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Louie Strigari

Dark Matter, Small-Scale Structure, and Dwarf Galaxies. Louie Strigari. Center for Cosmology and Particle Physics New York University 10.19.2007. Main Collaborators: James Bullock, Manoj Kaplinghat (UC Irvine). Local Group circa 2003. Name Year Discovered LMC 1519 SMC 1519

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Louie Strigari

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  1. Dark Matter, Small-Scale Structure, and Dwarf Galaxies Louie Strigari Center for Cosmology and Particle Physics New York University 10.19.2007 Main Collaborators: James Bullock, Manoj Kaplinghat (UC Irvine)

  2. Local Group circa 2003 NameYear Discovered LMC 1519 SMC 1519 Sculptor 1937 Fornax 1938 Leo II 1950 Leo I 1950 Ursa Minor 1954 Draco 1954 Carina 1977 Sextans 1990 Sagittarius 1994 • Possible that up to 3x more exist at these luminosities [e.g. willman et al 2004] • About a dozen satellites of M31 Louie Strigari, UC Irvine

  3. Local Group circa 2007 NameYear Discovered LMC 1519 SMC 1519 Sculptor 1937 Fornax 1938 Leo II 1950 Leo I 1950 Ursa Minor 1954 Draco 1954 Carina 1977 Sextans 1990 Sagittarius 1994 Ursa Major I 2005 Willman I 2005 Ursa Major II 2006 Bootes 2006 Canes Venatici I 2006 Canes Venatici II 2006 Coma 2006 Segue I 2006 Leo IV 2006 Hercules 2006 Leo T 2007 Bootes II 2007 ? Louie Strigari, UC Irvine

  4. Questions to be addressed • What is the smallest dark matter system? • Can we ever distinguish between cores and cusps? Is there a missing satellites problem is CDM? • Viable alternatives to CDM? What are their phenomenological implications? Louie Strigari, UC Irvine

  5. CDM: Cosmological Consequences Zentner & Bullock 2003 Louie Strigari, UC Irvine

  6. CDM: Predictions including ``astrophysics” We are seeing: 1) Earliest Forming halos 2) Largest before capture 3) Most massive today 4) Some combination Bullock et al. 2001; Chiu, Gnedin, Ostriker 2001; Somerville 200; Stoehr et al. 2002; Hayashi et al. 2003; Kravtsov et al. 2004; Gnedin & Kravtsov 2006; Diemand et al. 2006 Kravtsov et al 2004 Louie Strigari, UC Irvine

  7. Maximum Circular Velocities? Walker et al. ApJL 2007 Louie Strigari, UC Irvine

  8. Characteristic Mass of Satellites Via Lactea Error projections: 200 LOS stars 0.6 kpc appropriate scale to characterize well-known MW satellites Louie Strigari, UC Irvine

  9. Mass Constraints: Take I The `Old’ Dwarfs Likelihoods are marginalized over 6-dimensional parameter space defining the dwarfs. Very new data: M0.6 ~ [2-7] x 106 Msun (Walker et al. 2007) Largest mass galaxies are least luminous and least extended Strigari, Bullock, Kaplinghat, Diemand, Kuhlen, Madau ApJ 2007 Louie Strigari, UC Irvine

  10. Implications: Take I Strigari, Bullock, Kaplinghat, Diemand, Kuhlen, Madau ApJ 2007 Precise Mass function rules out most massive z=0 hypothesis Louie Strigari, UC Irvine

  11. Belukurov et al 2006 Louie Strigari, UC Irvine

  12. Mass Constraints: Take II The Old and the New 300 pc is better scale to characterize the new and old MW satellites Mass within tidal radius of Willman 1 ~ 2x the estimate of Martin et al. 2007 Mass is independent of halo luminosity (Mateo 1998) Louie Strigari, UC Irvine

  13. Implications: Take II Masses are similar, but the CDM mass function is steep over the same range Louie Strigari, UC Irvine

  14. CDM: Cosmological Consequences cusp core Simon et al. 2005, Kuzio de Naray et al. 2006 Low mass dark matter halos are less `cuspy’ than predicted in CDM Louie Strigari, UC Irvine

  15. Dwarf kinematics (Circa 2005) Are survival of globular clusters in Fornax a sign of a kpc-sized core? Gilmore et al 2007find no- dSph requires the existence of central cusps, and there is a characteristic dark matter core density Strigari et al. 2006 Louie Strigari, UC Irvine

