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Can Dark Matter Halos Produce<br />
Visible Effects in the Disk of the<br />
Milky Way?<br />
Evan Levine<br />
<strong>Leo</strong> <strong>Blitz</strong><br />
Carl Heiles
First indication<br />
of “scalloping”<br />
of the outer<br />
disk of the<br />
Milky Way<br />
Kulkarni, <strong>Blitz</strong><br />
and Heiles, 1982
HI midplane deviation<br />
from b = 0 O : The Warp<br />
Galactic<br />
center<br />
Henderson, Jackson & Kerr 1982
Can minihalos visibly<br />
affect the gas in the<br />
disk of the Milky way?
HI Surface Density<br />
Notice the skewing<br />
of the contours<br />
Henderson, Jackson & Kerr 1982
Leiden/Argentine/Bonn Survey<br />
of Galactic HI
By adding a<br />
small radial<br />
component<br />
to the LSR,<br />
for various<br />
velocities<br />
can<br />
symmetrize<br />
the Galaxy.<br />
HI Surface Density
Displacement of mean plane from b = 0 O<br />
Blue = pos<br />
Red = neg<br />
Lighter hues<br />
mean higher<br />
amplitude
View of warp from l = 315 o
Amplitude of the first 3 modes<br />
as a function of distance<br />
m = 1<br />
m = 0<br />
m = 2
Data vs. Model
The three main modes to scale<br />
Are these modes common in other galaxies?
Model Fit to the Data
The Warp from Different Perspectives
Scale Height and Surface Density
Thickness of the HI layer
Π LSR
Conclusions<br />
1. The Milky Way has larger amplitude<br />
m=0,1,2 modes in the HI mean plane<br />
at R > R 0. Higher order modes are<br />
much weaker.<br />
2. The m=0 mode implies that the Galaxy<br />
is moving through a hot IGM.<br />
3. Many galaxies may have these modes.<br />
4. Looking for DM halos by this method<br />
probably won’t work.
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