Cosmic Microwave Background Radiation: z= z= 10 David Spergel Princeton University

Standard Cosmological Model  General Relativity + Uniform Universe Big Bang Density of universe determines its fate + shape Density of universe determines its fate + shape  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 ripples Adiabatic, scale invariant, Gaussian Fluctuations Adiabatic, scale invariant, Gaussian Fluctuations Harrison-Zeldovich-Peebles Harrison-Zeldovich-Peebles Inflationary models Inflationary models

Quick History of the Universe Universe starts out hot, dense and filled with radiation Universe starts out hot, dense and filled with radiation As the universe expands, it cools. As the universe expands, it cools. During the first minutes, light elements formDuring the first minutes, light elements form After 500,000 years, atoms form After 500,000 years, atoms form After 100,000,000 years, stars start to formAfter 100,000,000 years, stars start to form After 1 Billion years, galaxies and quasarsAfter 1 Billion years, galaxies and quasars

Thermal History of Universe z radiation matter NEUTRAL IONIZED 

Growth 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 Results  ACBAR, VSA also tests physics of damping tail  Important confirmation of theory  Improves parameter constraints Readhead et al. (2004) Astro-ph/

Structure Formation

Model Predicts Universe Today SDSS Tegmark et al. Astro-ph/ Verde et al. (2003)

Consistent Parameters WMAP+CBI+ ACBAR All CMB(Bond) CMB+2dFGRS CMB+SDSS (Tegmark) bh2bh2bh2bh xh2xh2xh2xh h nsnsnsns 

Zentner & Bullock 2003

Top Hat Collapse  Focus on overdensity  Follow evolution of isolated sphere Expansion Expansion Turn-around Turn-around Virialization Virialization

Press-Schechter Formalism  Probability of being in an overdense region  Halo Mass Function

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 Simulation  CDM initial conditions  Hydrodynamics  Gas chemistry  Radiative Transfer  Simulations usually show the formation of a single massive star solar masses No fragmentation seen Abel 2003

First Stars  Massive stars with no primordial metals Very hot surface--- lots of ionizing photons Very hot surface--- lots of ionizing photons Destroys H2 -- suppresses star formationDestroys H2 -- suppresses star formation Short-lived Short-lived Supernova explosions?Supernova explosions? Shocks compress gas Shocks compress gas Shocks accelerate cosmic rays-- Compton cool and produce X-rays. X-rays ionize universe and produce H2 Shocks accelerate cosmic rays-- Compton cool and produce 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 Stars?  Direct detection of high z objects Galaxies Galaxies Gamma Ray Bursts Gamma Ray Bursts Quasar Quasar  Remnants Low z stars Low z stars Chemical Contamination Chemical Contamination  Reionization

Effects of Reionization on CMB  Temperature Power Spectrum Suppression of fluctuations at l > 40 Suppression of fluctuations at l > 40 Generation of new fluctuations at l > 10 Generation of new fluctuations at l > 10 Generation of small scale fluctuations Generation of small scale fluctuations  Polarization Generates large scale temperature polarization correlation Generates large scale temperature polarization correlation Generates large scale polarization- polarization correlation Generates large scale polarization- polarization correlation

Reionization and Temperature Spectrum  Suppression of small scale fluctuations  Additional fluctuations generated on large scales  Degenerate with variations in slope Suppression exp(-2  )

CMB Polarization  CMB polarization can be split into two pieces: E and B  Scattering converts local temperature quadrupole into E signal  Generates TE and EE signal

EE Polarization Signal  Amplitude and peak position sensitive to reionization history Holder & Hu 2003

Doppler 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 Observe?  Weak signal signal is statistical rather than a detection in each pixel  Foregrounds Synchrotron (dominant) Dust  Systematic Uncertainties

WMAP Results  Significant uncertainty in reionization redshift Will improve with more data Polarization auto-correlation  ~0.1 in 4 year data

Current Estimate of Optical Depth  Significant uncertainty Temperature data pushes fit towards low tau Temperature data pushes fit towards low tau Polarization data pushes fit towards high tau Polarization data pushes fit towards high tau

ACT:The Next Step  Atacama Cosmology Telescope  Funded by NSF  Will measure CMB fluctuations on small angular scales  Probe the primordial power spectrum and the growth of structure

ACT COLLABORATIONS Schools Government LabsMuseums …united through research, education and public outreach. PENN Haverford Princeton CUNY Toronto Cat Ó lica

Simulations of mm-wave data. Survey area High quality area 150 GHz SZ SimulationMBAC on ACT 1.7’ beam 2X noise PLANCK MAP PLANCK

Where will we be with CMB Bond et al. astro-ph/046195

Cosmic Timeline for ACT Science z = 1000 t = 4 x 10 4 yrs z = 7 t = 3 x 10 6 yrs z = 1 t = 1 x 10 9 yrs z =.25 t = 12 x 10 9 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 m n Additional cross-checks from correlations among effects Extraction of cosmological parameters Primary CMB CMB Lensing OV/KSZDiffuse Thermal SZ Cluster Surveys

Sunyaev-Zel’dovich (SZ) clusters e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- Coma ClusterT electron = 10 8 K Optical: Redshift and Mass mm-Wave: SZ – Compton Scattering X-ray Flux: Mass

SZ Signature Hot electron gas imposes a unique spectral signature NO SZ Contribution in Central Band 145 GHz decrement 220 GHz null 270 GHz increment 1.4 ° x 1.4 °

Coordinated Cluster Measurements Identify and measure >500 clusters in an unbiased survey with multi-wavelength observations Galaxy Cluster HOT Electrons Mass limits of 3 x estimated from simulations Science derived from N(mass,z)

CMB (  K) Lensing 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 = Image distortion – only a minor effect in the power spectrum. Must have a deep, high fidelity map to detect this effect.

Lensing of the CMB -34 (  K) ° 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 and CMB  CMB provides a source plane at z = 1100 with very well determined statistical properties (but poorer statistics)  CMB + Quasar & Galaxy Counts will measure bias  CMB lensing+ Galaxy lensing cross- correlation improves parameter measurements by roughly a factor of 3 (Mustapha Ishak) CMB + SN X-correlate Add Lensing CMB + Lensing

ACT \REGION: Target for future 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 generation CMB experiments  APEX (Atacama Pathfinder Experiment) UCB/MPI UCB/MPI 1.4mm and 2 mm obs. 1.4mm and 2 mm obs. SZ science SZ science  SPT (South Pole Telescope) 8m at South Pole 8m at South Pole Chicago group (2008) Chicago group (2008) Large area Large area Optimized for SZ/clustersOptimized for SZ/clusters

CMB Observations are an important cosmological tool  Large angle observations have helped solidify a “standard model of cosmology” that fits a host of astronomical observations  Small angle observations use this CMB backlight to probe the emergence of structure First stars: OV effect, polarization First stars: OV effect, polarization Cluster properties: SZ effect Cluster properties: SZ effect Distribution of mass: lensing Distribution of mass: lensing