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SN survey. SDSS-II SN survey: Constraining Dark Energy with intermediate- redshift probes. Hubert Lampeitl University Portsmouth, ICG. In collaboration with: - PowerPoint PPT Presentation
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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!
€
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
€
q0 = −0.34 ± 0.18for q0 = constant and flat universe
(C. Shapiro)
Principal components:
a1<0 only if the universe has acceleratedat one point:
€
α1 = −0.155 ± 0.086P=96%
Independent ofmatter content content
Hubert Lampeitl, ICG
Baryon Acoustic Oscillations (BAO)
z=1089
SDSS/2dF
z = 0.2z = 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)
€
DV = DM2 cz
H(z) ⎡ ⎣ ⎢
⎤ ⎦ ⎥
1/ 3
€
cs = 13 c
€
cs = 0
Distance DualityPhase space density of photons must be conserved in all metric theories of gravity (Etherington 1933, Ellis 1971)
€
α =0 !
BAO SN
LCDM
€
α≠0at2.4σ
More, Bovy, &Hogg 2009Avgoustidis, Verde, & Jimenez 2009
Constraining w with ISW
€
δTT
= −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
€
g(a) = δa≅ exp d ln a[Ωm(a)γ
0
a
∫ −1]
€
w ≥ −1:γ = 0.55 + 0.05[1− w(z =1)]
€
w < −1:γ = 0.55 + 0.02[1− w(z =1)]
Kaiser Effect:
€
β =Ω0.6 /b2dFGRS (Hawkins, 2003)
€
fg (z = 0.15) = 0.49 ± 0.15Including 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:
€
w = −0.74−0.22+0.17(stat)−0.41
+0.16(sys)