltenbacher & Mathews 2007; Gastaldello
et al. 2007; Yang et al. 2008; van den Bosch et al. 2008; Sun
et al. 2009, and references therein). Galaxy groups have also
been studied numerically (e.g. D'Onghia et al. 2005; Sommer-
Larsen 2006, and references therein).
1.2. Strong Lens Statistics
Fig. 1 shows the predicted contributions of different types of
haloes in the image separation distributions (from Oguri 2006,
Fig. 9) extracted from N-body simulations, where θ corresponds
to about twice the Einstein radius of the lens1. This plot shows
that there are large overlaps among the halo types, but also that
some scales are dominated by different regimes: on small scales,
the distribution is dominated by galaxy-scale dark-matter haloes,
with Re<2??, and on larger scales, by cluster-scale dark-matter
haloes, with Re>10??. In between, the distribution is dominated
by haloes generating strong lensing deflection of radii between
∼3??and ∼8??, whose mass is in the range 1013-1014M?, i.e. by
group-scale dark-matter haloes.
Hence according to simulations, strong lenses from interme-
which we discuss in Section 7.6.
Strong Lensing Deflector: In this paper, we refer to a "deflec-
tor" as the foreground mass distribution giving rise to multiple
images, and we focus on its central part. Specifically, a strong
lensing deflector refers to the area of the foreground mass dis-
tribution enclosed by the multiple images. This region can be
populated by more than a single galaxy on scales smaller than
the University of Hawaii. This work is based in part on data products
produced at TERAPIX and the Canadian Astronomy Data Centre as
part of the Canada-France-Hawaii Telescope Legacy Survey, a collabo-
rative project of NRC and CNRS. Based on observations made with the
NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
Science Institute, which is operated by the Association of Universities
for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
These observations are associated with programs 10876 and 11289.
1In this paper, we will use the Einstein radius Re to characterise the
Fig.1. The contributions of different types of haloes on the im-
age separation distribution, from Oguri (2006): galaxy (dashed);
groups (dot) and clusters (dot-dashed). The sum of distributions
of three types is shown by thick solid line.
Re, as it is the case for some of the galaxy groups reported in
this work. In order to avoid confusion, we use the term deflec-
tor instead of lensing galaxy. This is particularly important for
group scale deflectors since their mass may no longer be asso-
ciated to a single galaxy. This definition is well adapted to most
of the groups studied in this paper, where the multiple images
identification is clear and therefore the region enclosed by these
images is well defined. However, this is not the case for three of
the groups presented in this paper.
1.3. Strong Lensing in and by a Galaxy Group
We shall emphasise the distinction between strong lensing in a
galaxy group and by a galaxy group. Strong lensing in a galaxy
group corresponds to the observation of a strong lensing fea-
ture, with a typical Einstein radius of ∼ 2??, generated by a
galaxy group member. Since the high-density environment is
likely to enhance the strong galaxy-galaxy lensing cross sec-
tion (see Kovner 1987; M¨ oller et al. 2002; Fassnacht et al. 2006;
Oguri et al. 2005; King 2007; Newton et al. 2008, but see Faure
et al. (2008) in the cosmos field), many strong lensing systems in
groups (or clusters) have been reported (e.g. Kundic et al. 1997;
Fassnacht & Lubin 2002; Morgan et al. 2005; Williams et al.
2006; Momcheva et al. 2006; Auger et al. 2007; Tu et al. 2008;
Auger et al. 2008; Grillo et al. 2008; Treu et al. 2009; Inada et al.
2008). If the creation of multiple images is boosted by external
shear and convergence from a smooth group component, these
strong lensing systems are, to first order, generated by a galaxy-
scale dark-matter halo populated by a single galaxy (most of the
time an elliptical galaxy, but note that efforts are currently un-
derway to find lenses generated by haloes populated by spiral
galaxies, see Feron et al. 2008; Trott et al. 2008).
Page 3
Limousin et al.: Strong Lensing by Galaxy Groups3
On the other hand, strong lensing by a galaxy group corre-
sponds to the observation of strongly lensed features with a typ-
ical Einstein radius between ∼ 3??and ∼ 8??. This translates into
a projected mass enclosed within this radius around ∼ 1012.5-
1013M?, i.e. characteristic of a group-scale dark-matter halo.
Note that the highest limit of 8??adopted here is somewhat arbi-
trary and may be considered by others as a characteristic size of
a poor cluster.
1.4. Galaxy Groups in the Strong Lensing Legacy Survey
A straightforward method for finding lens systems is to identify
them directly within existing multi-band wide-field imaging sur-
veys. For this purpose, we have started to explore systematically
the Canada France Hawaii Telescope Legacy Survey (CFHTLS),
using a dedicated automatic search procedure optimised for the
detection of arcs. This subsample of the CFHTLS forms the
Strong Lensing Legacy Survey (SL2S, Cabanac et al. 2007).
This sample is not biased towards high masses by any prior X-
ray selection and because of the wide area covered, cosmic vari-
ance is neglected and the resulting sample of strong lenses is as-
sumed to be representative of what can be found in the Universe.
However, selection biases inherent to our detection technique do
exist and will be addressed in a forthcoming publication using
numerical simulations. The SL2S sample probes a wide range
of masses and a wide range of redshifts for the lenses. Thanks
to unsurpassed combined depth, area and image quality of the
CFHTLS, we have uncovered a new population of lenses, with
Einstein radii between ∼ 3??and ∼ 8??, i.e. generated by galaxy-
group scale-dark matter haloes. This new population effectively
bridges the gap between single galaxies and massive clusters,
opening a new window of exploration in the mass spectrum. The
purpose of this paper is to present the first representative sample
of such lenses. Note that this sample is not statistically complete
since the survey is not complete yet and that we do not under-
stand properly our selection function.
This paper is organised as follows: data used in this work are
presented in Section 2. Sections 3, 4 and 5 present the methodol-
ogy of the systematic analysis we apply on each group. Results
are presented in Section 6 and discussed in Section 7. In the
Appendix, each group is described individually, with some im-
ages. All our results are scaled to a flat, ΛCDM cosmology with
ΩM = 0.3, ΩΛ = 0.7 and a Hubble constant H0 = 70 kms−1
Mpc−1. All images are aligned with WCS coordinates, i.e. north
is up, east is left. Magnitudes are given in the AB system.
2. Data
Multicolour imaging from the CFHTLS constitutes the basis of
our analysis and is complemented with ongoing HST imaging
and ongoing ground-based spectroscopy.
2.1. The Canada-France-Hawaii Telescope Legacy Survey
2.1.1. Description
The CFTHLS is a major photometric survey of more than
450 nights over 5 years (started on June 1st, 2003, end-
ing 2008) using the wide field imager MegaPrime which
covers ∼1 square degree on the sky, with a pixel size
of 0.186??. The project is comprehensively described in
http://www.cfht.hawaii.edu/Science/CFHLS/ and links
Table 1. CFHTLS: Terapix T0004 release (July 2007). For a
point source S/N = 5 (AB to Vega u∗−0.35, g?+0.09, r?−0.17,
i?− 0.40, z?− 0.55)
Deep fieldsAB Magnitudes Limits
D1-25 seeing0.930.93
D2-25 seeing0.830.83
D3-25 seeing0.890.89
D4-25 seeing0.860.86
Wide fieldsAB Average Magnitudes Limits
W1 area (unmasked)
W2 area (unmasked)
W3 area (unmasked)
W4 area (unmasked)
44 (39) deg2
20 ( 16) deg2
40 ( 34) deg2
16 ( 13) deg2
therein. The CFHTLS has two components aimed at extragalac-
tic studies: a very Deep component made of 4 pencil-beam fields
of 1deg2and a Wide component made of 3 mosaics covering
170deg2in total, both in 5 broadband filters. The data are pre-
reduced at CFHT with the Elixir pipeline2which removes the
instrumental artifacts in individual exposures. The CFHTLS im-
ages are then evaluated, astrometrically calibrated, photomet-
rically inter-calibrated, resampled and stacked by the Terapix
group at the Institut d'Astrophysique de Paris (IAP) and fi-
nally archived at the Canadian Astronomy Data Centre (CADC).
Terapix also provides weightmap images, quality assessments
meta-data for each stack as well as mask files that mask stray-
light, saturated stars and defects on each image.
2.1.2. Terapix release T0004
The SL2S group sample presented here is based on the T0004
release (July 2007), corresponding to data obtained between the
Spring 2003 and the spring 2007. A detailed description of this
release is given at the Terapix web site3and CADC site4. The
T0004 release includes 120 deg2of stacked fields in the Wide
survey observed in broadband g?, r?and i?filters, and a stack of
the 35 Wide and 4 Deep fields in the 5 bands, for a total area of
124 deg2, or ca. 110 deg2of unmasked area, i.e. area not con-
taminated by instrumental artefacts from bright stars (internal
reflections, bleeding). Table 1 summarises the main characteris-
tics of the T0004 release. The 4 Deep fields are much deeper,
with a seeing ranging from 0.9??in u∗to 0.7??in z?. Because of
the observing strategy, the Wide survey image quality is prone to
large variations from 1??to 0.6??seeing in all bands. Nevertheless,
the Wide survey is more suited to our strong lensing selection
processes, because of its wide angular coverage.
