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

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

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

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 …?

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

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

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

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

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

Problems with ΩΛ=0.7

1. Why is it not 10120 ?

2. Why now?

ρ/ρcrit

log10(a)

RadiationMatter Dark

energy

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

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

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)

Gravitational Lensing of Background Galaxies

Hubble Space TelescopeChandra X-ray Observatory

Strong lensing shown here

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

Large Sky Surveys

Sloan Digital Sky Survey

Galaxy Power Spectrum

Ideally, surveys are flux-limited.

Sloan Digital Sky Survey

2 degree Field Galaxy Redshift Survey

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

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

Matter Power Spectrum Many techniques covering over 4 decades of size.

Max Tegmark + SDSS

λ, not k

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

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.

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

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”

WMAP Goal

Map entire mm-wave sky 5 frequencies 35 μK noise per 0.3° square

pixel 0.5% absolute calibration

Tegmark & Efstathiou

WMAP Radiometers

Pospiezalski, NRAO

Each “differencing assembly” measures ΔT in analog.

Both signals go through all amplifiers!

Other figures: NASA/WMAP Team

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

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

WMAP CMB-Only Map

Internal linear combination map

NASA/WMAP Team

Temperature Power Spectrum Spherical harmonic power spectrum—a radical compression of the map for

cosmological purposes.

NA

SA

/WM

AP

Te

am

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.

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.

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

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

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.

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!

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

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.

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

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

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

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

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.

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

Supernovae Interpretation

SN Hubble diagram constrains (ΩΛ-1.4Ωm)

If flat universe, then Ωm=0.29±0.04

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)

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)

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)

Summary

The leading ΛCDM model (dark energy + cold dark matter) is consistent with all the data!