Gdansk Jul 02 2005

THE DARK MATTER PROBLEM

Konrad Kuijken

Leiden Observatory

Gdansk Jul 02 2005

Overview

• Evidence for dark matter– Cosmic Microwave Background Radiation– The Milky Way– Galaxy dynamics– Gravitational lensing

• Alternatives

• What is it?

• Prospects

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CMB

• Last scattering surface at z~1100– Inhomogeneities at 1:105

level– Power spectrum powerful

probe of cosmology

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CMB

• Early fluctuations in density– Grow gently at first– Start to oscillate when

enter horizon– Photons escape at last

scattering when H atoms form and free electrons disappear (T~3000K).

– Tnow / Tlast scatt defines redshift of CMB

QuickTime™ and aTIFF (LZW) decompressor

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QuickTime™ and aTIFF (LZW) decompressor

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Wavelength

Tim

e

horizon

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CMB

• Early fluctuations in density– Grow gently at first– Start to oscillate when

enter horizon– Photons escape at last

scattering when H atoms form and free electrons disappear (T~3000K).

Peak 2

Peak 3

Peak 1

More baryons

PotentialDensity photons + plasma

Higher overdensities (same pressure, more inertia)

x

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CMB

• Early fluctuations in density– Grow gently at first– Start to oscillate when

enter horizon– Photons escape at last

scattering when H atoms form and free electrons disappear (T~3000K).

Ho

rizo

n c

ross

ing

Las

t sc

atte

rin

g

Peak 1

Peak 2

Peak 3

Time

More baryons

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CMB

• Spectrum of fluctuations in the CMB (WMAP)– baryon/photon ratio

enhances peaks 1,3,5,…– Strong measurement of

baryon density

– Consistent with Big Bang Nucleosynthesis

(Wayne Hu)

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CMB• Constraints on dark

matter content: measurement of matter/radiation equality– Radiation: a-4

– Matter: a-3

– Crossover near z~3000 (before last scattering!)

– Changes horizon crossing times for different fluctuation wavelengths

– Moves peaks in CMB angular spectrum!

– Higher (early) peaks move more than 1st (last) peak.

• 1st peak mostly constrains curvature

Horizon crossing

Las

t sc

atte

rin

g

Peak 1

Peak 2

Peak 3

Time

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CMB

• Parameter constraints on matter content from CMB

– Universe close to flat

– Assume exactly flat strong constraint on m

– Otherwise strong degeneracy between m, (and H0)

Spergel et al. 2003

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Structure formation

• Gravitational instability causes large-scale structure– Without dark matter, get insufficient structure growth– Foam-like LSS follows out of CDM

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Structure formation

• Gravitational instability causes large-scale structure– Without dark matter, get insufficient structure growth

– Foam-like LSS follows out of CDM

– Good agreement with observations down to few-Mpc scales

• Combined constraints from CMB (initial conditions) + present-day LSS (in galaxies!) give best constraints on total (cold dark) matter density

m h2.

• Result: 23% dark matter, 4% baryons, 73% dark energy

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Galaxy dynamics

• General evidence for stronger gravitational fields around galaxies than can be explained– by plausible stellar population M/L ratios– by the shape of the light distribution

• Galaxies are not WYSIWYG – But bathed in extended mass distributions -- dark halos

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• Tricky:– Radial velocities see no solid-body rotation, need distances– Proper motions are local, require absolute frame

• HI rotation curve:

• Proper motions:– (A-B)=220km/s / 8kpc (Sgr A*)– (A-B)=216km/s / 8kpc (HIPP)

The Rotation Curve of the Milky WayThe Rotation curve is roughly flat out to 20kpc. No Keplerian fall-off.

But rotation curves in other galaxies are much better measured

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Vertical kinematics

• Unique 3-D measurements of the potential – Solar neighbourhood:

• Vertical kinematics (Oort problem) – Distribution fn.: f(z,vz)=f(Ez)=f((z)+vz

2/2)

– Read off f from velocities at low z (where =0)– Vary to reproduce density at high z

z

Vz E=const.Local disk mass consistent with stars and gas observed

(Siebert et al 2003; Kuijken & Gilmore 1989,1991)

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How much mass resides in the disk?

• Simple model: Mestel disk• Flat rotation curve• Predicts at sun

• Measurements of total mass density:

Σ( )R V GRcirc= 2 2π

185 2M pcsun

dA/dF Bienayme 2000

dA/dF Holmberg & Flynn 2001

dK Kuijken 1991, Siebert & al. 2003

gK Flynn & Fuchs 1994

Census

Σ1 1 70 5. kpc = ±

0 0 076 0 015= ±. .

