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The Darkness of the Universe: Mapping Expansion and Growth

The Darkness of the Universe: Mapping Expansion and Growth. Eric Linder Lawrence Berkeley National Laboratory. Discovery! Acceleration. Exploring Dark Energy. First Principles of Cosmology E.V. Linder (Addison-Wesley 1997). Fundamental Physics.

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The Darkness of the Universe: Mapping Expansion and Growth

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  1. The Darkness of the Universe: Mapping Expansion and Growth Eric Linder Lawrence Berkeley National Laboratory

  2. Discovery! Acceleration

  3. Exploring Dark Energy First Principles of Cosmology E.V. Linder (Addison-Wesley 1997)

  4. Fundamental Physics Astrophysics  Cosmology  Field Theory a(t)  Equation of state w(z)  V() V ( ( a(t) ) ) SN CMB LSS The subtle slowing and growth of scales with time – a(t) – map out the cosmic history like tree rings map out the Earth’s climate history. STScI Map the expansion history of the universe

  5. Standard Candles Brightness tells us distance away (lookback time) Redshift measured tells us expansion factor (average distance between galaxies)

  6. Type Ia Supernovae • Exploding star, briefly as bright as an entire galaxy • Characterized by no Hydrogen, but with Silicon • Gains mass from companion until undergoes thermonuclear runaway • Standard explosion from nuclear physics Insensitive to initial conditions: “Stellar amnesia” Höflich, Gerardy, Linder, & Marion2003

  7. Standardized Candle Brightness tells us distance away (lookback time t) Brightness Time after explosion Redshift tells us the expansion factor a

  8. Standardized Candle Color vs. Magnitude -- “HR” diagram CMAGIC • New method: • Physics based • Less dispersion (4% in distance?) • Less sensitive to systematics from dust extinction Wang et al. 2003, ApJ 590, 944

  9. What makes SN measurement special?Control of systematic uncertainties Each supernova is “sending” us a rich stream of information about itself. Images Nature of Dark Energy Redshift & SN Properties Spectra data analysis physics

  10. Hubble Diagram ~2000 SNe Ia 10 billion years 0.6 1.0 0.4 0.8 0.2 redshift z  brightness (expansion)

  11. Supernova Properties Astrophysics Understanding Supernovae Nearby Supernova Factory G. Aldering (LBL) Cleanly understood astrophysics leads to cosmology

  12. Looking Back 10 Billion Years STScI

  13. Looking Back 10 Billion Years STScI

  14. Looking Back 10 Billion Years STScI To see the most distant supernovae, we must observe from space. A Hubble Deep Field has scanned 1/25 millionth of the sky. This is like meeting 10 people and trying to understand the complexity of the entire population of the US!

  15. Dark Energy – The Next Generation Dedicated dark energy probe SNAP: Supernova/Acceleration Probe

  16. Design a Space Mission HDF GOODS wide 9000 the Hubble Deep Field plus 1/2 Million  HDF • Redshifts z=0-1.7 • Exploring the last 10 billion years • 70% of the age of the universe deep colorful Both optical and infrared wavelengths to see thru dust.

  17. Controlling Systematics Same SN, Different z  Cosmology Same z, Different SN  Systematics Control

  18. Our Tools Expansion rate of the universe a(t) ds2 = dt2+a2(t)[dr2/(1-kr2)+r2d2] Einstein equation (å/a)2 = H2 = (8/3) m + H2(z) = (8/3) m + C exp{dlna [1+w(z)]} Growth rate of density fluctuationsg(z)= (m/m)/a Poisson equation2(a)=4Ga2 m= 4Gm(0) g(a)

  19. Cosmic Background Radiation WMAP/ NASA Snapshot of universe at 380,000 years old, when 1/1100 size now Hot and cold spots simultaneously the smallest and largest objects in the universe: single quantum fluctuations in early universe, spanning the universe at the time of decoupling. Planck satellite (2007)

  20. Complementarity =wa/2 Time variation Present value of “negativity” Supernovae tightly constrain dark energy models… And play well with others. SN+CMB have excellent complementarity, equal to a prior (M)0.01. Frieman, Huterer, Linder, & Turner 2003 SN+CMB can detect time variation w´ at 99% cl (e.g. SUGRA).

  21. Deceleration and Acceleration CMB power spectrum measures n-1 and inflation. Nonzero ISW measures breakdown of matter domination: at early times (radiation) and late times (dark energy). Large scales (low l) not precisely measurable due to cosmic variance. So look for better way to probe decay of gravitational potentials.

  22. Gravitational Lensing Gravity bends light… - we can detect dark matter through its gravity, - objects are magnified and distorted, - we can view “CAT scans” of growth of structure

  23. Gravitational Lensing N. Kaiser Lensing by (dark) matter along the line of sight “Galaxy wallpaper”

  24. Gravitational Lensing Lensing measures the mass of clusters of galaxies. By looking at lensing of sources at different distances (times), we measure the growth of mass. Clusters grow by swallowing more and more galaxies, more mass. Acceleration - stretching space - shuts off growth, by keeping galaxies apart. So by measuring the growth history, lensing can detect the level of acceleration, the amount of dark energy.

  25. Weak Lensing - Shear statistics only! systematics Error in shear estimation Less area, more source density, deeper sources, e.g. Space More area, less source density, shallower sources, e.g Ground  Large scales Small scales Unique suitability of space for weak lensing:◊ Control of systematics -- Small, stable, isotropic PSF; accurate photo-z◊Deep survey, area just grows with time, access to nonlinear mass spectrum (high l) adapted from C. Vale

  26. Weak Lensing - Cosmography Jain and Taylor 2003, Bernstein and Jain 2004, Zheng, Hui, & Stebbins 2004, Hu and Jain 2004 • Identify foreground structures, cross-correlate with background slices at various redshifts. • Removes some systematics: • - Uncorrected PSF shapes average to zero when cross-correlated with foreground • - Non-linear power spectrum form irrelevant so information from all scales is useful • But requires very accurate photometric redshifts

  27. √ Supernovae + Weak Lensing Bernstein, Huterer, Linder, & Takada • Comprehensive: no external priors required! • Independent test of flatness to 1-2% • Complementary: w0 to 5%, w to 0.11 (with systematics) • Flexible: if systematics allow, can cover 10000 deg2

  28. Linear Structure: Baryon Oscillations Eisenstein 2002 Matter Power Spectrum The same primordial imprints in the photon field show up in matter density fluctuations. Galaxy cluster size Hubble horizon today Since the photons and baryons are tightly coupled until z<1100, there are baryon “acoustic oscillations”, submerged amid dark matter.

  29. Structure Growth: Linear Baryon oscillations: -Standard ruler: we know the sound horizon by measuring the CMB; we measure the “wiggle” scale  geometric distance - Just like CMB – simple, linear physics -But, only works while mass perturbations linear, so need to look on very large scales, at z=1-2 - Require large, deep, accurate galaxy redshift surveys (millions of galaxies, thousand(s) of square degrees) - Possibly KAOS+SNAP or SNAP H survey -Complementary with SNif dark energy dynamic

  30. Exploring the Unknown When you have a mystery ailment,you want a diagnosis with blood tests, EKG, MRI,... Complementary probes give crosschecks, synergy, reduced influence of systematics, robust answers. Space observatory gives multiwavelength and high redshift measurements, high resolution and lower systematics. This gives us the ability to test the framework. Next:The Darkness of the Universe 4:The Heart of Darkness

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