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Galaxy Structure and Dark Matter. Michael Merrifield University of Nottingham. Title. UDF #3492. (Zwicky 1937). Coma Cluster. NGC 3198. (Begeman 1989). Ngc 3198. MO dified N ewtonian D ynamics. (Milgrom 1983). (Kent 1987). The Tully Fisher Relation. In “deep MOND,”. Tully-Fisher.

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  1. Galaxy Structure and Dark Matter Michael Merrifield University of Nottingham Title

  2. UDF #3492

  3. (Zwicky 1937) Coma Cluster

  4. NGC 3198 (Begeman 1989) Ngc 3198

  5. MOdified Newtonian Dynamics (Milgrom 1983) (Kent 1987)

  6. The Tully Fisher Relation In “deep MOND,” Tully-Fisher

  7. (Kent 1987)

  8. In Situ Measurements 1.1 20 Ma pc-2 DM 1.1 50 Ma pc-2 bar  0.4 1.1 bar In the Solar neighbourhood, we have: 1.1 70 Ma pc-2 Total mass within 1.1 kpc of the Galactic plane (Kuijken & Gilmore 1991) Census of mass in baryons within 1.1 kpc of the Galactic plane (Olling & Merrifield 2001) whereas more globally in the Milky Way: M(R0) 9.5 × 1010Ma Total dynamical mass within the Solar circle Mbar(R0) 5.5 × 1010Ma Census of mass in baryons within the Solar circle (Olling & Merrifield 2001) MDM(R0) 4.0 × 1010Ma 0.7Mbar(R0) Dark matter more spherically distributed than baryons

  9. Measuring Halo Shape One measure of the shape of the halo can be made using the thickness of a galaxy’s gas layer, assuming that it is in hydrostatic equilibrium: Flatter halo  dark matter concentrated closer to plane  Vertical gravitational pull reduces scaleheight of gas layer

  10. q = c/a 1.0 0.8 0.6 0.4 0.2 (Olling & Merrifield 2000)

  11. NGC 720 (Buote & Canizares 1996)

  12. Milky Way

  13. Moore et al. (2003) Moore et al. (2003)

  14. (Dubinski 1994) Milky Way

  15. Title

  16. Invisible Galaxies? MOND? • Never formed stars • Destroyed by • dynamical friction (Ciotti & Binney 2004) For a typical galaxy-scale halo, (Minchin et al. 2005) • First star blew out gas, • stopping star formation Where Have All the Satellites Gone?

  17. Navarro et al. (2004)

  18. The Milky Way Rotation Curve in CDM ...all of which gives plenty of “wiggle room” to make the CDM models fit! (Klypin, Zhao & Somerville 2002)

  19. NGC 6822

  20. (de Blok 2004) N6822 rotation curve: the prediction

  21. MOND Again (Sanders & McGaugh 2002)

  22. Elliptical Galaxies NGC 4472

  23. Romanowsky et al. (2003) PNe

  24. Combined dispersion profiles Isothermal halo MOND (Sanders & McGaugh 2002) Isotropic no dark matter model NGC 821 (Romanowsky et al 2003) NGC 3379 (Romanowsky et al 2003) NGC 4494 (Romanowsky et al 2003) NGC 4697 (Méndez et al. 2001) (Romanowsky et al. 2003)

  25. CDM prediction (Bullock et al. 2001) Explanation for “Naked” Ellipticals We have been able to rule out: • Systematic problems with data • Face-on highly-flattened systems • Strong radial bias in orbits Which leaves: • Lost dark matter halos • MOND • Low concentration • halos More data on the way…

  26. Conclusions There is overwhelming evidence that, on the scale of galaxies, dynamically-inferred masses exceed the observed baryonic masses For the last twenty years, the paradigm has been that the deficit is made up by non-baryonic dark matter It is by no means clear at this point that Occam’s Razor supports this interpretation (c.f. MOND) Save the paradigm  detect the dark matter! Summary

  27. Clusters of Galaxies

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