1 1 dark energy: illuminating the dark eric linder university of california, berkeley lawrence...
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Dark Energy: Dark Energy:
Illuminating the DarkIlluminating the Dark
Eric Linder University of California, BerkeleyLawrence Berkeley National Lab
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Discovery! AccelerationDiscovery! Acceleration
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Exploring Dark EnergyExploring Dark Energy
New quantum physics? Does nothing weigh something?
New gravitational physics? Is nowhere somewhere?
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Today’s InflationToday’s Inflation
Map the expansion history precisely and see the transition from acceleration to
deceleration.
Test the cosmology framework – alternative gravitation, higher dimensions, etc.
SNAP constraints
supe
r ac
cele
ratio
n
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Present Day InflationPresent Day Inflation
Map the expansion history precisely and see the transition from acceleration to
deceleration.
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Density History of the UniverseDensity History of the Universe
Map the density history precisely, back to the matter dominated epoch.
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Mapping Our HistoryMapping Our History
The subtle slowing down and speeding up of the expansion, of distances with time: a(t), maps out cosmic history like tree rings map out the Earth’s climate history.
STScI
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Cosmic ArchaeologyCosmic Archaeology
CMB: direct probe of quantum fluctuations
Time: 0.003% of the present age of the universe.
(When you were 0.003% of your present age, you were 2 cells big!)
Supernovae: direct probe of cosmic expansion
Time: 30-100% of present age of universe
(When you were 12-40 years old)
Cosmic matter structures: less direct probes of expansion
Pattern of ripples, clumping in space, growing in time.
3D survey of galaxies and clusters - Lensing.
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The Universe: Early and LateThe Universe: Early and Late
Relic imprints of quantum particle creation in inflation - epoch of acceleration at 10-35 s and energies near the Planck scale (a trillion times higher than in any particle acclerator).
These ripples in energy density also occur in matter, as denser and less dense regions.
Denser regions get a “head start” and eventually form into galaxies and clusters of galaxies. How quickly they grow depends on the expansion rate of the universe.
It’s all connected!
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COBE WMAP
Planck
What do we see in the CMB?What do we see in the CMB?
A view of the universe 99.997% of the way back toward the Big Bang - and much more.
POLARBEAR has 2.5x the resolution and 1/5x the noise
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Geometry of SpaceGeometry of Space
WMAP/NASA/Tegmark
CMB tells us about the geometry of space - flat? curved?
But not much about evolution (snapshot) or dark energy (too early).
Escher
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Type Ia SupernovaeType Ia Supernovae
• Exploding star, briefly as bright as an entire galaxy• Characterized by no Hydrogen, but with Silicon• Gains mass from companion until undergoes thermonuclear runaway
Standard explosion from nuclear physics
Insensitive to initial conditions: “Stellar amnesia”Höflich, Gerardy, Linder, & Marion 2003
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Standardized CandleStandardized Candle
Redshift tells us the expansion factor a
Time after explosion
Bri
ghtn
ess
Brightness tells us distance away (lookback time t)
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Standard CandlesStandard Candles
Brightness tells us distance away (lookback time)
Redshift measured tells us expansion factor (average distance between galaxies)
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Discovering SupernovaeDiscovering Supernovae
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Nearby Supernova Factory
Understanding SupernovaeUnderstanding Supernovae
High z: “Decelerating and Dustfree” HST Cycle 14, 219 orbits
Supernova Properties Astrophysics
G. Aldering (LBL)
Cleanly understood astrophysics leads to cosmology
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Images
Spectra
Redshift & SN Properties
data analysis physics
Nature ofDark Energy
Each supernova is “sending” us a rich stream of information about itself.
What makes SN measurement special?What makes SN measurement special? Control of systematic uncertaintiesControl of systematic uncertainties
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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Current Data: SNLSCurrent Data: SNLS
Supernova Legacy Survey:
Rolling search on CFHT 2003-08; spectra First year results (71 SN), Astier et al. 2006 Expect total of 500-700 SN at z<0.95
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Current Data: SNLSCurrent Data: SNLS
Cosmological Constraints: consistent with CDM
But current data has no leverage on the dynamics, i.e. w. Analyses assume constant w.
Astier et al. 2006 Spergel et al. 2006
2020
Looking Back 10 Billion YearsLooking Back 10 Billion Years
To see the most distant supernovae, we must observe from space.
A Hubble Deep Field has scanned 1/25 millionth of the sky.
This is like meeting 12 people and trying to understand the complexity of the entire US!
STScI
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Looking Back 10 Billion YearsLooking Back 10 Billion Years
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
STScI
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Dark Energy – The Next GenerationDark Energy – The Next Generation
SNAP: Supernova/Acceleration Probe
Dedicated dark energy probe
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Design a Space MissionDesign a Space Mission
colorful
wide
GOODS
HDF
~104 Hubble Deep Field [SN]
plus ~106 HDF [WL]
deepdeep• Redshifts z=0-1.7 • Exploring the last . 10 billion years • 70% of the age of . the universe
Both optical and near infrared wavelengths to see thru dust.
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New TechnologyNew Technology
Half billion pixel array
36 optical CCDs
36 near infrared detectors
New technology LBNL CCDs
Guider
Spectrographport
Visible
NIR
Focus starprojectors
Calibration projectors
JWST Field of View
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Astrophysical UncertaintiesAstrophysical Uncertainties
Systematic Control
Host-galaxy dust extinction
Wavelength-dependent absorption identified with high S/N multi-band photometry.
Supernova evolution Supernova subclassified with high S/N light curves and peak-brightness spectrum.