Page 4
4Limousin et al.: Strong Lensing by Galaxy Groups
2.2. Space Based Imaging
The strong lensing features detected from ground-based images
have been observed with the Hubble Space Telescope (HST) for
11 of the 13 groups presented in this paper. Observations were
done in snapshot mode (C15 and C16, P.I. Kneib, ID 10876
and 11289). 3 groups have been imaged in three bands with the
ACS camera (F814, F606 and F475), and the remaining in the
F606 band only with the WFPC2 camera. Space-based imaging
generally allows one to better resolve the strong lensing systems
we are interested in.
2.3. Spectroscopy
Various ongoing spectroscopic campaigns are targeting both the
galaxy group members as well as the multiply imaged systems.
We use the following facilities:
1. FORS2 on VLT: resolution of 600RI, exposure 2800 s, with
∆Λ from 5000 to 8000 Å.
2. LRIS on Keck: Dichroic 680 and 560 nm, exposure 600s and
1200s with a slit of 1.5??.
3. Gemini (ProgramGN-2007A-Q-114):
SL2SJ14300+5546 on June 2007 using GMOS LS+R400
grating at 7500 Å during 3750 s.
When available and relevant to this work, we will report some
of the results of our spectroscopic campaigns. Details of the ob-
serving runs and spectra will be presented in forthcoming publi-
cations. For SL2SJ14081+5429 and SL2SJ22214-0053, we re-
port the spectroscopic redshift measured by the Sloan Digital
Sky Survey (SDSS).
2.4. Photometric Redshifts
Photometric redshifts were estimated for all the groups, based
on the magnitudes of the brightest galaxy populating the strong
lensing deflector whose coordinates are given in Table 3.
Aperture magnitudes were extracted with sextractor 2.5 (Bertin
& Arnouts 1996) and photometric redshifts were estimated us-
ing the HyperZ software (Bolzonella et al. 2000). For all groups
but two (SL2SJ14300+5546 and SL2SJ14314+5533), 5 photo-
metric bands are available. Photometric redshifts, with 3σ error
bars are given in Table 3. They can be compared to the spectro-
scopic measurements available for 9 of the groups. We note that
in the case of 4 groups over 9, the spectroscopic redshifts are not
consistent with the 3σ confidence intervals of the photometric
redshifts estimates. However, the difference between each esti-
mate is smaller than 0.03. This has no influence on the lensing
properties of the galaxy groups and therefore does not bias our
In addition, we have been looking systematically in the NED
database at all known sources within 5?of each strong lensing
event to gather any observational data relevant to this study.
3. Building Luminosity Maps
Luminosity maps were created from the i-band isophotal mag-
nitudes of all the elliptical galaxies tagged as members of the
group. This is the deepest band that best represents the old stellar
population of elliptical galaxies. Catalogues of objects positions
and magnitudes have been generated using sextractor 2.5.
3.1. Selecting Group Members
We build matched g,r,i bands catalogues of all objects with a
radius of 5?of the lens centre. We compute the r−i colour of the
brightest galaxy populating the strong lensing deflector. We refer
to this quantity in the following as (r − i)0. We then consider all
galaxies whose r − i colour satisfy:
(r − i)0− 0.15 < r − i < (r − i)0+ 0.15 & i < maglim(z)
as possible galaxy group red-sequence members (e.g. Gladders
et al. 1998). We miss the faintest group members but the most lu-
minous ellipticals are correctly selected. When spectroscopy of
group members is available, we verified that our procedure does
select the spectroscopically confirmed group members. A more
robust selection will require us to analyse multi-object spec-
troscopy of the fields.
In order to compare the group luminosity maps across
the redshift range, we restrict our group member catalogue
to galaxies brighter than a magnitude threshold maglim(z).
This magnitude threshold is set by the apparent magnitude
of the faintest elliptical member of the highest redshift group
(SL2SJ22133+0048 at zphot= 0.83). That apparent magnitude is
converted into a rest-frame absolute luminosity, converted back
into a redshift-dependent apparent magnitude maglim(z) for each
3.2. Contamination
The red sequence technique is known to suffer from contamina-
tion. In our case, because the number count of objects per group
that satisfy Equ. 1 is small (less than 100), we visually inspected
each group member candidate and manually rejected galaxies
that were unlikely to be physically connected to the group (e.g.
higher redshift spiral galaxies). We also estimated contamination
from background/foreground objects serendipitously falling in
the same colour bin from random fields, i.e. fields large enough
to ensure that they are, on average, empty. Using CFHTLS deep
fields galaxy catalogues and applying Equ. 1 selection, we es-
timated the total background/foreground luminosity that adds
up to the group catalogues. This estimation is consistent with
what we have manually removed from our visual inspection.
Therefore, we prefer removing the background contamination
by eye since the method allows us to identify the contaminating
galaxies, whereas a statistical approach would lead to subtrac-
tion of constant luminosity sheets across groups and a loss of
positional information.
3.3. Luminosity Contours
We build luminosity maps to help us characterise the large-scale
luminous properties of the group sample. The CFHTLS i-band
image is divided into cells 20-pixels wide (corresponding to
3.7??). Considering the centre of each cell, we compute the to-
tal rest-frame i-band luminosity L by summing individual lumi-
nosities of the five closest group members, deduced from their
isophotal magnitude M:
L = 10(M?−M+DM+k+ev)/2.5
where M?is the Sun i-band absolute magnitude; DM is the dis-
tance modulus, k the k-correction factor and ev the passive evo-
lution correction, estimated from an elliptical template (Bruzual
& Charlot 2003). This total luminosity is divided by the circular
area enclosing the fifth neighbour: this gives a density within the
Page 5
Limousin et al.: Strong Lensing by Galaxy Groups5
considered cell that we express in units L?kpc−2. The computed
luminosity density map is then convolved with a Gaussian kernel
of width 3 cells.
of catalogued group members (on average 46 members).
We found that the size of the cells does not influence the
shape of the resulting luminosity contours. We checked that the
distance to the fifth neighbour is always larger than cell/√2,
which means we do not undersample any region of the field.
4. Weak Gravitational Lensing Analysis
We perform a one dimensional weak lensing (WL) analysis on
each group with the goal of probing the projected mass distri-
bution on large scales. This technique is well established and is
widely used on galaxy cluster scales (e.g. Bardeau et al. 2007;
Hoekstra 2007). The basic idea is the following: from the shape
of the background lensed galaxy population, we can estimate
the shear vector (or more precisely, the reduced shear, see e.g.
Mellier 1999). Its tangential component (with respect to the cen-
tre of the deflector) is directly proportional to the mass distribu-
tion of the deflector, whereas its radial component is expected to
be equal to zero in the case of perfect data. Given the relatively
tecting weak lensing by groups of galaxies is challenging. Until
now, weak lensing signals of such mass scales has been recov-
ered only by stacking groups (Hoekstra et al. 2001; Parker et al.
2005; Mandelbaum et al. 2006). Moreover, the strength of the
weak lensing signal is expected to decrease with the redshift of
the deflector, thus we expect to detect a weak lensing signal only
for the lower redshift groups. In any case, an upper limit on the
velocity dispersion of the structures studied in this work is of
interest. Because strongly lensed source redshifts are unknown,
weak-lensing derived velocity dispersion upper limits constitute
the only way to show that our sample contains only groups or
poor clusters and no massive clusters. Indeed, an Einstein radius
of ∼ 6??could be generated by a massive cluster lensing a low
redshift background source.
4.1. Weak Lensing Methodology
We have been following the methodology developed by Bardeau
We refer the reader to these papers for a detailed description of
involved in the analysis of the reduced and calibrated images.
The first step is to construct a photometric catalogue for
each individual image. Object positions and magnitudes were
extracted with sextractor 2.5. The second step of the analysis
is to extract a star catalogue which will be used to estimate the
local Point Spread Function (psf). We select stars and clean the
resulting catalogue as described in Bardeau et al. (2005). In or-
der to measure the shapes of the stars, we used the im2shape
software developed by Bridle et al. (2002). At this stage, we
have a map of the psf distribution over the entire field. The third
step is to compute the galaxy catalogues selected for the weak
lensing analysis. Galaxies are selected from the photometric cat-
alogues according to the criterion described in Bardeau et al.
(2005). To measure the shapes of galaxies, we first linearly in-
terpolate the local psf at each galaxy position by averaging the
shapes of the five closest stars. The number of 5 stars is found
to be large enough to locally interpolate the psf, whereas choos-
ing a much larger number would over-smooth the psf charac-
teristics. im2shape then computes intrinsic shapes of galaxies by
convolving a galaxy model with the interpolated local psf, and
determines which one is the most likely by minimising residu-
als. In the end, im2shape's output gives a most likely model for
the fitted galaxy characterised by its position, size, ellipticity and
orientation, and errors on all of these quantities. For the purpose
of the weak lensing analysis, we use the shape parameters de-
rived from the CFHTLS i band: observations in this photometric
band have been optimised for weak lensing purposes, thus data
quality in terms of seeing and source density is superior to the
other bands.
Note that the reliability of the im2shape software has been
validated through the simulated data of the STEP project
(Heymans et al. 2006) and the results show that no significant
bias is introduced by the deconvolution. It has been successfully
applied in a number of weak lensing works (Kneib et al. 2003;
Cypriano et al. 2004, 2005; Bardeau et al. 2005, 2007; Limousin
et al. 2007a,b; Medezinski et al. 2007; Carrasco et al. 2007).
