200 likes | 328 Views
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?
E N D
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? No-DM cosmology and lensing Theoretical physics Conclusions Outline
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
DM in individual galaxies Vc(R) ≈ (GM(R)/R)1/2 Vc≈ cst M(R) R (R) R-2 dark halo NGC 3198
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
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)
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
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
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)
MOND Milgrom (1983) : Works for a0 = 1.2 X 10-8 cm s-2 ≈ cH0/2π ≈c(/3)1/2
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)
Deep MOND regime – when (x)~x At large r always enter deep MOND Tully-Fisher relation
HSB & LSB galaxies HSB: LSB: (Sanders & McGaugh 2002)
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)
Baryonic DM in clusters of galaxies? MOND predicts that baryonic matter has to be found in the cores (ok sincevisible<baryons)
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
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+UU) -e2UU Theoretical physics
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 !
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?)