0 010 0 01= ±. .

Σ = ±52 13Σ = ±49 9

0 010 0 02= ±. .

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Flattening of the Halo

• Local potential ~ E4 (disk+halo)

• Flaring of HI layer: halo axis ratio ~0.8– At large radii vertical confining gravity mostly halo

Depends strongly on adopted Galactic

constants!

(Olling & Merrifield)

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Rotation curves of spirals

• Rotation curves: ‘extra gravity’ in outskirts of galaxies

• Extra gravity: extra massExtra gravity: extra mass

halo

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PNe and dark matter around elliptical galaxies

• PN.S project (PI N. Douglas)

– Slitless spectroscopy through narrow-band 5007 filter: find emission-line objects

– Simultaneous counterdispersed images: deduce position and velocity at once.

– Programme to study nearby elliptical galaxies

• Advantage of PNe: – probe large radii (integrated light too faint for

spectroscopy)– Represent old stellar population (?)

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PN.S optical design: slitless spectroscopy through narrow-band filter

Shutter

Focal plane calibration mask

O[III] filter (tiltable = tuneable)

gratings

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undispersed field[O III] filter, slitless,dispersed 0°

[O III] filter, slitless,dispersed 180°

PN

star

positions & velocities in one go!

PNe with counter-dispersed imaging

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reconstructed field;velocity = ½ separation

[O III] filter, slitlessdispersed 0°

[O III] filter, slitless,dispersed 180°

positions & velocities in one go!

PNe with counter-dispersed imaging

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WHT+PN.S:

March 2002

3 hrs :

197 PN velocities

to 7 Reff ,

v = 20 km/s

E1 , MB = -20.0

D = 11 Mpc

PNe in NGC 3379

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isotropic constant-M/L Hernquist model

long-slit data(Statler & Smecker-Hane

1999)

29 PNe Ciardullo et al. (1993)

NGC 3379: Dispersion profile

197 PNe from PN.S197 PNe from PN.S

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NGC 821,

NGC 3379,

NGC 4494:

PN p(R)

declining with R

NGC 821,

NGC 3379,

NGC 4494,

NGC 4697:

PN p(R)

declining with R

Combined dispersion profiles

isotropic constant-M/L Hernquist model

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Interpreting the Kinematics:Orbital anisotropy

• Radial orbits• at large R, most of

the motion in plane of sky

• Low velocity dispersion cf circular speed

• Peaked velocity distributions

• Tangential orbits• at large R, much of

the motion in line of sight

• High velocity dispersion cf circular speed

• Flat velocity distributions

which?

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Velocity distribution shaperelates to orbit anisotropy

Van der Marel & Franx 1993

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NGC 3379: orbit models

PN velocities

LOSVDs shown

in radial bins:

• data• simulated from

data• model

• ~isotropic orbits

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NGC 3379: orbit models

• best fit

• permitted

• excluded

Circular velocity

profile:

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Results:• constant M/L ruled out at 1 • flat rotation curve ruled out at 6

NGC 3379: orbit models

• cumulative M/L at 5 Reff : = 6 - 9• cf. models of stellar pop M/L: = 4 - 9

(Gerhard et al. 2001, after Maraston 1998)

• at virial radius: non-baryonic fraction = 48 - 86% cf. cosmological fraction = 85 - 86%

(Spergel et al. 2003)

dark matter at large radius?

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Caution

• Orbital anisotropy hard to measure– Need 100s of velocities or accurate spectra

• Assumed spherical symmetry– What if we see a face-on disk or triaxial galaxy?

• PNe trace overall stellar population?– If colder component, density more concentrated– Underestimate mass if don’t correct density

Gdansk Jul 02 2005

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Caution

• Dekel et al. (2005) disk merger simulations – Make ‘young’ stars

during simulation– Colder, tighter

component– Trace PNe?

dark halo

stars

Enc

lose

d m

ass

r/Reff

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Caution• Orbital anisotropy hard to measure

– Need 100s of velocities or accurate spectra

• Assumed spherical symmetry– What if we see a face-on disk or triaxial galaxy?

• PNe trace overall stellar population?– If colder component, density more concentrated– Underestimate mass if don’t correct density

• Are the dynamics in equilibrium?

