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

2. UDF #3492

3. Coma Cluster (Zwicky 1937)

5. Ngc 3198 (Begeman 1989) NGC 3198

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

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

8. (Kent 1987)

9.  1.1  70 M a 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)  1.1  50 M a pc -2 bar In the Solar neighbourhood, we have: In Situ Measurements whereas more globally in the Milky Way:  1.1  20 M a pc -2 DM  0.4  1.1 bar M(R 0 )  9.5 × 10 10 M a Total dynamical mass within the Solar circle M bar (R 0 )  5.5 × 10 10 M a Census of mass in baryons within the Solar circle (Olling & Merrifield 2001) M DM (R 0 )  4.0 × 10 10 M a  0.7 M bar (R 0 ) Dark matter more spherically distributed than baryons

10. 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  Measuring Halo Shape

11. 1.0 0.8 0.6 0.4 0.2 q = c/a (Olling & Merrifield 2000)

13. (Buote & Canizares 1996) NGC 720

14. Milky Way

15. Moore et al. (2003)

16. Merger Tree Time Position Stars Gas Galaxy Merger Tree

17. Milky Way (Dubinski 1994)

19. Title

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

21. Navarro et al. (2004)

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

23. NGC 6822

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

25. (Sanders & McGaugh 2002) MOND Again

26. NGC 4472 Elliptical Galaxies

27. PNe Romanowsky et al. (2003)

28. Combined dispersion profiles Isotropic no dark matter model Isothermal halo MOND (Sanders & McGaugh 2002) 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)

29. 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…

30. Summary 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!

31. Clusters of Galaxies