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Galaxy Formation University of Durham Carlos Frenk Institute of Computational Cosmology University of Durham Goal: understand origin and evolution of cosmic structures • Review of standard Big Bang model • Growth of small fluctuations (linear theory) • Fluctuations in the microwave background radiation • The formation of galaxies and clusters You should be familiar with: • Basic concepts in Big Bang theory • The contents of the Universe • The expansion properties of the Universe Books: Cole & Lucchin: Cosmology • The identity of the dark matter • The nature of the dark energy • Origin of cosmic structure Peacock: Liddle: -- about the right level Galaxy Formation -- advanced Cosmology -- basic background http://star-www.dur.ac.uk/~csf/homepage/GalForm_lectures Institute for Computational Cosmology The Big Bang Theory Institute for Computational Cosmology Empirical evidence for the Big Bang University of Durham 1. The expansion of the universe of galaxies What it is: • Theory that the Universe as we know it began 10 – 15 billion years ago • Initial state was a hot, dense, uniform sea of particles that filled space uniformly and was expanding What it describes: • galaxies are receding from us with speed proportional to their distance • expansion is the same for all observers 2. The microwave background radiation • heat left over from Big Bang explosion • comes from everywhere in space (homogeneous and isotropic) • it was emitted when the universe was 300000 years old How the universe expands and cools How the light chemical elements formed How matter congealed to form stars and galaxies 3. The abundance of the light elements • BB theory predicts that 75% of mass is hydrogen, 24% is helium and 1% • These are precisely the abundances observed in distant gas clouds! What it does not describe: • • Carlos Frenk Institute of Computational Cosmology University of Durham Connection to three outstanding problems in 21st Physics: University of Durham • • • Galaxy Formation University of Durham What caused the expansion (expanding initial state assumed) Where did matter come from (energy assumed to be there from start) is the rest (nb: elements heavier than H and 4He were produced billions of years later inside stars) Institute for Computational Cosmology Institute for Computational Cosmology The content of our universe University of Durham What is the Universe made of? Institute for Computational Cosmology University of Durham What is the universe made of? density Ω = critical density ρ = ρmass + ρrel + ρvac critical density = density that makes univ. flat: • Radiation (CMB, T=2.726±0.005 K) • Massless neutrinos • Massive neutrinos • Baryons o (of which stars) • Dark matter (cold dark matter) Dark matter ≡ matter that does not emit light at any wavelength University of Durham Galaxy rotation curves (Ω = 1 for a flat univ.) Ωr = 4.7 x 10-5 Ων = 3 x 10-5 Ων = 6 x 10-2 (<mν>/ev) Ωb = 0.037 ± 0.009 Ωs = 0.0023 ± 0.0003 Ω dm ≅ 0.26 ΩΛ ≅ 0.7 • Dark energy (cosm. const. Λ) —> Ω = Ωb + Ωdm+ ΩΛ ≅ 1 (assuming Hubble parameter h=0.7) Flat Vc Institute for Computational Cosmology M(<r) ∝ r ⇒ dark halos around galaxy Institute for Computational Cosmology Mapping the dark matter University of Durham University of Durham Light rays are deflected by gravity (E=mc2) Computer simulation of galaxy halo Distant galaxy Observer 0.5 Mpc/h Galaxy clusters (Gravitational lens) Institute for Computational Cosmology Institute for Computational Cosmology Gravitational lensing University of Durham University of Durham The visible and dark sides of the universe • There is ~5 times more dark matter than there is ordinary (baryonic) matter (~90% of the mass of the Universe is dark matter) → Most of the dark matter is NOT ordinary (baryonic) matter Light from distant galaxies is deflected by dark matter in cluster, distorting the galaxies’ images into arcs Institute for Computational Cosmology → Weakly interacting massive particles (WIMPS) Institute for Computational Cosmology Non-baryonic dark matter candidates University of Durham Type hot candidate mass Looking for WIMPS University of Durham CERN neutrino a few eV warm Sterile neutrino keV-MeV cold axion neutralino Geneva 10-5eV->100 GeV Institute for Computational Cosmology Institute for Computational Cosmology The search for dark matter University of Durham University of Durham UK DM search (Boulby mine) Boulby