The Strong Lensing Legacy Survey
(SL2S)
Bernard Fort
ESO Santiago November 22, 2006
UPMC/CNRS
SL2S project
Extract and study a large sample of strong gravitational
lenses from the CFHTLS wide field survey
> 300, possibly 1000
with a lens redshift up to z =1:
Scientific collaboration
Institut d’astrophysique de Paris (France)
C. Alard, B. Fort, Y. Mellier, Hong Tu (Shangaii NU), J-F Sygnet,
Laboratoire d’Astrophysique de Tarbes-Toulouse (France)
R. Cabanac, G. Soucail, E. Belsole (Cambridge UK), R. Pelo
Laboratoire d’astrophysique de Marseille (France)
J.-P. Kneib, E. Julo (ESO), L. Tasca, O. le Fevre
UC Santa Barbara (USA)
R. Blandford, P. Marshall, R. Gavazzi, ..
University de Victoria (Canada)
D. Crampton (HIA) , K.. Thanjavur (UVic), J. Willis (UVic)
Durham University (G-B)
M. Swimbank
Outline of the presentation
• CFHT Legacy Survey: a big reservoir of
strong lenses
• Automated procedure to search lenses
- arcs in groups and (distant) clusters
- gravitational rings
• SL2S scientific goals
• Future
CFHTLS/Deep field
170 deg2 (U, G, R, I, Z),
I=24.5: 3.8 millions of galaxies
Lensing in cosmology
image magnification
Cosmology geometry
Cosmology
Newtonian
potentia
Newtoniangravitational
potential
Multiple QSOs or arcs around galaxies
- QSO: Cosmic Lens All-Sky Survey
12/5000 distant radiosources
are lensed by a foreground (E) galaxy
(Browne et al 2002)
- Galaxy:20 lensed Lyman-α
background galaxies for 20,000
massive, E / bulge-dominated galaxies
with z>0.4,R<20,B-R>2.2
(APM survey: Willis et al, 2000)
For galaxy (QS0) - galaxy lenses (gravitational rings)
- big Elliptical represents 2/3 of the lenses
- Optical depth ~ 10-3
Giant arcs in cluster of galaxies
RCS giant arcs sample
from Gladders et al 2005.
Some arcs have
Einstein radius up to 50 "
(A0024, RCS 0224)
Number of DM halos
Multiple QSOs/Rings
galaxy, Re ~ 1-3"
group Re ~ 3-7"
?
cluster, Re ~ 7-20"
Luminous X-clusters
Comoving number density of DM halos
from Mo & White 2002
SL2S prediction and detection numbers
.
predicted n / 1 sq°
Rings
-> 10-20
Groups ->
1-2
Clusters ->
0.4
expected CFHTLS
Rings
Groups
Clusters
SHMO
Others
> 1000
>100
> 50
> 300
?
observations
?
How to
find rings
and arc
groups?
.
From Oguri 's simulations 2005
Can we find intermediate mass lenses ?
M ~ 3-30 1012 Mo
SIS mass distribution:
(3’’< a < 7’’)
?
a ~ 1-3” for a lens galaxy
a ~ 10-50” for a cluster of galaxies
Visual detection of giant arcs in CFHTLS
(from Mellier 2005).
Automated detection procedures
Arcfinder (Alard 2006)
Ringfinder (Gavazzi et al 2006
Physical nature of arcs
2.5 seing~14 pixel
arc thickness ~ seeing
search a local elongation with w=seeing
Arcs detector
Arc reconstruction by a small scale estimator of a local
elongation (seeing width) of light distribution
y 2.M
xo,yo
scanning aperture M x M pixel unit (M ~7)
unit, optimal mexican hat filtering
x
2.Mpx
(x,y) local axis aligned on second
moments of light distribution
E(xo,yo)
map
local estimator
E(xo,yo) =
I(xo + x, yo) dx
2.M . Max [-M<x<M] [ I(xo + x, yo+y) dy]
Detection example
with a typical CFHTLS
arc candidate
From Alard 2006
E(x,y) map
A selected sample of SL2S lenses (10/46T002)
SL2S/COSMOS 5921+638
Ringfinder fails for rings with Re<2.7 ’’
CFHTLS/HST
Preliminary results with CFHTLS
groups
<zl> ~ 0.65
distant clusters
release T002
release T003
~ 30°°
from Cabanac et al. 2006
Parametric modeling with lenstool
SL2SJ085446-012137
SL2SJ085446-012137
HST modeling of SL2SJ085446-012137
Bright Galaxy {0,0}
Main potential
Dx= -0.098’’+/- 0.05
Dy= -0.522’’+/-0.08
But arc redshift ?
Second galaxy produces 2 extra images splitting
7 images configuration
First HST follow-up
November 2006
Main fields of investigations
Structure of halos in groups and distant clusters for
comparison with simulations:
- center of DM halos relatively to the
center of brightest central galaxies,
nature of fossile groups
- relative mass and light ratio and evolution
with zl
- SL+WL determination of C200= R200/rs for a large mass
spectrum from G to clusters as a function of zl
- detection of triaxial halos, study of sub-halos (Rcut),
-2D spectroscopy of very distant magnified
galaxies and search for galaxies at z>6
«Arcfinder» is not efficient for Re > 2.5-3’’
but
we also want
to find the most numerous
population of distant gravitational rings
hidden in the CFHTLS ?
