The dark matter in galaxy. Françoise Combes

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1 The dark matter in galaxy formation Françoise Combes

2 Large-scale structures in the local Universe Nearby clusters and super-clusters 2

3 Super-cluster, defined by velocities Contains the super-cluster of Virgo, Hydra-Centaurus, Pavo-Indus Structure in way of dilution (160Mpc, M ) Shapley Coma Perseus-Pisces Tully et al

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5 Gott et al (03) Conformal map Logarithmic Scale Great wall SDSS 1370 Mpc 80% larger than The great wall CfA2 5

Large galaxy surveys CfA-2 18 000 galaxy spectra (1985-95) SSRS2, APM.

6 Large galaxy surveys CfA galaxy spectra ( ) SSRS2, APM.. SDSS: Sloan Digital Sky Survey: 1 million galaxy spectra images of 100 millions objects, Quasars 1/4 of the surface of the sky (2.5m telescope) Apache Point Observatory (APO), Sunspot, New Mexico, USA SEGUE (stars )SDSS-IV in 2014 deeper, APOGEE (Milky Way), eboss Baryonic Oscillations, MANGA (nearby galaxies), 2dF GRS: Galaxy Redshift Surveys: galaxy spectra AAT-4m, Australia et UK (400 spectra per pose) 6

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8 2dF Galaxy Redshift Survey galaxies, Colless et al (2003) 8

9 Comparaison with CfA2 & SDSS (Gott 2003) 9

10 Principles of Formation A problem not yet completely solved A few fundamental ideas: Gravitationnal instabilities, Jeans limiting size and mass In an Universe in expansion, structures are not collapsing exponentially, but grow only linearly Velocity in the comoving frame v u du/dt +(u grad)u = -grad -1/ grad p; d /dt + div u =0 = 4 G same equations with instead of Primordial density fluctuations / << 1 definition / = 10

11 Free-fall time t ff = (G 1 ) -1/2 Expansion time-scale t exp = (G < >) -1/2 The structures grow as the characteristic radius of the Universe ~ R(t) ~ (1 + z) -1 For the baryons, which cannot collapse and grow before recombination at z ~1000 The growth factor would only be of 10 3, insufficient, since fluctuations at this Epoch are at the level of 10-5 Last scattering surface (COBE, WMAP, Planck) T/T ~ 10-5 at large scale 11

12 Expansion of the Universe & redshift 12

13 The sky is uniform at =3mm Once the constant level is subtracted dipole (V= 600km/s) at 10-3 After subtraction of the dipole, The Milky Way, emissions i of thermal dust, synchrotron, etc.. Subtraction of the Milky Way Random fluctuations T/T ~

14 Universe homogeneous and isotropic until recombination and growth of structures Last scattering surface at t= yrs Anisotropies measured In the cosmological background 14

15 The cosmic spheres To observe far, is equivalent to look back in time Size of the horizon today 46 billion light-years The light path has been 13.8 billion years One looks back up to ~13 billion years 15

16 The various epochs Horizon, Big Bang CMB, Cosmic micro-wave background Dark Age Formation of first galaxies Formation of massive galaxies Formation of Earth Milky Way 16

17 5% Dark matter 25% Dark energy 70% Planck results (after COBE & WMAP) m = 0.27 = b =0.05 Ho = 68km/s/Mpc Age = 13.8 Gyr Flat Universe 17

18 A single perturbation Creation of a depression Sound wave at c / 3 Sound horizon at recombination R~150Mpc BAO: Galaxies in over-densities Baryonic acoustic oscillations 18

19 Multiple Perturbations Superposition of Several single waves Signal reduced because of random phases Daniel Eisenstein 19

20 Only the non-baryonic dark matter, which particules do not interact directly with photons, only through h gravity can begin to collapse and grow before recombination, just after matter-radiationradiation equivalence The dark matter can thus grow in density before the baryons, at all scale after equality, but only the perturbations larger than the horizon before equality (free streaming) z > z eq Radiation z < z eq Matter > ct ~(1 + z) -2 ~(1 + z) -1 < ct ~ cste ~(1 + z) -1 20

21 ~ R -3 matter ~ R -4 photons Equivalence point E Radiation Matter IONISED NEUTRAL 10 4 z 10 3 Time 21

22 Growth of adiabatic fluctuations ti at scales of Mo (8 Mpc) They grow until they contain the horizon mass They keep constant t (calibration t=0, arrow) The matter fluctuations ( ) "standard model" follow the radiation, and grow only after the Recombination R The CDM fluctuations grow from the point E equivalence matter -radiation 22

