Cosmic Microwave Cosmic Microwave Background Radiation:Background Radiation:

z=1000 - z= 10z=1000 - z= 10

David SpergelDavid Spergel

Princeton UniversityPrinceton University

Standard Cosmological ModelStandard Cosmological Model

General Relativity + Uniform Universe Big BangGeneral Relativity + Uniform Universe Big Bang Density of universe determines its fate + shapeDensity of universe determines its fate + shape

Universe is flat (total density = critical density)Universe is flat (total density = critical density) Atoms 4%Atoms 4% Dark Matter 23%Dark Matter 23% Dark Energy (cosmological constant?) 72%Dark Energy (cosmological constant?) 72%

Universe has tiny ripplesUniverse has tiny ripples Adiabatic, scale invariant, Gaussian FluctuationsAdiabatic, scale invariant, Gaussian Fluctuations Harrison-Zeldovich-PeeblesHarrison-Zeldovich-Peebles Inflationary modelsInflationary models

Quick History of the UniverseQuick History of the Universe

Universe starts out hot, Universe starts out hot, dense and filled with dense and filled with radiationradiation

As the universe expands, As the universe expands, it cools. it cools.

• During the first minutes, light During the first minutes, light elements formelements form

• After 500,000 years, atoms formAfter 500,000 years, atoms form• After 100,000,000 years, stars start After 100,000,000 years, stars start

to formto form• After 1 Billion years, galaxies and After 1 Billion years, galaxies and

quasarsquasars

Thermal History of UniverseThermal History of Universe

z

104 103

radiation

matterNEUTRAL

IONIZED

Growth of FluctuationsGrowth of Fluctuations

•Linear theory

•Basic elements have been understood for 30 years (Peebles, Sunyaev & Zeldovich)

•Numerical codes agree at better than 0.1% (Seljak et al. 2003)

Best fit model

cosmic variance

Temperature

Temperature-polarization

1 deg

85% of sky

CBI ResultsCBI Results

ACBAR, VSA also tests physics of damping tailACBAR, VSA also tests physics of damping tail Important confirmation of theoryImportant confirmation of theory Improves parameter constraintsImproves parameter constraints

Readhead et al. (2004)Readhead et al. (2004)

Astro-ph/0409569Astro-ph/0409569

Structure FormationStructure Formation

Model Predicts Universe Model Predicts Universe TodayToday

SDSS Tegmark et al.

Astro-ph/0310723

Verde et al. (2003)

Consistent ParametersConsistent Parameters

WMAP+CBI+WMAP+CBI+ACBARACBAR

All CMB(Bond)All CMB(Bond) CMB+CMB+

2dFGRS2dFGRS

CMB+SDSS CMB+SDSS (Tegmark)(Tegmark)

bbhh22 .023 .023 + .001 .0230 .0230 + .0011 .023 .023 + .001 .0232 .0232 + .0010

xxhh22 .117 .117 + .011 .117 .117 + .010 .121 .121 + .009 .122 .122 + .009

hh .73 .73 + .05 .72 .72 + .05 .73 .73 + .03 .70 .70 + .03

nnss.97 .97 + .03 .967 .967 + .029 .97 .97 + .03 .977 .977 + .03

.83 .83 + .08 .85 .85 + .06 .84.84 + .06 .92 .92 + .08

Zentner & Bullock 2003

Top Hat CollapseTop Hat Collapse

Focus on overdensityFocus on overdensity Follow evolution of Follow evolution of

isolated sphereisolated sphere ExpansionExpansion Turn-aroundTurn-around VirializationVirialization

Press-Schechter FormalismPress-Schechter Formalism

Probability of being in Probability of being in an overdense regionan overdense region

Halo Mass FunctionHalo Mass Function

Do Stars Form in the Halos?Do Stars Form in the Halos?

•Can the gas cool?

