1. Dark Matter in Galaxies (+beyond)

2. Early Evidence for Dark Matter Zwicky 1933: Coma has  =1000 km/s + R~1 Mpc  M~1x10 15 M . Zwicky 1933: Coma has  =1000 km/s + R~1 Mpc  M~1x10 15 M . From galaxy light, inferred M/L~400. From galaxy light, inferred M/L~400. He called missing mass “dark matter”. He called missing mass “dark matter”. Mostly regarded as a clever exercise; missing mass was simply some form of unseen baryons. Mostly regarded as a clever exercise; missing mass was simply some form of unseen baryons.

3. “Proof” of Dark Matter Rubin 1970: Flat rotation curve for M31. Rubin 1970: Flat rotation curve for M31. Rubin et al 1978: RC of 200 galaxies  Only about ~10% of matter in galaxies is in stars+gas; ~90% is dark matter. Rubin et al 1978: RC of 200 galaxies  Only about ~10% of matter in galaxies is in stars+gas; ~90% is dark matter.

4. Dark Matter in Spirals Rotation curves almost always flat at large R. Rotation curves almost always flat at large R. Outer RC generally probed with HI. Outer RC generally probed with HI. “Cosmic Conspiracy”: RC often doesn’t show feature at transition from baryon  DM. “Cosmic Conspiracy”: RC often doesn’t show feature at transition from baryon  DM. Sofue & Rubin 2001

5. Dark Matter in Spirals: Inner RC H  /CO rotation curves probe inner part (Swaters et al 2003). H  /CO rotation curves probe inner part (Swaters et al 2003). NFW not always great fit, but questions about non- circular motions. NFW not always great fit, but questions about non- circular motions. Simon etal 04 used 2-D velocity maps, “tilted ring” model; still disfavored NFW. Simon etal 04 used 2-D velocity maps, “tilted ring” model; still disfavored NFW. Simon et al 2004

6. Dark Matter Extent of Milky Way Milky Way DM probes: Milky Way DM probes: Rotation curve Rotation curve Stellar v esc. Stellar v esc. Satellite galaxies Satellite galaxies M31 timing M31 timing Local group+ timing Local group+ timing All are consistent with SIS of 180 km/s. All are consistent with SIS of 180 km/s. For R<200 kpc, M~10 12, M/L~100 For R<200 kpc, M~10 12, M/L~100 Zaritsky 1999

7. Dark Matter in Ellipticals Line-of-sight velocity dispersion. Line-of-sight velocity dispersion. Strong lensing. Strong lensing. X-rays. X-rays. The Planetary Nebulae controversy. The Planetary Nebulae controversy. Gerhard et al. 2001

8. Dark Matter in Ellipticals Line-of-sight velocity dispersion. Line-of-sight velocity dispersion. Strong lensing. Strong lensing. X-rays. X-rays. The Planetary Nebulae controversy. The Planetary Nebulae controversy. Keeton et al. 1998 log M/L B Redshift

9. Dark Matter in Ellipticals Line-of-sight velocity dispersion. Line-of-sight velocity dispersion. Strong lensing. Strong lensing. X-rays. X-rays. The Planetary Nebulae controversy. The Planetary Nebulae controversy. Mushotzky et al 1994

10. Dark Matter in Ellipticals Line-of-sight velocity dispersion. Line-of-sight velocity dispersion. Strong lensing. Strong lensing. X-rays. X-rays. The Planetary Nebulae controversy. The Planetary Nebulae controversy. Dekel et al 2005

11. Dark Matter in Clusters  (R): cD stars + member galaxies.  (R): cD stars + member galaxies. Degeneracy with  and (NFW)  ; can be partly broken using M/L. Degeneracy with  and (NFW)  ; can be partly broken using M/L. Inconsistent with NFW + isotropy; needs outer parts to be radial, which is predicted. Inconsistent with NFW + isotropy; needs outer parts to be radial, which is predicted. Kelson et al 2002

12. Dark Matter in Clusters: Baryon Fraction Add up baryons: Add up baryons: Starlight + M/L Starlight + M/L X-ray gas mass X-ray gas mass or Sunyaev- Zeldovich effect or Sunyaev- Zeldovich effect Total mass from: Total mass from: X-ray temp. X-ray temp. or Lensing or Lensing Baryon fraction in clusters ~10%, perhaps higher. Baryon fraction in clusters ~10%, perhaps higher. Grego et al 2001 Vikhlinin et al 2005

13. M/L (R) Putting it all together: M/L increases with scale, then flattens (?) after cluster scales. Putting it all together: M/L increases with scale, then flattens (?) after cluster scales. M/L(1000 Mpc)~300   m ~0.2. M/L(1000 Mpc)~300   m ~0.2. Bahcall et al 2001

14. Weak Lensing: Detecting DM in LSS Distortion angle: Distortion angle: Derivative gives Distortion matrix: Derivative gives Distortion matrix: which for small angles can be written: which for small angles can be written:

15. Weak Lensing: Theory  is convergence,  is shear.  «  ignored.  is convergence,  is shear.  «  ignored.  measures magnification (i.e. increase in area). Not usually determinable.  measures magnification (i.e. increase in area). Not usually determinable. What’s measured is reduced shear g ≡  /(  -1) What’s measured is reduced shear g ≡  /(  -1) From this, aperture mass can be measured. From this, aperture mass can be measured.

