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Dec. 1-8, 2010

DARK MATTER IN GALAXIES Jianling Gan Shanghai Astronomical Observatory http://www.sissa.it/ap/dmg/index.html. Dec. 1-8, 2010. Overview The concept of Dark Matter Dark Matter in Spirals , Ellipticals , dSphs Dark Matter at outer radii . Global properties

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Dec. 1-8, 2010

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  1. DARK MATTER IN GALAXIES Jianling Gan Shanghai Astronomical Observatory http://www.sissa.it/ap/dmg/index.html Dec. 1-8, 2010

  2. Overview The conceptof Dark Matter Dark Matter in Spirals, Ellipticals, dSphs Dark Matter at outerradii. Global properties Directand IndirectSearchesof Dark Matter

  3. What is Dark Matter? In a galaxy, the radial profile of the gravitating matter M(r) and that of the sum of all luminous components ML(r) do not match. A MASSIVE DARK COMPONENT is introduced to account for the disagreement: Its profile MH(r) must obey: The DM phenomenon can be investigated only if we accurately meausure the distribution of: Luminous matter. Gravitating matter.

  4. The Realm of Galaxies The range of galaxies in magnitude, types and central surface density : 15 mag, 4 types, 16 mag arsec2 Centralsurfacebrightness vs galaxymagnitude Spirals : stellar disk +bulge +HI disk Ellipticals & dSph: stellar spheroid The distribution of luminous matter :

  5. SPIRALS

  6. Stellar Disks M33 - outer disk truncated, very smooth structure NGC 300 - exponential disk goes for at least 10 scale- lengths scale radius Bland-Hawthorn et al 2005 Ferguson et al 2003

  7. Wong & Blitz (2002) Gas surface densities HI Flattish radial distribution Deficiency in centre CO and H2 Roughly exponential Negligible mass

  8. Circularvelocitiesfromspectroscopy - Opticalemissionlines (H, Na) - Neutralhydrogen (HI)-carbonmonoxide (CO) Tracer angular spectral resolution resolution HI 7" … 30" 2 … 10 km s-1 CO 1.5" … 8" 2 … 10 km s-1 H, … 0.5" … 1.5" 10 … 30 km s-1

  9. ROTATION CURVES (RC) • Symmetriccircular rotation of a disk characterizedby • Sky coordinatesof the galaxycentre • SystemicvelocityVsys • CircularvelocityV(R) • Inclination angle  = azimuthal angle Exampleof a recent high quality RC: Radial coordinate in unitsof RD V(R/RD) V(2) R/RD

  10. Early discovery from optical and HI RCs observed disk no RC follows the disk velocityprofile Rubinet al 1980 Mass discrepancy AT OUTER RADII

  11. Extended HI kinematicstraces dark matter - - Light (SDSS) HI velocity field NGC 5055 SDSS Bosma, 1981 GALEX Bosma, 1981 Radius (kpc) Bosma 1979 The mass discrepancyemergesas a disagreementbetween light and mass distributions

  12. Evidencefor a Mass Discrepancy The distributionofgravitatingmatterisluminositydependent. Tully-Fisher relation existsat locallevel (radiiRi) no DM slope Yegorova et al 2007

  13. Dark Matter Profiles from N-body simulations In ΛCDM scenario the density profile for virialized DM halos of all masses of all masses is empirically described at all times by the universal NFW formula (Navarro+96,97). More massive and halos formed earlier have larger overdensitiesd. Concentration c=R200/ rsis an alternative density measure.

  14. The concentration scales with mass and redshift (Zhao+03,08; Gao+08, Klypin+10): At low z, c decreases with mass. -> Movie 1

  15. Aquarius simulations, highest resolutions to date. Results: CuspyEinasto profiles (Navarro+10). No difference for mass modelling with NFW ones with a dependent slightly on mass.

  16. mag. PSS 6 RD Rotation Curves Coaddedfrom 3200 individualRCs TYPICAL INDIVIDUAL RC low high

  17. The Conceptof the Universal Rotation Curve (URC) The Cosmic Variance of the value of V(x,L) in galaxies of same luminosity L at the same radius x=R/RD is negligible compared to the variations that V(x,L) shows as x and L varies. The URC out to 6 RD is derived directly from observations How to extrapolate the URC out to virial radius? Needed -> Movie 2

  18. Extrapolating the URC to the Virial radius Shankar et al 2006 Virial halo masses and VVIR are obtained - directly by weak-lensing - indirectly by correlating dN/dL with theoretical DM halo dN/dM

  19. An Universal Mass Distribution ΛCDM theoretical URC from NFW Observed URC profileand MMW theory NFW theory low obs high obs Salaucci+,2007

  20. Rotation curve analysis From data to mass models Vtot2 = VDM2 + Vdisk2 + Vgas2 • from I-band photometry • from HI observations Dark halos with constant density cores Dark halos with cusps (NFW, Einasto) Model has three free parameters: disk mass, halo central density and core radius (halo length-scale).