4.2. Background Galaxies: Selection and Redshift
We select as background lensed sources the galaxies whose i-
band magnitudes fall between 21.5 and 24, hence close to the
completeness magnitude for all groups (Table 3). The mean den-
sity of background galaxies equals to ∼12 per square arcminute.
Applying the same magnitude cuts to the four CFHTLS deep
fields catalogues, we find a density of ∼15 per square arcminute,
slightly larger than the mean density of background galaxies
kept only objects whose shape parameters are reliably measured,
as detailed in Bardeau et al. (2005, 2007).
In order to relate the strength of the weak lensing signal to
a physical velocity dispersion characterising the group poten-
tial, one needs to estimate the mean geometrical factor Dls/Ds,
where Dls is the angular diameter distance between the lens
(here the group) and the source and Dsis the angular diameter
distance between the observer and the source. For this estima-
tion, we consider the photometric redshift catalogue from the
T0004 release of the CFHTLS-Deep survey, which corresponds
to the deep stacks of the repeated observations of four indepen-
dent MegaCam fields. These data are therefore collected with
the same instrument in the same photometric bands as the data
used in this work. The CFHTLS-Deep is much deeper (at least
one magnitude deeper in r) and the multicolour observations in 5
bands allow the determination of photometric redshifts. We have
used the publicly available photometric redshift catalogue pro-
vided by Roser Pello5which has been calibrated and validated
with spectroscopic samples (Ienna & Pell´ o 2006). We applied
to this catalogue the same magnitude selection criteria that we
applied to our background galaxy catalogue (i.e. i between 21.5
and 24). For each group, we compute the average geometrical
factor Dls/Dsby integrating this redshift probability distribution
between 0 and 5. We also compute the effective source redshift
zeffthat is defined by the redshift at which the geometrical factor
becomes equals to the mean geometrical factor. Both quantities
are given in Table 3.
Coupon et al. (2008) recently estimated photometric redshift
for 35 deg2of the Wide survey. Since our group catalogue is
based on a search of 100 deg2, all groups do not fall in the study
by Coupon et al. (2008). Moreover, they provide photometric
redshifts for galaxies brighter than i = 22.5 whereas our back-
5http://www.ast.obs-mip.fr/users/roser/CFHTLS T0004/
Page 6
6Limousin et al.: Strong Lensing by Galaxy Groups
ground galaxy catalogues contains objects as faint as i = 24.
Therefore, we cannot benefit from this work in assigning photo-
metric redshifts individually to each background galaxy.
Coupon et al. (2008) also estimate photometric redshifts for
the Deep fields down to i = 24. A thorough comparison of both
catalogues is beyond the scope of this paper, but we can check
if the presented results change significantly if we use this cat-
alogue instead of ours. We apply the same magnitude selection
to the Coupon et al. (2008) catalogue and recompute the quan-
tities of interest. The main quantity we are interested in is the
weak lensing inferred mass. Therefore, we present in Table 3
in brackets the masses derived using the Coupon et al. (2008)
catalogue that can be compared to the masses derived using our
catalogue. We find the difference between each estimate to be
much smaller than the associated error bars. Therefore, we con-
clude that adopting one photometric catalogue or the other does
not change significantly the presented results.
4.3. Fitting the Shear Profile
For each group, we look for a shear signal centred on the lens
between 150kpc and 1.2Mpc from the lens. In the case of
SL2SJ08544-0121, a bimodal group, we use the barycentre of
the light distribution instead since the lens does not dominate the
light distribution. We fit an Singular Isothermal Sphere model
(SIS) to the signal within this range. The choice of this model is
motivated by the fact that we do not expect to get a weak lensing
signal strong enough that could allow us to probe more com-
plicated mass profiles. We use the average geometrical factor to
convert the fitted Einstein radius into an SIS velocity dispersion
5. Strong Gravitational Lensing Analysis
The strong lensing features can be divided in two categories. Of
the 13 groups, 8 exhibit a typical 'cusp' configuration where a
multiply imaged system forms a characteristic arc on one side of
the deflector, sometimes with a counter image on the other side
of the deflector. The other 5 groups have more complex strong
lensing configurations for which identification of multiple im-
ages is challenging and for which no strong lensing modelling is
possible at this stage. More details on each strong lensing con-
figuration are discussed in the Appendix.
For the 8 cusp groups, we apply a simple mass modelling
in order to estimate the Einstein radius, using the lenstool code
(see Jullo et al. 2007, for a description of the method and how
error bars are derived). The refinement of this modelling will de-
pend on the number of available observational constraints. A re-
alistic parametric mass modelling requires at least 5 parameters.
For instance a Singular Isothermal Ellipsoid (SIE) has position
(x,y), ellipticity (e), position angle (PA) and Einstein radius. For
a multiply imaged system where a background source is imaged
n times, and assuming its redshift is known, we have 2×(n-1)
constraints. Only if n ≥4 can we constrain an SIE profile. In
the cusp sample, we have typically only one multiply imaged
system, composed of 3 to 4 images which translates into 4 to
6 observational constraints. When the number of observational
constraints does not allow to probe 5 free parameters, we set
the ellipticity and position angle to 0, leading to a non-elliptical
mass distribution. The main robust quantity we aim to derive
is the Einstein radius. For the non-cusp group, we evaluate the
Einstein radius simply by measuring the distance between the
strong lensing feature and the brightest group galaxy.
Optimisations are performed in the image plane, assuming
a positional uncertainty equals to 0.1??. The ellipticity of the
mass distribution was forced to be smaller than 0.6 (in units
(a2− b2)/(a2+ b2)) as motivated by numerical simulations
(Jing & Suto 2002). Table 2 summarises information relevant to
strong lensing modelling: number of constraints available; opti-
mised parameters (position, ellipticity, position angle, Einstein
radius); RMS in the image plane and reduced χ2, which quanti-
fies the goodness of the fit. We note that for two systems, we are
unable to correctly retrieve the observational constraints, with
RMS larger than the positional uncertainty: SL2SJ08544-0121,
RMS=0.28??and SL2SJ02215-0647, RMS=0.2??.
6. Results
The main properties of the groups are summarised in Table 3 and
illustrated in the following figures. The name of each group cor-
responds to the equatorial coordinates (J2000) of the brightest
member. In the Appendix, we dedicate a paragraph to detail the
properties of each group together with the following images:
1. A large scale 10?× 10?CFHTLS i band image. The white
cross shows where the lens is located. We draw luminos-
ity contours (corrected for passive evolution) equal to 105,
3×105, 106, 3×106and 107L?kpc−2.
2. A 1-square-arcminute colour image from g,r,i CFHTLS
imaging centred on the deflector.
3. The HST image (when available) centred on the deflector,
with the image size given in the figure caption. The image
is in colour when observations are available in three bands
(F475, F606 and F814), and is in F606 otherwise.
Some of these visual information are summarised in Fig. 2,
where we show the large scale CFHTLS images for the 12
groups (all except SL2SJ08591-0345 for which data is incom-
plete, see Section 6.7).
6.1. Einstein Radii & Redshift Distributions
The group sample presented here spans z = 0.30 to z = 0.83,
with a mean redshift < z >= 0.50. We report in Table 3 the fitted
Refor the 8 cusp groups, as well as the measured Refor the re-
maining 5 non cusp groups. They span 2.5??to 8??. We expect the
distribution of Re to decrease with increasing Re(Fig. 1). This
is not seen here, but we need to correct this distribution for se-
lection biases. Clearly we will miss more Re∼ 2??than Re∼ 5??
systems with our detection robot (simply because a small Reis
more likely to be embedded within the light distribution of the
lensing galaxy and missed for that reason).
6.2. Luminosities
In all cases, we find that the brightest galaxy populating the
strong lensing deflector is the brightest group member. Total
luminosities, corrected for passive evolution, are reported in
Table 3. Fig. 3 shows the luminosity as a function of redshift.
We find that the group sample presented in this work is homoge-
neous in terms of total luminosities.
6.3. Weak Lensing
We report the inferred SIS velocity dispersion for each group in
Table 3. Fig. 4 shows the fitted σSISas a function of redshift.
As expected, we see that the weak lensing constraints are tighter
Page 7
Limousin et al.: Strong Lensing by Galaxy Groups7
SL2S Group
θ (degree)
Table 2. Summary of the strong lensing modelling. Number of constraints Nb and optimised SIE parameters. Error bars rep-
resents 1σ confidence level on the parameters inferred from the mcmc optimisation. Values into brackets are not optimised.
This corresponds to models where the number of observational constraints is smaller than the number of free parameters
characterising the SIE profile. The goodness of the fit is quantified by the RMS in the image plane and the reduced χ2. e is
the ellipticity of the mass distribution (in units (a2− b2)/(a2+ b2)).
Fig.3. Luminosities (corrected for passive evolution) versus
group redshifts.
for the lowest redshift groups. Considering the whole sample,
we see that σSIS∼ 500kms−1with large error bars and an up-
per limit of ∼900kms−1. Therefore, we verify that no massive
cluster with σSIS> 1000 kms−1, which would lens a close back-
ground source, is included in our sample and that it consists of
groups or poor clusters only. Note, however, that the highest red-
shift structure included in the present work has a velocity disper-
sion between 432 and 1218 kms−1. The upper limit is therefore
consistent with a galaxy cluster, see Section 6.8.
