1. Dark Matter on Galactic Scales (and the Lack Thereof)
Michael Merrifield
University of Nottingham
Title

2. 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. Dark matter more spherically distributed than baryons
In Situ Measurements
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)
1.1  50 Ma pc-2
bar
Census of mass in baryons within 1.1 kpc of the Galactic plane (Olling & Merrifield 2001)
1.1  20 Ma pc-2 DM
 0.4 1.1
bar
whereas more globally in the Milky Way:
M(R0)  9.5 × 1010 Ma
Total dynamical mass within the Solar circle
Mbar(R0)  5.5 × 1010 Ma
Census of mass in baryons within the Solar circle (Olling & Merrifield 2001)
MDM(R0)  4.0 × 1010 Ma
 0.7 Mbar(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. 1.0
0.8
0.6
0.4
0.2
q = c/a
(Olling & Merrifield 2000)

12. NGC 720
(Buote & Canizares 1996)

13. CDM (Dubinski 1994)
Milky Way

14. Moore et al. (2003)
Moore et al. (2003)

15. Navarro et al. (2004)

17. Title

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. N6822 rotation curve: the prediction
(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. Romanowsky et al. (2003) Dark matter like spiral galaxies
MOND “prediction”
(Milgrom & Sanders 2003)
Dark matter like
spiral galaxies
No dark matter,
isotropic orbits
Romanowsky et al. (2003)
PNe

25. Napolitano et al. (2004)

26. Save the paradigm  detect the dark matter!
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