  21. halocentral density coreradius luminosity MASS MODELLING RESULTS highest luminosities lowest luminosities halo disk disk halo halo disk Allstructural DM and LM parameters are related withluminosity.g Smallergalaxies are denser and have a higherproportionof dark matter. fractionof DM

  22. Dark HaloScalingLaws There exist relationships between halo structural quantiies and luminosity. Investigated via mass modelling of individual galaxies - Assumption:MaximunDisk, 30 objects -the slopeof the halo rotation curve near the center givesthe halocore density - extendedRCsprovidean estimate ofhalocoreradiusrcrc Kormendy & Freeman (2003) o o ~ LB- 0.35 rc ~ LB0.37  ~LB0.20 rc The central surface density  ~ orc=constant 3.0 2.5 2.0 1.5 1.0 

  23. The distributionof DM aroundspirals UsingindividualgalaxiesGentile+ 2004, de Blok+ 2008  Kuzio de Naray+ 2008, Oh+  2008, Spano+ 2008, Trachternach+ 2008, Donato+,2009 A detailedinvestigation: high quality data and modelindependentanalysis

  24. DDO 47 NGC3621 General results from several samples including THINGS, HI survey of uniform and high quality data - Non-circularmotions are small. - No DM haloelongation - ISO halosoftenpreferredover NFW Tri-axiality and non-circularmotionscannotexplain the CDM/NFW cusp/corediscrepancy

  25. ELLIPTICALS

  26. The Stellar Spheroid Surface brightness follows a Sersic (de Vaucouleurs) law Re : the effective radius • By deprojecting I(R) we obtain the luminosity density j(r): ESO 540 -032 Sersicprofile

  27. Modelling Ellipticals Measure the light profile Derive the total mass profilefrom DispersionvelocitiesofstarsPlanetaryNebulae X-raypropertiesof the emitting hot gas Combiningweak and strong lensing data Disentangle the dark and the stellar components

  28. Line-of-sight, projected Velocity Dispersions, 2-D kinematics SAURON data of N 2974

  29. The Fundamental Plane: central dispersion velocity, half light radius and central surface brightness are related Bernardi et al. 2003 SDSS early-type galaxies Fromvirialtheorem • Fitting r ~ a Ib gives: (a<2, b~0.8) → M/L not constant ~ L0.14 Hyde & Bernardi 2009 Shankar & Bernardi 2009 The FP “tilt” is due to variations in: Dark matter fraction? Stellar population? Likely.

  30. Stars dominate inside ReDark matterprofileunresolved Dark-Luminous mass decomposition of dispersion velocities Assumed IsotropyThree components: DM, stars, Black Holes Mamon & Łokas 05

  31. Weakand strong lensing SLACS: Gavazzi et al. 2007) Gavazzi et al 2007 Inside R_e, the total (spheroid + dark halo) mass increases in proportionto the radius

  32. Mass Profiles from X-ray Nigishita et al 2009 Temperature Density M/L profile NO DM Hydrostatic Equilibrium

  33. dSphs

  34. Dwarf spheroidals: basic properties Low luminosity, gas-free satellites of Milky Way and M31 Large mass-to-light ratios (10 to 100 ), smallest stellar systems containing dark matter Luminosities and sizes of Globular Clusters and dSph Gilmore et al 2009

  35. Kinematics of dSph • 1983: Aaronson measured velocity dispersion of Draco based on observations of 3 carbon stars - M/L ~ 30 1997: First dispersion velocity profile of Fornax (Mateo)2000+: Dispersion profiles of all dSphs measured using multi-object spectrographs Instruments: AF2/WYFFOS (WHT, La Palma); FLAMES (VLT); GMOS (Gemini); DEIMOS (Keck); MIKE (Magellan) 2010: full radial coverage in each dSph, with 1000 stars per galaxy

  36. Dispersion velocity profiles Wilkinson et al 2009 dSph dispersion profiles generally remain flat to large radii

  37. Mass profiles of dSphs Jeans equation relates kinematics, light and underlying mass distribution Make assumptions on the velocity anisotropy and then fit the dispersion profile Results point to cored distributions Jeans’ models provide the most objective sample comparison

  38. Degeneracy between DM mass profile and velocity anisotropy Cusped and cored mass models fit dispersion profiles equally well However: dSphscoreddistributionstructuralparametersagreewiththoseofSpirals and Ellipticals Halocentral density vs coreradius Walker et al 2009 Donato et al 2009

  39. Global trend of dSph haloes • Sculptor AndII Mateo et al 1998 Gilmore et al 2007

  40. The stellar mass of galaxies The luminousmatterin the formofstarsM*is a crucialquantity. Indispensabletoinfer the amountof Dark Matter M*/L ofa galaxyobtainedvia Stellar PopulationSynthesismodels Fitted SED Dynamical and photometric estimates agree

  41. WEAK LENSING

  42. Weak Lensing around galaxies Criticalsurface density • Lensingequationfor the observedtangentialshear Donato et al 2009

  43. Mandelbaum et al 2009 HALO MASSES ARE A FUNCTION OF LUMINOSITY

  44. Comparing DM halos of Spirals, LSBs & dSphs URC-halo mass profile Mh(r) = F(r/Rvir, Mvir) Unique halo mass profile Mh(r) = G(r) Unique value of halo central surface density Salucci+ 2007 Walker+ 2010 Walker+ 2010 Donato et al. 2009

  45. DETECTING DARK MATTER

  46. Anti-proton spectrum

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