SDSS-II SN survey:Constraining Dark Energy with intermediate-redshift probes

Hubert LampeitlUniversity Portsmouth, ICG

In collaboration with: H.J. Seo, T. Giannantonio, C. Shapiro, R.C. Nichol, B. Bassett,

W.J. Percival, T. Davis, B.Dilday, J. Frieman, P. Garnavich, M. Sako, M. Smith, J. Sollerman

SN survey

Why intermediate-redshift probes?In most cosmological analysis several different probes are combined in orderTo derive the most constraining parameters on cosmologyMost popular: SN + BAO + CMB but GS & ISW

Stretch over a very wide redshift range (in case of CMB z=1089)

In case of Supernova Ia combinations from Several Instruments (Nearby, ESSENCE, SNLS, HST): eg. Davis et al. 2007, Kowalski et al. 2008, Hicken et al, 2009, Kessler et al. 2009)

Cross check: Are the results consistent if we limit ourself to one redshift range?- Less prone for systematic effects, but less stringent limits

Systematic and statistical uncertainties for SN are now on same level! Increasing the sample doesn’t help!

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w = −0.969−0.063+0.059(stat)−0.066

+0.063(sys)

Kowalski et al. 2008

Eisenstein et al. 2005

Komatsu et al., 2009

Why intermediate-redshift probes?In most cosmological analysis several different probes are combined in orderTo derive the most constraining parameters on cosmologyMost popular: SN + BAO + CMB but GS & ISW

Stretch over a very wide redshift range (in case of CMB z=1089)

In case of Supernova Ia combinations from Several Instruments (Nearby, ESSENCE, SNLS, HST): eg. Davis et al. 2007, Kowalski et al. 2008, Hicken et al, 2009, Kessler et al. 2009)

Cross check: Are the results consistent if we limit our self to one redshift range?- Less prone for systematic effects, but less stringent limits

Systematic and statistical uncertainties for SN are now on same level! Increasing the statistic doesn’t help!

€

w = −0.969−0.063+0.059(stat)−0.066

+0.063(sys)

Kowalski et al. 2008

Kessler et al, 2009

Possible and identified problemswith Supernova

-Restframe u-band (UV lightcurve ~ 10%)

- evolution of SN spectra over redshift and progenitor type

- SN demographics

--> k-corrections

- Dust in host galaxy (RV=3.1 vs. 2.2)

- local peculiar velocities (Hubble bubble)

- selection effects

- photometric cross survey calibration . . .

Foley et al., 2008

NugentHasiao

Goals:

SDSS-II SNe Survey

Hubert Lampeitl, ICG, 29/5/2008484 confirmed SN with IAU designation

Hubert Lampeitl, ICG

Z = 0.013

Z = 0.47

Additional spectroscopic observation time awarded on BOSS spectrograph to follow up and get redshifts for SN candidates without confirmed redshift

SDSS-II SN survey: 1st year- 103 spectroscopically confirmedSN with z=[0.045;0.42] from 2005after stringent quality cuts

- All fit with MLCS2k2 for variousLC fitter choices (evaluationof LC fitter systematic, Kessler et al, 2009)

-Fiducial model chosen to reflect current understanding

LCDM

q0=-0.33

z=0.34z=0.13

Scatter ~0.14 mag

Case for acceleration

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q0 = −0.34 ± 0.18for q0 = constant and flat universe

(C. Shapiro)

Principal components:

a1<0 only if the universe has acceleratedat one point:

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α1 = −0.155 ± 0.086P=96%

Independent ofmatter content content

Hubert Lampeitl, ICG

Baryon Acoustic Oscillations (BAO)

z=1089

SDSS/2dF

z = 0.2

z = 0.35

Eisenstein et al., 2005Percival et al., 2007DV(0.35)/DV(0.2) = 1.812 ± 0.062

BAO provides a ‘standard ruler’

1:1 scaling wit a(t)

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DV = DM2 cz

H(z)

⎡

⎣ ⎢ ⎤

⎦ ⎥

1/ 3

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cs = 13 c

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cs = 0

Distance DualityPhase space density of photons must be conserved in all metric theories of gravity (Etherington 1933, Ellis 1971)

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α =0 !

BAO SN

LCDM

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α≠0at2.4σ

More, Bovy, &Hogg 2009Avgoustidis, Verde, & Jimenez 2009

Constraining w with ISW

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δT

T= −2 ˙ φ /c2∫ dl /c

Giannantonio et al., astro-ph/0801.4380 private communicationSDSS DR6 Main galaxy sample & LRG ISW detected on with ~3s

& growth of structure

Peacock, Nature 410, 169 (2001)

Linder, PhRvD 72 (2005)€

˙ ̇ δ + 2H ˙ δ − 4πGδ = 0

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g(a) =δ

a≅ exp d ln a[Ωm(a)γ

0

a

∫ −1]

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w ≥ −1: γ = 0.55 + 0.05[1− w(z =1)]

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w < −1: γ = 0.55 + 0.02[1− w(z =1)]

Kaiser Effect:

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β =Ω0.6 /b

2dFGRS (Hawkins, 2003)

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fg (z = 0.15) = 0.49 ± 0.15

Including bias

Constraining Cosmological Parameters

BAO

SDSS-SN

ISW

GS

flatcurved

(1 sigma errors)

Curvature constrained by WMAP:

Systematic uncertainties

• Main uncertainty: U-band anomaly caused by uncertainties in spectral library -0.41 (sys) in w

• Combining other identified systematic effects uncertainty results in +/- 0.16 (sys) in w

Hard to quantify and easily underestimated!

SummarySupernova drawn from SDSS-II SN survey finds under the Assumption of a flat universe indication of an accelerating universe with a probability>97%

No compelling evidence for a violation of distance duality found using SN & BAO. Possible indication of systematic effect in one of the probes.

Combining the SDSS SN data with either ISW or GS givesLimits on w:

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w = −0.74−0.22+0.17(stat)−0.41

+0.16(sys)