•Metals usually dominate the cooling --- but there are no metals

•Molecular hydrogen is the only significant cooling in primordial gas

•Molecular hydrogen usually forms on dust…but there is no dust

•Formation through H+

Numerical SimulationNumerical Simulation

CDM initial conditionsCDM initial conditions HydrodynamicsHydrodynamics Gas chemistryGas chemistry Radiative TransferRadiative Transfer Simulations usually Simulations usually

show the formation of show the formation of a single massive stara single massive star100 - 1000 solar masses100 - 1000 solar masses

No fragmentation seenNo fragmentation seenAbel 2003

First StarsFirst Stars

Massive stars with no primordial metalsMassive stars with no primordial metals Very hot surface--- lots of ionizing photonsVery hot surface--- lots of ionizing photons

• Destroys H2 -- suppresses star formationDestroys H2 -- suppresses star formation Short-livedShort-lived

• Supernova explosions?Supernova explosions? Shocks compress gasShocks compress gas Shocks accelerate cosmic rays-- Compton cool and Shocks accelerate cosmic rays-- Compton cool and

produce X-rays. X-rays ionize universe and produce H2produce X-rays. X-rays ionize universe and produce H2

• Gamma-ray bursts?Gamma-ray bursts?• Enrich environment with metalsEnrich environment with metals

Can We Observe the First Can We Observe the First Stars?Stars?

Direct detection of high z objectsDirect detection of high z objects GalaxiesGalaxies Gamma Ray BurstsGamma Ray Bursts QuasarQuasar

RemnantsRemnants Low z starsLow z stars Chemical ContaminationChemical Contamination

ReionizationReionization

Effects of Reionization on Effects of Reionization on CMBCMB

Temperature Power SpectrumTemperature Power Spectrum Suppression of fluctuations at l > 40Suppression of fluctuations at l > 40 Generation of new fluctuations at l > 10Generation of new fluctuations at l > 10 Generation of small scale fluctuationsGeneration of small scale fluctuations

PolarizationPolarization Generates large scale temperature Generates large scale temperature

polarization correlationpolarization correlation Generates large scale polarization-Generates large scale polarization-

polarization correlationpolarization correlation

Reionization andReionization andTemperature SpectrumTemperature Spectrum

Suppression of small Suppression of small scale fluctuationsscale fluctuations

Additional fluctuations Additional fluctuations generated on large scalesgenerated on large scales

Degenerate with Degenerate with variations in slopevariations in slope

Suppression exp(-2)

CMB PolarizationCMB Polarization

CMB polarization can CMB polarization can be split into two be split into two pieces: E and Bpieces: E and B

Scattering converts Scattering converts local temperature local temperature quadrupole into E quadrupole into E signalsignal

Generates TE and EE Generates TE and EE signalsignal

EE Polarization SignalEE Polarization Signal

Amplitude and peak Amplitude and peak position sensitive to position sensitive to reionization historyreionization history

Holder & Hu 2003

Doppler Effect ContributionDoppler Effect Contribution

•Vanishes to linear order (except at the largest scales)

•Doesn’t vanish to 2nd order (Ostriker-Vishniac effect)

•Inhomogeneous reionization leads to additional fluctuations

Why Is Polarization Difficult to Why Is Polarization Difficult to Observe?Observe?

Weak signalWeak signal signal is statistical rather than a detection in signal is statistical rather than a detection in

each pixeleach pixel ForegroundsForegrounds

Synchrotron (dominant)Synchrotron (dominant) DustDust

Systematic UncertaintiesSystematic Uncertainties

WMAP ResultsWMAP Results

Significant uncertainty in Significant uncertainty in reionization redshiftreionization redshift

Will improve with more data Will improve with more data Polarization auto-correlationPolarization auto-correlation ~0.1 in 4 year data~0.1 in 4 year data

Current Estimate of Optical Current Estimate of Optical DepthDepth

Significant uncertaintySignificant uncertainty Temperature data pushes fit towards low tauTemperature data pushes fit towards low tau Polarization data pushes fit towards high tauPolarization data pushes fit towards high tau

ACT:The Next ACT:The Next StepStep

Atacama Cosmology Atacama Cosmology TelescopeTelescope

Funded by NSFFunded by NSF Will measure CMB Will measure CMB

fluctuations on small fluctuations on small angular scalesangular scales

Probe the primordial Probe the primordial power spectrum and the power spectrum and the growth of structuregrowth of structure

ACT COLLABORATIONSACT COLLABORATIONS

SchoolsGovernment Labs Museums

…united through research, education and public outreach.

PENN

Haverford

Princeton

CUNYTorontoCatÓlica

Simulations of mm-wave data.