16. Weak Lensing: Observations Galaxies not round/standard candles, so must do statistics on large patches of sky. Galaxies not round/standard candles, so must do statistics on large patches of sky. CFHT (170 sq deg): M vir  L 1.5±0.2. CFHT (170 sq deg): M vir  L 1.5±0.2. M/L(early) ~twice M/L(late) M/L(early) ~twice M/L(late) Hoekstra et al 2005

17. Dark Matter Candidates: Baryonic MACHOs? Not planetary-mass ones… MACHOs? Not planetary-mass ones… Brown dwarfs? 2MASS/SDSS finds stellar mass function turns down at M * <0.1M . Brown dwarfs? 2MASS/SDSS finds stellar mass function turns down at M * <0.1M . Gas  M HI would have to be solid/liquid to evade detection. Gas  M HI would have to be solid/liquid to evade detection. Alcock et al 1998 Pfenniger & Revaz 2004

18. Dark Matter Candidates: Neutrinos Neutrinos 2eV suppress structure formation too much. Neutrinos 2eV suppress structure formation too much. Sterile neutrino with >1keV mass still viable; essentially acts “cold”. Sterile neutrino with >1keV mass still viable; essentially acts “cold”. Narayanan et al. 2000

19. Dark Matter Candidates: Particles WIMPs, particularly LSPs: mass >GeV. WIMPs, particularly LSPs: mass >GeV. Neutralinos: New parity associated with supersymmetry (a way for fermions  bosons). Neutralinos: New parity associated with supersymmetry (a way for fermions  bosons). Axions: Invented to explain why weak force violates CP, but strong force does not. Axions: Invented to explain why weak force violates CP, but strong force does not. 10 -6 <m ax <10 -3 eV: Upper limit from SN1987A cooling; lower from BBN. 10 -6 <m ax <10 -3 eV: Upper limit from SN1987A cooling; lower from BBN. Currently neutralinos and axions are best candidates for dark matter; neither has been detected or is predicted in Standard Model. Currently neutralinos and axions are best candidates for dark matter; neither has been detected or is predicted in Standard Model.

20. Dark Matter Detection To detect, generally look for signatures of Earth moving through DM fluid (seasonal). To detect, generally look for signatures of Earth moving through DM fluid (seasonal).

21. Really Cold and Collisionless? 2 problems with CDM: Too cuspy, too much substructure. 2 problems with CDM: Too cuspy, too much substructure. Dark matter not cold? Dark matter not cold? Self-interacting (Spergel & Stein- hardt): Must avoid core collapse! Self-interacting (Spergel & Stein- hardt): Must avoid core collapse! Fuzzy: 10 -22 eV Bose condensate. Fuzzy: 10 -22 eV Bose condensate. Decaying: ~½ of DM decays into fast particles. Decaying: ~½ of DM decays into fast particles. Disappearing: Goes into 5 th dimension via brane. Disappearing: Goes into 5 th dimension via brane. Fluid: Scalar field with quartic potential yields “pressure”. Fluid: Scalar field with quartic potential yields “pressure”.

22. Modified Newtonian Dynamics (MOND) MOND proposes that on large scales, F=(GMa0) 1/2 /r. MOND proposes that on large scales, F=(GMa0) 1/2 /r. Can fit RCs of galaxies extremely well. Can fit RCs of galaxies extremely well. Can almost fit CMB: 3 rd peak is key. Can almost fit CMB: 3 rd peak is key. Runs into trouble in clusters and Ly-  forest. Runs into trouble in clusters and Ly-  forest. MOND+baryonic DM? Hmm… MOND+baryonic DM? Hmm… Aguirre et al 2001

23. Bullet Cluster: Dark Matter is Collisionless Interacting cluster lensing+X-rays shows that mass doesn’t trace baryons. Interacting cluster lensing+X-rays shows that mass doesn’t trace baryons. Exactly as predicted by CDM: Dark matter passes thru, gas is shocked. Exactly as predicted by CDM: Dark matter passes thru, gas is shocked. Difficult with baryonic DM because high velocities would destroy cold, unseen baryons. Difficult with baryonic DM because high velocities would destroy cold, unseen baryons. Clowe et al 2006