mine Looking for dark matter … down the mine (where cosmic rays can’t penetrate) Institute for Computational Cosmology Institute for Computational Cosmology University of Durham What is the universe made of? University of Durham So, the Universe contains: UK DM search (Boulby mine) • Ordinary matter • Dark matter Boulby mine (Ωb=0.04) (Ωdm= 0.21) Anything else? Looking for dark matter … down the mine Yes! (where cosmic rays can’t penetrate) It has the opposite effect to gravity Institute for Computational Cosmology University of Durham Evidence for Λ from high-z supernovae flux .. a =- 43p G 2 3w a-3 Þ The cosmic expansion must have been accelerating since the light was emitted 1 a-4 const? 0 a If ρ = ρ vac = const , If ρvac = ρvac (z,x) and Perlmutter et al ‘98 c a 1 ρtot = ρmass + ρrel + ρvac 3w a/a0=1/(1+z) Institute for Computational Cosmology Institute for Computational Cosmology Friedmann equations University of Durham Ωm ΩΛ SN type Ia (standard candles) at z~0.5 are fainter than expected even if the Universe were empty Dark energy Dark energy is a property of space itself. d =- 3 pc da where 0 p w 2 2 expansion accelerates dρ 2 = 0 ⇒ p = − ρc ⇒ w = −1 da cosmological constant ⇒ quintessence Institute for Computational Cosmology Evolution of Cosmic Scale Factor in FRW Model University of Durham The origin of galaxies ρ= ρmass + ρrel + ρvac ∨ a ,r o ct fa le a cs ic m so c a-3 ∨ a-4 ∨ const = 0 .1 = 1 vac > 0 = 1 > 1 = 8 time Λ>0 Institute for Computational Cosmology Inflation Initially, Universe is trapped in false vacuum Universe decays to true vacuum keeping ρv~ const Universe oscillates converting energy into particles Scalar field Φ University of Durham a If k 2 kc 2 0 and 8p G 3 vac a a 2 2 const w =- 1 8p G 3 t ⇒ Inflation Friedmann equations t aµe t 1 2 3 8p ⇒ Universe expands exponentially Institute for Computational Cosmology Generation of primordial fluctuations Cosmic Inflation University of Durham University of Durham Observable universe Quantum fluctuations are blown up to macroscopic scales during inflation t=10-35 s Chaotic theory predicts: Inflation inflation 2. Flat geometry (Ω =1) √ (eternal expansion) 4. Small ripples in mass distribution Institute for Computational Cosmology Institute for Computational Cosmology University of Durham University of Durham ^ Or if pressure forces dominate inside the perturbation Institute for Computational Cosmology University of Durham Institute for Computational Cosmology University of Durham Institute for Computational Cosmology Institute for Computational Cosmology The origin of cosmic structure University of Durham QUANTUM FLUCTUATIONS: Inflation (t~10-35 s) k 2 n k n= 1 Gau ss iana mplitu des Damping (nature of dark matter) + P(k)=Akn T2(k,t) Transfer function Rh(teq) Cold dark matter Horizon crossing Mezaros damping P(k) baryons • Hot DM (eg ~30 ev neutrino) - Top-down formation • Cold DM (eg ~neutralino) n= 1 radiation Free streaming - Bottom-up (hierachical) Institute for Computational Cosmology ng Ba big the er aft ars ye 00 00 38 The microwave background radiation University of Durham The microwave background radiation T=2.73 K Plasma t=0 Institute for Computational Cosmology John Mather 2006 Nobel laureate t=380 000 yrs The microwave background radiation Dependence of ∆T/T on cosmological params University of Durham ion lat ng inf Ba big the er aft s ar ye 00 00 38 Max Tegmark Plasma T=2.73 K z=∞ z =1000 Institute for Computational Cosmology The CMB The CMB University of Durham University of Durham 1992 1992 The cosmic microwave background radiation (CMB) provides a window to the universe at t~3x105 yrs George Smoot - Nobel Prize 2006 In 1992 COBE discovered temperature fluctuations (∆T/T~10-5) consistent with inflation predictions Institute for Computational Cosmology Institute for Computational Cosmology The CMB WMAP temp anisotropies in CMB University of Durham University of Durham 1992 Amplitude of fluctuations The amplitude of the CMB ripples is exactly as predicted by inflationary cold dark matter theory 2003 The position of the first peak FLAT UNIVERSE Institute for Computational Cosmology The origin of cosmic structure University of Durham Inflation (t~10-35 s) 2 n k n= 1 Gau ss iana mplitu des 2. QUANTUM FLUCTUATIONS: CMB (t~3x105 yrs) Institute for Computational Cosmology The 2dF Galaxy Redshift Survey A collaboration between (primarily) UK and Australia 250 nights at the AAT 1. FLAT GEOMETRY: k