Does dark matter really exist

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Does dark matter really exist?

• Benoit Famaey
• Oxford University
• 11.03.2005, FNRS contact group

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Outline

• 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

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DM in galaxy clusters

• 1933 Zwicky, Coma cluster KU/2 0 with
  K 3Mltv2rgt/2 and U -GM2/(2 Mpc)
  ?M/Mvis 20
• Gravitational lensing i
  4GMcluster/c2 (dcluster-1 - dsource-1)1/2

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DM in individual galaxies

• Vc(R) (GM(R)/R)1/2
• Vc cst ? M(R) ? R ? ?(R) ? R-2
• ? dark halo
• NGC 3198

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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

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

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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

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• 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 ? in potentials of bar and of spiral
  to gas dynamics
• Provides good fit to microlensing

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• 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 V82 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)

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MOND

• Milgrom (1983)

Works for a0 1.2 X 10-8 cm s-2 cH0/2p
c(?/3)1/2
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Bekenstein-Milgrom equations
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MOND in the Milky Way

• Inside 5 kpc agta0 ? MOND Newton
• Fhalo Vc2/r (1rc2/r2)-1
• If FMOND Vc2 /r
  and ?(x) x/(1x)
  Then FMOND - FNewton
  Vc2/r (1Vc2/ra0)-1
• At R0, Fhalo/(FMOND - Fnewton) 0.95
  (Famaey Binney 2005)

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Tully-Fisher relation

• Deep MOND regime when ?(x)x
• At large r always enter deep MOND

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HSB LSB galaxies
HSB
LSB
?
?
(Sanders McGaugh 2002)
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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)

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Baryonic DM in clusters of galaxies?
MOND predicts that baryonic matter has to be
found in the cores (ok since ?visiblelt ?baryons)
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No-DM cosmology and lensing

• Needs relativistic theory of MOND
• Early Universe not in MOND regime if a0cst
• 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

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Theoretical physics

• 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?

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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 !

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• 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?)