« Ringfinder»
Sloan Lens ACS Survey (SLACS)
Bolton 2004, Treu 2005, Koopmann 2005
Searching composite spectra for a
signature of two aligned galaxies
ACS images
Coupling lensing and stellar dynamics
Lens modelling give the mass at rEinstein and S*+ S DM
Stars see the potential for r < reff
(~ potential slope g)
Jeans equation
c(s ( M* / L, g, n v anisotropy) = s (M* / L, g, nv anisotropy) - s* spectro
observation
from Koopmann & Treu 2005
SLACS
Lensing -> recovers the Ellipticals fundamental plane
For isolated E (external shear perturbation < 0.035)
<sL/s*> = 1.01 +/- 0.065 rms
r(r) ~ r - 2.01 +/- 0.03 near Einstein Radius (~Flat Rot.Curve)
PA and ellipticity of light and DM trace each other (M ~75%)
*
No evolution (<10%) of parameters with z (but for SLACS lens
galaxies the average redshift is around <ZL>~0.2)
How to recognize a ring
Simulations of rings around E-lenses
HST
circular source
CFHTLS
circular lens
?
arc(let)s
arc(let)s
True G-Ring but
spiral like!
a HDF source
a HDF Elliptical
?
seeing = 0.8 arcsec
Finding CFHTLS ring candidates
Detection: Based on color information (often rings are blue and lenses
are red (early-type galaxies)
Method: Fit a B-aR profile consistent with the lens color. Identify a sharp
elongated blue excess at 0.8<r<2.5'' above the (B-aR) noise.
~10-20 candidates/deg2
(Raphael Gavazzi 2006)
SL2S 02 25 11- 04 54 33
A Sample of ringfinder candidates in D1
A spectroscopic follow-up of the arcs is necessary to confirm the candidates
Test with the CFHTLS-COSMOS field
4117 (E/So or Sa) galaxies with 18 <I < 22 are selected.
783 with a small residual blue light in the annulus.
72 candidates above the reference threshold.
Indeed all the blue cosmos rings are recovered
(but obviously not the red ones).
Near future: optimisation + (R-Z, etc.) tests
#########################################################################
# ID
RA
DEC
Re
F814w
z
#
#########################################################################
C009
C012
C013
C018
C056
C148
C208
C211
C216
C221
C921
C929
red ring
red ring
red ring
red ring
10:00:09.7
10:00:12.6
10:00:13.9
10:00:18.4
10:00:56.7
10:01:48.1
10:02:08.5
10:02:11.2
10:02:16.8
10:02:21.1
09:59:21.7
09:59:29.9
02:24:55
02:20:15
02:22:49
02:38:45
02:12:26
02:23:25
02:14:22
02:11:39
02:29:55
02:34:40
02:06:38
02:13:52
2.6
0.82
1.7
1.7
2.02
1.48
1.59
3.6
2.1
1.6
0.68
2.4
19.3
18.3
18.9
23.2
18.9
19.3
19.88
21.27
17.96
19.2
18.3
17.4
0.39
0.39
0.36
0.73
0.42
0.39
0.41
0.91
0.59
0.42
0.44
0.25
Gavazzi June 2006
A SL2S cosmological tests with rings ?
Hypothesis: Treu's results
<sL/s*> =1. +/- 0.065
r(r) ~ r - 2.01+/-0.03 at Re
~ Flat Rot. Curve
(DM light-conspiracy)
Re
Re/sL = Dol Dls /D os
Re/s* = G (W, L, or w0,w1)
Lens modeling
Log r
VLT spectroscopy
First Year results
(~1/5 of the CFHTLS field)
- 47 multiple arc(let) systems in groups and distant
clusters were discovered and are being observed
with the HST
- > 100 gravitational ring candidates tbc!
-
many singly highly magnified lens events with m>3-5)
- Several multi-plan lenses and a few possible dark rings
Futur
Several other large (cosmic shear) surveys are planned
Deep lens survey
RCS2
Kids-VST/OmegaCAM
VISTA-IR galaxy survey
LSST
Pan-StARRS
SNAP Space survey
28 deg2 on going
1000 deg2 started
1000 deg2
near IR rings ?
10 000 deg 2
10 000 deg 2
1000 deg 2 ?
2008
2012
>2011
Extending the technique to near IR
survey
• Systematic scan of high magnification regions for Lyman-a
emission at z~5-8. Recently z~6 galaxies found this way.
• Small primeval halos: 106 Mo - first stars?
• Dynamical studies with 2D spectroscopy of brightest
distant arcs to get rotation curves (Karun Thanjavur,
David Crampton, Jon Willis)
SNAP
Joint Dark Energy Mission: NASA (75%) & DOE (25%)
launch 2014-2015
6 years survey: super novae and weak lensing
SNAP: 2m telescope, instrument FOV 1 deg2
Imaging / spectro.
one deep field (15 deg2), one large field (~300 deg2 ?)
