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VLBA Parallaxes Across the Milky Way and the Distance to NGC 4258

VLBA Parallaxes Across the Milky Way and the Distance to NGC 4258. Mark J. Reid Harvard-Smithsonian Center for Astrophysics. Trigonometric Parallax. d(kpc) = 1 / p(mas) Nearest stars: d = 1 pc p = 1 ” Center of Milky Way: d ~ 10 kpc p ~ 0.1 mas Other galaxies

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VLBA Parallaxes Across the Milky Way and the Distance to NGC 4258

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  1. VLBA Parallaxes Across the Milky Way and the Distance to NGC 4258 Mark J. Reid Harvard-Smithsonian Center for Astrophysics

  2. Trigonometric Parallax d(kpc) = 1 / p(mas) Nearest stars: d = 1 pc p = 1” Center of Milky Way: d ~ 10 kpc p ~ 0.1 mas Other galaxies d ~ 1 Mpc p ~ 1 mas D(parsecs) = 1 / A(arcseconds) 1 parsec = 3.26 light years = 205,000 A.U. p d 1 A.U.

  3. Used Fraunhofer’s last telescope • measured first stellar parallax: • 61 Cygni: p = 0.314” in 1838 • (p = 0.287”) p = 0.37” ± 0.03” Friedrich Wilhelm Bessel p = 0.25” ± 0.03” Friedrich Wilhelm Bessel (1838)

  4. 118,000 stellar parallaxes sp ~ 0.001 arcseconds 10% accuracy at 100 pc… mapped solar neighborhood HIPPARCOS(HIgh Precision PARallax COllecting Satellite) (Perryman et al 1997 A&A 323 49)

  5. Pleiades Distance Problem • Hipparcos: D = 120.2 ± 1.9 pc • Ground based D = 131  135 pc • HST (3 parallaxes): D = 134.6 ± 3.1 pc • VLBA (4 parallaxes): D = 136.2 ± 1.2 pc • Carl Melis et al (in prep) uncertainty dominated by cluster depth (2.3pc), not measurement accuracy

  6. Fringe spacing (eg, VLBA): qf~l/D ~ 1 cm / 8000 km = 250 mas Centroid Precision: 0.5 qf / SNR ~ 10 mas Systematics: path length errors ~ 2 cm (~2 l) shift position by ~ 2qf ~ 500 mas Relative positions (to QSOs): DQ ~ 1 deg (0.02 rad) cancel systematics: DQ*2qf ~ 10 mas Very Long Baseline Interferometry: VLBA, VERA & EVN • Radio waves “see” through galaxy • Can “synthesize” telescope the size of the Earth

  7. Hipparcos range What does the Milky Way look like? Gaia range (± 10 to 20 mas); but cannot see through dust in Galactic plane VLBI range (± 5 to 20 mas): can “see” through plane to massive star forming regions that trace spiral structure

  8. The BeSSeL Survey Team M. Reid, T. Dame (CfA) K. Menten, A. Brunthaler, B. Zhang, Y. Wu, M. Sato, Y. Choi, A. Sanna (MPIfR) X-W Zheng, Y. Xu (Nanjing) L. Moscadelli (Arcetri) A. Bartkiewicz (Torun) K. Hachisuka (Shanghai) K. Rygl (Netherlands)

  9. Parallax for W 49N H2O masers p = 90 ± 7 mas (D=11.1 ± 0.9 kpc) Zhang+ (2013)

  10. Mapping Spiral Structure • Parallaxes: VLBA, EVN & VERA • >100 parallaxes for massive • young stars • Tracing most spiral arms, eg… • Outer arm traced • Perseus arm “gap” • Local arm significant • Model entire data set: • R0 = 8.34 ± 0.16 kpc • Q0 = 240 ± 8 km/s • ¶Q/¶R ~ 0 Reid et al 2014

  11. Local Group Proper Motions M33 • 1920s van Maanen claimed to see M33 spin! • mas/yr motions  Spiral nebulae nearby (Galactic) • Hubble argued more distant (extra-galactic) • van Maanen’s error not found

  12. Extragalactic Proper Motions M33 • van Maanen experiment: M33/19 – M33/IC133 masers VLBA: Dmx = 30 +/- 2, Dmy = 10 +/- 5 mas/yr HI: Dvx = 106 +/-20, Dvy = 35 +/- 20 km/s D = 750 +/- 50 +/- 140 kpc sm sv Brunthaler+ 2006 • Next: M31 (Andromeda) 5 masers higher rotation speed

  13. NGC 4258 • Seyfert 2 galaxy • H2O masers in edge-on warped disk Radius 0.15 -> 0.30 pc Rotation speed ~ 1000 km/s Period ~ 1000 years M ~ 4 x 107 Msun • Decade of VLBA and GBT observation • Geometric model  Distance • With HST observations, recalibrate Cepheid PL relation Herrnstein, Greenhill, Moran, Miyoshi…

  14. NGC 4258: Accretion Disk (r ~ 0.1 pc)

  15. Modeling Disk Dynamics A = V2 / r & r= D q M ~ r V2 Center of P-V diagram VLBA map Very small Humphreys et al (2013)

  16. Modeling Disk Dynamics

  17. Estimating H0 • DNGC4258 = 7.60 ± 0.17 ± 0.20 Mpc (total ±3%) Extremely accurate, direct distance to a galaxy. • H0 = Vrec/ D very uncertain (Vrec = Vobs – Vpec) But, very useful for re-calibrating Cepheids… H0,NGC4258 = 72.0 ± 3.0 km/s/Mpc (see Riess+ 2011,12) H0,NGC4258 = 70.6 ± 3.3 km/s/Mpc (see Efstathiou 2014) • Established H2O megamaser method for distances. Observe similar AGN disks in galaxies where Vpec << Vrec and estimate H0 directly without standard candels.

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