23 Power spectrum Theory of inflation: The spectrum is assumed scale independent, and the power law is such that the perturbations always enter the horizon with an equal amplitude / ~ M/M = A M -a a = 2/3, or (k) 2 = P(k) = k n with n~1 P(k) () ~k at large scale but P(k) tilted k -3 at small scale (Peebles 82) Comes from the free streaming effect below the horizon 23

24 Inflation: Horizon and flatness problems Coincidence: why m + = 1 The curvature of Universe increases very fast with time, a fine tuning would be needed (10-25 ) at t =0? Horizon: on: regions not linked by causality, outside the horizon on at the epoch of recombination (t= ans) have the same flux Size of horizon at this epoch ~1 degree, seen today Horizon =1: unstable equilibrium 24

25 Inflation: the solution Curvature: ( 1) grows as a(t) An inflation of e 60 = is required Horizon: All the sky map of the CMB comes from the same horizon 25

26 Mechanism of inflation Scalar field (inflaton?), with false vacuum, metastable, in =0 Rolls towards the true vacuum in 0. Releases a lot of energy Compensated by the negative gravitational energy a(t) ~exp(ht) exponential expansion, during sec dv( /dt ~0, slow roll Creation of WIMPZILLA? (M ~10 13 GeV, non-thermal) Energy of the quantum vacuum: Same mechanism for the acceleration of the expansion today? Dark energy Inflation stops at 0 26

27 Quantic fluctuations From the Heisenberg uncertainty principle, the field is always uncertin The time of the stop at sec also t= d (d /dt) The curvature of the Universe also, this implies more fluctuations of density and temperature gravitationnalg waves 27

28 Experience BICEP-2 at South Pole (telescope at right). At left the South Pole Telescope (SPT) Both operate at the mm-submm wavelengths March 2014: Announce of BICEP-2

29 Leah Tiscione The gravitational waves generate polarisation in the CMB by deforming space, and thus the primordial plasma (p, e-) (A)Before the wave. (B) an electron sees the deformations, universe is hotter along the compression C. The unpolarised wave is scattered by the e- (hot or cold) and become polarised The sum (F) is n longer symmetric. The hot (+ energetic) wins (G)

30 Geometry of E-modes and B-modes: Very different symmetries Rot E = 0 div B = 0 The gravitationnal waves can create both, and E-modes can then be scattered in B-modes But primordial B-modes are the signature of primordial waves The E-modes are created by electron scattering before the recombination ( yrs) but well after inflation

31 Stacking ~ cold spots (left) and hot spots (right) in Planck The effect is only of 0.8 microkelvin. These E-modes could give through scattering some B-modes To be distinguished from primordial B-modes, generated by inflation ESA / Planck Collaboration

32 Part of it could be due to dust polarisation

Apparition of fluctuations Quantum Mechanics (MQ):

causally connected regions ae found suddenly

(mode) quantic ~a~exp(ht) Horizon =c/h ~cste Frozen

33 Apparition of fluctuations Quantum Mechanics (MQ): virtual particles in the vacuum During inflation,, causally connected regions ae found suddenly disconnected: particles cannot annihilate Wavelength (mode) quantic ~a~exp(ht) Horizon =c/h ~cste Frozen waves > horizon Creation of gravit waves (tensor mode ) Temperature ~1/H Kinney

34 Modification of P(k) Fluctuations in temperature P rad k n Matter P mat k n During the first moments of the Universe, P(k) is modified For CDM: all scales grow in parallel during the matter dominated epoch But the pressure plays a role in the radiation dominated epoch Scales thatt enter the horizon at this epoch grow more slowly l Scales < horizon penalised by k -4 Scales > horizon continue to grow This modification of small scale produces the «tilt» 34

35 Imprint of oscillations The turning point scale: size of the horizon at the epoch of equivalence matter-radiationradiation yrs after the Big Bang Oscillations of baryons wavelength x2 Eisenstein et al

36 Baryonic acoustic peak Waves detected today In the baryons distribution galaxies SDSS Eisenstein et al

37 The measure of the baryonic oscillations serves as a ruler for the evolution of expansion of fthe Universe Measure of billions of galaxies With their redshifts Computation of The power spectrum 37

38 Baryonic oscillations: standard ruler Alcock & Paczynski (1979) Test of the cosmological constant Observer c z/h D Can test the bias b Galaxies/dark matter Eisenstein et al. (2005) galaxies SDSS c z/h = D Possibility to determine H(z) 38

