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Six years of Dark Energy: present and Six years of Dark Energy: present and future prospectsfuture prospects
Ariel Goobar
Physics Department, Stockholm University
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SCPSCP:Perlmutter et al + :Perlmutter et al + High-ZHigh-Z Team:Riess Team:Riess et alet al
Supernova Cosmology Project (SCP)
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5 AD: concordance model 5 AD: concordance model (see also Tonry et al 2003, Barris et al 2004)(see also Tonry et al 2003, Barris et al 2004)
statsyst04.006.007.075.0
Independent evidence also from eg:LSS (eg Peacock et al)
ISW (eg Boughn & Crittenden)
Cluster abundances (eg Bahcall et al)
Age of Universe
X-ray clusters (Allen et al 04)
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SN1a: systematic effects SN1a: systematic effects
• Non-Type Ia contamination• Malmquist bias• K-corrections and SN colors• Extinction by host galaxy dust • Extinction by intergalactic dust• SN brightness evolution• Shape-brightness relation• Instrumental corrections• Lightcurve fitting technique/host
galaxy subtraction• Gravitational lensing• Exotica: axion-photon oscillations, etc• …
No extinction correction. Reddened SNe excluded
With extinction correction
Largest source of identified syst in Knop et al: uncertainty in the intrinsic colors of SN1a ar short
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Spectroscopic tests of standard candleSpectroscopic tests of standard candle
subluminous
overluminous
CaII (3900) velocity
subluminous
Folatelli et al, Garavini et al , Lidman et al
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Turning 6! Very-high Z supernovae Turning 6! Very-high Z supernovae from ACS/HST from ACS/HST (Riess et al 2004)(Riess et al 2004)
•>19 SNe discovered from space, up to z=1.7
•Reported CL-regions due to statistical errors
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Extinction correctionsExtinction corrections
• z-dependence in reported Av ?
• Problems with K-corrections/assumed intrinsic colors in UV part of the SNIa spectrum?
• Changing dust properties ?
• Selection effects?
• Watch out for priors on AV! Riess et al assume P(Av)~exp(-Av)
• A careful study of extinction correction systematics for z>0.9 SNe (as done in Knop et al for z<0.9) is still missing.
SN97ff: assumed extinction- free, E-host
Riess et al 2004 (gold sample)
Uncertainties ?
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Gray(er) IG dustGray(er) IG dust
• Large dust grains (weak wavelength dependence) may populate the IG-medium (Aguirre 1999,2000)
• Evolution of dust density: two limiting cases considered:
1. dust (1+z)3 [Model A]
2. dust (1+z)3 for z<0.5 &
dust(z>0.5)= dust(z=0.5) [Model B, ”replenishing dust”]
• Hard to rule out from SN-colors
• X-ray point-sources at very high-z, (e.g. Paerels et al) do not exclude e.g Model B
• SDSS QSO colors (2740 objects, z<2) <0.2 mag extinction for SN1a at z=1; faintness of SNe unlikely due to only IG-dust
AG,Bergström & Mörtsell, A&A, 2002
Mörtsell & AG, JCAP, 2003
Concordance
Model A
ModelB; M=1
Milne
Dust is still a serious concern for precision cosmology with SNe.
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MC + cosmology fitting code specifically developed to understand science reach and systematic uncertainties in observations of high-z SNe, e.g. due to intervening dust gravitational lensing, search biases, non-SNIa contamination, etc. A.G et al (2002) Astronomy & Astrophysics, 392,757
Download: www.physto.se/~arielDownload: www.physto.se/~ariel
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bias in the cosmology fitbias in the cosmology fitdue to lensingdue to lensing
• GL →asymmetric mag. distributions
• Bias in cosmological results
• However, with proper statistical treatment bias can be kept low + fraction of compact objects in DM derived
co
Mörtsell, Gunnarson, AG, ApJ, 2001; SNAP simulations, Mörtsell, AG, Bergström. ApJ, 2001; Amanullah, Mörtsell, AG; A&A, 2003
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Is Dark Energy = Is Dark Energy = ? ?
