does dark matter really exist?

Does dark matter Does dark matter really exist?really exist?

Benoit FamaeyBenoit Famaey

Oxford UniversityOxford University

11.03.2005, FNRS contact group11.03.2005, FNRS contact group

OutlineOutline

I.I. DM in clustersDM in clusters

II.II. DM in galaxiesDM in galaxies

III.III. CDM cosmologyCDM cosmology

IV.IV. Milky Way modelMilky Way model

V.V. MONDMOND

VI.VI. MOND in the MWMOND in the MW

VII.VII. Tully-Fisher relationTully-Fisher relation

VIII.VIII. HSB & LSB galaxiesHSB & LSB galaxies

IX.IX. Giant elliptical Giant elliptical galaxiesgalaxies

X.X. Baryonic DM in Baryonic DM in clusters?clusters?

XI.XI. No-DM cosmology and No-DM cosmology and lensinglensing

XII.XII. Theoretical physicsTheoretical physics

XIII.XIII. ConclusionsConclusions

DM in galaxy clustersDM in galaxy clusters

1933 : Zwicky, Coma cluster1933 : Zwicky, Coma clusterK+U/2 = 0K+U/2 = 0with K ≈ 3M<vwith K ≈ 3M<v22

rr>/2>/2 and U ≈ -GM and U ≈ -GM22/(2 Mpc)/(2 Mpc) M/MM/Mvisvis ≈ 20 ≈ 20

Gravitational lensing: Gravitational lensing: i ≈ [4GM i ≈ [4GMclustercluster/c/c22 (d (dclustercluster

-1-1 - d - dsourcesource-1-1)])]1/21/2

DM in individual galaxiesDM in individual galaxies

VVcc(R) ≈ (GM(R)/R)(R) ≈ (GM(R)/R)1/21/2

VVcc ≈ cst ≈ cst M(R) M(R) R R (R) (R) R R-2-2

dark halo dark halo

NGC 3198NGC 3198

DM distribution from DM distribution from CDM cosmologyCDM cosmology

Supernovae data Supernovae data accelerating Universe accelerating Universe + WMAP + WMAP « concordance » « concordance » CDM modelCDM modelFlat Universe Flat Universe = 1 = 1

mattermatter = 0.3 and = 0.3 and = 0.7 = 0.7

Primordial nucleosynthesisPrimordial nucleosynthesis baryons baryons ≈ 0.04 ≈ 0.04 DM non-baryonic DM non-baryonic + cold (CDM) i.e. massive particles such as + cold (CDM) i.e. massive particles such as neutralino ~ 1 TeV to grow hierarchical neutralino ~ 1 TeV to grow hierarchical structure structure

High resolution simulations of High resolution simulations of clustering CDM halos clustering CDM halos (e.g. Diemand et al. (e.g. Diemand et al. 2004)2004)

Central cusp Central cusp r r--

with with > 1 > 1 Milky Way model Milky Way model (Klypin et al. 2002)(Klypin et al. 2002)

Milky Way model from gas dynamicsMilky Way model from gas dynamics

HI 21-cm (l,v) diagramsHI 21-cm (l,v) diagrams

Circular orbit at radius R:Circular orbit at radius R:

VVrr = [V = [Vcc(R)/R - V(R)/R - Vcc(R(R00)/R)/R00] R] R0 0 sin lsin l

Enveloppe: terminal velocity curveEnveloppe: terminal velocity curve

VVrr = sign(l) V = sign(l) Vcc(R(R00sin l) - Vsin l) - Vcc(R(R00) sin l) sin l

Bissantz et al. (2003)Bissantz et al. (2003) : potential from : potential from COBE near-IR luminosity density including COBE near-IR luminosity density including bar and spiral structure in disk with bar and spiral structure in disk with spatially constant M/Lspatially constant M/L

Fit M/L and Ω in potentials of bar and of Fit M/L and Ω in potentials of bar and of spiral to gas dynamicsspiral to gas dynamics

Provides good fit to microlensingProvides good fit to microlensing

No DMNo DM Milky Way provides good fits to gas Milky Way provides good fits to gas dynamics and microlensing within 5 kpcdynamics and microlensing within 5 kpc

But VBut Vcc(R(R00) = 185 km/s instead of 220 km/s) = 185 km/s instead of 220 km/s

DM haloDM halo

= 1/2 V= 1/2 V∞∞22 ln(r ln(r22 + r + rcc

22))

Negligible contribution inside 5 kpcNegligible contribution inside 5 kpc

NOTNOT cuspy if cuspy if mass inside 5 kpc shifted from baryons to mass inside 5 kpc shifted from baryons to DM, non-circular motions in (l,v) vanish DM, non-circular motions in (l,v) vanish (even shallow halo smoothes bumps)(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