39 Hierarchical formation In the model best fitting the observations today CDM (cold dark matter), the first structures to form are the smallest ones, then by merger they form the largest (bottom-up) k 2 =P(k) ~ k n, with n=0.91 at large scales k -3 at small scales tilt when ρ r ~ ρ m at the horizon scale M/M ~M -1/2 -n/6 when n > -3, formation hierarchical ( M/M ) Abel & Haiman 00 39

40 Density fluctuations Tegmark et al

41 Hierarchical galaxy formation The smallest structures form first, with sizes of dwarf galaxies or globular clusters By successive merger & accretion more and more massive systems form They are less and less dense M R 2 et 1/R 41

42 Fractal structures in the Universe Galaxies are not distributed homogeneously but follow a hierarchy The galaxies gather in groups, then in clusters of galaxies themselves included in superclusters (Charlier 1908, 1922, Shapley 1934, Abell 1958). In 1970, de Vaucouleurs shows an universal law Density sizee - with = 1.7 Benoît Mandelbrot in 1975: «fractal» concept Applies to the Universe Density around an occupied point ( r ) r - Slope = -1, corresponding to D = 2 M ( r ) ~ r 2 42

43 Numerical simulations With initial luctuations assumed gaussian, the non-linear regime is followed Mainly for gas and baryons (CDM easily taken into account by semi-analytic models à la Press-Schechter) 43

44 44

45 Gas CDM dark matter Simulations i (Kauffmann et al) Galaxies 45

46 Since the Big- Bang The observations look back in time z=1000 z=10 Big-Bang Recombination yr Dark Age 1 st stars, QSO yr up to 95% of the age of the Universe until our horizon Cosmic dawn End of dark age z=6 End of reionisation 10 9 yr Evolution of Galaxies z=0.5 z=0 Solar system yr 46 Today yr

47 Reionisation Progressive percolation of ionised regions 47

48 Too many small scale structures Today, CDM simulations predict 100 times too many small halos around galaxies like the Milky Way 48

10 5-10 6 K Nicastro et al 05, Danforth et al 06

49 WHIM Where are the baryons? 6% in galaxies; 3% in galaxy clusters (gas X) ~20% Lyman-alpha forest with cosmic filaments Shull et al 05, Lehner et al % in the «Warm-Hot» WHIM K Nicastro et al 05, Danforth et al 06 ICM ~60% not yet identified! The majority of baryons are not in galaxies DM 49

50 Dark matter in galaxy clusters In clusters, the hot gas dominates the visible mass The majority of baryons have become visible! f b = b / m ~ 0.15 The radial distribution of dark matter/visible is reversed The mass becomes more and more visible with radius (David et al 95, Ettori & Fabian 99, Sadat & Blanchard 01) The fraction of baryons varies from 60 to 90% f b according to clusters (Gonzalez et al 2013, Dvorkin et al 2014) 50

$Distribution ib ti of the fraction of hot$ versus M 500 (Gonzalez et al 2013) Stars

51 Distribution ib ti of the fraction of hot gas f gas, stars f *, and baryons f bary versus M 500 (Gonzalez et al 2013) Stars are included in ICL (intra-cluster light, ~10%) 51

52 Luminosity of run away stars Could be comparable to stars in galaxies? CIBER: balloon to detect the infrared radiation background CIB Zemcov et al

53 Models versus observations Semi-analytic models Difficulty to reproduce observations Baugh 2006, Eke et al 2006 Dvorkin et al

54 Cold gas accretion in galaxies Conventional scenario: shock heating at the virial temperature (10 6 K for a galaxy of MW type) Simulations with more resolution show 2 accretion modes The cold gas flows along filaments, the cold gas fraction is larger for small halos (M CDM < M o ) Temperature Keres et al 2005 Density Density 54

55 Cold accretion in filaments Temperature Density of cold gas Quenching of the star formation Origin of the bimodality? Dekel & Birnboim (2006) 55

56 Feedback: Starburst or AGN Di Matteo et al

57 Conclusion: DM & formation of galaxies The expansion limits the action of gravity, structures collapse slowly Necessity of dark matter, with ihno interaction i with ihphotons Formation of dark galaxies At recombination, z~1000, T~3000K, atoms infall into dark galaxies to form stars Density fluctuations: created naturally by the inflation Hierarchical formation of structures (index of the power law) Prediction of a large numer of small halos, not observed Feedback processes due to the formation of supernovae or AGN and cold gas accretion 57

Cosmology II: The thermal history of the Universe

.. Cosmology II: The thermal history of the Universe Ruth Durrer Département de Physique Théorique et CAP Université de Genève Suisse August 6, 2014 Ruth Durrer (Université de Genève) Cosmology II August