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Probing the Galactic Potential Using the μ arcsec astrometric observations of Disk Stars

Probing the Galactic Potential Using the μ arcsec astrometric observations of Disk Stars. T. Sumi (Nagoya STE) K.V. Johnston (Columbia) S. Tremaine (IAS) D.N. Spergel (Princeton). MOA-II1.8m telescope （ New Zealand/Mt. John Observatory at NZ, 44  S ）. Mirror : 1.8m

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Probing the Galactic Potential Using the μ arcsec astrometric observations of Disk Stars

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  1. Probing the Galactic Potential Using the μarcsec astrometric observations of Disk Stars • T.Sumi (Nagoya STE) • K.V. Johnston (Columbia) • S.Tremaine (IAS) • D.N.Spergel(Princeton)

  2. MOA-II1.8m telescope（New Zealand/Mt. John Observatory at NZ, 44S） Mirror : 1.8m CCD : 8kx10k pix. FOV : 2.2 square deg.

  3. MACHO fraction depends on halo model

  4. Proper motion ~300 I-band frames, 4years  ~1mas/yr

  5. Streaming motions of the bar Sun Color Magnitude Diagram faint bright Vrot=~50km/s

  6. Steven Majewski (Virginia) SIM Key Project:Taking Measure of the Milky Way Kathryn Johnston (Wesleyan) Ricky Patterson (Virginia) I. Neill Reid (STScI) David Spergel (Princeton) Scott Tremaine (Princeton) Takahiro Sumi (Princeton) Jeff Crane (OCIW) Peter Frinchaboy (Virginia) Ricardo Muñoz (Virginia) Clara Moskowitz (Wesleyan) Christina Hampton (Virginia) David Nidever (Virginia) Roberta Johnson (Caltech) Mei-Yin Chou (Virginia) Cameron Hummels (Wesleyan) Mike Siegel (Texas) Tony Sohn (Korean Astro Obs) Kyle Westfall (Wisconsin) David Law (Caltech) Bill Kunkel (Carnegie) James Bullock (UC-Irvine) Rachael Beaton (Virginia) [John Bahcall (IAS)] Doug Geisler (Concepción) Wolfgang Gieren (Concepción) Eva Grebel (Basel) Carl Grillmair (Caltech) SIM Science Team Meeting – Washington8 January 2006

  7. KP Proposed Scope (1999) • Mass Potential of Galaxy (tidal tails & satellites in halo) • Mass and Mass Distribution (shape, radial profile) of MW • “Lumpiness” of the Halo • Dynamics of the Disk • Surface Mass Density (Oort limit) • Milky Way Rotation Curve • Dynamics of the Central Galaxy • Dynamics of Bulge • Orientation and Motions of the Bar • Fundamental and Legacy Measurements • Proper motions of every known MW satellite galaxy & globular • Proper motions for large number of selected open clusters • Solar rotation speed, p & dynamical distance to GC

  8. Halo & Disk model Hernquist 1990 Halo mass: Disk density: Radial dispersion:

  9. Spiral arms model Potential: Radial verlocity: m:number of spirals K=C/R:radial wave number p:pattern speed :epicyclic frequency F:reduction factor

  10. Parameters (kpc)

  11. Disk stars

  12. SIM Mission time & the number of targets 240hr 10μas  N=810

  13. Markov Chain Monte Carlo Likelihood: n:number density of stars V:volume ~p-4(p-3)

  14. Provability distribution of p V~p-3

  15. Recovery by MCMC. (N=810)

  16. Consistency Check • 10 MCMC runs

  17. Accuracy v.s. Numer of stars

  18. Accuracy v.s. parallax accuracy

  19. Disk stars

  20. Accuracy v.s. 

  21. Summary • SIM can constrain Rotation curve in 3% up to 20 kpc • δMN-1/2 • δM do NOT depnd on δp until 500μas •  should be >60 • Knowing the error distribution is important • APOGEE, RVs with <0.5 km/s for 1-2 x 10^5 stars

  22. Likelihood surface. (N=810) 68%,95%CL.

  23. 2005: Satellite Galaxy Tails • Extensive new data on Sgr tidal streams • 2 new wraps of debris (Pakzad et al. 2005) • Evidence for interaction w/LMC 2 Gyrs ago (Majewski, Nidever et al., in prep) • Proper motion predictions for the LMC-Sgrinteraction made. • Extensive RV survey of Sgr core (~1500 stars)

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