We are not able, given the data at hand, to pursue a more
refined 2-D weak lensing study from which we could infer the
shape of the mass distribution over the field and compare more
precisely with the luminosity contours. Indeed, it is already chal-
lenging to infer an SIS velocity dispersion from our 1-D analysis
and error bars are large. A 2 dimensional analysis would involve
more free parameters and is not feasible here.
Isothermal Sphere to the reduced shear profile, as a function of
group redshifts. Dashed lines corresponds to upper limits only.
Velocity dispersions inferred from fitting a Singular
6.4. Mass-to-Light Ratios
From the above, we are able to compute mass-to-light ratios.
From the weak lensing analysis, we compute the projected mass
of the group within a circular aperture of 2Mpc centred on the
lens (except SL2SJ08544-0121, a bimodal group that we centre
on the barycentre of the light distribution). Then we consider
the total luminosity, corrected for passive evolution. Values are
given in Table 3 and illustrated in Fig. 5. The mean value is equal
to ∼250 (i band, solar units, corrected for passive evolution),
with an upper limit of 500.
6.5. Trends with Luminosity
If the mass is proportional to the luminosity of the systems, we
expect the SIS velocity dispersion to correlate with the luminos-
ity of the galaxy groups. We show in Fig. 6 velocity dispersions
inferred from the weak lensing analysis as a function of lumi-
nosities (corrected for passive evolution). The expected trend is
Page 8
8Limousin et al.: Strong Lensing by Galaxy Groups
Fig.5. Mass to Light ratio for the group sample, taking into
account passive evolution correction. Dashed lines corresponds
to upper limits only.
Fig.6. SIS velocity dispersion inferred from the weak lensing
analysis as a function of luminosity (corrected for passive evo-
suggested but not statistically significant due to the large error
6.6. Number Density
We have found 13 group scale lenses within a field of ∼ 100
squaredegrees(Table1).Thisgivesaroughestimateof thenum-
ber density of ∼ 0.13 groups per square arcminute. We note that
some group candidates found on the CFHTLS images were not
confirmed on the HST imaging and not included here. Moreover,
at this stage of the project, we do not understand properly our se-
lection function. Selection biases inherent to our detection tech-
nique exist and will be addressed in a forthcoming publication
using numerical simulations. Once the SL2S will be completed
and the selection function understood, we will be able to com-
pare the distribution of observationally determined Re to the
test of the ΛCDM scenario.
6.7. The Case of SL2SJ08591-0345
This system at zspec = 0.647 is presented in the Appendix in
more detail. The observational setup makes this system special:
the lens is located close (75??=508kpc) to the edge of the field
of view. Therefore, it is very likely that we are missing a sig-
nificant part of this interesting structure (note the exotic strong
lensing configuration). Therefore, we do not report a value of the
luminosity for this group, neither do we pursue any weak lensing
6.8. The Case of SL2SJ22133+0048
The weak lensing analysis of this system located at zphot =
0.83 yields a velocity dispersion between 432 and 1218 kms−1
which makes it consistent with a galaxy cluster. We note that its
Einstein radius is rather small for a galaxy cluster, about 3.4??.
It is possible that SL2SJ22133+0048 is indeed a galaxy clus-
ter with a velocity dispersion larger than 1000 kms−1lensing
a close background source. An estimate of the redshift of the
strongly lensed background source would help to alleviate the
doubt. We also note that the redshift of this structure has been
estimated photometrically. If this estimation is biased such that
this structure is located at lower redshift, then we are currently
overestimating its velocity dispersion.
7. Discussion
In this Section, we discuss the results obtained on the group sam-
ple. Our statements are clearly limited by the large error bars
obtained on the quantities of interest, in particular on the weak-
lensing mass estimates. Therefore, part of the following discus-
sion is qualitative only.
7.1. Mass is Traced by Light
The strong lensing system is always found to coincide with the
peak of the light distribution, as can be seen in Fig. 2 (see, how-
ever, the case of SL2SJ08544-0121 discussed in the Appendix).
Because a strong lensing system is always associated with a sig-
nificant mass concentration (occurrence of strong lensing im-
plies Σ > Σcritic), this suggests that the light is a good tracer of
the mass and this justifies the choice of the strong lensing sys-
tem as the group centre when we perform a weak lensing anal-
ysis. We note that this statement is limited to the fact that the
centres of the luminosity and mass distributions are located ap-
proximately at the same position. We cannot say much at this
point because of the limitations of the weak lensing analysis
(Section 6.3).
7.2. A Homogeneous Sample ?
The sample is homogeneous in term of luminosities ranging be-
tween 1 and 4 1012L?(Fig. 3). However, Fig. 2 shows that the
Page 9
Limousin et al.: Strong Lensing by Galaxy Groups9
luminosity contours have very different shapes from one group
to another and that all but two (SL2SJ09413-1100 at z = 0.38
and SL2SJ02254-0737 at z = 0.51) have complicated shapes,
suggesting that these intermediate mass structures may be dy-
namically young.
7.3. Evolution with Redshift ?
We looked at possible evolution of the mass-to-light ratio with
redshift in Fig. 5. However, given the large error bars on this
quantity, we cannot reliably infer any trend.
7.4. Comparison to Other Studies
There have been at least two different estimations of the mass-
to-light ratio of galaxy groups from weak lensing. The first mea-
surement of the average mass-to-light ratios was performed by
Hoekstra et al. (2001) in the CNOC2 survey. They stacked the
weak lensing signal obtained for 50 groups that have been se-
lected on the basis of a dynamical analysis of group candidates.
Their weak lensing detection points towards much less massive
systems than the one presented in this paper: their best-fit sin-
gular isothermal sphere yields a velocity dispersion of 274+48
kms−1. However, they find a mass-to-light ratio of 254 ± 110h
(solar units, B band rest frame corrected for evolution).
Subsequently, another similar study on a sample of 116
CNOC2 galaxy groups was performed by Parker et al. (2005).
Given more statistics, they were able to split the group sample
into subsets of poor and rich groups. Their poor galaxy groups
were found to have an average velocity dispersion of 193 ± 38
kms−1and a mass-to-light ratio of 134 ± 26h (solar units, B
band rest frame), while their rich galaxy groups have a velocity
dispersion of 270 ± 39 kms−1and a mass-to-light ratio of 278
± 42h, thus finding evidence for a steep increase in the mass-to-
light ratio as a function of mass.
The groups presented in the present work are more massive
than the rich galaxy group sample from Parker et al. (2005).
Given the error bars obtained on the mass-to-light ratios, it is
difficult to reliably compare our findings to those from Parker
et al. (2005). However, considering the 6 groups for which we
achieved a weak lensing detection, we get a mean velocity dis-
persion of 623 kms−1and a mean mass-to-light ratio of 242,
consistent with the results of Parker et al. (2005). Note that these
values are close to mass-to-light ratios of galaxy clusters (e.g.
Carlberg et al. 1997; Bardeau et al. 2007).
Our results suggest that after the steep increase in mass-to-
light ratio as a function of mass pointed out by Parker et al.
(2005) which seems to occur at velocity dispersions around
200kms−1(or mass scale of order ∼1013M?), mass-to-light
ratios reach a plateau and do not evolve much from the mass
scale of groups with velocity dispersions around 300kms−1
up to rich galaxy clusters with velocity dispersion larger than
1000kms−1. The group sample studied in this article therefore
helps to bridge the gap between estimates of the mass-to-light
ratio of galaxy groups with velocity dispersions in the range
200-300 kms−1and for galaxy clusters.
7.5. The Naked Cusp Sample
Eight galaxy groups reported in this article exhibit typical cusp
configurations, with a clear tangential arc on one side of the de-
flector. For 5 of these groups, we have not been able to find
the expected counter image which is usually located on the
other side of the deflector, even when HST imaging was avail-
able. This incomplete cusp configuration is called 'naked cusp'
(see, e.g. Schneider et al. 1992; Oguri & Keeton 2004). In two
cases, SL2SJ02215-0647 and SL2SJ08544-0121, the counter
image of the cusp is clearly identified on the HST images. In
SL2SJ22133+0048, the detection of the counter image is ten-
tative only. Moreover, note that the case of SL2SJ08544-0121
is a bit special since this cusp configuration is not located at
the centre of the total light distribution, whereas the other cusp
groups are. To summarise, we find that most of the cusp groups
are naked. It may be that the current observations did not allow
us to find the counter images, but this naked state of a cusp can
be linked with lens statistic issue. If CDM haloes have central
density slopes < 1.5, Oguri & Keeton (2004) predict that a sig-
nificant fraction (> 20%) of large separation lenses should have
naked cusp image configurations. Therefore, our results could
suggest that the groups studied in this work may have shallow
central density slopes.
7.6. Other Intermediate Separation Lenses
We claim this work to be the first representative sample of strong
lensing systems generated by group scale dark matter haloes,
with intermediate image separation (in the range ∼ 3??− 8??).
However, at least five intermediate separation lenses have been
reported so far, even though the authors did not always con-
sider the group-scale haloes as being responsible for the image
separation, and are interpreting the results in terms of massive
galactic scale haloes. A remarkable example is the so called
Cosmic Horseshoe (Belokurov et al. 2007; Dye et al. 2008), an
almost complete Einstein ring of radius 5??from a luminous red
galaxy at z = 0.44. The authors argued that this is the most
massive galaxy lens discovered so far, with a mass enclosed
within its Einstein radius of 51012M?, making this galaxy as
massive as the entire Local Group. We rather suggest that this
lensing system is simply produced by a group-scale dark-matter
halo, whose centre is populated by the luminous red galaxy.
