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LCDM: Successes and Challenges

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LCDM: Successes and Challenges LCDM: Successes and Challenges Avishai Dekel Center for Astrophysics and Planetary Science The Hebrew University of Jerusalem Beyond WIMPs: From Theory to Detection June 2015 Astronomers have been measuring Dark Matter since 1933 (Zwicky – missing mass) Novikov Dark-Matter Halos in Galaxies dark halo flat rotation curve v v R R GM (R) V 2 = 3,000 light years RR → M(R) ∝ R 30,0000 ly Dark Matter or modified gravity? DM in Galaxy Clusters: Gravitational Lensing HST Large-Scale Cosmic Flows - POTENT Great Attractor Dekel & Bertschinger 1990 Dark-Matter Density us Large-Scale3D dark-matter Mass densityDistribution Great Attractor Perseus Pisces Great Void Most Mass is Non-baryonic Dark Matter Planck+ 2015: Total Mass Ω m=0.308 ± 0.012 Baryons Ω b=0.0478 ± 0.0004 Formation of Structure History Early Universe Cosmic Microwave Background Dark Ages Galaxy Formation time Gravitational instability small-amplitude fluctuations: ρ gravitatinal instability: galaxy cluster ρ void 0 The Initial Fluctuations At Inflation: Gaussian, adiabatic r r r δ (x) = δ r e ki ⋅x Fourier transform: ∑r k k ~ r Power Spectrum: P(k) ≡ <|δ (k |) 2 > ∝ k n kmax 2 2/1 3 −(n+ 6/)3 rms perturbation: δ rms = < δ > ∝ ∫ Pk d k ∝ M k=0 Correlation function: r r r ~ r r r ξ (r) ≡ < δ (x)δ (x + r ) > ∝ ∫|δ (k |) 2 e− ki ⋅r d 3k ∝ r −(n+ )3 dP = 1[ +ξ(r)] n dV CDM Power Spectrum of linear fluctuations horizon M H ∝ t δ H Scale-invariance: δ mass H same δ at horizon δ H δ growth when matter is self-gravitating ρrad ρmass kmax teq t0 time < δ 2 > 2/1 ∝ P d 3k ∫ k 3/2 3/2 − 3/2 k =0 δ ∝ (t / tH ) ∝ t M CDM +1 δ Pk k M − 3/2 k −3 HDM HDM CDM free streeming ∝ Ω Meq mass kpeak m h k Formation of Large-Scale Structure Linear fluctuation growth δ <<1 → δ ∝ a ∝ t 3/2 n + 3 rms fluctuation at mass scale M P ∝ k n → δ ∝ M −α 0 < α = ≤ 3/2 k 6 −α /1 α Typical objects forming at a: 1 ~ δ ∝ M a → M * ∝ a CDM: bottom-up HDM: top-down 2 2/1 2 2/1 δρ δρ ρ ρ 1 1 free CDM streaming HDM 0 0 M M DM Particle Mass 4 4 HDM: relativistic till z eq ~10 , T~10 K -> m ~ ev, 15 MH~10 M (clusters-superclusters) 9 WDM: M H~10 M (small galaxies) -> m ~ kev 6 CDM: M H~10 M (dwarf galaxies) -> m ~ Gev Micro -Macro Connection Cold Dark Matter Hot Dark Matter (ν) The Cosmic Web in LCDM SDSS Galaxy Redshift Survey Cosmic Microwave Background Planck 2015: CMB Temperature Map δT/T~10 -5 arcmin ΛCDM matches in detail the CMB TT fluctuations It allows accurate parameter determination curvature Planck 2015 initial fluctuations dark matter baryons Polarization by scattering off electrons; re-ionization by stars & quasars at z~10 Planck 2015 Success of the LCDM Power Spectum Success of the LCDM Power Spectum Standard ΛCDM Model Parameters 2015: Planck (+BAO+SN) Total density Ω m+λ = 1.000 ± 0.005 Dark energy density . ΩΛ = 0.692 ± 0.012 Mass density . Ωm = 0.308 ± 0.012 Baryon density .. Ωb = 0.0478 ± 0.0004 -1 -1 Hubble constant H 0=67.8 ± 0.9 km s Mpc Age of universe t 0=13.80 ± 0.02 Gyr Fluctuation spectral index n s=0.968 ± 0.006 Fluctuation amplitude σ8=0.830 ± 0.015 Optical depth τ =0.066 ± 0.016 Beyond the Standard ΛCDM Model 2015: Planck (+BAO+SN) Total density Ω tot = 1-Ωk = 1.000 ± 0.005 Equation of state w = -1.006 ± 0.045 Tensor/scaler fluctuations r < 0.11 (95 % CL) Running of spectral index dn/dlnk = -0.03 ± 0.02 Neutrino mass ∑ m ν < 0.23 eV (95% CL) # of light neutrino families N eff =3.15 ± 0.23 Dark-Matter Halos The Cosmic Web of Dark Matter dark-matter halo the millenium cosmological simulation N-body simulation of Halo Formation Spherical Collapse ρ max ≈ 5.5 ρ universe ρ radius vir ≈ 200 perturbation ρ virial equilibrium time 1 GM GM virial equilibrium: E = − = − 2 Rvir Rmax Halo Virial Scaling Relations 2 GM v Virial equilibrium: Vv = Rv M v −3 Spherical collapse: 3 = 200 ρu = 200 ρu0 a 4( π )3/ Rv 3 2/3 3 −3 M v∝Vv a ∝ Rv a 4 To get the observed Tully-Fisher Relation: L~Vdisk need only small adjustments Galaxy Formation A Recent Paradigm Shift Disks: rotating, gas and young stars, blue Spheroids: pressure-support, old stars, red Hubble Deep Fields: Time Evolution Peak of galaxy formation at z~2-4 (t=1-3 Gyr) Standard Picture: Spherical Collapse Rees & Ostriker 77, Silk 77, White & Rees 78, Fall & Efstathiou 80 … Proto-halo expansion, turnaround, collapse to a virialized DM halo – at overdensity ~ 200 AM by tidal torques prior to maximum expansion Spin λ~(J/M)/RV~0.04 independent of mass and time Spherical gas infall into the halo 6 Virial shock heating to T v~10 K Radiative cooling, cylindrical accretion to disk AM is conserved. Halo AM determines disk size and structure: R disk ~ λ Rhalo Bulge by mergers & disk instability Standard Paradigm: Mergers radiative cooling cold hot spheroid merger disk accretion dark-matter halos cold gas - disk - starburst, spheroid - old stars Stellar+AGN feedback leads to red-and-dead Ellipticals TidalA Galaxy interaction Merger & Merger Mergers: Simulations versus Observations Cosmic-web Streams AMR RAMSES (including mergers) Teyssier, Dekel feed galaxies box 300 kpc res 30 pc z = 5.0 to 2.5 Streams Feeding a High-z Galaxy Tweed, Dekel, Teyssier RAMSES Res. 50 pc 100 kpc An Extended Tilted Ring about the Disk gas density Danovich, Dekel+ 15 30 kpc stream lines expressway entrance Clumpy Disk Ceverino, Dekel et al. 10 kpc z=4-2.1 Stream-Fed Galaxies at High z external stimulation by mergers, cold streams counter-rotation, tidal compression wet compaction to “blue” nugget and black hole thick disk hot halo quenching bulge VDI outflows SFR spheroid clumpy disk late disk hot halo The main mode of galaxy formation Challenges to LCDM The Tully-Fisher Relation From Halo Virial Relations to Observed TF 3 2/3 4 M v∝Vv a L∝Vdisk Massive galaxies no outflows M ∝ M L ∝ M ∗ v ∗ 4 − 5.0 L ∝ Vdisk rotation curve shape Vdisk /Vv ∝Vv Low -mass galaxies 2 strong outflows M ∗ / M v ∝Vv -0.2 4 low-mass gals are blue L/ M∗ ∝ M∗ L ∝Vdisk Vdisk ≈Vv Challenge: reproduce simultaneously the slope, zero-point, scatter, and