Survival or disruption of CDM micro-haloes: implications for detection experiments
Collaborators: Oleg Y. Gnedin, Ben Moore,
Jürg Diemand and Joachim Stadel
Tobias Goerdt
האוניברסיטה העברית בירושלים
Micro-haloes• Cosmological ΛCDM N-body simulations:
– First objects in universe (z ~ 26)– ~1015 in the Milky Way today– Solar system radius– Earth mass
Diemand et al. 2005
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
Survival issues
• Encounters with stars and substructure
• Tidal forces in Milky way
• Do they get disrupted?Testing their stability to impulsive gravitational
encounters
N-body tests• Equilibrium dark matter halo:
– cuspy density profile (α = 1.0, β = 3.0, γ = 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
Numerical results
• Density profiles
after relaxation• Single encounter• c = 1.6• Varying impact
parameter b
• Arrow: rvir
• After potential relaxation• Single encounter• c = 1.6• Varying impact
parameter b
Mass lost
Successive encounters:• Density profiles• Multiple
encounters• c = 1.6• Impact parameter:
0.02 pc• Significant
fraction unbound• Cuspy central
regions remain intact
Cumulative mass loss
• Different micro-haloes
• Multiple encounters• Impact parameter
b = 0.02 pc.
Final masses
• Probability density distribution function
• Different haloes• Monte Carlo
approach• Simulating micro-halo
in solar neighbourhood
Annihilation flux
• Relative annihilation flux
• Both micro-haloes• b = 0.02 pc• Multiple encounters• Mass loss decreases
flux of factor of two or three
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
Any questions?
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