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Dark energy workshop. Copenhagen Aug. 2007. Why the SNLS ?. One of the biggest high-z supernova survey ~500+ supernovae at the end of the survey. + a huge catalogue of galaxies in the lines of sight. Questions to be addressed:

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dark energy workshop

Dark energy workshop

Copenhagen Aug. 2007


Why the SNLS ?

One of the biggest high-z supernova survey ~500+ supernovae at the end of the survey. + a huge catalogue of galaxies in the lines of sight

Questions to be addressed:

-Can the intrinsic scatter in the Hubble diagram be further reduced?

-Is it possible to detect a correlation between residuals and magnification?

-Is it possible to say something about the dark matter distribution of the galaxies?


First estimate (a feasibility check)

700 simulated type Ia Sne using SNLS Sne observations (Astier et al 2006)

Magnification of each supernova is estimated using SNOC The SuperNova Observation Calculator Goobar et al (astro-ph/0206409)

Most Sne are demagnified and some are significantly magnified

small effect

Cosmological results

and due to lensing ~ 2-3 %

Uncertainties due to lensing ~ 1-2%

Lensing accounts for 7.5% of the dark energy task force figure of merit

is it possible to detect a signal
Is it possible to detect a signal ?

Expected standard candle


(calculated from a cosmological model)



Plots of residuals vs magnification

For estimations of the magnification

errors, a work on the GOODs fields

has been used

(Jonsson et al astro-ph/0612324)

Expected linear correlation




(no correlation)

(linear correlation)

2 different samples:

-with lensing effects

-without lensing effects

Confidence level of >99%


Analysis chain

Actual data

Galaxy catalogue including magnitudes in the g r i (u) and z -bands + photometric redshift

Using the Faber-Jackson relation for ellipticals and the Tully-Fisher relation for spirals we can relate luminosity with mass (for a given model).

Galaxy type





Estimation of the mass of the galaxy using galaxy models like SIS or NFW

Estimation of the eta-parameter

Using PEGASE : a UV to NIR spectral evolution model of galaxies




all sorts of


Estimation of the magnifi-cation of each SNe

Using Q-LET, a multiple lens plane algorithm which calculates the magnification with respect to a homogeneous universe


Pegase (a UV to NIR spectral evolution model of galaxies)

-Photometric redshift code

-Fits redshifted spectral templates


Absolute B-band magnitudes


The Faber-Jackson/Tully-Fisher relations

The Faber-Jackson or Tully-Fisher relations relates the velocity dispersion and the Luminosity of the galaxy.

F-J relation (ellipticals)

Mitchell et al. (2005)

T-F relation (spirals)

Bohm et al. (2004)

Using a specific model (SIS or NFW) then relates the luminosity to the mass which is finite providing you choose a cut-off radius.

Truncation halo:

The radius inside which the mean mass density is 200 times the present critical density



The smoothness parameter

All “unobserved” matter is put into a smoothly distributed component.

Good test whether the galaxy model is OK




Another formula relating mass and luminosity Hoekstra et al. (2005)

Masse of elliptical galaxies

Mean mass

Jonsson et al.



Mean mass

Hoekstra et al.


Using the formula of Hoekstra et al. for spirals and ellipticals

Using the F-J/T-F relations for the second field