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Measuring Dark Matter Properties via Astrometry: Insights from Dwarf Spheroidal Galaxies

This work, led by Louie Strigari and collaborators, explores the properties of dark matter through astrometric measurements in dwarf spheroidal galaxies, such as Fornax. By examining line-of-sight velocities and the spatial distribution of stars, the research addresses key issues related to the density profiles of dark matter halos. Utilizing advanced instrumentation like the Space Interferometry Mission (SIM), the study aims to refine our understanding of dark matter distributions, core vs. cusp degeneracy, and the implications for galaxy formation and dynamics.

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Measuring Dark Matter Properties via Astrometry: Insights from Dwarf Spheroidal Galaxies

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  1. Measuring Dark Matter Properties with Astrometry Louie Strigari TASC 2006 10/20/2006 In collaboration with: James Bullock, Manoj Kaplinghat, Stelios Kazantzidis, Steve Majewski

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

  3. Dwarf Spheroidal Galaxies Fornax To observer Walker et al. 2006 • Exhibit no rotation • DM dominated • Information on DM halo from line of sight velocities

  4. Line of sight profiles Fornax Strigari et al. 2006 • Degeneracy with cores and cusps in all systems • Nothing prevents dark halos from being very extended

  5. Projections • Degeneracy remains unbroken even with 10,000 stars • Space Interferometry Mission (SIM): extragalactic astrometry with micro-arcsec resolution http://planetquest.jpl.nasa.gov/SIM/sim_index.cfm • Errors of order km/s on a few hundred stars at a typical dSph distance Louie Strigari UC Irvine

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

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

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

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

  10. Reconstructing the central slope II. (Cores) Line of Sight Proper motions + + =

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