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次世代位置天文衛星による 銀河系ポテンシャル測定

次世代位置天文衛星による 銀河系ポテンシャル測定. T. Sumi (Nagoya STE) K.V. Johnston (Columbia) S. Tremaine (IAS) D.N. Spergel (Princeton) S. Majewski (Virginia) Sumi et al. 2009. KP ： Taking Measure of the Milky Way: Proposed Scope (1999). Mass Potential of Galaxy (tidal tails & satellites in halo)

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次世代位置天文衛星による 銀河系ポテンシャル測定

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  1. 次世代位置天文衛星による銀河系ポテンシャル測定次世代位置天文衛星による銀河系ポテンシャル測定 • T.Sumi (Nagoya STE) • K.V. Johnston (Columbia) • S.Tremaine (IAS) • D.N.Spergel(Princeton) • S. Majewski (Virginia) Sumi et al. 2009

  2. KP：Taking Measure of the Milky Way: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

  3. method 1, generate stars following model density Σ, mean v and dispersion σ, at R=0-25kpc 2, assign observational err in pphot 3, select sample 4, observe ptri, μ, vlos with err 5, modeling by MCMC

  4. Spiral arms model Potential: Radial verlocity: Φa: amplitude of spiral arm R0: distance to GC m: number of spiral arms k=C/R: radial wave number p: pattern speed : epicyclic frequency F: reduction factor 16 parameters in total ~10% of local disk surface density

  5. Sampling & observation M-giant: MV=-2 mag Photometric parallax: pphot=0.15p Sample uniform in R In R=4-20kpc ptri=10μas μ=0.2+0.6ptri vlos=1km/s APOGEE, H-band RVs with <0.5 km/s for 1-2 x 105 stars

  6. Markov Chain Monte Carlo Likelihood: Conditional probability:P Σ:number density of stars ε: error function V:volume ~p-4(p-3) S: selection function Ux: phase space distribution

  7. Recovery by MCMC. (N=850, fit R0) δphot=15% δtri=10μas

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

  9. Accuracy vs. Number of stars

  10. Accuracy vs. parallax accuracy N=850, fix R0

  11. Disk stars

  12. Accuracy v.s.  N=850

  13. Summary • Our method is immune to bias in sample selection • Next generation astrometoric survey can constrain Mass distribution in ~1% at 4-20 kpc (currently ~10% at<8kpc) with N=a few 100~1000 • δM does NOT depend on δptri until ~100μas GAIA does good work. • Measure R0 in ~2% • max should be >60 • (Knowing the error distribution is important)

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

  15. 8kpc   Obs. G.C. (face on, from North) the Galactic Bar structure 1, Microlensing Optical depth,  (Alcock et al. 2000; Afonso et al.2003; Sumi et al. 2003;Popowski et al. 2004; Hamadache et al. 2006;Sumi et al. 2006) M=1.61010M, axis ratio (1:0.3:0.2), ~20

  16. 2.Red Clump Giants • Metal-rich horizontal branch stars • Small intrinsic width in luminosity function (~0.2mag) =20-30, axis ratio 1:0.4:0.3 Stanek et al. 1997

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

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