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Dec. 1-8, 2010

DARK MATTER IN GALAXIES. Alessandro Romeo. Onsala Space Observatory Chalmers University of Technology SE-43992 Onsala, Sweden. Dec. 1-8, 2010. Overview Dark m atter in SPIRALS Dark matter in ELLIPTICALS Dark matter in DWARF SPHEROIDALS Detecting dark matter Conclusions.

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Dec. 1-8, 2010

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  1. DARK MATTER IN GALAXIES Alessandro Romeo Onsala Space Observatory Chalmers University of Technology SE-43992 Onsala, Sweden Dec. 1-8, 2010

  2. Overview Dark matter in SPIRALS Dark matter in ELLIPTICALS Dark matter in DWARF SPHEROIDALS Detecting dark matter Conclusions

  3. SPIRALS

  4. Stellar Discs M33verysmoothstructure NGC 300 - exponential disc goes for at least 10 scale- lengths scale radius Bland-Hawthornet al 2005 Ferguson et al 2003

  5. Wong & Blitz (2002) Gas surfacedensities GAS DISTRIBUTION HI Flattishradialdistribution Deficiency in the centre CO and H2 Roughlyexponential Negligible mass

  6. Earlydiscoveryfromoptical and HI RCs observed disk no RC followsthe disk velocityprofile disk Rubinet al 1980 Mass discrepancy AT LARGE RADII

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

  8. mag Salucci+07 6 RD Rotation Curves Coaddedfrom 3200 individualRCs TYPICAL INDIVIDUAL RCs OF INCREASING LUMINOSITY Low lum high lum

  9. The Concept of Universal Rotation Curve (URC) The Cosmic Variance of the value of V(x,L) in galaxies of the same luminosityL at the sameradius x=R/RD is negligible compared to the variations that V(x,L) shows as xandL vary. The URC out to 6 RD isderiveddirectlyfromobservations Extrapolationof URC out tovirialradiusbyusing

  10. A Universal Mass Distribution ΛCDM URC Observed URC NFW theory low obs high obs Salucci+,2007

  11. Rotation curve analysis From data to mass models Vtot2 = VDM2 + Vdisk2 + Vgas2 • fromI-bandphotometry • from HI observations Dark haloswithconstant density cores (Burkert) Dark haloswithcusps(NFW, Einasto) The mass modelhas 3 free parameters: disk mass, halocentral density and core radi radius (halolength-scale). NFW Burkert

  12. halocentral density coreradius luminosity MASS MODELLING RESULTS highestluminosities lowestluminosities halo disk disk halo halo disk All structural DM and LM parameters are related to luminosity.g Smallergalaxies are denser and have a higherproportionof dark matter. fractionof DM

  13. Dark HaloScalingLaws Thereexistrelationshipsbetweenhalostructuralquantiies and luminosity. Investigated via mass modellingofindividualgalaxies - Assumption:MaximunDisk, 30 objects -the slopeof the halo rotation curve near the center givesthe halocore density - extendedRCsprovidean estimate ofhalocoreradiusrc • Kormendy & Freeman (2004) o o ~ LB- 0.35 rc ~ LB0.37  ~LB0.20 rc The centralsurfacedensity  ~ orc=constant 3.0 2.5 2.0 1.5 1.0 

  14. SPIRALS: WHAT WE KNOW A UNIVERSAL CURVE REPRESENTS ALL THE INDIVIDUAL RCs MORE PROPORTION OF DARK MATTER IN SMALLER SYSTEMS RADIUS AT WHICH THE DM SETS IN FUNCTION OF LUMINOSITY MASS PROFILE AT LARGER RADII COMPATIBLE WITH NFW DARK HALO DENSITY SHOWS A CENTRAL CORE OF SIZE 2 RD

  15. ELLIPTICALS

  16. The Stellar Spheroid Surfacebrightnessofellipticalsfollows a Sersic (de Vaucouleurs) law Re : the effectiveradius • Bydeprojecting I(R) weobtain the luminosity density j(r): ESO 540 -032 Sersicprofile

  17. The Fundamental Plane: central velocity dispersion, half-light radius and surface brightness are related SDSS early-typegalaxies Bernardi et al. 2003 Fromvirialtheorem Hyde & Bernardi 2009 Fitting gives: a=1.8 , b~-0.8) then: FP “tilt” due tovariationswithσ0of: Dark matterfraction? Stellar population?

  18. Dark-Luminous mass decomposition of velocity dispersions • Not a unique model – example: a giant elliptical with reasonable parameters RESULTSThe spheroid determines the velocity dispersionStars dominate inside ReMore complications when:presence of anisotropiesdifferent halo profile (e.g. Burkert) 1011 Two components: NFW halo, Sersic spheroid Assumed isotropy Mamon& Łokas05 Dark matterprofileunresolved

  19. Weakand strong lensing SLACS: Gavazzi et al. 2007) Gavazzi et al 2007 Inside Re, the total (spheroid + dark halo) mass increasesproportionallyto the radius UNCERTAIN DM DENSITY PROFILEI

  20. Mass ProfilesfromX-ray Nigishitaet al 2009 Temperature Density M/L profile NO DM HydrostaticEquilibrium • CORED HALOS?

  21. ELLIPTICALS: WHAT WE KNOW A LINK AMONG THE STRUCTURAL PROPERTIES OF STELLAR SPHEROID SMALL AMOUNT OF DM INSIDE RE MASS PROFILE COMPATIBLE WITH NFW AND BURKERT DARK MATTER DIRECTLY TRACED OUT TO RVIR

  22. dSphs

  23. 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 Gilmoreet al 2009

  24. Velocity dispersion profiles STELLAR SPHEROID Wilkinson et al 2009 dSph dispersion profiles generally remain flat up to large radii

  25. Mass profiles of dSphs Jeans’ models provide the most objective sample comparison • Jeans equation relates kinematics, light and underlying mass distribution • Make assumptions on the velocity anisotropy and then fit the dispersion profile n(R) PLUMMER PROFILE DENSITY PROFILE Results point to cored distributions Gilmoreet al 2007

  26. Degeneracy between DM mass profile and velocity anisotropy Cusped and cored mass models fit dispersion profiles equally well Walkeret al 2009 However: dSphscoredmodelstructuralparametersagreewiththoseofSpirals and Ellipticals σ(R) km/s Halocentral density vs coreradius NFW+anisotropy = CORED Donato et al 2009

  27. DSPH: WHAT WE KNOW PROVE THE EXISTENCE OF DM HALOS OF 1010 MSUN AND ρ0 =10-21 g/cm3 DOMINATED BY DARK MATTER AT ANY RADIUS MASS PROFILE CONSISTENT WITH AN EXTRAPOLATION OF THE URC HINTS FOR THE PRESENCE OF A DENSITY CORE

  28. DETECTING DARK MATTER

  29. DM

  30. CONCLUSIONS The distribution of DM halos around galaxies shows a striking and complex phenomenology. Observations and experiments, coupled with theory and simulations, will (hopefully) soon allow us to understand two fundamental issues: The nature of dark matter itself The process of galaxy formation

  31. Thanks ….. • That’s enough with Dark Matter! • Switch on the light ;-)

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