cosmological observations—2004 what the data tell us about dark energy and the contents of the...
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![Page 1: Cosmological Observations—2004 What the data tell us about dark energy and the contents of the universe Joe Fowler Princeton University DPF 2004, Riverside](https://reader035.vdocument.in/reader035/viewer/2022062421/56649d375503460f94a106df/html5/thumbnails/1.jpg)
Cosmological Observations—2004
What the data tell us about dark energy and the contents of the universe
Joe FowlerPrinceton University
DPF 2004, Riverside
August 28, 2004
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Current Picture of the Universe
General relativity Homogeneous & isotropic Began with hot big bang Quantum fluctuations grew during
inflation Galaxies & other structures grew
gravitationally from these tiny early fluctuations
HST Images
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Evidence for a Hot Big Bang
Released: March 2004
Hubble Ultra Deep Field
1. Hubble expansion (recession of distant objects)
2. Thermal cosmic background radiation
3. Light element abundances
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Contents of the Universe
ΛCDM Model At least 96% of the universe is mysterious!
Compenents sum to the critical density
Dark Energy( or anti-gravity)
73%
Baryonic Dark Matter
4%
Luminous Baryonic Matter0.4%
Cold Dark Matter23%
Luminous Baryonic Matter
Baryonic Dark Matter
Cold Dark Matter
Dark EnergyΛ
Note that “Λ” here may be a dynamical field a la quintessence, an Einsteinian cosmological constant, or …?
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Evolution in an FRW Universe History and fate are determined by proportion of stuff Express energy densities as Ω, i.e. scaled by the critical density Today, ρcrit = 5000 eV cm-3 = 6 protons per m3
Open
(Ω=0.
3)
Flat (m
atter
)
Closed (Ω=5)
Open
(Ω=0.
3)
Flat (m
atter
)
Closed (Ω=5)
ΛCDM
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Roles of Inflation
1. Solves the “horizon problem” (all visible universe was once in causal contact)
2. Explains the source of inhomogeneities
3. Flatness is unstable—but inflation drives towards flatness early on
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Matter, Energy and Geometry Generally only the 2 black lines are considered: flat or matter-only.
Ωmatter
ΩΛ Accelerating now
Decelerating now
ClosedFlatOpen
Matter only
Current model
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Lines of Evidence for Dark Energy
Observation Result Interpretation1. Distant supernovae ~25% too dim Expansion
accelerating
2a. CMB acoustic peak ℓ = 220 Flat universe
2b. Matter distribution Ωm ~ 25% Rules out flat, matter-only
3. CMB + LSS power (fits) All of the above
spectra
4. Integrated Sachs-Wolfe Mass at z~0.5 If flat Λ>0 (a 2 – 3σ) correlated w/ CMB
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What is the Dark Energy?
Vacuum energy opens up more possibilities than curvature.
Two key question for observations:
1. Does Λ evolve?
2. What is its equation of state w ≡ P/ρ?
Gij – Λgij = 8πG Tij Curvature of empty space
or
Gij = 8πG Tij + Λgij Vacuum energy
w < -1/3 is required if Λ is repulsive
w = -1 is a true cosmological constant
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Problems with ΩΛ=0.7
1. Why is it not 10120 ?
2. Why now?
ρ/ρcrit
log10(a)
RadiationMatter Dark
energy
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Baryon Fraction from Big Bang Nucleosynthesis
Ωb = 0.041 ± 0.004(assuming h=0.7)
Tyt
ler
et a
l, 20
00
•Light elements form in first few minutes (D, 3He, 4He, Li)
•Ratio of baryon to photon density determines proportions
•We know photons (CMB)
•Must measure primordial abundance of light elements
Burles, Nollett & Turner, 2004
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Dark Matter Distribution in the Universe
Dark matter clustering drives structure formation on scales larger than galaxies.
Must be “cold” to support the smallest scales observed.
R. Cen
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Techniques for Studying Matter Distribution
Plan: study the evolution of structure by measuring it locally
Number counts of galaxy clusters Velocity fields of galaxies Weak gravitational lensing Galaxy spatial power spectrum Cold intergalactic gas (Lyman-α forest)
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Gravitational Lensing of Background Galaxies
Hubble Space TelescopeChandra X-ray Observatory
Strong lensing shown here
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Weak Lensing
Relies on shear: preferential warping of background galaxies parallel to contours of foreground matter.
A statistical hunt for ellipticity Shape noise (galaxies have ellipticity ~ 0.3; PSF…) Shape bias: are some shapes easier to find?
