Transcript THE DARK MATTER PROBLEM Konrad Kuijken Leiden Observatory

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
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
– 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
Time 
• Early fluctuations in
density
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Wavelength 
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CMB
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 (T~3000K).
Density
photons +
plasma
More baryons
x
Potential
Peak 2
Peak 3
Higher overdensities (same pressure, more inertia)
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More baryons
CMB
Peak 1
• Early fluctuations in
density
Peak 2
Peak 3
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Last scattering
– 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).
Time 
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
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(Wayne Hu)
CMB
– 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
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Peak 1
Time 
Horizon crossing
Peak 2
Peak 3
Last scattering
• Constraints on dark
matter content:
measurement of
matter/radiation equality
CMB
• Parameter constraints on matter content from CMB
Spergel et al. 2003
– Universe close to flat
– Assume exactly flat  strong constraint on m
– Otherwise strong degeneracy between m,  (and H0)
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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
QuickTime™ and a
• Combined constraints from CMB
(initial conditions) + present-day LSS
decompressor
are needed to see this picture.
(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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RotationCurve
curve isof
roughly
flat out
TheThe
Rotation
the Milky
Way
to 20kpc.
• Tricky:
No Keplerian fall-off.
– Radial velocities see no solid-body rotation, need distances
– Proper motions are local, require absolute frame
But rotation curves in other galaxies
• HI rotation curve:
are much better measured
• 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
E=const.
z
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Local disk mass
consistent with stars
and gas observed
(Siebert et al 2003;
Kuijken & Gilmore
1989,1991)
How much mass resides in the disk?
• Simple model: Mestel disk
• Flat rotation curve
2
• Predicts 185 M sun pc at sun
2
( R)  Vcirc
2GR
• Measurements of total mass density:
dA/dF
 0  0.076  0.015
Bienayme 2000
dA/dF
 0  010
.  0.01
Holmberg & Flynn 2001
dK
1.1kpc  70  5
Kuijken 1991, Siebert & al. 2003
gK
Census
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  52  13
  49  9
 0  010
.  0.02
Flynn & Fuchs 1994
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
(Olling &
Merrifield)
Depends strongly on
adopted Galactic
constants!
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Rotation curves of spirals
• Rotation curves:
‘extra gravity’ in outskirts of
halo
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
O[III] filter (tiltable
= tuneable)
Focal plane calibration mask
gratings
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PNe with counter-dispersed imaging
positions & velocities in one go!
PN
star
[O III] filter, slitless,
dispersed 0°
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undispersed field
[O III] filter, slitless,
dispersed 180°
PNe with counter-dispersed imaging
positions & velocities in one go!
[O III] filter, slitless
reconstructed field; [O III] filter, slitless,
velocity = ½ separation dispersed 180°
dispersed 0°
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PNe in NGC 3379
E1 , MB = -20.0
D = 11 Mpc
WHT+PN.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,
4494:
NGC 4697:
PN p(R)
declining with R
isotropic
constant-M/L
Hernquist model
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Interpreting the Kinematics:
Orbital anisotropy
• Tangential orbits
• Radial orbits
• at large R, much of
the motion in line
of sight
• High velocity
dispersion cf
circular speed
• Flat velocity
distributions
• 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 shape
relates to orbit anisotropy
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Van der Marel & Franx 1993
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 :
• cf. models of stellar pop M/L:
=6-9
=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
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Caution
• Dekel et al. (2005) disk
merger simulations
stars
Enclosed mass
– Make ‘young’ stars
during simulation
– Colder, tighter
component
– Trace PNe?
dark halo
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)
• 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, 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
`Lens pushes sources away’
`Radial squeezing’
• Weak shear: measure shapes of halos as well as overall
power spectrum of dm (not average density though)
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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)
Przepraszam?
Excuse me?
TAK!
• Rotation curve shapes and
amplitudes well-explained
• Pioneer effect?
• Naturally explains Tully-Fisher
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NIE!
• Cosmic expansion as if there is
no dark matter
• Unclear how well it does on clusters
• Halo shapes?
• Galaxy stability?
Co to jest?
• Baryons?
– Nucleosynthesis and CMB bounds
– Brown dwarf, cool white dwarf counts
Nie!!
• 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.
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M31 microlensing
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
• 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)
•
•
•
•
•
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
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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
Doubts
Prospects
ZŁY
DOBRY
• 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?
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• 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
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)
SDSS DR2
• Overlaps:
– UKIDSS
– SDSS
– 2dFGRS
– CFHLS
– COSMOS
• 960 sq deg.
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CFHLS
2dFGRS
KIDS
(Leiden, Groningen,
Munchen, Bonn,
Paris, Naples,
Imperial, Edinburgh,
Cambridge)
• Overlaps:
– 2dFGRS
– VISTA!
• 720 sq deg.
• Perfect for VLT
and AAT, APEX,
ALMA
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2dFGRS
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 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-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
PNe as astrophysical tool!
– 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!
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