Indeed, this galaxy is the brightest object in the group of ∼26
members as revealed by the SDSS photometry. As suggested by
the nearly perfect circle outlined by the ring, no external shear
was required in the model of the system, which is not surpris-
ing because the deflector traces the centre of the group halo.
This important discovery led to a more systematic data min-
ing looking for large separation lenses in the Sloan Digital Sky
Survey: the CAmbridge Sloan Survey Of Wide ARcs in the skY
(CASSOWARY6). Recently, Belokurov et al. (2009) reported
two new large separation lenses, with Einstein radius equal to 4??
and 8??. More recently, Lin et al. (2008), in a systematic search
for bright arcs in the SDSS, reported a strongly lensed z = 2
galaxy by a deflector whose Einstein Radius equals 3.82??. We
also mention an intermediate separation lens (Re∼ 2.5??) found
in the CLASS survey, B2108+213 (McKean et al. 2005; More
et al. 2008).
We expect to find new intermediate separation lenses on
completion of the CFHTLS, which, in combination with group
scale lenses from other promising dedicated searches in surveys
such as the SDSS7, will increase the statistics of intermediate
separation lenses, thus allowing us to get insights on this inter-
mediate mass range.
7one month after this work was submitted, Kubo et al. (2008) re-
ported the finding of five new group scale lenses in the SDSS
Page 10
10Limousin et al.: Strong Lensing by Galaxy Groups
8. Conclusion
We have presented a sample of 13 strong lensing features with
scale dark-matter haloes. This is the first representative sam-
ple (not yet complete) of intermediate image separations lenses,
bridging the gap between galaxy and cluster scales. Our conclu-
sions are the following:
1. The strong lensing analysis yields Einstein radii between
2.5??and 8??.
2. We have studied the luminosity distribution to infer proper-
ties on large scales: the strong lenses coincide with the peak
of the light distribution; most of the luminosity maps have
complicated shapes, suggesting dynamically young struc-
3. A weak lensing analysis yields σSIS ∼ 500kms−1with
large error bars and an upper limit of ∼900kms−1for the
whole sample. This confirms that our sample consists of rich
4. σSISseems to increase with luminosity but given the large
error bars this is not statistically significant.
5. The mass-to-light ratio for the sample is found M/Li∼ 250
(solar units, corrected for evolution), with an upper limit of
We note again that our conclusions are limited by the large error
bars obtained on the weak lensing inferred mass estimates.
Complementary observations are ongoing: we are currently
analysing multi object spectroscopy of group members as well
as near infrared WIRCAM imaging. This sample will be com-
plemented in the near future with other observations in order to
help address issues of structure formation and evolution.
Once the Strong Lensing Legacy Survey will be completed
and the selection function well understood, we will compare
the distribution of observed Einstein radii to the predictions
from Oguri (2006), which may provide an interesting test of the
ΛCDM scenario.
ML acknowledges the Agence Nationale de la Recherche
(Project number 06-BLAN-0067) and the Centre National
d' Etudes Spatiales (CNES) for their support. The Dark
Cosmology Centre is funded by the Danish National Research
Foundation. JR is grateful to Caltech for its support. JPK ac-
knowledges the Centre National de la Recherche Scientifique
for its support. Part of this project is done under the
support of National Natural Science Foundation of China
No. 10878003, 10778752, 973Program No. 2007CB815402,
Shanghai Foundation No. 08240514100, 07dz22020, and the
Leading Academic Discipline Project of Shanghai Normal
UniversityDZL805. ML acknowledges S´ ebastien Bardeau for
making its sheartool package available, and Masamune Oguri
for providing the data used to generate Fig. 1. We acknowl-
edge the referee for a careful reading of the submitted paper
and constructive suggestions. This research has made use of
the NASA/IPAC Extragalactic Database (NED) which is oper-
ated by the Jet Propulsion Laboratory, California Institute of
Technology, under contract with the National Aeronautics and
Space Administration.
Alard, C. 2009, ArXiv e-prints 0901.0344
Auger, M. W., Fassnacht, C. D., Abrahamse, A. L., Lubin, L. M., & Squires,
Auger, M. W., Fassnacht, C. D., Wong, K. C., et al. 2008, ApJ, 673, 778
Bardeau, S. 2004, PhD thesis, Universit´ e Paul Sabatier, Toulouse III, France
Bardeau, S., Kneib, J.-P., Czoske, O., et al. 2005, A&A, 434, 433
Bardeau, S., Soucail, G., Kneib, J.-P., et al. 2007, A&A, 470, 449
Belokurov, V., Evans, N. W., Hewett, P. C., et al. 2009, MNRAS, 392, 104
Belokurov, V., Evans, N. W., Moiseev, A., et al. 2007, ApJ, 671, L9
Bertin, E. & Arnouts, S. 1996, A&A, 117, 393
Bolzonella, M., Miralles, J.-M., & Pell´ o, R. 2000, A&A, 363, 476
Bridle, S., Kneib, J.-P., Bardeau, S., & Gull, S. 2002, in The shapes of galax-
ies and their dark halos, Proceedings of the Yale Cosmology Workshop ,
New Haven, Connecticut, USA, 28-30 May 2001. Edited by Priyamvada
Natarajan., ed. P. Natarajan, 38–+
Bruzual, G. & Charlot, S. 2003, MNRAS, 344, 1000
Cabanac, R. A., Alard, C., Dantel-Fort, M., et al. 2007, A&A, 461, 813
Carlberg, R. G., Yee, H. K. C., & Ellingson, E. 1997, ApJ, 478, 462
Carrasco, E. R., Cypriano, E. S., Neto, G. B. L., et al. 2007, ApJ, 664, 777
Condon, J. J., Cotton, W. D., Greisen, E. W., et al. 1998, AJ, 115, 1693
Coupon, J., Ilbert, O., Kilbinger, M., et al. 2008, ArXiv e-prints 0811.3326
Cypriano, E. S., Lima Neto, G. B., Sodr´ e, Jr., L., Kneib, J.-P., & Campusano,
L. E. 2005, ApJ, 630, 38
Cypriano, E. S., Sodr´ e, L. J., Kneib, J.-P., & Campusano, L. E. 2004, ApJ, 613,
D'Onghia, E., Sommer-Larsen, J., Romeo, A. D., et al. 2005, ApJ, 630, L109
Dye, S., Evans, N. W., Belokurov, V., Warren, S. J., & Hewett, P. 2008, MNRAS,
388, 384
Faltenbacher, A. & Mathews, W. G. 2007, MNRAS, 375, 313
Fassnacht, C. D. & Lubin, L. M. 2002, AJ, 123, 627
Fassnacht, C. D., McKean, J. P., Koopmans, L. V. E., et al. 2006, ApJ, 651, 667
Faure, C., Kneib, J. ., Hilbert, S., et al. 2008, ArXiv e-prints 0810.4838
Feron, C., Hjorth, J., McKean, J. P., & Samsing, J. 2008, ArXiv e-prints
Finoguenov, A., Ponman, T. J., Osmond, J. P. F., & Zimer, M. 2007, MNRAS,
374, 737
Gastaldello, F., Buote, D. A., Humphrey, P. J., et al. 2007, ApJ, 669, 158
Gladders, M. D., Lopez-Cruz, O., Yee, H. K. C., & Kodama, T. 1998, ApJ, 501,
Grillo, C., Lombardi, M., Rosati, P., et al. 2008, A&A, 486, 45
Helsdon, S. F. & Ponman, T. J. 2000, MNRAS, 315, 356
Helsdon, S. F. & Ponman, T. J. 2003, MNRAS, 339, L29
Heymans, C., Van Waerbeke, L., Bacon, D., et al. 2006, MNRAS, 368, 1323
Hoekstra, H. 2007, MNRAS, 379, 317
Hoekstra, H., Franx, M., Kuijken, K., et al. 2001, ApJ, 548, L5
Ienna, F. & Pell´ o, R. 2006, in SF2A-2006: Semaine de l'Astrophysique
Francaise, ed. D. Barret, F. Casoli, G. Lagache, A. Lecavelier, & L. Pagani,
Inada, N., Oguri, M., Shin, M.-S., et al. 2008, ArXiv e-prints 0809.0912
Jing, Y. P. & Suto, Y. 2002, ApJ, 574, 538
Jullo, E., Kneib, J.-P., Limousin, M., et al. 2007, New Journal of Physics, 9, 447
Kassiola, A., Kovner, I., & Blandford, R. D. 1992, ApJ, 396, 10
King, L. J. 2007, MNRAS, 956
Kneib, J., Hudelot, P., Ellis, R. S., et al. 2003, ApJ, 598, 804
Kovner, I. 1987, ApJ, 321, 686
Kubo, J. M., Allam, S. S., Annis, J., et al. 2008, ArXiv e-prints 0812.3934
Kundic, T., Hogg, D. W., Blandford, R. D., et al. 1997, AJ, 114, 2276
Limousin, M., Kneib, J. P., Bardeau, S., et al. 2007a, A&A, 461, 881
Limousin, M., Richard, J., Jullo, E., et al. 2007b, ApJ, 668, 643
Lin, H., Buckley-Geer, E., Allam, S. S., et al. 2008, ArXiv e-prints 0809.4475
Mamon, G. A. 2007, in Groups of Galaxies in the Nearby Universe, ed.
