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Does dark matter really exist?

Does dark matter really exist?. Benoit Famaey Oxford University 11.03.2005, FNRS contact group. DM in clusters DM in galaxies CDM cosmology Milky Way model MOND MOND in the MW Tully-Fisher relation. HSB & LSB galaxies Giant elliptical galaxies Baryonic DM in clusters?

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Does dark matter really exist?

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  1. Does dark matter really exist? Benoit Famaey Oxford University 11.03.2005, FNRS contact group

  2. DM in clusters DM in galaxies CDM cosmology Milky Way model MOND MOND in the MW Tully-Fisher relation HSB & LSB galaxies Giant elliptical galaxies Baryonic DM in clusters? No-DM cosmology and lensing Theoretical physics Conclusions Outline

  3. DM in galaxy clusters • 1933 : Zwicky, Coma cluster K+U/2 = 0 with K ≈ 3M<v2r>/2 and U ≈ -GM2/(2 Mpc) M/Mvis ≈ 20 • Gravitational lensing: i ≈ [4GMcluster/c2 (dcluster-1 - dsource-1)]1/2

  4. DM in individual galaxies Vc(R) ≈ (GM(R)/R)1/2 Vc≈ cst  M(R)  R  (R)  R-2  dark halo NGC 3198

  5. DM distribution from CDM cosmology • Supernovae data  accelerating Universe + WMAP  « concordance » CDM model Flat Universe  = 1 matter = 0.3 and  = 0.7 • Primordial nucleosynthesis  baryons ≈ 0.04  DM non-baryonic + cold (CDM) i.e. massive particles such as neutralino ~ 1 TeV to grow hierarchical structure

  6. High resolution simulations of clustering CDM halos (e.g. Diemand et al. 2004) Central cusp   r- with  > 1 • Milky Way model (Klypin et al. 2002)

  7. Milky Way model from gas dynamics • HI 21-cm (l,v) diagrams • Circular orbit at radius R: Vr = [Vc(R)/R - Vc(R0)/R0] R0 sin l • Enveloppe: terminal velocity curve Vr = sign(l) Vc(R0sin l) - Vc(R0) sin l

  8. Bissantz et al. (2003) : potential from COBE near-IR luminosity density including bar and spiral structure in disk with spatially constant M/L • Fit M/L and Ω in potentials of bar and of spiral to gas dynamics • Provides good fit to microlensing

  9. No DM Milky Way provides good fits to gas dynamics and microlensing within 5 kpc • But Vc(R0) = 185 km/s instead of 220 km/s  DM halo  = 1/2 V∞2 ln(r2 + rc2) Negligible contribution inside 5 kpc NOT cuspy if mass inside 5 kpc shifted from baryons to DM, non-circular motions in (l,v) vanish (even shallow halo smoothes bumps)

  10. MOND Milgrom (1983) : Works for a0 = 1.2 X 10-8 cm s-2 ≈ cH0/2π ≈c(/3)1/2

  11. Bekenstein-Milgrom equations

  12. MOND in the Milky Way Inside 5 kpc a>a0  MOND = Newton Fhalo = Vc2/r (1+rc2/r2)-1 If FMOND = Vc2 /r and (x) = x/(1+x) Then FMOND - FNewton= Vc2/r (1+Vc2/ra0)-1 At R0, Fhalo/(FMOND - Fnewton) = 0.95 (Famaey & Binney 2005)

  13. Deep MOND regime – when (x)~x At large r always enter deep MOND Tully-Fisher relation

  14. HSB & LSB galaxies HSB: LSB:   (Sanders & McGaugh 2002)

  15. Giant elliptical galaxies • Radial velocities of Planetary Nebulae (Romanowsky et al. 2003) up to very large radii in NGC 821, NGC 3379 and NGC 4494 • Quasi-Keplerian fall !! • Quasi no-DM, but merger of disks !! • Very high accelerations, very small discrepancy in MOND (Milgrom & Sanders 2003)

  16. Baryonic DM in clusters of galaxies? MOND predicts that baryonic matter has to be found in the cores (ok sincevisible<baryons)

  17. Needs relativistic theory of MOND Early Universe not in MOND regime if a0=cst Results for CMB of McGaugh (1999) confirmed by WMAP (McGaugh 2004) Gravitational lensing: GR implies strong correlation between visible and DM distributions in lenses  Kochanek (2002) argued in favour of modified gravity No-DM cosmology and lensing

  18. Conformal gravity(Mannheim & Kazanas 1989, Edery et al. 2003) Ftot = F + 0c2/2 No dark energy Not exactly MOND Less deflection for null geodesics Nonsymmetric gravity(Moffat 2004) g = g() + g[] Non-abelian effects of quantum gravity inspired from QCD (Deur 2003) Relational gravity(Roscoe 2004) Theory that does not accept empty space-time as a solution Effect of the vacuum(Milgrom 1999) in -Universe,  has an effect on inertia at accelerations ~ c 1/2 (~a0) TeVeS(Bekenstein 2004) g’= e-2(g+UU) -e2UU Theoretical physics

  19. Conclusions • OR GR is THE correct theory of gravitation • THEN dark matter must exist BUT strong coupling with visible matter (Tully-Fisher, bumpy rotation curves, lack of DM in giant ellipticals, lensing…)  detecting a neutralino end of the mystery !

  20. OR amazing observational successes of MOND are the peak of an iceberg, i.e. the correct gravitational theory • Must make proper dynamical models of galaxies within MOND (simulate spiral structure) + CMB, large-scale structure predictions, gravitational waves astrophysics with relativistic theories such as TeVeS • See if we can also eliminate the “dark energy”AND… understand the link with the rest of physics (quantum gravity?)

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