1.40<1%

≈2%Survey area

High quality area

150 GHz SZ Simulation MBAC on ACT 1.7’ beam2X noise

PLANCK

MAP

PLANCK

Where will we Where will we be with CMBbe with CMB

Bond et al.

astro-ph/046195

Cosmic Timeline for ACT ScienceCosmic Timeline for ACT Science

z = 1000t = 4 x 104 yrs

z = 7t = 3 x 106 yrs

z = 1t = 1 x 109 yrs

z = .25t = 12 x 109 yrs

now

• First galaxies • Universe is reionized• Ostriker-Vishniac/KSZ

• Surveys of Sunyaev-Zel’dovich (SZ) clusters• Diffuse thermal SZ

• Initial conditions for structure formation

• N(mass,z) – Evolution of Cosmic Structure• Lensing of the CMB• The growth of structure is sensitive to w and mn

• Additional cross-checks from correlations among effects

• Extraction of cosmological parameters

Primary CMB CMB Lensing OV/KSZ Diffuse Thermal SZ Cluster Surveys

Sunyaev-Zel’dovich (SZ) clustersSunyaev-Zel’dovich (SZ) clusters

e-

e-

e-

e-

e-

e-

e-

e-

e-

Coma Cluster Telectron = 108 K

Optical: Redshift and Mass

mm-Wave: SZ –Compton Scattering

X-ray Flux: Mass

SZ SignatureSZ SignatureHot electron gas imposes a unique spectral signature

NO SZ Contribution in Central Band

145 GHzdecrement

220 GHznull

270 GHzincrement

1.4°x 1.4°

Coordinated Cluster Coordinated Cluster MeasurementsMeasurements

Identify and measure >500 clusters in an

unbiased survey with multi-wavelength observations

Galaxy Cluster

HOT Electrons

• Mass limits of 3 x 1014 estimated from simulations• Science derived from N(mass,z)

CMB

-1850

(K)

0

1820

Lensing of the CMBLensing of the CMB

1.4°x 1.4°

• Lensing arises from integrated mass fluctuations along the line of sight.

• The CMB acts as a fixed distance source, removing the degeneracy inherent to other lensing measurements.

• Signal at l = 1000-3000

• Image distortion – only a minor effect in the power spectrum.

• Must have a deep, high fidelity map to detect this effect.

Lensing of the CMBLensing of the CMB-34

(K)

0

34

1.4°x 1.4°

Lensing Signal

• RMS signal well above noise floor.

• Isolate from SZ and point sources spectrally.

• Identify with distinctive 4-point function.

2% of CMB RMS

Cross-Correlating Lensing Cross-Correlating Lensing and CMBand CMB

CMB provides a source plane at z = 1100 with CMB provides a source plane at z = 1100 with very well determined statistical properties (but very well determined statistical properties (but poorer statistics)poorer statistics)

CMB + Quasar & Galaxy Counts will measure CMB + Quasar & Galaxy Counts will measure biasbias

CMB lensing+ Galaxy lensing cross-CMB lensing+ Galaxy lensing cross-correlation improves parameter correlation improves parameter measurements by roughly a factor of 3 measurements by roughly a factor of 3 (Mustapha Ishak)(Mustapha Ishak)

CMB + SN

X-correlate

Add LensingCMB + Lensing

ACT \REGION: Target for ACT \REGION: Target for future lensing surveysfuture lensing surveys

ACT will begin surveying in 2006

We already plan deep multi-band imaging with SALT of low extinction part of ACT strip (200 square degrees)

Would be a very interesting target for a lensing survey

ACT is but one of several next ACT is but one of several next generation CMB experimentsgeneration CMB experiments

APEX (Atacama APEX (Atacama Pathfinder Experiment)Pathfinder Experiment)

UCB/MPIUCB/MPI 1.4mm and 2 mm obs.1.4mm and 2 mm obs. SZ scienceSZ science

SPT (South Pole SPT (South Pole Telescope)Telescope)

8m at South Pole8m at South Pole Chicago group (2008)Chicago group (2008) Large areaLarge area

• Optimized for SZ/clustersOptimized for SZ/clusters

CMB Observations are an important CMB Observations are an important cosmological toolcosmological tool

Large angle observations have helped solidify a Large angle observations have helped solidify a “standard model of cosmology” that fits a host of “standard model of cosmology” that fits a host of astronomical observationsastronomical observations

Small angle observations use this CMB backlight to Small angle observations use this CMB backlight to probe the emergence of structureprobe the emergence of structure

First stars: OV effect, polarizationFirst stars: OV effect, polarization Cluster properties: SZ effectCluster properties: SZ effect Distribution of mass: lensingDistribution of mass: lensing