Survival or disruption of CDM micro-haloes: implications for detection experiments

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Survival or disruption of CDM micro-haloes
implications for detection experiments
Tobias Goerdt
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• Collaborators Oleg Y. Gnedin, Ben Moore,
• Jürg Diemand and Joachim Stadel

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Micro-haloes

• Cosmological ?CDM N-body simulations
• First objects in universe (z 26)
• 1015 in the Milky Way today
• Solar system radius
• Earth mass

Diemand et al. 2005
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Dark matter annihilation

• Dense cuspy cores
• Self-annihilation of DM
• Gamma-ray emission
• High proper motions (arc-minutes / year)
• Uniquely distinguishable
• Observable by Glast

Koushiappas 2006
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Survival issues

• Encounters with stars and substructure
• Tidal forces in Milky way
• Do they get disrupted?
• Testing their stability to impulsive
  gravitational encounters

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N-body tests

• Equilibrium dark matter halo
• cuspy density profile (a 1.0, ß 3.0, ? 1.2)
  
• Mvir 1 x 10-6 Msun, rvir 0.01 pc
• 106 particles
• Concentration c 3.2 or c 1.6
• Perturbing star
• Single particle
• M 0.7 Msun
• 300 km s-1 (solar neighbourhood)
• Single and multiple encounters
• Varying impact parameters

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Numerical results

• Density profiles
• after relaxation
• Single encounter
• c 1.6
• Varying impact parameter b
• Arrow rvir

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Mass lost

• After potential relaxation
• Single encounter
• c 1.6
• Varying impact
• parameter b

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Successive encounters

• Density profiles
• Multiple encounters
• c 1.6
• Impact parameter 0.02 pc
• Significant fraction unbound
• Cuspy central regions remain intact

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Cumulative mass loss

• Different micro-haloes
• Multiple encounters
• Impact parameter
• b 0.02 pc.

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Final masses

• Probability density distribution function
• Different haloes
• Monte Carlo approach
• Simulating micro-halo in solar neighbourhood

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Annihilation flux

• Relative annihilation flux
• Both micro-haloes
• b 0.02 pc
• Multiple encounters
• Mass loss decreases flux of factor of two or three

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Summary

• Cuspy cores stable to encounters with disk and
  halo stars
• Mass lost from the outer region
• Typical mass loss from a halo decreases flux of a
  factor of two or three
• Still visible in Glast

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Any questions?