Tyson et al 2002
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Large Sky Surveys
Sloan Digital Sky Survey
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Galaxy Power Spectrum
Ideally, surveys are flux-limited.
Sloan Digital Sky Survey
2 degree Field Galaxy Redshift Survey
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Galaxy Power Spectrum Systematics
Tegmark et al 2003 astro-ph/0310725
Redshift distortion (due to peculiar velocity)
Galaxy “bias”
Seljak et al 2004 astro-ph/0406594
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The Lyman-α Forest
Absorption by H atoms in bulk IGM (λ=121 nm). Test ΛCDM at unique range of z and small size.
QuasarClouds containing Neutral Hydrogen
Hubble Space Telescope
Keck HIRES
Figure: Bill Keel
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Matter Power Spectrum Many techniques covering over 4 decades of size.
Max Tegmark + SDSS
λ, not k
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Power Spectrum Results1. Completely consistent with ΛCDM model
2. Dark Energy Consistent with pure cosmological constant
3. Inflation Simplest possible scenario Primordial slope n=0.98 ± 0.02 Tensor/Scalar ratio r < 0.36 (95% CL)
4. Neutrinos Massive reduce structure on small scales 3 ~degenerate families: Σ m < 0.42 eV 3 massless + 1 (LSND): m < 0.79 eV ruling
out LSND solutions at 2σ Max Tegmark + SDSS
Seljak et al, 2004
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Cosmic Microwave Background
As universe cooled below 3000 K, became transparent. Most thermal photons last scattered then (at z=1089). CMB is the most distant light we’ll ever be able to see. Probes the initial conditions for structure formation.
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CMB Basic Facts
Thermal blackbody at T=2.725±0.003 K Emitted at T~3000 K Isotropic to ~30 x 10-6
Residuals
FIRAS spectrum
2.731
2.721
Fixsen et al 1996
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Wilkinson Microwave Anisotropy Probe
Twin telescopes facing 140o apart.
Always measuring differences of Temp.
Amplifiers kept at 90 K without refrigeration.
NASA/WMAP Team
Once the “Princeton Isotropy Experiment” = “PIE in the sky”
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WMAP Goal
Map entire mm-wave sky 5 frequencies 35 μK noise per 0.3° square
pixel 0.5% absolute calibration
Tegmark & Efstathiou
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WMAP Radiometers
Pospiezalski, NRAO
Each “differencing assembly” measures ΔT in analog.
Both signals go through all amplifiers!
Other figures: NASA/WMAP Team
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WMAP Mission Profile
Launched June 30, 2001 3 months to L2 (1,500,000 km distant) Survey for 2—5 yrs
At L2, WMAP can keep the sun, moon, and earth behind it at all times.
All figures: NASA/WMAP Team
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WMAP Sky Maps in 5 Frequencies
Lowest frequency(galactic electrons)
Highest (some dust)
+200 μK
-200 μK
All
figu
res:
NA
SA
/WM
AP
Te
am
22 GHz 30 GHz
40 GHz
60 GHz90 GHz
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WMAP CMB-Only Map
Internal linear combination map
NASA/WMAP Team
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Temperature Power Spectrum Spherical harmonic power spectrum—a radical compression of the map for
cosmological purposes.
NA
SA
/WM
AP
Te
am
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Acoustic Peaks
Peaks correspond to a well-understood physical size (145 Mpc): they are “standard rulers.”
Peak at ℓ=220 indicates no global curvature from z=0 to z=1089.
Ratio of peaks #1/#2 constrains baryon density.
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Temperature-Polarization (TE) Cross-power Cross-power spectrum
sensitive to ionization resulting from early hot stars.
Data at ℓ>20 fit the cosmology dictated by the TT power spectrum.
Only DASI has detected polarization anisotropy (EE) as of August 28, 2004.
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WMAP Interpretation
Extremely strong support for: Hot big bang model Existence of baryons, dark matter, and dark energy
(4/23/73 ratio) Gaussian primordial fluctuations + inflation
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WMAP Surprises
1. The first stars ignited much earlier than thought: 200 Myr (1.5% of current age).
2. Very low quadrupole
How can WMAP tell?• Early stars massive• Massive stars hot (UV)• UV ionizes nearby gas• Ionized atoms polarize CMB• Polarization correlates with T
NASA/WMAP Team
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WMAP Results by the numbers
1. Age of the universe: 13,700,000,000 years (± 1.5%)
2. Age when stars first shone: 200,000,000 years
3. Age at last scattering: 379,000 years (z=1089±1)
4. Expansion rate (Hubble constant): 71 km s-1 Mpc-1 (± 5%)
5. Flatness: Ωt = 1.02±0.02
6. Optical depth to last scattering τ = 0.17±0.04
7. Apparent fate of the universe: Expand forever (?)
These figures include constraints from, for example, 2dF galaxy redshift survey and Supernovae Ia.
