Dynamics of Colliding Galaxies

Simulations allow us to watch galaxies collide and merge:

What can we learn from them?

Galaxies merge via dynamical friction against dark matter halos

• Galaxies plow through one another's dark matter halo, setting up a trailing wake.
• This wake acts as a ``drag'' on the orbital motion, causing orbit to decay.
• Galaxies fall together and merge.

Halos ``soak up'' the orbital energy and angular momentum, essentially making galaxy collisions very sticky.

Tidal Tails can probe the structure of dark matter halos

• Tails form when tidal forces ``stretch'' galaxies, imparting kinetic energy to disk particles.
• The length and mass of tidal tails is sensitive to the gradient of the gravitational potential.
• Tails can map the potential well of the dark halo.

Studies of tidal tails can constrain dark matter theories.

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