Hinshaw etal ‘06 Structure (t~13x109yrs) Cold dark matter 221,000 redshifts to bj<19.45 median z=0.11 Institute for Computational Cosmology Survey complete and catalogue released in July/03 Sloan Digital Sky Survey ~300,000 galaxy redshifts so far, 500,000 eventually Evolution of spherical perturbations Calculating the evolution of cosmic structure University of Durham Rh(teq) Mezaros damping P(k) n= 1 University of Durham Free streaming Large scales Institute for Computational Cosmology N-body simulation Small scales Institute for Computational Cosmology University of Durham University of Durham Neutrino (hot) dark matter Ων=1 (mν = 30 ev) Non-baryonic dark matter candidates Ca ndida te Axion s Neutrinos Free-streaming length so large that superclusters form first and galaxies are too young Mass -5 10 eV 30 eV Neutralin os (SUSY) >20 Ge V Primordial black hole s >10 g 15 Cold DM Hot DM Neutrinos cannot make an appreciable contribution to Ω and mν<< 30 ev Cold DM Cold DM Zf=0.5 Zf=2.5 CfA redshift survey Frenk, White & Davis ‘83 Institute for Computational Cosmology University of Durham Cold dark matter University of Durham dalla Vechia, Jenkins & Frenk CDM Ω=0.2 In CDM structure forms hierarchically Institute for Computational Cosmology Early CDM N-body simulations gave promising results 150 Mpc/h QuickTimeª and a YUV420 codec decompressor are needed to see this picture. HDM Ω=1 CfA redshift survey Davis, Efstathiou, Frenk & White ‘85 Institute for Computational Cosmology Comoving coordinates Institute for Computational Cosmology The Millennium simulation QuickTimeª and a 3ivx D4 4.5.1 decompressor are needed to see this picture. QuickTimeª and a 3ivx D4 4.5.1 decompressor are needed to see this picture. Springel et al Nature June/05 Helly & Frenk 06 1 Mpc Dependence of ∆T/T on cosmological params real SDSS University of Durham CMB CfA 2dF survey Galaxies Springel, Frenk & White Nature, May ‘06 simulated ΛCDM Max Tegmark Institute for Computational Cosmology Cosmological parameters from WMAP+2dFGRS University of Durham University of Durham Accelerated expansion The cosmic power spectrum: from the CMB to the 2dFGRS ΛCDM provides an excellent description of mass power spectrum from 10 -1000 Mpc z=0 WMAP ΛCDM CMB: • Convert angular separation to distance (and k) assuming flat geometry 2dFGRS • Extrapolate to z=0 using linear theory SpergelInstitute etal for Computational ‘03 Cosmology Sanchez et al 06 Institute for Computational Cosmology Conclusions University of Durham Inflation (t~10-35 s) The origin of cosmic structure University of Durham 1. FLAT geometry: 2. Small (quantum) ripples CMB (t~3x105 yrs) Galaxies (t~13x109yrs) Cold dark matter Ripples seen as hot & cold spots in cosmic radiation Galaxies form • Recent measurements of fluctuations in the temperature of the microwave background confirm this paradigm. Institute for Computational Cosmology Institute for Computational Cosmology University of Durham Open questions Open questions University of Durham Tools: • What is the dark matter? • What is the dark energy? • What happened in the first 10 s after the Big Bang? • How, in detail, did stars and galaxies form? • How much farther will the simulations go? -35 • Satellites to study the CMB & distant galaxies • Large telescopes • Direct dark matter searches • Particle accelerators (CERN) • Supercomputer simulations Ideas: • Theoretical physics & mathematics Institute for Computational Cosmology Institute for Computational Cosmology University of Durham The paradigm of structure formation ΛCDM • Material content: • Initial conditions: • Growth processes: • Parameters: Cold dark matter, baryons, Λ From quantum fluctuations during inflation: |δk|2 k; Gaussian ampl. Gravitational instability; gas (cooling, star formation, etc) 0 . 26 , b 0 . 04 , h 0 . 70 , CDM 2 3 H 0 0 . 7, 8 0.9 Galaxies form hierarchically Institute for Computational Cosmology Conclusions: open questions University of Durham The future of cosmology University of Durham Open questions: ? ? Detection (or manufacture) dark matter The origin of the dark energy ? The astrophysics of galaxy formation ? ? UK DM search (Boulby mine) Institute for Computational Cosmology • Direct searches for CDM (Boulby, CDMS, G Sasso) • Constraints on w (high-z SN, lensing, high-z clustering) • Surveys of galaxies at high-z (VLT, SIRTF, ALMA, NGST) • Supercomputers simulations • New ideas on w Institute for Computational Cosmology
