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?