THE DARK MATTER PROBLEM

1
THE DARK MATTER PROBLEM

• Konrad Kuijken
• Leiden Observatory

2
Overview

• Evidence for dark matter
• Cosmic Microwave Background Radiation
• The Milky Way
• Galaxy dynamics
• Gravitational lensing
• Alternatives
• What is it?
• Prospects

3
CMB

• Last scattering surface at z1100
• Inhomogeneities at 1105 level
• Power spectrum powerful probe of cosmology

4
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 (T3000K).
• Tnow / Tlast scatt defines redshift of CMB

Time ?
horizon
Wavelength ?
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CMB
More baryons
Peak 1
x?

• 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 (T3000K).

Density photons plasma
Potential
Peak 2
Peak 3
Higher overdensities (same pressure, more inertia)
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CMB
More baryons
Peak 1

• 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 (T3000K).

Time ?
Horizon crossing
Last scattering
Peak 2
Peak 3
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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 z3000 (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

Peak 1
Time ?
Horizon crossing
Last scattering
Peak 2
Peak 3
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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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The Rotation Curve of the Milky Way
The Rotation curve is roughly flat out to 20kpc.
No Keplerian fall-off. But rotation curves in
other galaxies are much better measured

• 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)

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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)vz2/2
  )
• Read off f from velocities at low z (where ?0)
• Vary ? to reproduce density at high z

Vz
Local disk mass consistent with stars and gas
observed (Siebert et al 2003 Kuijken Gilmore
1989,1991)
Econst.
z
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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

dA/dF Bienayme 2000
dA/dF Holmberg Flynn 2001
dK Kuijken 1991, Siebert al. 2003
gK Flynn Fuchs 1994
Census
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Flattening of the Halo

• Local potential E4 (diskhalo)
• Flaring of HI layer halo axis ratio 0.8
• At large radii vertical confining gravity mostly
  halo

(Olling Merrifield)
Depends strongly on adopted Galactic constants!
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Rotation curves of spirals

• Rotation curves extra gravity in outskirts of
  galaxies

• Extra gravity extra mass

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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
OIII filter (tiltable tuneable)
Focal plane calibration mask
gratings
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PNe with counter-dispersed imaging
positions velocities in one go!
PN
star
undispersed field
O III filter, slitless, dispersed 0
O III filter, slitless, dispersed 180
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PNe with counter-dispersed imaging
positions velocities in one go!
reconstructed field velocity ½ separation
O III filter, slitless dispersed 0
O III filter, slitless, dispersed 180
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PNe in NGC 3379
E1 , MB -20.0 D 11 Mpc
WHTPN.S March 2002 3 hrs
197 PN velocities to 7 Reff , ?v 20 km/s
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NGC 3379 Dispersion profile
long-slit data (Statler Smecker-Hane 1999)
isotropic constant-M/L Hernquist model
29 PNe Ciardullo et al. (1993)
197 PNe from PN.S
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Combined dispersion profiles
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
Should we take this seriously?
isotropic constant-M/L Hernquist model
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Interpreting the KinematicsOrbital anisotropy

• Tangential orbits
• at large R, much of the motion in line of sight
• High velocity dispersion cf circular speed
• Flat velocity distributions

• Radial orbits
• at large R, most of the motion in plane of sky
• Low velocity dispersion cf circular speed
• Peaked 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
Circular velocity profile

• best fit

• permitted

• excluded

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NGC 3379 orbit models

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

• 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 dont correct density

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Caution

• Dekel et al. (2005) disk merger simulations
• Make young stars during simulation
• Colder, tighter component
• Trace PNe?

Enclosed mass
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 dont correct density
• Are the dynamics in equilibrium?

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Outer envelope of M87 (Weil et al. 1997)

• Flattened outer envelope
• Asymmetric ? unrelaxed

30 (135kpc)
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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, KuijkenDubinski 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)4?G? 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)

Excuse me?
Przepraszam?

• 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?

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Co to jest?

• Baryons?
• Nucleosynthesis and CMB bounds
• Brown dwarf, cool white dwarf counts
• Compact objects (MACHOs)?
• 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
Prospects
ZLY
DOBRY

• Lets 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?

• 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

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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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KIDS(Leiden, Groningen, Munchen, Bonn, Paris,
Naples, Imperial, Edinburgh, Cambridge)
CFHLS
SDSS DR2
2dFGRS

• Overlaps
• UKIDSS
• SDSS
• 2dFGRS
• CFHLS
• COSMOS
• 960 sq deg.

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KIDS(Leiden, Groningen, Munchen, Bonn, Paris,
Naples, Imperial, Edinburgh, Cambridge)
2dFGRS

• Overlaps
• 2dFGRS
• VISTA!
• 720 sq deg.
• Perfect for VLT and AAT, APEX, ALMA

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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 (zlt0.2)
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Galaxy-galaxy lensing

• 45 sq. deg from RCS survey (Hoekstra, Yee,
  Gladders 2004)

Galaxy-mass correlation
Halo radii
Halo shapes
KIDS 7x smaller errors (pairs) Good photo-zs
(b/g), spectroscopic zs (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-zs!

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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 MACHOS
• 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!
dziekuje!