I. Saviane, V. D. Ivanov, & J. Borissova, 203–+
Mandelbaum, R., Seljak, U., Cool, R. J., et al. 2006, MNRAS, 372, 758
McKean, J. P., Browne, I. W. A., Jackson, N. J., et al. 2005, MNRAS, 356, 1009
Medezinski, E., Broadhurst, T., Umetsu, K., et al. 2007, ApJ, 663, 717
Mellier, Y. 1999, ARA&A, 37, 127
M¨ oller, O., Natarajan, P., Kneib, J.-P., & Blain, A. W. 2002, ApJ, 573, 562
Momcheva, I., Williams, K., Keeton, C., & Zabludoff, A. 2006, ApJ, 641, 169
More, A., McKean, J. P., Muxlow, T. W. B., et al. 2008, MNRAS, 384, 1701
Morgan, N. D., Kochanek, C. S., Pevunova, O., & Schechter, P. L. 2005, AJ, 129,
Newton, E. R., Marshall, P. J., & Treu, T. 2008, ArXiv e-prints 0810.3934
Oguri, M. 2006, MNRAS, 367, 1241
Oguri, M. & Keeton, C. R. 2004, ApJ, 610, 663
Oguri, M., Keeton, C. R., & Dalal, N. 2005, MNRAS, 364, 1451
Osmond, J. P. F. & Ponman, T. J. 2004, MNRAS, 350, 1511
Parker, L. C., Hudson, M. J., Carlberg, R. G., & Hoekstra, H. 2005, ApJ, 634,
Rasmussen, J. & Ponman, T. J. 2007, MNRAS, 380, 1554
Page 11
Limousin et al.: Strong Lensing by Galaxy Groups11
SL2S Group
∼ 6.8
4.0±3.1 (3.9±3.0)
3.6±3.5 (3.5±3.4)
6.3±2.5 (6.2±2.4)
< 680
3.7±3.4 (3.7±3.3)
∼ 4.5
< 4.83
< 6.8 (6.6)
< 4.64
< 684
< 6.8 (6.6)
< 569
5.5±3.7 (5.3±3.6)
< 2.56
< 4.7 (4.4)
∼ 3.6
< 3.06
< 726
< 6.9 (6.2)
< 1.22
< 463
< 3.1 (2.8)
∼ 2.5
< 3.98
< 870
< 11.1 (9.9)
∼ 8
13.1±10.2 (10.8±8.5)
Table 3. Summary of the main properties of SL2S groups J2000.0 coordinates of the main galaxy populating the deflector; spectroscopic redshift zspec; photometric redshift
zphot; Einstein radius derived from the strong lensing modelling, when possible. For the non cusp group, we report with a ˜ the distance between the lensed feature and
the brighest group member; Einstein radius derived from fitting a Singular Isothermal Sphere (SIS) to the weak lensing signal; mean geometrical factor Dls/Dsand
corresponding effective redshift zeff; velocity dispersion; projected mass derived from weak lensing computed within a circular aperture of radius equals to 2Mpc, in
units 1014M?(masses derived using the Coupon et al. (2008) photometric redshift catalogue are given within brackets); density of background galaxies, expressed
in objects per square arcminute; total i band rest frame luminosity corrected for evolution, in units 1012L?; seeing of the i band observations; i band completeness
magnitude. Einstein radii and seeings are expressed in arcseconds.
Page 12
12 Limousin et al.: Strong Lensing by Galaxy Groups
Schneider, P., Ehlers, J., & Falco, E. E. 1992, Gravitational Lenses (Berlin:
Sommer-Larsen, J. 2006, MNRAS, 369, 958
Sun, M., Voit, G. M., Donahue, M., et al. 2009, ApJ, 693, 1142
Treu, T., Gavazzi, R., Gorecki, A., et al. 2009, ApJ, 690, 670
Trott, C. M., Treu, T., Koopmans, L. V. E., & Webster, R. L. 2008, ArXiv e-prints
Tu, H., Limousin, M., Fort, B., et al. 2008, MNRAS, 1169
van den Bosch, F. C., Pasquali, A., Yang, X., et al. 2008, ArXiv e-prints 0805.002
Williams, K. A., Momcheva, I., Keeton, C. R., Zabludoff, A. I., & Leh´ ar, J. 2006,
ApJ, 646, 85
Willis, J. P., Pacaud, F., Valtchanov, I., et al. 2005, MNRAS, 363, 675
Yang, X., Mo, H. J., & van den Bosch, F. C. 2008, ApJ, 676, 248
Appendix A: Presentation of each Group
We dedicate below a paragraph to each group to describe its
main properties. The information are summarised in Table 3 and
illustrated in the Appendix images.
A.1. Group Description
SL2SJ09013-0158 at zphot = 0.30 (Fig. ??): The luminosity
distribution is elongated in the north-south direction. We report
a straight arc between the two main bright central galaxies: this
is a typical beak-to-beak configuration (Kassiola et al. 1992).
This arc is found closer to the northern galaxy (∼ 7??) than the
southern one. No HST image is available for this group. A radio
source has been reported by Condon et al. (1998) between the
two bright central galaxies. Given the coordinates and associated
errors of this radio source, it could be associated with one of the
two smaller central galaxies.
SL2SJ22214-0053 at zspec= 0.334 (Fig. ??): The SDSS pro-
vides a redshift measurement for the main galaxy populating the
deflector of 0.334, and a velocity dispersion of 281±45kms−1.
The strong lensing deflector is populated by a single bright
SL2SJ08544-0121 at zspec= 0.351 (Fig. ??): The strong lens-
ing deflector is populated by a single bright galaxy whose ellip-
ticity and position angle equals 0.3 and 25±5 degrees, respec-
tively. The luminosity contours are elongated in the east-west
direction and define a position angle consistent with that of the
bright galaxy. We also find the position angle of the SIE halo
(∼21 degrees, Section 5) to be consistent with that of the bright
Note (Fig. ??) that the innermost luminosity contour at 107
L?kpc−2encompass the SL system but also two bright galax-
ies located ∼ 54??east from the SL system, making this light
distribution bimodal. This is the only group for which the lumi-
nosity distribution is not clearly dominated by the lens, making
this configuration rather exceptional: the large Einstein radius
(∼ 5??) points toward a massive structure associated with this
lens, but the luminosity distribution is found bimodal. This sug-
gest a dynamically young structure in the process of formation.
This bright galaxy has a spectroscopic redshift measured from
Keck of 0.3514. We detect two multiply imaged systems: the
brightest one is perturbed by a small satellite galaxy whose red-
shift is equal to 0.3517 (FORS2); and the outer one is seen on
the ACS colour image (Fig. ??). Note how the northern counter
image is found much further (∼ 8??) than the main arc (∼ 5??),
suggesting a strong contribution from the external shear associ-
ated with the host galaxy group. The HST data brings significant
additional information on this lensing feature.
SL2SJ09413-1100 at zspec= 0.385 (Fig. ??): The luminosity
contours look circular. The strong lensing deflector is populated
by a bright galaxy whose stellar halo is extended and presents a
large ellipticity (b/a=0.59) with a position angle of 74 degrees.
Interestingly, this position angle is found compatible with the
orientation of the luminosity contours. Note that this is the only
group for which the central galaxy presents an extended stellar
halo. We measured a spectroscopic redshift for this galaxy us-
ing FORS2 to be 0.385. We report a blue arc composed by two
merging images north of the deflector, with its counter image.
We have not been able to find another counter image on the other
side of the deflector, even after subtraction of the galaxy on the
HST images.
SL2SJ14081+5429 at zspec= 0.416 (Fig. ??): The luminosity
distribution is elongated in the north-south direction. The cen-
tre of this group is dominated by three bright galaxies aligned
in the north-south direction. The brightest one (A, magi=18.03)
is the central one, that is also closest to the arc feature. North
of A is a galaxy B (magi=18.37) and south of is a galaxy C
(magi=18.46). The SDSS provides a redshift measurement for A
(z = 0.415979) and for B (z = 0.411022). A straight arc without
any detected feature is located between bright central galaxies.
SL2SJ14300+5546 at zspec= 0.435 (Fig. ??): The luminosity
distribution is elongated in the east-west direction. The strong
lensing deflector is populated by a single galaxy whose redshift
equals 0.435 (Gemini). A tangential arc is found south-east of
the deflector. The position angle of the galaxy populating the
deflector (∼45 degrees) is consistent with the position angle de-
fined by the luminosity distribution.
SL2SJ02140-0532 at zspec= 0.444 (Fig. ??): The luminosity
distribution is elongated in the north-south direction. The strong
lensing deflector is populated by three galaxies. The two bright-
est ones have redshift measured spectroscopically from Keck
(0.4422 and 0.4439) and may be bound gravitationally. We re-
port an arc north of the deflector composed by two merging im-
a possible counter image south of the deflector which seems to
have colour compatible with the other images. However, on the
ACS data, it is clear that this feature cannot be associated with
the proposed multiply imaged system. This is also confirmed by
the modelling: no acceptable fit was able to reproduce the mul-
tiple images as one could have inferred from the ground based
data. We note, however, that a recent independent study by Alard
(2009) considers the southern image as part of the multiply im-
aged system. Spectroscopy of each feature is needed in order to
remove the uncertainty. The HST data brings significant addi-
tional information on this lensing feature: not only does it help
to identify the different images belonging to the same system,
but it also resolves substructures within each lensed image, in-
creasing the number of constraints for the analysis. The halo of
the deflector is oriented with a position angle well constrained at
111±3 degrees. This is the same direction as the one defined by
the luminosity contours.