Although appears to be the ”simplest” explanation to the data, there are fundamental theoretical problems:
1) why so small? 2) why is the vacuum density so close to matter
density now?
present SN data consistent with with w=-1, i.e cosmological constant, although rapid evolution has been suggested...
Tobias Goobar, age 6
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Rapidly changing w?Rapidly changing w?
• Alam et al (2003,2004) proposed fitting SN data with truncated Taylor expansion for DE.
• Claim: signs for rapid evolution in w: Metamorphosis
Seems like reasonable parametrization, however...•The expression of w comes from derivatives of ansatz in H(z) •Parts of parameter-space causes divergences•As z increases, limiting value of wDE≠-1•Parametrization ”forces” Metamorphosis
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Theoretical systematicsTheoretical systematics
Jönsson, AG, Amanullah, Bergström, astro-ph/0404468
Test: simulate + fit 500 experiments , z-distribution and uncertainties as in Tonry + Barris et al
cosmology
w diverges
w|>15
Metamorphosis not required to explain the fits!
”Transition redshift” set by prior on M
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Theoretical systematicsTheoretical systematics
Jönsson, AG, Amanullah, Bergström, astro-ph/0404468
Test: simulate + fit 500 experiments , z-distribution and uncertainties as in Tonry + Barris et al
cosmology
w diverges
w|>15
Metamorphosis not needed to explain the fits!
”Transition redshift” set by prior on M
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Theoretical systematicsTheoretical systematics
Jönsson, AG, Amanullah, Bergström, astro-ph/0404468
Test: simulate + fit 500 experiments , z-distribution and uncertainties as in Tonry + Barris et al
cosmology
w diverges
w|>15
Metamorphosis not needed to explain the fits!
”Transition redshift” set by prior on M
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Major ongoing/future SN programs Major ongoing/future SN programs
• Low redshift: starting in 2004
Carnegie Supernova Project ~200 SN1a with z<0.07´(UBVRIJHK)
SuperNova Factory ~300 SN1a z<0.08
• Intermediate redshift: starting 2005(?)
SLOAN ~300 0.1<z<0.4
• High-z
SNLS: 2003-2008; 700 SNe 0.3<z<0.9
ESSENCE:2002-2005; 200 SNe 0.2<z<0.7
• Very High-z (z>1) 2003-2005
PANS/GOODS + SCP: ~50 (1 < z < 2)
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Dark Energy statistical precision from CFHT Dark Energy statistical precision from CFHT Legacy SurveyLegacy Survey
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Dark Energy and Dark Matter. Dark Energy and Dark Matter. - Long term future Supernova Project - Long term future Supernova Project
SNAP/JDEM satellite: several thousend very high-z Sne/year + weak lensing survey
~2-meter mirror 0.7° FOV
imaging + spectroscopy 0.35-1.7 m,
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The Next Generation: SNAP/JDEM – good The Next Generation: SNAP/JDEM – good controll of systematicscontroll of systematics
SNAP
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SNAP precision on w’SNAP precision on w’
Planck data provides complementarity equal to a prior (M)0.01.
Frieman, Huterer, Linder, Turner 2002
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SNAP: Weak Gravitational SNAP: Weak Gravitational LensingLensing
Distortion of background images by foreground matter
Unlensed LensedCredits: R.Ellis
SNe + Weak Lensing SNe + Weak Lensing (cf A.Taylor)(cf A.Taylor)
√ • Comprehensive: no external priors required!
• Independent test of flatness to 1-2%
• Complementary: w0 to 5%, w to 0.11 (with systematics)
Bernstein, Huterer, Linder, & Takada
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Summary & ConclusionsSummary & Conclusions
• Quite healthy 6 year old! Evidence for DE seems robust w.r.t identified systematic effects..
• is Dark Energy=?
No convincing evidence against it!• stat ~ syst → need better quality data to
make use of large statistics to come…• New very high-z from ground and space
extremely exciting but sytematics not yet fully studied.
• Large number of ongoing projects will provide several hundreds (thousends?) of nearby and distant supernovae.
• SNAP/JDEM a very exciting mission with capability of resolving the DE mysteri...but launch in 2014???