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Outer envelope of M87 (Weil et al. 1997)

30’ (135kpc)30’ (135kpc)

• Flattened outer envelopeFlattened outer envelope

• Asymmetric Asymmetric unrelaxed unrelaxed

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Dynamical consequences of dark matter in galaxies

• Static: – rotation curves, dispersion profiles

• Dynamics: – Disk stability (Ostriker & Peebles 1970)

– Angular momentum exchange with bars, warps (Athanassoula 2003, Kuijken&Dubinski 1995)

– Mergers:• Dynamical friction (energy loss to dark halo)

– e.g., LMC or Sgr orbit

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Gravitational lensing• No dynamical equilibrium assumptions• Direct measurement of projected mass distribution

– Cluster masses (X-ray, dynamics, lensing) agree

• Weak shear: measure shapes of halos as well as overall power spectrum of dm (not average density though)

`Lens pushes sources away’

`Radial squeezing’

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Alternative• MOND (Milgrom 1984)

– Below accelerations of ca 10-10 gravity gets stronger: ((|g/a0|)g)=4G where g= and 1 for large g

– (x) x for small x gives for weak accelerations g(GMa0/r2)1/2 1/r

– Relativistic version ‘TeVeS’ (Bekenstein 2004)

TAK!

• Rotation curve shapes and amplitudes well-explained

• Pioneer effect?• Naturally explains Tully-Fisher

NIE!

• Cosmic expansion as if there is no dark matter

• Unclear how well it does on clusters• Halo shapes?• Galaxy stability?

Excuse me?Przepraszam?

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Co to jest?

• Baryons?– Nucleosynthesis and CMB bounds– Brown dwarf, cool white dwarf counts

• Compact objects (MACHO’s)?– Microlensing experiments– LMC results (MACHO, EROS): 0-20% of dark halo can

be made up of objects with masses of planets-stars– Detailed interpretation complex because of unknown 3-

D structure of LMC.

Nie!!

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M31 microlensing

• Pixel lensing• Higher optical depth than to LMC• Compare near & far side of disk

– Very different M31 halo path lengths– Discriminate MW vs M31 halo vs M31 disk– Constrain M31 halo flattening

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MEGA project (Crotts, P.I.; de Jong, PhD thesis)

• INT monitoring, 1999-2004• Find variables in PSF-matched difference

images• 14 events• Consistent with lensing by bulge and disk

only• AGAPE team used same data,

claim ~ 20% halo fraction

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Doubts

• Let’s detect the particle!

• Has dynamical friction against a dark halo ever been seen?– Satellites (clouds), bars,

warps, polar ring formation

• Do all galaxies have dark halos?– NGC 3379

• What are the shapes of dark halos?

Prospects

• Direct detection experiments continue

• Improved constraints from CMB

• PNe as tracers of outer dynamics probe galaxy halos

• Weak lensing measurements for projected shapes and radial profiles

ZŁY DOBRY

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The KIDS survey and dark matter• VST/OmegaCAM survey

• 1700 sq deg. ugriz + YJHK• Median z ~ 0.8• Weak lensing

– Galaxy halo masses, radii, shapes– Power spectrum of large-scale mass

distribution– Evolution of angular diameter distance

• Halo objects– Faint high proper-motion stars (white,

brown dwarfs)

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• Overlaps:– UKIDSS– SDSS– 2dFGRS– CFHLS– COSMOS

• 960 sq deg.

2dFGRSSDSS DR2

CFHLS

KIDS(Leiden, Groningen, Munchen, Bonn, Paris, Naples, Imperial, Edinburgh, Cambridge)

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• Overlaps:– 2dFGRS– VISTA!

• 720 sq deg.

• Perfect for VLT and AAT, APEX, ALMA

2dFGRS

KIDS(Leiden, Groningen, Munchen, Bonn, Paris, Naples, Imperial, Edinburgh, Cambridge)

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KIDS vs. SDSS

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Weak gravitational lensing

`Lens pushes sources away’

`Radial squeezing’

80,000,000 background galaxies

200,000 foreground galaxies (z<0.2)

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Galaxy-galaxy lensing45 sq. deg from RCS survey (Hoekstra, Yee, Gladders 2004)

Galaxy-mass correlation

Halo radii

Halo shapes

KIDS:

7x smaller errors (#pairs)

Good photo-z’s (b/g), spectroscopic z’s (lenses)

Study effect by galaxy type

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‘w’ (weak lensing)

• Weak lensing constraints– Lensing effect depends on relative distances

of source and lens

– Measure lensing strength as function of redshift

– Deduce distance as function of redshift– Geometrical test of expansion history: w (5%)– Needs well-controlled photo-z’s!

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Summary • Dark matter is with us

– CMB, large-scale structure formation– Galaxy dynamics– Gravitational lensing

• It is mostly non-baryonic– CMB, nucleosynthesis arguments

• Halos do not consist of MACHO’S– Microlensing experiments to LMC and M31

• Evidence for ‘live’ dark halos would be nice– Shapes– Dynamical friction

• Laboratory detection of a DM particle would be nice!

PNe as astrophysical tool!