Page 13
Limousin et al.: Strong Lensing by Galaxy Groups13
SL2SJ02254-0737 at zspec= 0.511 (Fig. ??): The luminosity
contours look circular. The strong lensing deflector is populated
by a single galaxy whose redshift equals 0.511 (Gemini). We
observe a tangential arc north of the lens galaxy, likely to be
composed by two merging images, with an additional counter
image a bit further east. The location of the deflector coincide
with a radio emission reported by Condon et al. (1998).
SL2SJ22130-0030 at zphot = 0.61 (Fig. ??): The luminosity
distribution is elongated in the north-south direction. The HST
image reveals that the strong lensing deflector is populated by a
very compact group of at least 6 galaxies. We report a blue arc
east of the deflector, and a likely counter image presenting the
same colour as the arc on the other side of the deflector.
SL2SJ02215-0647 at zspec = 0.618 (Fig. ??): We find a gap
of 1.3 magnitude in the R band between the brightest and the
second brightest galaxy, not enough to be considered as a fos-
sil group. The strong lensing deflector is populated by a single
galaxy whose redshift equals 0.618 (FORS2). We report an arc
south of the deflector, composed by two merging images. There
is a counter image south-east of the deflector, as well as an ad-
ditional counter image located on the other side of the deflec-
tor, resolved by HST data. We report a possible second multiply
imaged system constituted by two images with same CFHTLS
SL2SJ14314+5533 at zphot = 0.64 (Fig. ??): The luminosity
distribution is elongated in the south-east north-west direction.
A small tangential arc is found around bright galaxies. We can-
not conjugate any images that may merge to form the arc. It is
possible that this blue lensed feature in fact is singly imaged.
SL2SJ08591-0345 at zspec = 0.647 (Fig. ??): The lens is lo-
cated close (75??=508kpc) to the edge of the field of view. It is
very likely that we are missing a significant part of this group.
Therefore, we have not been reported any values of this group
luminosity, neither did we pursue any weak lensing analysis for
this group. We observe a rather exotic strong lensing configu-
ration: the deflector is populated by three bright galaxies and
two smaller ones. One of the bright one has a redshift of 0.647
(FORS2). The multiple images draw an oval contour around the
deflector. It is difficult at this point to know how many multiple
images we observe and if they are coming from a single or mul-
tiple background sources. An advanced modelling of this exotic
lens would be very interesting and will require deep multi colour
space based data with dedicated ground based spectroscopy.
SL2SJ22133+0048 at zphot = 0.83 (Fig. ??): The luminosity
distribution is elongated in the south-east north-west direction.
The strong lensing deflector is populated by a single galaxy. A
tangential arc composed by two merging images is found east of
the deflector. A possible counter image on the other side of the
deflector is detected on the space based images. The location of
et al. (1998). Our weak lensing analysis yields a velocity disper-
sion between 432 and 1218 kms−1. The upper limit is therefore
consistent with a galaxy cluster. Since its Einstein radius is es-
timated to be about 3.4??, it is possible that SL2SJ22133+0048
is indeed a galaxy cluster with a velocity dispersion larger than
1000 kms−1lensing a close background source. An estimate of
the redshift of the strongly lensed background source would help
to alleviate the doubt. We note also that the redshift of this struc-
ture has been estimated photometrically. If this estimation is bi-
ased and if this structure is located at lower redshift, then we are
currently overestimating its velocity dispersion.
Page 14
14Limousin et al.: Strong Lensing by Galaxy Groups
Fig.2. Large scale 10?×10?CFHTLS i band image for all groups but one (SL2SJ08591-0345 for which data are missing). Picture are
ranked by increasing redshifts as in Table 3. Redshift is reported on each picture, with three digits precision when spectroscopically
measured. The white cross shows where the lens is located. Black contours correspond to luminosity contours (corrected for passive
evolution) equal to 105, 3×105, 106, 3×106and 107L?kpc−2.


text:
2008 BMW 3 Series User Reviews
2008 BMW 3 Series Review Ratings
Average Ratings from 75 reviews
- Performance:
- Appearance:
- Build Quality:
- Overall:
Review Highlights Click to filter reviews below
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Displaying 1 - 10 of 75 2008 BMW 3 Series reviews.
Sean writes:
2008 BMW 3 Series 328xi Coupe Review
The car.
The stock run-flat tires are a little stiff, replaced them with ultra performance
Fell In Love Fast, — Great solid car, much more solid luxurious feel than the previous 3-series. Terrifyingly great handling, 6 -speed manual trans, quick little car!
8 of 8 people found this review helpful.
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Looking for a Used 3 Series in your area?CarGurus has 38,006 nationwide 3 Series listings starting at $1,988.
legaleagle4 writes:
2008 BMW 3 Series 335xi Review
acceleration, braking, gas mileage, free maintence, power seats
too many warning symbols. Central locks don't open when turning car off. Garage door opener won't work when engine is off.
I Smile Every Time I Get In. Watch Out 4 Tickets. My Daughter (princess Leadfoot) Keeps Borrowing It — I bought this as a CPO with about 17,000 miles. Performance and handling are fabulous. Road feel is solid as can be. 40 Mile round trip commute mileage is 22 MPG - long trips about 26 MPG, running on 89 octane. Most fun since my 1966 Shelby GT 350. Paint and interior are great. Traction in snow is terrific.
Primary Use: Commuting to work
5 of 5 people found this review helpful.
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Michael writes:
2008 BMW 3 Series 328i Coupe Review
You gotta have it
Although BMW covers all scheduled service, it's still costly to maintain. Just four tires cost me almost $1500
3 Series Is King Over The Road — Great car just a lil demanding maintance wise, i do drive a lot so i have to service it almost every two months just to keep it in top shape. The gas mileage is amazing, on the highway i get almost 33mpg. The only problem i 've had has been with my tail lights, the car blew several lights bulbs & now the problem has moved to the front end. Other than that it's an amazing car.
5 of 5 people found this review helpful.
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ajaf316i writes:
2008 BMW 3 Series 335xi Coupe Review
Power, handling, general driving abilities and feel
price, maintenance
335xi — This is a driver's car, and while I have rated it average in some aspects, let's remember that those ratings would only hold true compared to the average car. In other words, this wasn't designed to be a cost efficient family car. It's a thoroughbred sports car. So the only stuff that matters is what it does well that a sports car should, everything else is a bonus. Superb on gas btw, if you feel like just cruising on the highway at around 60 mph, I have seen consumption as good as 38 mpg for a trip. I did a 50 mile drive once just cruising, slapped it into 6th and let it go at just around 60. Extremely enjoyable because of how well it settles on the road, mind you, it is a stiff ride and is not comfortable in the city. Again, it's got the features of a thoroughbred sports car, so don't compare it to your camry or heck don't even compare it it's sedan counterpart, because the only thing the two share are the name. Their purposes and parts other than (barring the engine, gearbox etc.) are completely different, which is sort of why now BMW decided to slash out the 3 coupe and just call it the 4. Maintenance is painful, it's German and everything about it is expensive. Spark plugs set me back 350 dollars. You get the idea. Overall, if you want driving reward, close your eyes and buy one. If you have other things that matter just as much, test drive it a couple of times, you may just end up with the sedan, definitely wouldn't recommend this for anyone seating more than 2 adults all the time. The backseats are good compared to other coupes, but unless everyone in your family is young and under 5'10.. things get tight.
Primary Use: Sport/fun (spirited driving, track racing, off-roading, etc.)
sionlim writes:
2008 BMW 3 Series 335i Convertible Review
killer looks, handles well. red leather,. interior and sound system off the hook.
expensive, really low keeps hitting the curb when i park. small interior. electrical on motors seem to be a german problem.
A Drivers Car — Confident in its corners and passing. the looks are incredible, people really like the car. Makes your jump a beat everytime you hear the engine. everything about this car is perfect. The Hard top convertible adds structual integrity, The hard top is a feat of mechanical engineering. DId i mention if looks could kill!. Please remember that BMW has a bumper to bumper warranty for 4 years and my advice is to get the extra warranty when making the purchase to 6 its worth it as brakes alone costs 1000. So u cant imagine if anything serious goes wrong. Also They have a problem with the HVTP system from the Turbos and the car can die at anytime when pushed hard, A 10year warranty comes with the 07-08 due to the lemon law act. Many who have the N54 engine experienced it. other than that its still a phenomenal feeling to drive in their twin turbo machines.
Primary Use: Sport/fun (spirited driving, track racing, off-roading, etc.)
Jackie writes:
2008 BMW 3 Series 335i Coupe Review
Everyone gets out of my way in the outside lane of the motorway!
Fuel economy.... but who cares?!
What On Earth Will I Go For Next....? — Love it! Better than the porsche! Not so good in the snow mind you - but it's faster, more comfortable and better fun to drive than the porsche. Love the colour too - will definitely be keeping this car for a wee while yet!
Primary Use: Commuting to work
Andrew writes:
2008 BMW 3 Series Review
Engaging driver's car...
Miss my big petrol engines...
