The SuperNova Legacy
Survey
Vanina Ruhlmann-Kleider
CEA/DAPNIA/SPP
1)
2)
3)
4)
2006 LHC days in Split
About type Ia supernovæ
The SNLS
First year results
Conclusions
3 October 2006
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An example of SNIa
flux vs time:
"light-curve"
a SNIa
explosion
spectrum: type
and redshift, z
A supernova = an exploding star as bright as the host galaxy
Reproducible intrinsic luminosity : SNe Ia ~ standard candles
2006 LHC days in Split
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~flux
SNe Ia as standard candles
o 1990s: a simple temporal
stretch correction aligns the
light-curves in a sample of
nearby SNe Ia
days
o Study cosmology with distant
SNe Ia
• The High-Z project (95-97):
10 SNe Ia in 0.3<z<0.97
• The SuperNova Cosmology
Project (93-98): 42 SNe Ia in
0.18<z<0.83
2006 LHC days in Split
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further back in time
fainter 
Cosmology from SNe Ia : 1997-98
~ apparent fluxB0.01
= L /4πdL2
with
dL(z,H0,ΩM,ΩΛ,w)
2006 LHC days in Split
z
0.1
1 more redshift 
more expansion
 the Universe expansion is accelerating
3 October 2006
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SNLS
o CFHT :
- 474 nights (2003-2008)
- runs of 18 nights
- 4 observation fields of 1°x1°
- each field: every 3-4 nights
a run, 5 to 7 runs in a row
o MegaCam:
- 1°x1° CCD imager
- 340 millions of pixels
- pixel resolution: 0.18“
- four filters ( : 300-1100nm)
 ~1000 SNe Ia in 5 years with redshifts in 0.1 – 1.3
2006 LHC days in Split
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SNLS vs first generation experiments
Ex: the High-Z experiment:
o Small CCD camera 
few nights of observation
 only 10 high z SNe Ia
 poor light-curve sampling
o Only two filters
2006 LHC days in Split
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SNLS "rolling search"
2005
2006
SN discovery and photometric follow-up continuously monitored
in 4 filters with good precision + spectroscopic time allocated on
8-10 meter class telescopes
large and homogeneous sample of high-z spectroscopically
confirmed SNe Ia, measured with good photometric accuracy
2006 LHC days in Split
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Data analysis
An example of raw image:
entire 4x9 CCD mosaic
one exposure of 300sec
filter r (<>=620nm)
size: 1.4 Gb
2004/10/21
whole survey: 15 Tb
2006 LHC days in Split
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SN detections
SN Ia events found by CCD image subtraction:
Reference image
Current image
Subtraction
SN
Many steps: image cleaning and alignment, photometric calibration,
match reference and current image qualities…
2006 LHC days in Split
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An example of light-curve
spectrum analysis triggered  type Ia confirmed, z=0.627
i, r, z, g filters
Full LC :
test compatibility
with SN Ia model
apparent fluxB,
difference wrt
average light-curve
model
2006 LHC days in Split
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1st year results: Hubble diagram with 71 SNe Ia
~(apparent fluxB
-absolute fluxB)
to (0.26,0.74):
High-Z SN+ SCPresiduals
teams, residuals
to(0.3, 0.0):
published, 2006
2006 LHC days in Split
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1st year results: constraints on cosmological parameters
w=-1
assuming ΩM+ΩΛ=1:
ΩM=0.263±0.043±0.032 (w=-1)
w=-1.023±0.090±0.054
2006 LHC days in Split
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(with BAO)
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Conclusions and prospects
o SNLS: continuous high z SN detection and follow-up, optimised
data taking and light-curve sampling, very good photometric
accuracy;
o 1st year data: 71 spectroscopically confirmed SNe Ia at high
redshift (0.1-1.0)  cosmology with dark energy confirmed &
constraint on w improved;
o Prospects:
• 5 years: ~700 spectroscopically identified SNe Ia;
• refine photometric calibration of MegaCam, esp. in near IR filter;
• better control of systematics: dispersion of SNIa light-curves,
contamination of Hubble diagram by non-SNe Ia.
 large sample of low redshift SNe from SDSS soon available
2006 LHC days in Split
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A possible type Ia explosion mechanism
 reproducible intrinsic luminosity : SNe Ia ~ standard candles
2006 LHC days in Split
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Systematics, 1st year paper
photometric
accuracy
selection
bias
SN Ia model
SN Ib/Ic contamination:  0.5 in the 1st year sample
2006 LHC days in Split
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Origin of SN Ia dispersion: host galaxy "type"
stretch
fainter SNe
brighter SNe
But
so far,
z
2006 LHC
days inno
Splitindication of a correlation
3 October 2006between host type and 16
flux vs z: cosmology or evolution in Ia properties with z ?
low z SNe
SNLS SNe
So far, no evidence for
an evolution with z
2006 LHC days in Split
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flux vs z: cosmology or evolution in Ia properties with z ?
another example:
Conley et al. 2006, AJ, submitted
low-z and high-z
SNLS risetimes
consistent at 1σ
tr: rise
time
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