Cosmological Observations —2004

What the data tell us about dark energy and the contents of the universe DPF 2004, Riverside August 28, 2004

Princeton

Joe Fowler

University

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 1.

2.

3.

Hubble expansion (recession of distant objects) Thermal cosmic background radiation Light element abundances

Released: March 2004

Hubble Ultra Deep Field

Contents of the Universe   ΛCDM Model At least 96% of the universe is mysterious!

Compenents sum to the critical density

Dark Energy Luminous Baryonic Matter Baryonic Dark Matter Cold Dark Matter Dark Energy 73% Luminous Baryonic Matter 0.4% Cold Dark Matter 23% Baryonic Dark Matter 4% 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, ρ crit = 5000 eV cm -3 = 6 protons per m 3 ( ( Ω=5)

1.

2.

3.

Roles of Inflation Solves the “horizon problem” (all visible universe was once in causal contact) Explains the source of inhomogeneities 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.

Ω Λ

Current model Matter only

Ω matter

Lines of Evidence for Dark Energy Observation 1. Distant supernovae Result ~25% too dim Interpretation Expansion accelerating 2a. CMB acoustic peak 2b. Matter distribution ℓ = 220 Ω m ~ 25% Flat universe Rules out flat, matter-only 3. CMB + LSS power spectra (fits) All of the above 4. Integrated Sachs-Wolfe (a 2 – 3σ) Mass at z~0.5 correlated w/ CMB If flat  Λ>0

What is the Dark Energy?

G ij – Λg ij = 8 πG T ij Curvature of empty space G ij

or

= 8 πG T ij + Λg ij Vacuum 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?

w < -1/3 is required if Λ is repulsive w = -1 is a true cosmological constant

1.

Problems with Ω Λ =0.7

Why is it not 10 120 ? Radiation Matter Dark energy 2.

Why now?

ρ/ρ crit log 10 (a)

Baryon Fraction from Big Bang Nucleosynthesis •Light elements form in first few minutes (D, 3 He, 4 He, Li) •Ratio of baryon to photon density determines proportions •We know photons (CMB) •Must measure

primordial

abundance of light elements Burles, Nollett & Turner, 2004 Ω b = 0.041 ± 0.004

(assuming h=0.7)

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 Chandra X-ray Observatory

Strong

lensing shown here Hubble Space Telescope

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.

2 degree Field Galaxy Redshift Survey Sloan Digital Sky Survey

Galaxy Power Spectrum Systematics Redshift distortion (due to peculiar velocity) Galaxy “bias” Tegmark et al 2003 astro-ph/0310725 Seljak et al 2004 astro-ph/0406594

The Lyman α Forest Clouds containing Neutral Hydrogen   Absorption by H atoms in bulk IGM ( λ=121 nm).

Test ΛCDM at unique range of z and small size.

Hubble Space Telescope Quasar Keck HIRES Figure: Bill Keel

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

Max Tegmark + SDSS λ,

not

k

1.

2.

3.

4.

Power Spectrum Results Completely consistent with ΛCDM model Dark Energy  Consistent with pure cosmological constant Inflation    Simplest possible scenario Primordial slope n=0.98 ± 0.02

Tensor/Scalar ratio r < 0.36 (95% CL) Neutrinos    Massive  reduce structure on small scales 3 ~degenerate families: Σ m  < 0.42 eV 3 massless + 1 (LSND): m  out LSND solutions at 2 σ < 0.79 eV ruling 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

2.731

FIRAS spectrum

2.721

Residuals Fixsen et al 1996

Wilkinson Microwave Anisotropy Probe    Twin telescopes facing 140 o apart.

Always measuring differences of Temp.

Amplifiers kept at 90 K without refrigeration.

Once the “Princeton Isotropy Experiment” = “PIE in the sky” NASA/WMAP Team

WMAP Goal Map entire mm-wave sky    5 frequencies 35 μK noise per 0.3° square pixel 0.5% absolute calibration Tegmark & Efstathiou

Each “differencing assembly” measures ΔT in analog.

Both signals go through all amplifiers!

WMAP Radiometers Pospiezalski, NRAO 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 +200 μK Lowest frequency (galactic electrons) 22 GHz 30 GHz 40 GHz -200 μK Highest (some dust) 90 GHz 60 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.

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).

• • • • • How can WMAP tell?

Early stars massive Massive stars hot (UV) UV ionizes nearby gas Ionized atoms polarize CMB Polarization correlates with T 2.

Very low quadrupole NASA/WMAP Team

WMAP Results by the numbers 1. Age of the universe: 2. Age when stars first shone: 3. Age at last scattering: 4. Expansion rate (Hubble constant): 5. Flatness: 6. Optical depth to last scattering 13,700,000,000 years ( ± 1.5%) 200,000,000 years 379,000 years (z=1089 ± 1) 71 km s -1 Mpc -1 ( ± 5%) Ω t = 1.02

± 0.02

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 Early stars Massive clusters distort CMB maps

CMB seen now has passed through all these objects!

Clusters “heat” the CMB (SZ Effect) Primary CMB Ionization effects Grav lensing of CMB Cluster surveys 0.4 Myr ~200 Myr 1000-5000 Myr 3000 — 13,700 Myr now

CMB Future: Polarization from Gravity Waves Polarization B modes are “handed” and

not

produced by scalar perturbations.

A strong signature of inflation.

But at what level?...

DASI collaboration, 2002 Hu & Dodelson, 2002 E modes B modes Wayne Hu

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 3 σ ISW Detections  In a flat universe, any ISW implies dark energy.

Need 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 @ 3 σ an allowed WMAP solution with no Λ and high matter content.

X-ray catalog / CMB angular correlation function Xray x CMB data

Λ

CDM Model 1 σ, 2σ range of null MC Boughn & Crittenden, 2004

Hubble’s Diagram and the Expanding Universe    Uniform expansion  v=H o d 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 3 HST discoveries before / after SN2002hp ( ~ 2 months) HST-ACS

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 Jerk Riess et al 2004

Supernovae Interpretation   SN Hubble diagram constrains ( Ω Λ -1.4

Ω m ) If flat universe, then Ω m =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!