1. Gdansk Jul 02 2005 THE DARK MATTER PROBLEM Konrad Kuijken Leiden Observatory

2. 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

3. Gdansk Jul 02 2005 CMB Last scattering surface at z~1100 –Inhomogeneities at 1:10 5 level –Power spectrum powerful probe of cosmology

4. Gdansk Jul 02 2005 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). –T now / T last scatt defines redshift of CMB Wavelength  Time  horizon

5. Gdansk Jul 02 2005 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 Potential Density photons + plasma Higher overdensities (same pressure, more inertia) xx

6. Gdansk Jul 02 2005 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). Horizon crossing Last scattering Peak 1 Peak 2 Peak 3 Time  More baryons

7. Gdansk Jul 02 2005 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)

8. Gdansk Jul 02 2005 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 Last scattering Peak 1 Peak 2 Peak 3 Time 

9. Gdansk Jul 02 2005 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 H 0 ) Spergel et al. 2003

10. Gdansk Jul 02 2005 Structure formation Gravitational instability causes large-scale structure –Without dark matter, get insufficient structure growth –Foam-like LSS follows out of CDM

11. Gdansk Jul 02 2005 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 h 2. Result: 23% dark matter, 4% baryons, 73% dark energy

12. Gdansk Jul 02 2005 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

13. Gdansk Jul 02 2005 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 Way The Rotation curve is roughly flat out to 20kpc. No Keplerian fall-off. But rotation curves in other galaxies are much better measured

14. Gdansk Jul 02 2005 Vertical kinematics Unique 3-D measurements of the potential  –Solar neighbourhood: Vertical kinematics (Oort problem) –Distribution fn.: f(z,v z )=f(E z )=f(  (z)+v z 2 /2) –Read off f from velocities at low z (where  =0) –Vary  to reproduce density at high z z VzVz E=const. Local disk mass consistent with stars and gas observed (Siebert et al 2003; Kuijken & Gilmore 1989,1991)

15. Gdansk Jul 02 2005 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

16. Gdansk Jul 02 2005 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)

17. Gdansk Jul 02 2005 Rotation curves of spirals Rotation curves: ‘extra gravity’ in outskirts of galaxies Extra gravity: extra mass Extra gravity: extra mass halo

18. Gdansk Jul 02 2005 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 (?)

19. Gdansk Jul 02 2005 PN.S optical design: slitless spectroscopy through narrow-band filter Shutter Focal plane calibration mask O[III] filter (tiltable = tuneable) gratings

20. Gdansk Jul 02 2005 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

21. Gdansk Jul 02 2005 reconstructed field; velocity = ½ separation [O III] filter, slitless dispersed 0° [O III] filter, slitless, dispersed 180° positions & velocities in one go! PNe with counter-dispersed imaging

22. Gdansk Jul 02 2005 WHT+PN.S: March 2002 3 hrs : 197 PN velocities to 7 R eff,  v = 20 km/s E1, M B = -20.0 D = 11 Mpc PNe in NGC 3379

23. Gdansk Jul 02 2005 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.S

24. Gdansk Jul 02 2005 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

25. Gdansk Jul 02 2005 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?

26. Gdansk Jul 02 2005 Velocity distribution shape relates to orbit anisotropy Van der Marel & Franx 1993

27. Gdansk Jul 02 2005 NGC 3379: orbit models PN velocities LOSVDs shown in radial bins: data simulated from data model ~isotropic orbits

28. Gdansk Jul 02 2005 NGC 3379: orbit models best fit permitted excluded Circular velocity profile:

29. Gdansk Jul 02 2005 Results: constant M/L ruled out at 1  flat rotation curve ruled out at 6  NGC 3379: orbit models cumulative M/L at 5 R eff : = 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?

30. Gdansk Jul 02 2005 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

31. Gdansk Jul 02 2005 Caution Dekel et al. (2005) disk merger simulations –Make ‘young’ stars during simulation –Colder, tighter component –Trace PNe? dark halo stars Enclosed mass r/R eff

32. Gdansk Jul 02 2005 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?

33. Gdansk Jul 02 2005 Outer envelope of M87 (Weil et al. 1997) 30’ (135kpc) Flattened outer envelope Flattened outer envelope Asymmetric  unrelaxed Asymmetric  unrelaxed

34. Gdansk Jul 02 2005 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

35. Gdansk Jul 02 2005 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’

36. Gdansk Jul 02 2005

37. Alternative MOND (Milgrom 1984) –Below accelerations of ca 10 -10 gravity gets stronger:  (  (|g/a 0 |)g)=4  G  where g=  and  1 for large g –  (x)  x for small x gives for weak accelerations g  (GMa 0 /r 2 ) 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?

38. Gdansk Jul 02 2005 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!!

39. Gdansk Jul 02 2005 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

40. Gdansk Jul 02 2005 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

41. Gdansk Jul 02 2005 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 ZŁYZŁY DOBRY

42. Gdansk Jul 02 2005 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)

43. Gdansk Jul 02 2005 Overlaps: –UKIDSS –SDSS –2dFGRS –CFHLS –COSMOS 960 sq deg. 2dFGRS SDSS DR2 CFHLS KIDS (Leiden, Groningen, Munchen, Bonn, Paris, Naples, Imperial, Edinburgh, Cambridge)

44. Gdansk Jul 02 2005 Overlaps: –2dFGRS –VISTA! 720 sq deg. Perfect for VLT and AAT, APEX, ALMA 2dFGRS KIDS (Leiden, Groningen, Munchen, Bonn, Paris, Naples, Imperial, Edinburgh, Cambridge)

45. Gdansk Jul 02 2005 KIDS vs. SDSS

46. Gdansk Jul 02 2005 Weak gravitational lensing `Lens pushes sources away’ `Radial squeezing’ 80,000,000 background galaxies 200,000 foreground galaxies (z<0.2)

47. Gdansk Jul 02 2005 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

48. Gdansk Jul 02 2005 ‘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!

49. Gdansk Jul 02 2005 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!