  16. What can we learn from dwarfs? Velocity Anisotropy Truth = core Truth = cusp Louie Strigari, UC Irvine

  17. Proper Motions  • Require accuracy on stellar transverse velocities of 5 km/s • At < 100 kpc, this corresponds to accuracy 10 micro-arcseconds/yr R Louie Strigari, UC Irvine

  18. SIM PlanetQuest (Space Interferometry Mission) Reflex Motion of Sun from 100pc (axes 100 µas) SIM Positional Error Circle(4µas) Parallactic Displacement of Galactic Center Hipparcos Positional Error Circle (0.64 mas) . Apparent Gravitational Displacement of a Distant Star due to Jupiter 1 degree away HST Positional Error Circle (~1.5 mas) Astronomy = “star naming” Astrometry = “star measuring” Adapted from: http://planetquest.jpl.nasa.gov/SIM/sim_index.cfm Louie Strigari, UC Irvine

  19. Previous Considerations • Wilkinson et al 2000 use a two-parameter model for the DM density profile • They determine that the inner slope is well-constrained Louie Strigari, UC Irvine

  20. Constraints with SIM Strigari, Bullock, Kaplinghat ApJL 2007 Inner slope is never well-constrained. However, log-slope at several hundred pc is constrained. This is sufficient to distinguish cores and cusps. Louie Strigari, UC Irvine

  21. Distinguishing Cores from Cusps Strigari, Bullock, Kaplinghat ApJL 2007 SIM key project would entail 1000 hrs of observing time and 200 stars from multiple dSphs Louie Strigari, UC Irvine

  22. Warm Dark Matter Abazajian 2006 Hogan & Dalcanton 2000 Seljak et al 2006, Viel et al 2006 find mwdm > 14 keV [Tremaine-Gunn Bound] Spergel & Steinhardt 2000, Ostriker and Steinhardt 2003, Bode, Ostriker, & Turok 2001, Cen 2000, Sanchez-Salcedo 2003 Louie Strigari, UC Irvine

  23. Warm Dark Matter Fornax Ly-alpha + velocity dispersion imply small WDM cores -Strigari et al ApJ 2006 Louie Strigari, UC Irvine

  24. Dark Matter from Early Decays • What if dark matter freezes-out, then decays to a `superweakly’ interacting particle? [Feng, Rajaraman, Takayama 2003] • Large velocity at production: 0.1-1c • Free-streaming scale: Q-1/3 • Reduced Phase-Space Density See also Kang, Kawasaki, Steigman 1993; Starkman, Kaiser, Malaney 1994 Cembranos et al., Kaplinghat (2005) Is dark matter from decays just a one-parameter family of models? Louie Strigari, UC Irvine

  25. Dark Matter from Late Decays • Mass splitting is a free parameter: what if they are of order GeV? (Universal Extra Dimensions) • Free-streaming scale now depends on the lifetime: (Meta-CDM) 1014 sec. 1012 sec. Distinguishing between cold and `warm’ dark matter now requires separate investigation of dwarf galaxies and LSS Neutrino WDM Strigari, Kaplinghat, Bullock PRD 2006 Louie Strigari, UC Irvine

  26. The low energy gamma-ray background: Are WIMPs stable? G Cembranos, Feng, Strigari, PRL 2007 MeV gamma-ray background unexplained by astrophysical sources Louie Strigari, UC Irvine

  27. Dark matter, gamma-rays, 511 keV photons Cembranos & Strigari M ~ MeV  ~ 1020/M(TeV) Teegarden & Watanabe Picciotto & Pospelov 2005, Hooper & Wang 2005, Kasuya & Kawasaki 2006, Finkbeiner & Weiner 2007, Pospelov & Ritz 2007 Louie Strigari, UC Irvine

  28. Indirect Dark Matter Detection Flux = Particle Physics x Astrophysics Strigari, Koushiappas, Bullock, Kaplinghat PRD 2007 Louie Strigari, UC Irvine

  29. Indirect Dark Matter Detection Boost factor Strigari et al. PRD 2007 Louie Strigari, UC Irvine

  30. The most dark matter dominated galaxies: Willman 1, Coma, Ursa Major II These galaxies may be visible in gamma-rays with GLAST Dark substructure `boosts’ the fluxes Louie Strigari, UC Irvine

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