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CMB Future: Secondary Anisotropies
Study structure as it forms
0.4 Myr ~200 Myr 1000-5000 Myr 3000—13,700 Myr
now
Primary CMB Ionization effects Grav lensing of CMB Cluster surveys
Early stars Massive clustersdistort CMB maps
Clusters “heat” the CMB (SZ Effect)
CMB seen now has passed through all these objects!
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CMB Future: Polarization from Gravity Waves
E modes B modes
Wayne Hu
Hu & Dodelson, 2002
Polarization B modes are “handed” and not produced by scalar perturbations.
A strong signature of inflation.
But at what level?...
DASI collaboration, 2002
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Matter Distribution Imprinted on CMB
The “Late-time integrated Sachs-Wolfe effect”
•CMB blue shifts entering large overdensities.
•In matter-only universe, red shift on exit cancels this out.
•In a Λ-dominated universe, expansion outweighs clustering.
•Higher T correlates with high mass density.
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Several 2 to 3σ ISW Detections
In a flat universe, any ISW implies dark energy.
Boughn & Crittenden, 2004
X-ray catalog / CMB angular correlation functionNeed a tracer of mass.
WMAP +•SDSS (red) 2.0σ•NVSS (radio) 2.2σ•HEAO-A1 (X-ray) 2.5σ
Combined analysis of last 2 yields(1.13±0.35) x Λ CDM prediction.
ISW alone rejects @ 3σ an allowed WMAP solution with no Λ and high matter content.
Xray x CMB dataΛ CDM Model
1σ, 2σ range of null MC
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Hubble’s Diagram and the Expanding Universe
Uniform expansion v=Hod But the next order is interesting! Trace the dynamics of
the expanding universe. Requires an extremely bright light standard: Supernovae
“Distance modulus”
Δm = 5 factor of 10 in luminosity distance
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Type Ia Supernovae
Type I = deficient in Hydrogen; Ia have Si+ absorption Requires “real time” data analysis Can now find SN Ia on demand and pre-schedule the
follow-up spectroscopy
SN2002hp ( ~ 2 months) HST-ACS
3 HST discoveries before / after
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Type Ia Supernovae as Standard Candles
Model is an accreting white dwarf, passing the Chandrasekhar limit Actually, a 1-parameter family in:
1. Peak brightness
2. Rate of decline
3. Color
Can reduce dispersion 3x
N.B.: evolution slows by (1+z)
1 month
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Evidence for Recent Accelerated Expansion Hubble diagram curvature
consistent with universe that’s accelerating now
Effect is only a ~25% dimming of SNe around z=0.5
Possible confounding effects: Evolution Extinction (by very
gray, homogeneous dust) No evidence for either, but we
must be very sure.
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Evidence for Earlier Deceleration 16 new SN from
HST at typical z~1 As expected from
ΛCDM, dimming trend reverses!
Strongly suggests not evolution or dust
Riess et al 2004
Jerk
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Supernovae Interpretation
SN Hubble diagram constrains (ΩΛ-1.4Ωm)
If flat universe, then Ωm=0.29±0.04
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Cosmic Concordance
The model may be crazy, but everything is consistent (so far):
Flat universe Dark energy (~70%) Still need non-baryonic DM
(and not neutrinos)
(Pre-2004)
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Probing Inflation (and is it correct?)
CMB degenerate in: n the primordial perturbation spectral index τ the optical depth through reionized universe r the ratio of scalar to tensor fluctuations (the upper limit 0.35 is
already approaching what some simple models predict)
Large scale structure surveys and E-mode CMB polarization can help break these.
Detect the B-modes of CMB polarization (next decade?) B-modes would rule out ekpyrotic (cyclic) scenarios
WMAP should soon tell us how hard this will be (foregrounds)
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Probing Dark Energy
Require more studies covering the z<2 range: Supernovae—need dedicated, wide-field, fast camera Cluster counts—need a distance-independent probe
(S-Z effect surveys coming online in 2-3 years)
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Summary
The leading ΛCDM model (dark energy + cold dark matter) is consistent with all the data!