the luminosity function TF Relation: Simulations vs Observations V4 EAGLE simulations Schaye+ 2015 TF Relation: Simulations vs Observations Observations 5 McGaugh & Stark M*~V NIHAO Simulations Wang, Dutton+ 2015 Steeper when V is measured at a larger r because V(r) is declining for massive galaxies TF Relation: Simulations vs Observations Observations McGaugh & Stark NIHAO Simulations Wang, Dutton+ 2015 5 M*~V The TF slope depends on which V is used Reyes+ 2011 M~V 3.5 M~V 4.2 The Challenge in the TF Relation Need to reproduce simultaneously the - slope ~3-5 - zero-point - small scatter ±0.2 dex and - the galaxy luminosity function Given the DM virial relations, the key for the adjustments is the systematic variations of V disk /V vir and M */M vir (or M bar /M vir ) These variations depend on halo properties, gas inflow, SFR, and especially on feedback! Adiabatic contraction of DM must be avoided – otherwise V disk gets too high (zero-point). Feedback! The small scatter is because galaxies evolve along the relation: more gas -> higher SFR -> larger M * -> higher V Mass Function: Galaxies vs DM Halos Halos (Press-Schechter) Scale of non-linear fluctuations faint-end quenching 2 2/1 MPS (a) by δ (MPS ,a) =δcollapse ≈ 7.1 M-2 halos M (a) A power-law power spectrum PS n Pk ∝ k α = (3+ n) / 6≈1/ 6 M-1 M ≈10 13 M a /1 α galaxies PS Θ log n(M) exp(-M1/3) ~ ~ e-M n(M ) ∝ M −2+α exp( − 5.0 M 2α ) ~ M ≡ M / M PS bright-end quenching 6 8 10 12 14 log M Evolution of Star-Formation Rate Density 11.5 Peak in M halo ~10 M early, small-mass late, high-mass quenching quenching Quenching of Star Formation in Massive Galaxies Virial Shock Heating Dekel & Birnboim 2006 11.8 critical halo mass ~~10 Mʘ −1 −1 Kravtsov+ tcool <tcompress slow cooling -> shock in hi -z massive hot halos cold streams penetrate fast cooling –> no shock Cold Streams in Big Galaxies at High z 10 14 all hot cold filaments Mvir 10 12 in hot medium Mshock ~M * [M ʘ] Mshock >>M * Mshock all cold 10 10 M* Dekel & 0 1 2 3 4 5 Birnboim 06 redshift z Shock Heating Triggers AGN Feedback M>M shock More than enough energy is available in AGNs Hot gas is vulnerable to AGN feedback, while cold streams are shielded →Shock heating is the trigger for AGN feedback in massive halos Kravtsov et al. Merger: Galaxies with a Central Black Hole Strong Feedback on Small and Large Scales photo-ionization cold hot AGN + hot 1 medium UV on dust SN dynamical friction feedback feedback in groups 0 10 9 10 10 10 11 10 12 10 13 10 14 Mvir [M ʘ] Small Scale Issues - Missing dwarfs / Too big to fail - Cusp -core Missing Dwarfs in a Milky-Way Halo simulation V>30 km s -1: ~10 subhalos, 2 dwarfs V>10 km s -1: ~10 5 subhalos, ~20 dwarfs Milky -Way Dwarfs Low-mass Galaxies are of Low Surface Brightness DM dominated: Low M star /M DM DDO154 simulations observations Low-Surface-Brightness & Dwarf Galaxies The dark-halo cusp/core problem −α −3+α r 0 r 0 ρ(r) = ρ s 1+ rs rs simulated cusp α≥ 1 log ρ observed core α=0 α=3 rs log r Observed Cores vs.
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