The Current State of Observational Cosmology JPO: Cochin(05/01/04)

The Current State of Observational Cosmology

JPO: Cochin(05/01/04)

Rumours of Great Progress…

• We know the component pieces: Photons, Neutrinos, Baryons, Dark Matter & Dark Energy.

• We know the history: Inflation, Baryogenesis, Dark Matter Domination, Growth of Structure, Dark Energy Domination.

• We know the parameters: “Precision Cosmology”.

The Truth is More Complex…

• We Know Some of the Components, But There Are Huge Gaps in Our Knowledge!

• We Understand Some of the Phases, But Calculate Others Incorrectly, and for Others there Are Equally Valid, Non-Standard, Alternatives!

• We Know Some Parameters to Percents, Others to Factors of Two and Others Are Uncertain to Order of Magnitude!

Foundation and Pillars..

• Homogeneous, Isotropic, Big Bang.– large scale uniformity (1930s -> present)– Hubble law (1930s -> present)– light element nucleosynthesis (1960s -> present)– temporal evolution observed directly (1960s -> present)– black body radiation field (1980s, COBE -> present)

• Baryons, Photons, Neutrinos, DM & DE.– Lyman alpha clouds, CBR spectrum (1960s -> present)– dark matter in clusters and halos (1930s, 1970s -> present)– supernovae show acceleration (2000s -> present)

Pillars contd…

• Nearly Scale Invariant (n~1) Spectrum.– dimensional analysis (Harrison, Peebles & Zeldovich)

(1960s)

– inflationary (or ekpyorotic) theory(1980s -> present)

– Fourier analysis of large scale structure(2000s)

• Geometrical Flatness (total = 1).

– Simplicity and dimensional analysis (1960s)

– CBR spectrum, direct measurement of parts (2000s)

Each piece is supported by multiple arguments and measurements. Edifice is robust!

Foundation: General Relativity

The Universe is an Initial Value Problem…..

• Globally, the universe evolves according to the Friedman equation:

338

2

22 Λ+±=⎟

⎠⎞

⎜⎝⎛=

akG

aaH critmρπ&

Hubble constantdensity parameter

cosmologicalconstant

H2H2

In Dimensionless Form

Λ++= km1

Pillars

Intellectual Paradigm: An Iterative Process

• Pure Theory (or assumption).

• Detailed and Massive Computation of Outcomes.

• Global Astronomical Surveys to Check Predictions.

Primary Illustrative Examples

1. CBR Fluctuations (z ~1000, COBE & WMAP).

2. Lyman Alpha Clouds ( 6 > z > 3).

3. Galaxy Formation History ( 3 > z > 0).

4. Galaxy Surveys (z ~ 0).

Initial Conditions

COBE:1991

Best Fit Concordance Model (Steinhardt, 2002)

WMAP (2002-2003)

WMAP CBR SKY

WMAP Spectrum

But…

• Degeneracy in parameter estimation remains (so other measures are essential for accurate parameter estimation).

• Low multi-poles are too low (a real issue or statistical fluctuations?).

• E-E correlations not yet available (needed to confirm re-ionization result).

CBR Parameter Degeneracy

Bridle, Lahav, Ostriker and Steinhardt: 2003

Computing the Universe

• Transformation to comoving coordinates x=r/a(t)

• comoving cube, periodic boundary conditions

• Lbox >>nl

Lbox

Physics Input

• Newton’s law of gravitation.

• Standard equations of hydrodynamics.

• Atomic physics (for heating and cooling).

• Radiative transfer.

• [ Maxwell’s equations in MHD form ].

• ------------------------------------------------

• Heuristic treatment of star-formation.

Multiscale Challenge

dynamic range requirement:> 105 spatial> 1010 mass

QSO Line Absorption from IGM

• TVDPM on Large Eulerian grids.

• Moderate over-density gas.

• Metals, ionization state computed.

• Line numbers and

profiles computed.

Hot gas filaments in the intergalactic mediumCen & Ostriker .

Testing Cosmological Models:Lyman Alpha Forest

5<z<2Lbox~10 Mpc

Intergalactic filaments at z=3Zhang, Meiksin, Anninos & Norman (1998)

Simulated Spectrum

Lyman Alpha Clouds

• Number of absorption lines vs redshift.

• Number of absorption lines vs column density.

• Velocity width distribution of lines.

• Spatial correlation of line strengths.

• --------------------------------------------

• All show good agreement:theory vs observation.

Direct Observations of Galaxy Formation History

Nagamine, Fukugita

Cen and Ostriker

(2001)

Star Formation Cosmic History

Springel and Hernquist

(2002)

Star Formation Cosmic History

Large Scale Structure Surveys (1990s)

• Gaussian random field ρ(x)

• Linear power spectrum P(k)

Las Campanas Redshift SurveyCOBE

APOSDSS

2000s

Sloan Digital Sky Survey: 2003200,000 galaxies

Cmbgg OmOlCMB

Cmbgg OmOlCMB

+

LSS

Inflation

Cmbgg OmOlCMB

Testing inflation

Cmbgg OmOlCMB

+

LSS

Testing inflation

What’s theMatter?

Cmbgg OmOlCMB

How much dark matter is there?

Cmbgg OmOlCMB

+

LSS

How much dark matter is there?

Cmbgg OmOl

How clumpy is the Universe?

Cmbgg OmOlCMB


Cmbgg OmOlCMB

+

LSS


Neutrinos

Cmbgg OmOlCMB

Cmbgg OmOlCMB

+

LSS

Where we are now….

2004

In Detail: Best Current Cosmological Model (prior: ΛCDM)

• tot = 1 (assumption)• cdm = 0.260 ± 0.037• baryon = 0.0486 ± 0.00019• lambda = 0.691 ± 0.036• n = 0.966 ± 0.023• H0 = 68.3 ± km/s/Mpc• 8 = 0.894 ± 0.057• scat =0.103 ± 0.054

Tegmark et al: astro-ph

A Joker In The Deck ???

(is the CDM paradigm wrong at small scales ? )

•Too many small galaxies predicted?

•Central galaxy densities predicted too large?

•Too many satellite galaxies predicted?

•Too many galaxies in voids predicted?

•Too late ionization predicted?

Will the Problems Give Clues To The Nature Of The Dark Matter ?

• Standard: Weakly Interacting Cold Dark Matter.• Variant: Strongly Self-Interacting Dark Matter.• Variant: Warm Dark Matter.• Variant: Decaying Dark Matter.• Variant: Repulsive Dark Matter.• Variant: Massive Black Holes as dark matter• Etc, etc,…

Warm Dark Matter

20 megaparsec boxes at redshift z = 1 (0.35 keV particle)

Warm Dark Matter (Closeup)

Standard Cold Dark Matter, 1.0 Megaparsec Warm Dark Matter (1.5keV), 1.0 Megaparsec

Summary

• Overall, concordance LCDM model succeeds very well.• CBR provides most precise tests; but other methods

essential to remove degeneracy.• Significant uncertainty of some parameters remains.• Some discrepancies on large scales (lensing) and on small

scales (cusps, satellites) are perhaps significant.• Much straightforward “engineering” to be done.• And yet we do not know the nature of either the dark

matter or the dark energy!

Questions for the Particle Physicists

• If inflation is agreed on, please converge on a model and please predict: n-1.

• Please tell us if we should expect primordial black holes to exist and, if so, how will they grow with time.

• Please tell us if Λor Q is better motivated by fundamental physics.

• Any consensus views on Warm, Self-Interacting, Fuzzy, Repulsive etc dark matter?

The Current State of Observational Cosmology JPO: Cochin(05/01/04)

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