Bekenstein-Milgrom equations

MOND in the Milky Way

Inside 5 kpc a>a0 MOND = Newton

Fhalo = Vc2/r (1+rc

2/r2)-1

If FMOND = Vc2 /r and

(x) = x/(1+x) Then FMOND - FNewton= Vc

2/r (1+Vc2/ra0)-1

At R0, Fhalo/(FMOND - Fnewton) = 0.95

(Famaey & Binney 2005)

Tully-Fisher relation

• Deep MOND regime – when (x)~x

• At large r always enter deep MOND

HSB & LSB galaxies

(Sanders & McGaugh 2002)

LSB:

HSB:

Giant elliptical galaxiesGiant elliptical galaxies

Radial velocities of Planetary Nebulae Radial velocities of Planetary Nebulae (Romanowsky et al. 2003) (Romanowsky et al. 2003) up to very large radii up to very large radii in NGC 821, NGC 3379 and NGC 4494in NGC 821, NGC 3379 and NGC 4494

Quasi-Keplerian fall !! Quasi-Keplerian fall !! Quasi no-DM, but merger of disks !!Quasi no-DM, but merger of disks !! Very high accelerations, very small Very high accelerations, very small

discrepancy in MOND discrepancy in MOND (Milgrom & Sanders (Milgrom & Sanders 2003)2003)

Baryonic DM in clusters Baryonic DM in clusters of galaxies?of galaxies?

MOND predicts that baryonic matter has to be found in the cores

(ok since visiblevisible<< baryons)baryons)

No-DM cosmology and No-DM cosmology and lensinglensing

Needs relativistic Needs relativistic theory of MONDtheory of MOND

Early Universe not in Early Universe not in MOND regime if MOND regime if aa00=cst =cst

Results for CMB of Results for CMB of McGaugh (1999)McGaugh (1999) confirmed by WMAP confirmed by WMAP (McGaugh 2004)(McGaugh 2004)

Gravitational lensing: Gravitational lensing: GR implies strong GR implies strong correlation between correlation between visible and DM visible and DM distributions in lenses distributions in lenses

Kochanek (2002)Kochanek (2002) argued in favour of argued in favour of modified gravitymodified gravity

Theoretical physicsTheoretical physics Conformal gravityConformal gravity

(Mannheim & Kazanas 1989, (Mannheim & Kazanas 1989, Edery et al. 2003)Edery et al. 2003)

FFtot tot = F + = F + 00cc22/2/2No dark energyNo dark energyNot exactly MONDNot exactly MOND

Less deflection for null Less deflection for null geodesicsgeodesics

Nonsymmetric gravityNonsymmetric gravity (Moffat 2004)(Moffat 2004)

gg = g = g(()) + g + g[[]] Non-abelian effectsNon-abelian effects of of

quantum gravity inspired quantum gravity inspired from QCD from QCD (Deur 2003)(Deur 2003)

Relational gravityRelational gravity (Roscoe 2004)(Roscoe 2004)

Theory that does not Theory that does not accept empty space-accept empty space-time as a solutiontime as a solution

Effect of the vacuumEffect of the vacuum (Milgrom 1999)(Milgrom 1999)

in in -Universe, -Universe, has an has an effect on inertia at effect on inertia at accelerations ~ c accelerations ~ c 1/2 1/2

(~a(~a00)) TeVeSTeVeS (Bekenstein 2004)(Bekenstein 2004)

g’g’= e= e-2-2(g(g+U+UUU))-e-e22UUUU

ConclusionsConclusions

OROR GR is THE correct theory of gravitation GR is THE correct theory of gravitation

THEN dark matter must exist THEN dark matter must exist BUT strong coupling with visible matter BUT strong coupling with visible matter (Tully-Fisher, bumpy rotation curves, (Tully-Fisher, bumpy rotation curves, lack of DM in giant ellipticals, lensing…)lack of DM in giant ellipticals, lensing…)

detecting a neutralino detecting a neutralino end of the mystery ! end of the mystery !

OROR amazing observational successes of amazing observational successes of MOND are the peak of an iceberg, i.e. the MOND are the peak of an iceberg, i.e. the correct gravitational theorycorrect gravitational theory

Must make proper dynamical models of Must make proper dynamical models of galaxies within MOND (simulate spiral galaxies within MOND (simulate spiral structure) structure) + CMB, large-scale structure predictions, + CMB, large-scale structure predictions, gravitational waves astrophysics with gravitational waves astrophysics with relativistic theories such as TeVeSrelativistic theories such as TeVeS

See if we can also eliminate the “dark See if we can also eliminate the “dark energy” AND… energy” AND… understand the link with the rest of physics understand the link with the rest of physics (quantum gravity?)(quantum gravity?)