17.3.2008 marek kowalski moriond 2008 - cosmology the “union” supernova ia compilation and new...

17.3.2008 Marek Kowalski Moriond 2008 - Cosmology

The “Union” Supernova Ia Compilation and new Cosmological Constraints

Marek Kowalski Humboldt Universität zu Berlin

for theSupernova Cosmology Project

Moriond 2008


The Union SNe Compilation M

1 00.72 0.280 1

fainter

8 new SNe


Analysis aspects

Consistent Lightcurve FitsSALT fitter used for all SNe using mostly original band-passes (Guy et al 2005/2007).

Blind analysisThe analysis (i.g. cuts) were developed on a blinded data set, all luminosities were offsetby a hidden redshift-dependent amount.

Robust analysisInitial cosmological fit using median statistics.3-sigma outliers removed. Assignment of sample dependent dispersion.

Stretch and color corrected luminosity:

Large sample of SNe allows new studies of systematic errors


A heterogenous data sample


Study of - mean deviation- residual slope

A heterogenous data sample


Test for Tension

high-zlow

-z

mean deviation: OK


Test for Tension

high-zlow

-z

residual slope: (OK)


Testing SN evolution by subdividing the sample

Evolution test:Redshift

No significant evidence for evolution!

Evolution test:Population


Systematic errors

0.0 0.1 0.2 0.3 0.4 0.5-1.5

-1.0

-0.5

0.0

m

Union SNe

with systematics

Nuisance parameters for systematic errors: μ =mmax −M +α (s −1) − βc + ΔM + ΔM i

common for all z>0.2 SNe sample dependent


Comparison with previous compilations

Union

Union

Union

Riess GoldDavis 2007

Union w/oNew SCP SNe

without the 8new nearby SNe

184 SNe 192 SNe 307 SNe


Perlmutter et al., 1999

Results: Cosmological fit parameters

M

M

m = 0.274 ± 0.016(stat) ± 0.012(sys)

Ωm = 0.285 ± 0.020(stat) ± 0.010(sys)

Ωk = −0.001 ± 0.010(stat) ± 0.005(sys)

Combination of SNe with: BAO (Eisenstein et. al., 2005)CMB (WMAP-5 year data, 2008)

For a flat Universe:

… and with curvature:


Equation of state: w =p/

w =−0.969 ±0.061(stat) ±0.065(sys)SNe + BAO + CMB

... and allowing for curvature: w =−1.001±0.071(stat) ±0.081(sys)

With systematics


Redshift dependent w

w=w0 + (1-a) wa

w0+ w

a= 0


Redshift dependent w

Assuming step-wise constant w:

A floating non-SNe bin to decouple low from high-redshift constraints


Summary

The Union SN compilation provides a consistently analyzed data set, and with new nearby SNe, is the largest available.

Investigations of systematics show no significant tension between the individual samples as well as no evidence for SN evolution. The strongest constraints to date on the dark energy density and the equation of state parameter w, however, essentially no constraints at z>1.

A detailed paper has been submitted to ApJ and the data will soon be made available on the web (see http://supernova.lbl.gov)

17.3.2008 marek kowalski moriond 2008 - cosmology the “union” supernova ia compilation and new...

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