My Views On My 3-series Diesel M-sport... — M-sport handling is fantastic, makes it a thoroughly enjoyable and engaging drive. Typically excellent BMW build quality throughout. Sporty coupe looks with sensible rear seats. MPG from the diesel engine is excellent as well. Very pleased with the car overall.
Kristoffer writes:
2008 BMW 3 Series 328i Review
STEERING. Engine. Ride quality on the freeway. Value.
Cup holders. Brake Dust.
I Understand Why Enthusiasts Are In Love. — I used to think that the 3 series was severely overrated and way too common. But after test driving one, I finally understood why auto journalists and enthusiasts constantly praise this car! Coming from a '98 GS400, I was used to swift acceleration, but a numb driving experience. This 328i accelerates just as well as the GS, which had 300hp, but lets me feel like I am connected with the road. PLUS! Driving on the highways is a smooth and SOLID experience. And I actually like the run flats. I thought it would be harsh especially because I came from a Lexus, but they're not bad at all. Plus driving on LA-area freeways did not prove to be punishing at all, so I have no complaints there! The only options I got were the iDrive, iPod adapter, and the Steptronic tranny, and I got an amazing price. Plus it's fuel efficient (I'm averaging about 22mpg combined), and coupled with the 4 years/50K miles free maintenance, this was the better value compared to the Lexus IS I almost considered. I definitely recommend this car! If you love driving, exhaust notes, and a good value, this is the car to buy. One of the few downsides I have with this car is the so-so cup holders and the brake dust that constantly accumulates! But I have a strict no-drinking/eating in my car and the brake dust just wipes off, so really the downsides are minor. I recommend!
Mark writes:
2008 BMW 3 Series 328i Coupe Review
To many to name
Will add one when I find one
Jake writes:
2008 BMW 3 Series 328xi Review
One of the highest quality cars you'll find on the road, perfect for the
It costs more than a Toyota or Honda and I'm sure I'll now be subjected
I Have Found My Perfect Daily Driver — An unbelievably balanced car, it has performance when you need it, and it is always a smooth drive, whether you're pushing the car or not. Everything about the car feels solid and driving it is so effortless, it quickly becomes an extension of your body. The 6-speed manual transmission is the smoothest I've ever used, and I tend to forget that I'm driving an all-wheel drive car. Also, I admit that I love tech and gadgets, and this car is full of them: GPS, iPod adapter, bluetooth connection for hands-free cell phone calls, auto climate, auto headlights, auto windshield wipers, voice commands, RFID in the key fob (I never have to take the key out of my pocket to unlock the doors or start the engine), iDrive system, etc. The list goes on...
Displaying 1 - 10 of 75 2008 BMW 3 Series reviews.
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Best All Around Car Money Can Buy (maybe A Bit Too Much Money, Though)
After driving my 2010 Jetta Sportwagen for 50,000 miles, I test drove the new 328d that BMW was finally offering in North America. I was looking for an automatic for my daily commute (my Jetta was a ... Read More
Great Car For The Wife To Get Tickets In
I love the power delivery of the inline six cylinder. There is almost zero turbo lag and it feels like an NA car with a larger engine. I would prefer a manual transmission, but the eight speed autom... Read More
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This car is fun to drive! The handling and acceleration are amazing. The hardtop is a great feature, making the car usable all-year round. When the roof is closed, it's like driving a sports car. When... Read More
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Very nice drivers car, last of the real bimmers with a real engine, in line 6 helped with a turbo, to propel the car even at 100 miles/h , car shoots away and keeps accelerating ! Is as happy on the... Read More
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I loved everything about this car, from the amazing interior with dazzling lights, phenomenal sound system, spot on handling and smooth ride, super comfortable seats, voice command. Not a lot of room... Read More
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It's a perfectly reasonable car. Goes fast when you want it too, uses less gas when you want that. Back seat is big enough so the kids don't complain. Just wish it were a bit less bland. I used to... Read More
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Great Looking Car And A Ton Of Fun To Drive
It has unbelievable pick up, handling and braking. Drives like a sports car but has the comfort and options of a luxury car (Bluetooth, Navigation, Sirius Radio, Heated Seats) Amazing/unique looking ... Read More
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subset: commoncrawl


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NPD: Killzone 2 deploys 58K copies in April
Killzone 2 passed the one million milestone a little while back, but it doesn't seem to be content with that. No, in fact, it's still selling copies, as the NPD numbers from April show the game unloaded 58,000 more units onto US soil, Gamasutra reports. This brings the US total for the game up to 677,000 copies, or about 4,739,000,000 dead Helghan.
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Al Raha Beach Hotel
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TravelPod Member ReviewsAl Raha Beach Hotel Abu Dhabi
Fabulous hotel, private, quiet with exclusive access to the Corniche. Service and staff attention to detail excellent. Whilst not in the city centre, easy to reach by taxi or using free shuttle service provided by the hotel. Definitely would recommend.
This review is the subjective opinion of a TravelPod member and not of TravelPod.com.
TripAdvisor Reviews Al Raha Beach Hotel Abu Dhabi
Travel Blogs from Abu Dhabi
Full on 48 hours!
What an awesome way to turn 50! Our chill time started 48 hours ago with my birthday celebrations, had a most wonderful day - thoroughly spoilt with beautiful gifts, lots of birthday messages and not to mention brunch at Toast, followed by several hours at the zoo and finishing up with all the clan and partners at Bad Apples for tapas and drinks, …
Day 1.. Bon Voyage -Bound for London
... Class "capsule seat"
I had no sooner sat down and I was presented with a glass of Champagne, followed closely by a warm face towel. As you can see by the picture, there is plenty of leg room. I actually had to move my seat forward a little to put my feet up comfortably on the foot rest.
Not long after take off the cabin crew took my lunch order.
I chose the Chicken for starters, followed by Lamb and ...
A marathon of food and no sleep
... br> Landing at Abu Dhabi airport was fascinating because the land out the window was flat and brown with some green scrub. different from any other landscape I have seen before. The desert seems to be encroaching on the airport. But at the same time they are expanding in all different directions.
Crystal is a talker -- in that she is not afraid to ask people where they are from and getting a lot more info -- mostly about their trip. We ...
... a mission to do on our way. Margaret asked us for some special tea she liked, only one shop in London where you can get it and guess what? it wasn't on our route. After a train and the subway and a bit of a walk with pull bags and our backpacks all very full. We got there at five to ten and they open at ten, only to find that they will post to Australia. Never mind she is ...
Hello Jet Lag
We arrived in Abu Dhabi around midnight and flew out at 2:35am. Feeling somewhat sleep deprived, our body's were feeling rather confused with the crossing over into different time zones. After nearly missing our flight out of Sydney, we were determined not to make the same mistake again. We definitely didn't want to end up being "those people", you know the annoying passengers that get their names called out over ...


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Tech Helproom
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lost names on folder and pictures
Likes # 0
Posted August 13, 2012 at 11:26PM
I have lost the titals in My Pictures. I cannot see the names of the pictures or folders. I know I have to click on View Lists but then I have forgotten what else I have to do to bring the titals back.
- Tags:
- lost
- pictures
- folder
- titalsinmypictures
Likes # 0
Posted August 14, 2012 at 11:14AM
Check through this - enter link description here
Likes # 0
Posted August 14, 2012 at 12:07PM
Not sure how to do this I know I can see the file names once I open up the folders but not in the Picture folder itself. I clicked on the first folder in My Pictures held the shift key down doubled clicked now I have lost the file names in the folder also along with the file names in the main folder (My Pictures) could you please tell me in your own words what I should do. I was once told to click on File / Lists? then something else and all the names came back but now will they come back in the folders Once I have got them back that is but How
Likes # 0
Posted August 14, 2012 at 12:32PM
I haven't experienced this before so can't really fully explain although I have been trying to replicate your problem but can't.
Maybe this link will be easier to follow - enter link description here
If it has only just recently happened why not consider a system restore to a time just prior to the problem occurring?
Likes # 0
Posted August 15, 2012 at 1:04AM
I have remembered the cure. Click on View / Lists. Then hold down shift key and click on thumb nails in view. The file names come back. Thank you for offering to help. I hope I have helped you with the answer
Likes # 0
Posted August 15, 2012 at 2:21AM
northumbria61, steady now... count to 10 ;)
We're glad you got it sorted out March Wind
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Quiz! How Well Do You Know the Hunger Games: Mockingjay Pt 1 Actors?
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April 27th, 2012
Hmm… where to begin? Lana Del Rey's current single gets a complete makeover thanks to Simms&Belle, who are probably better known as Mark Foster and Isom Innis of Foster the People. Going for a sweaty club banger, the two make the song completely unrecognizable, save Lana's vocals, which are reduced to a few lines and […]
Tags: Azealia Banks, Blue Jeans, Lana Del Rey, remix, Simms&Belle, Stream, The Wedge
Posted in Blog, The Wedge | Posted by Cam


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Dr. Robert J. Gross, MD
Psychiatry, Hoyt Street Physicians
- 2386 NW Hoyt St
Portland, OR 97210
- 1 Office Location
- (503) 228-5909
Dr. Robert J. Gross has been practicing medicine for 48 years. Dr. Gross graduated from the Emory University School of Medicine in 1966. He practices medicine in Portland, OR and specializes in Psychiatry.
Gender: Male
Years in Practice: 48 Years
Languages Spoken: English
Medical School: Emory University School of Medicine
Graduation Date: 1966
Hospital Affiliations: Not Available
Specialties: Psychiatry