Measuring Dark Matter Properties with Astrometry Louie Strigari TASC /20/2006 In collaboration with: James Bullock, Manoj Kaplinghat, Stelios Kazantzidis, Steve Majewski

CDM WDM Dark Matter and Galaxy Central Densities Louie StrigariUC Irvine cusp core Simon et al 05 SuperWIMPS & Meta-CDM

Dwarf Spheroidal Galaxies  Exhibit no rotation  DM dominated  Information on DM halo from line of sight velocities Walker et al Fornax To observer

Strigari et al  Degeneracy with cores and cusps in all systems  Nothing prevents dark halos from being very extended Line of sight profiles Fornax

Projections  Degeneracy remains unbroken even with 10,000 stars  Space Interferometry Mission (SIM): extragalactic astrometry with micro-arcsec resolution  Errors of order km/s on a few hundred stars at a typical dSph distance UC IrvineLouie Strigari

Hipparcos Positional Error Circle (0.64 mas) How Precise is SIM? HST Positional Error Circle (~1.5 mas) Reflex Motion of Sun from 100pc (axes 100 µas) Parallactic Displacement of Galactic Center Apparent Gravitational Displacement of a Distant Star due to Jupiter 1 degree away SIM Positional Error Circle (4µas). Adapted from:

R   = velocity anisotropy of the stars Constructing moments for proper motions Dark matter

4th moment 2nd moment Error estimates n = number of stars in sample

Reconstructing the central slope I. (NFW) Proper motions Line of Sight = + +

Reconstructing the central slope II. (Cores) ++ = Proper motionsLine of Sight