~ 1Billlion $
•
 DUNE (Dark Universe Explorer): similar survey but
1.2-1.5m telescope and imaging only
instrument FOV 1 deg2
~ 300 M€
•Prediction snap n ~ 4000 and 14000 strong lenses
Conclusions
SL2S will be the largest SL database available for the next 5 years,
possibly 1000 SL, if we have spectroscopic follow-up.
- SL2S will extend the lensing studies of galaxy mass evolution at large z
and groups (a new classe of SGL)
- Numerous rings and arc systems for a large mass spectrum allow
statistical tests (cf Oguri 2005).
-offer the possibility to observed magnified galaxies at z > 6
- SL2S is a benchmark for the preparation of SL analyses with SNAP or
DUNE-like survey.
CFHTLS highly magnified drop-out galaxies
Singly Highly-Magnified Event
m>
3
SIE
NWF
From Omont et al. 2005
10 – 30 % of all very distant sources (z>4) are magnified with
m>10 (Keeton’s prediction 04 astro-ph/0405143)
Multiple arc system from cosmic string
HST field
same HST field + string loop
Finding arcs within clusters members
Typical cases in A1689
Note the cluster shear effect: testing the potential slope
SDSS survey for giant arcs
Sloan 8000 deg2 images to detect clusters using
the red sequence technique 0.1<z<0.6
- follow_up with UH88 gives 240 clusters
- 141 with sub-arcsecond seeing
- 16 with giant arcs and 9 with shortest arcs
Inner arc
Hennawi et al 2006
Arc systems with an elliptical lens.
Singly magnified image
of a distant galaxy
Radial arc
Cusp arc
Einstein Cross
From Kneib et al 1993
Fold arc
An overlook on lensing probability
(Ofek, Rix & Maoz 2003)
Distribution halos
X-section + conection
Light -> total mass
L*-> s*->sL
Cosmological
parameters Dls/Dos
Evolution (z)
Parametrization ->
Optical depth
per unit redshift
t(q, zs)
Merging rate
Luminosity,
M evolution,..
Prob[zlense] variations with various parameters
varying q
zsource
W m , Wl
or wo,w1;..
mass evolution
Merger evolution
(Ofek, Rix & Maoz 2003)
More information
http://www.cfht.hawaii.ed
u/~cabanac/SL2S/
The SL2S I:
Cabanac et al. 2006
French/ESA programs
Sloan Lens ACS Survey (SLACS)
Bolton 2004, Treu 2005, Koopmans 2005)
Sample ~ 120 candidates with ongoing HST snap survey
A three-step procedure to search more rings
1- CFHTLS imagery
to select possible SL
ncandidates < 200 /°
2- spectroscopy
(VIMOS)
Goal find
nring ~ 10/°
OII 3127Å
Zs=1.32
4000 Å
ZL=0.63
3- HST snap
>80%
confirmation rate
If successful SL2S => nring ~ 1000 !
Multiple images formation
Convergence
+ shear
O
L
S
gravitational lense effects
+
Fermat principle
From SLACS to CFHTLS rings
Finding rings in the
CFHTLS-wide is a great
challenge (seeing effect),
but if successful SL2S
Sloan Lens ACS Survey (SLACS) Bolton 2004,
Treu 2005, Koopmans 2005 Study ~ 20/120
candidates with ongoing HST snap survey
=> nring ~ 1500 !
Sciences: Evolution lens
parameters with z (profile
slope, total mass, M/L,..)
at larger redshift (0.2-0.8)
than the SLOAN survey
(<z>~0.2)
Estimation of the optical depth
Analytical method
Schechter distribution L(z)/L*(z)
of SIS halos
+
Faber-Jackson
(Tully-Fisher) law
+
Observational relation
(SLOAN) sDM = f(s*)
Treu et al. 2006
Elliptical -> sL = s*
or
simulation
Comoving number n NFW (z)
(Mo and White 2000)
+
<cross-section XSNFW (z)>
dt/dz = n(qE, z) (1+z)3 XS c.dt/dz
Fraction of multiply lensed QSOs
~2.10-3
<zlens> ~ 0.4
<Dsource> ~ 4 Gpc
no = 0.5 10-2 Mpc-3, < REinstein> ~ 1 arcsec
for SIS:
t
~ no < p (REinstein)2 > Ds ~ 10-3
JVAS + Cosmic Lens All-Sky Survey
12/5000 distant radiosources
are lensed by a foreground (E) galaxy
(astro_ph/0211069, Browne et al; Chae 2002,
2004 , Chen et al, 2004, ApJ 607, L71)
Arc modelling with pixel deprojection
b/a
0.8
0.7
HST/ACS : a modelling of a
D2/CFHTLS arc by Gavazzi et al. 2005
b
4"
5"
Arcs geometry depends on the projection matrix
Projected potential derivatives * Dol . Dls / Dos