Supernova Legacy Survey (SNLS)

Goal: Characterize the Dark Energy equation of state

“w” parameter

A component of the

CFHT Legacy Survey

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SNLS Collaboration• Toronto Group: Carlberg*, Mark Sullivan, Andy Howell,

Kathy Perrett, Alex Conley• Victoria Group: Chris Pritchet*, Don Neill, Dave Ballam• French Group: Reynald Pain, Pierre Astier, Julien

Guy, Nicolas Regnault, Jim Rich, Stephane Basa• Follow-up Collaborators:

– Oxford: Isobel Hook (Gemini & VLT)– LBL: Saul Perlmutter & Peter Nugent (Keck)– Caltech: Richard Ellis* (Keck)– Carnegie: Wendy Freedman*, Mark Phillips

(Magellan)• PLUS many students and associates• * CIAR

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H2(z) = Ho2[

ΩM(1+z)3 + ΩR(1+z)2

+ ΩΛ(1+z)3(1+w)]

Distancer = ∫c /H(z) dzinfer w.relative distances!

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Supernova scary for dark energy?

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Secondary SNLS goal: understanding Supernovae Ia

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Survey Design: Increasing the Precision

• Goal – to boost the S/N per sne to ~1-2.• Single telescope “Always on” rolling survey

– 5 epochs per lunation• Multi-filter (g, r, i, z SDSS)• Careful calibration effort (goal 1%, current 3%)• New k-correction details (redshift of spectrum)• Depth sufficient to get to z=1+• After five Years:

– 2000 detected (to z~1.1-1.2)– 1000 sent for spectroscopy (optimized)– 700 confirmed Ia

• Currently only reduced 1st year.

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Ia/ Ia*54%

Not Ia35%

Unidentified11%

Ia/ Ia*79%

Not Ia3%Unidentified

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Gemini: success of SN photo-zGemini: success of SN photo-zBefore implementation:Before implementation:

Consistent with Consistent with previously published previously published rates:rates:

–Lidman et al. (SCP): 50-62%Lidman et al. (SCP): 50-62%

–Matheson et al. (ESSENCE): Matheson et al. (ESSENCE): 44%44%

–Median z=0.5Median z=0.5

Using photo-z: ~70-Using photo-z: ~70-80% confirmed as SNe 80% confirmed as SNe Ia at Gemini (median Ia at Gemini (median z=0.81)z=0.81)

Only 3% (1/38) non-Ia Only 3% (1/38) non-Ia SNe when using photo-SNe when using photo-zz

Howell et al. (2005)

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Typical light-curve

z=0.36

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The supernova distance model

Peak B luminosity depends on:

• Colour: Bluer-brighter relation (B-V)0

• Rate of fading: Slower-brighter relation

• Fit w, ΩM, M, α, β, σint (extra: ΩR and w(z))

Χ2=1 requires σint = 0.14 magnitudes (i.e. last 14% jitter not yet understood)

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First Results – Hubble Diagram (Astier et al. 2005)

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Comparison with previous SN resultsComparison of SNLS first

year (72 SNe; solid contours) to previous SN results – Knop et al 2003

(~50 SNe; dotted contours).

Shaded area shows projected end of survey

constraints

The superior colour and time sampling of SNLS

allows tighter constraints on the cosmological

parameters.

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The Baryon Acoustic Oscillation scale

Data provides an angular scale which measures the ratio of the distances to the SDSS galaxies at z=0.35 and the CMB at z=1089

We use A=0.469±0.017

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Sne Ia plus BAOw = -1.02 ± 0.09 (stat)

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Systematic Errors Checks

• No colour residual– (there is a distance-colour relation at z>0.8)– (very noisy photometry at z>0.8)

• No “stretch” residual, yet• No significant malmquist bias• Independent analyses confirm “clean” data• But, upcoming data is much better.

– Better sampling in time and colour– Lower noise for z band– Calibration improvements

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Colour trouble at z>0.8 (noise induced)low significance distances

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The Motivation for variable w

• Widely used model for Dark Energy (and inflation) is a quantum scalar field, φ(x,t).

• Energy density, ρ = ½ [dφ/dt]2 + V(φ).• Pressure, P = ½ [dφ/dt]2 - V(φ).• w = P/ρ is near -1 for slowly varying φ.

)(

)(2

2

1

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1

V

Vw

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Empirical fit for w(z)

Two common models:

• w(z) = w0 + w1 z

– Taylor series, – behaves badly at high z– Works well over accessible range– Preferred here for comparison to others

• w(a) = w0 + w1 (1-a), a = 1/(1+z)

– Similar to above, weaker constraints.

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1001 Bootstrap resamplings, fitting for all parameters, displaying only two.

Green contours are SNLS Ia constraint

Red contours are the Baryon Acoustic Oscillation constraint of Eisenstein et al.

Black (very similar to green, Ia, alone) are joint constraint.

Median z~0.6. Ellipse orientation is approx w0 ≈ -1 -0.6w1. (flatness constraint from WMAP makes barely detected difference)

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Marginal stretch dependenceSplit at median stretch, using only s<0.97 (left), and s>0.97 (right).

Restricted to z<0.7 to avoid higher z color correction complications at higher z. Sample is reduced to 53 and 35, for low and high s, respectively.

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w = wo+ w1z w = wo + w1(1-a)

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Statistical Error only!

End of SNLS result, assuming 8x more data at both high and low redshift.

Comparable to WFMOS, but...systematics are problematic.

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Conclusions

• Current data consistent with constant DE– w = -1.02 ± 0.09

• Future work will improve limit 2-3x

• If <0.02 mag “all-in” systematics, then SNLS will provide dw/da to ± 0.3 (1 sigma)

• Systematic errors are the challenge.

• New results coming: “3rd year” analysis