Galaxy Structure and Dark Matter

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Title
Galaxy Structure and Dark Matter
Michael Merrifield University of Nottingham
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UDF 3492
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Coma Cluster
(Zwicky 1937)
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Ngc 3198
NGC 3198
(Begeman 1989)
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(Kent 1987)
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Tully-Fisher
The Tully Fisher Relation
In deep MOND,
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(Kent 1987)
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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)
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 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
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Measuring Halo Shape
One measure of the shape of the halo can be made
using the thickness of a galaxys gas layer,
assuming that it is in hydrostatic equilibrium
Flatter halo
?
dark matter concentrated closer to plane
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Vertical gravitational pull reduces scaleheight
of gas layer
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(Olling Merrifield 2000)
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NGC 720
(Buote Canizares 1996)
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Milky Way
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Moore et al. (2003)
Moore et al. (2003)
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Merger Tree
Galaxy Merger Tree
Position
Gas
Stars
Time
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Milky Way
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Title
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Where Have All the Satellites Gone?
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Navarro et al. (2004)
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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)
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NGC 6822
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N6822 rotation curve the prediction
(de Blok 2004)
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MOND Again
(Sanders McGaugh 2002)
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NGC 4472
Elliptical Galaxies
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PNe
Romanowsky et al. (2003)
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Combined dispersion profiles
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)
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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
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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
Occams Razor supports this interpretation (c.f.
MOND)
Save the paradigm ? detect the dark matter!
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Clusters of Galaxies