Flux calibration error Program to construct a set of 1% error flux standard stars.
Malmquist bias Supernova discovered early with high S/N multi-band photometry.
K-correction Construction of a library of supernova spectra.
Gravitational lensing Measure the average flux for a large number of supernovae in each redshift bin.
Non-Type Ia contamination
Classification of each event with a peak-brightness spectrum.
For accurate and precision cosmology, need to identify and control systematic uncertainties.
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Beyond GaussianBeyond Gaussian
Gravitational lensing:
Few hi z SN poor PDF sampling
Flux vs. magnitude bias
Holz & Linder 2004
Extinction bias:
One sided prior biases results
Dust correction crucial; need NIR
Linder & Miquel 2004
No extinction (perfect) Extinction correction
W With AV bias With AV+RV bias
Current data quality
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Controlling SystematicsControlling Systematics
Same SN, Different z Cosmology Same z, Different SN Systematics Control
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Baryon Acoustic OscillationsBaryon Acoustic Oscillations
The same primordial imprints in the photon field show up in matter density fluctuations.
Baryon acoustic oscillations = patterned distribution of galaxies on very large scales (~150 Mpc).
In the beginning... (well, 10-350,000 years after)
It was hot. Normal matter was p+,e- – charged – interacting fervently with photons.
This tightly coupled them, photon mfp << ct, and so they acted like a fluid.
Density perturbations in one would cause perturbations in the other, but gravity was offset by pressure, so they couldn’t grow - merely oscillated.
On the largest scales, set by the sound horizon, the perturbations were preserved.
(CMB)
Galaxy cluster
size
M. White
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- Standard ruler: we know the sound horizon by measuring the CMB; we measure the “wiggle” scale distance
- Like CMB is simple, linear physics – but require large, deep, galaxy redshift surveys (millions of galaxies, thousand(s) of deg2)
- Possibly WFMOS spectral or SNAP photometric survey
- Complementary with SN if dark energy dynamic
Baryon Acoustic OscillationsBaryon Acoustic Oscillations
But...
Observations give nonlinear, galaxy power spectrum in redshift space
Theory predicts linear, matter power spectrum in real space
(Plus selection effects of galaxy markers)
Large scale power: mode coupling Bias
Small scale power: velocity distortions
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SN
factory
SNLS
Baryon Osc.
SNAP
HST
Cluster
SN
Perlmutter
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Growth History of StructureGrowth History of Structure
While dark energy itself does not cluster much, it affects the growth of matter structure.
Fractional density contrast = m/m evolves as
+ 2H = 4Gm
Sourced by gravitational instability of density contrast, suppressed by Hubble drag.
Matter domination case:
~ a-3 ~ t-2, H ~ (2/3t). Try ~ tn.
Characteristic equation n(n-1)+(4/3)n-(3/2)(4/9)=0. Growing mode n=+2/3, i.e.
~ a
.. .
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Gravitational PotentialGravitational Potential
Poisson equation
2(a)=4Ga2 m= 4Gm(0) g(a)
Growth rate of density fluctuations g(a) = (m/m)/a
In matter dominated (hence decelerating) universe, m/m ~ a so g=const and =const.
By measuring the breakdown of matter domination we see the influence of dark energy.
• Direct count of growth - number of clusters vs. z [tough]
• Decay of potentials thru CMB ISW effect [cosmic variance]
• Effect of potentials on light rays - gravitational lensing
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Gravitational LensingGravitational Lensing
Gravity bends light… - we can detect dark matter through its gravity, - objects are magnified and distorted, - we can view “CAT scans” of growth of structure
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Gravitational LensingGravitational Lensing
“Galaxy wallpaper” Lensing by (dark) matter along the line of sight
N. Kaiser
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Gravitational LensingGravitational Lensing
Lensing measures the mass of clusters of galaxies.
By looking at lensing of sources at different distances (times), we measure the growth of mass.
Clusters grow by swallowing more and more galaxies, more mass.
Acceleration - stretching space - shuts off growth, by keeping galaxies apart.
So by measuring the growth history, lensing can detect the level of acceleration, the amount of dark energy.
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Cluster Cluster AbundancesAbundances
Optical: light mass Xray: hot gas gravitational potential mass
Sunyaev-Zel’dovich: hot e- scatter CMB mass
Weak Lensing: gravity distorts images of background galaxies
TraditionalDifficult for z>1Detects light, not massMass of what?
Clean detectionsDifficult for z>1Need optical survey for redshiftDetects flux, not massOnly cluster centerAssumes simple: ~ne
2
Clean detectionsIndepedent of redshiftNeed optical survey for redshiftDetects flux, not massAssumes ~simple: ~neTe
Detect mass directlyCan go to z>1Line of sight contaminationEfficiency reduced
Clusters -- largest bound objects. DE + astrophysics. Uncertainty in mass of 0.1 dex gives wconst~0.1 [M. White], w~?
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Cosmic ToolkitCosmic Toolkit
The Founder: Supernovae Ia distance-redshift The Players on the Field: SN Ia, Weak Lensing
The main challenge will be control of systematics -- clean astrophysics to learn new physics
Geometric Methods – “lightbulb”: a standard; don’t care how filament works (test it) SN Ia, SN II, Weak Lensing[CCC], Baryon Oscillations
Geometry+Mass – “flashlight”: need to know about lens and battery [nonlinear mass distribution] Weak Lensing[structure], Strong Lensing
Geometry+Mass+Gas – “torch”: need to know about the wood, flame, wind [hydrodynamics] SZ Effect, Cluster Counts