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The Dark Matter Problem astrophysical perspectives

The Dark Matter Problem astrophysical perspectives. 陈学雷 中国科学院国家天文台. What can we learn from astrophysics? . The data evidence of DM abundance of DM distribution of DM. The questions Nature of DM property of DM (mass, interaction, ...) role of DM in cosmic history

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The Dark Matter Problem astrophysical perspectives

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  1. The Dark Matter Problemastrophysical perspectives 陈学雷 中国科学院国家天文台

  2. What can we learn from astrophysics? The data evidence of DM abundance of DM distribution of DM The questions Nature of DM property of DM (mass, interaction, ...) role of DM in cosmic history origin of DM, and relation with DE

  3. Outline What we have learned evidence of DM and its abundance DM is not baryonic DM is not hot WIMP: the classic CDM What we are learning cuspy halos and missing satellites alternative models of DM CDM strikes back: the mundane answers The role of DM (an example) DM decay and reionization

  4. Evidence of DMgalaxy rotation curve

  5. dynamics of galaxy cluster Virial theorem U=2K K =  mi vi2 U ~ GM2/R Coma cluster mass to light ratio (B) typical cluster: 100/h-300/h Sun stellar pop: 1-10 Sun critical: 1390 h +- 35%

  6. X-ray cluster hydrostatic equilibrium beta model:

  7. Strong Gravitational Lensing

  8. Weak Lensing mass reconstruction Image ellipticity -> shear-> invert the equation RXJ1347.5-1145 (Bradac et al 2005)

  9. DM Abundance • mass to light ratio x light density • cluster baryon fraction/BBN baryon abundance • cluster mass function • evolution of cluster mass function Bahcall: m=0.2 Blanchard: m=1.0

  10. WMAP result Spergel et al 2003 WMAP Combined fit: mh2=0.135+-0.009 m=0.27+-0.04 Results depend on Supernovae and Hubble constant data.

  11. Can DM be baryons? If all DM is baryonic, it is in conflict with Big Bang Nucleonsynthesis and Cosmic Microwave Background anisotropy.

  12. MAssive COmpact Halo Objects (MACHO) LMC The result of MACHO experiment (Alcock et al 1996): 20% of halo can be due to MACHO

  13. Abundance of DM: WIMP? dark -- weakly interacting? In early Universe, even weak interaction is effective, abundance given by freeze out when H = n <Av>, the dark matter abundance is comparable to weak interaction

  14. Collisional Damping and Free Streaming Kinetic decoupling at T ~ 1 MeV (Chen, Kamionkowski, Zhang 2001) Initial density perturbation is damped by the free streaming of the particles before radiation-matter equality perturbations on scales smaller than rFS is smoothed out.

  15. Structure Formation at freeze-out if weakly interacting hot dark matter relativistic m< 1 keV warm dark matter quasi-relativistic 1 keV < m < 10 keV cold dark matter non-relativistic m > 10 keV at freeze-out The failure of HDM: clusters form before galaxy, can not account small scale structures.

  16. The first dark halos Diemand, Moore, Stadel 2005 Due to collisional damping and free-streaming, the smallest halo (no sub-structure) is 10-6 solar mass (earth mass) for neutralino. Dection of such halo may probe the nature of DM.

  17. substructure of DM halo missing satellites? B. Moore et al simulated Local Group mass system

  18. Dark matter halo profile simulation (Navarro, Frenk, white 1996): cusp observation: core NFW96, rotation curve

  19. Alternatives to CDM WDM: reduce the small scale power Self-Interacting Dark Matter (Spergel & Steinhardt 2000) Strongly Interacting Massive Particle Annihilating DM Decaying DM Fuzzy DM

  20. WDM From Jing 2000

  21. SIDM DM strongly interact with itself, but no EM interaction can create an core in hierachical scenario (eventually core collapse -> isothermal profile) Interaction strength: comparable to neutron-neutron Difficulty: make spherical clusters: against lensing

  22. SIMP • Motivation: • SIDM may have QCD interaction but not EM • Not detectable in WIMP search, blocked. CMB & LSS constraint: Before decoupling, photons and baryons are tightly coupled, interaction with baryon will cause additional damping of perturbation

  23. Test DM interaction with CMB and LSS Chen, Hannestad, Scherrer 2002

  24. missing satellites: CDM solution • satellites do exist, but star formation suppressed (after reionization?) • satellites orbit do not bring them to close interaction with disk, so they will not heat up the disk. • Local Group dwarf velocity dispersion underestimated • halo substructure may be probed by lensing (still controversial) • galaxy may not follow dwarf

  25. Rotation curve • Is density profile really universal? scatter in concentration • What is the real slope • NFW: 1.0 Moore 1.5, ..., Power et al, Diemand et al, 1.2 • Observation • beam smearing? 21cm vs H • some agree w/ cusp, but most dwarf slope 0.2 • Cusp cheat as core • vg != vc , because of inclination, effect of bulge and bar, gas supported by pressure, star orbit in triaxial halo, ... (Rhee et al 2004, Hayashi etal 2003)

  26. active DM: decaying particle • Reionization Rephaeli & Szalay 1981; Salati & Wallet 1984; • Ionization of Reynolds layer, ISM, IGM Sciama 1982-1996; Melott, 1984; but see Bowyer et al 1999 • Resolve the conflict between SCDM model and =0.3 Gelmini, Schram & Valle, 1984; Turner, Steigman, Krauss, 1984; Doroshkevich, Khlopov, 1984 • If decay early, can affect BBN Audouze, Lindley, Silk 1985; Starkman 1988, Dimopoulos et al 1988 • If decaying particle heavy, may give Ultra High Energy Cosmic Rays Frampton & Glashow 1980; Ellis, Steigman, Gaisser 1981; Berezinsky, Kachelriess & Vilenkin 1997; Birkel & Sarkar 1998

  27. Decaying dark matter & small scale crisis Cen 2001

  28. Candidates of decaying DM active neutrino, sterile neutrino, unstable susy particle, crypton, super heavy dark matter, R-violating gravitino, moduli, axino, SWIMP, quintessino, Q-ball, topological defect, primodial black hole ...

  29. decaying DM & reionization surprise from WMAP: early reionization standard picture of reionization

  30. Thermal History with Decaying DM Long lived particle short lived particle

  31. Constraints on decaying DM

  32. Summary • Observations are in general agreement with LCDM, most data consistent with low DM density (0.2-0.3), but there are different voices. • Small scale crisis: the problem is complicated, explanations inside/outside LCDM paradigm are available • Many properties of DM can be studied with astrophysical observation • Some observations unexplained in simplest version of LCDM (tight Tully-Fisher relation, downsizing in galaxy formation, ...) • Open questions: role of DM in cosmic evolution? relation with DE?

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