Micro-arcsec Astrometry with the VLBA. Harvard-Smithsonian Center for

Transcription

1 Micro-arcsec Astrometry with the VLBA Mark J. Reid Harvard-Smithsonian Center for Astrophysics

2 Micro-arcsec Astrometry with the VLBA Fringe spacing: θ f ~λ/d ~ 1 cm / 8000 km = 250 μas Centroid Precision: 0.5 θ f / SNR ~ 10 μas Systematics: path length errors ~ 2 cm (~2 λ) shift position by ~ 2θ f Relative positions (to QSOs): ΔΘ ~ 1 deg (0.02 rad) cancel systematics: ΔΘ 2θ f ~ 10 μas

3 Where is the Galactic Center? Sun Galactic Center Harlow Shapley Globular clusters based on Cepheid distances Projected onto Galactic Plane

4 Galactic Center Stellar Orbits M = 4 x 10 6 M sun VLT: 2 μm R < 50 AU sun Den. > M sun /pc 3 sun p 5 μ Ghez et al / Genzel et al 0.04 What can radio observations tell us?...

5 Where is the Galactic Center? VLA λ = 6 cm 1.3 cm 5 Sgr A* Zhao Jun-Hui

6 Where is the Galactic Center? Combined IR + Radio astrometry shows Sgr A* at focal position of stellar orbits (+/-10 mas) Stars move fast. Does Sgr A* move fast?

7 The Proper Motion of Sgr A* 2 Ref. QSOs: ΔΘ ~ o Expect to see effect of Sun s orbit around Galactic Center: 6 mas/yr along Gal. Plane 90 cm VLA image: LaRosa et al

8 Proper Motion of Sgr A* Parallel to Galactic Plane: (+/ ) mas/yr Θ o /R o = 29.5 km/s / kpc Perpendicular to Gal. Plane: 7.2 km/s motion of Sun Could re-define Galactic Plane Now: HI & Sun in plane New: LSR orbit & Sgr A* in plane fit to data IAU Gal. Plane Sgr A* s motion to Gal. Plane /- 0.9 km/s! Reid & Brunthaler (2004)

9 ~10 6 stars orbiting Sgr A* Calculate orbit segments Stellar c.o.m. changes Sgr A* moves to keep total system c.o.m. constant SMBH Brownian motion Σm i << M SgrA. MV ~ mv Σm ~ 2 ~ 2 i M SgrA. MV mv

10 Latest Results: Sgr A* Proper Motion IR Stellar Orbits: M IR ~ 4 x 10 6 M sun R < 50AU Radio Observations: Sgr A* motionless M > 10% of M IR Observed size: R < 0.5 AU IR + Radio data combined: Dark mass = luminous source Density > M sun /pc 3 O h l i id f Overwhelming evidence for a Super-Massive Black Hole

11 Must Sgr A* be a SMBH? Object Density Method Mass within Radius (M sun /pc 3 ) (M sun ) M HST 3x pc NGC VLBA : H 2 O 4x pc Sgr A* IR Star orbits 4x AU Sgr A* >10 22 VLBA p.m. >4x AU SMBH R Sch 4x10 6 3* AU 3R Sch = 30 8 kpc VLBI 0.8 mm 20 μas News Flash: Fringes: Hawaii 1.3mm (60 μas)! ( μ ) Doeleman et al

12 Milky Way Viewed From Inside Sgr A* Thomas Lucas Productions, Inc. ( ti

13 Parallax 1.01

14 Orion Nebular Cluster Parallax D = 414 +/- 7 pc 389 +/- 22 pc Sandstrom et al (2007) 437 +/- 19 pc Hirota et al (2007) 414 +/- 7 pc Menten et al (2007) Menten, Reid, Forbrich & Brunthaler (2007)

15 Milky Way Parallaxes Distance estimates: Kinematic = 4.3 kpc Photometric = 2.2 kpc (R. Humphreys 1970 s) W3(OH) T. Megeath (Spitzer Space Telescope)

16 Kinematic Distances D V Θ o V Doppler shift: V Dop = V - V sun Model (Gal. Rotation): V mod (R o,θ o,l,d) R o Adjust D to match V mod to V Dop

17 W3OH Parallax Xu, Reid, Zheng & Menten (2006) π = / mas

18 W3OH Parallax D photo ~ D parallax D k way off In Perseus Arm, not in Outer Arm Large peculiar V Schematic Model of Milky Way: Schematic Model of Milky Way: Taylor-Cordes / Georgelin & Georgelin

19 S 252 Parallax Maser 2 3 QSOs; Maser 1 Reid et al (2008) π = / mas

20 Methanol Maser Parallaxes Kinematic distances (D k ): Problem: D k > D π Partial fix: R o < 8.5 kpc and/or Θ o > 220 km/s Sgr A* p.m. requires Θ o /R o = 29.5 km/s/kpc = 236 / 8.0 = 251 / 8.5 Brunthaler, Menten, Moscadelli, Reid, Xu, & Zheng Honma et al; Hachisuka et al

21 Peculiar Motions of Star Forming Regions In rotating frame: R o = 8.5 kpc Θ o = 220 km/s Clear systematic motions Update Galaxy model: R o =85kpc 8.5 Θ o = 251 km/s Systematic motions smaller, but significant

22 Peculiar Motions of Star Forming Regions Galactic model: R o = kpc Θ o = 251 km/s & Solar Motion: U = 8 km/s V = 18 km/s W = 10 km/s Residual motions considerably smaller

23 Solar Motion Hipparcos & VLBA U: Gal. Center W: North Gal. Pole Maser parallax/p.m. Sgr A* proper motion Dehnen & Binney (1998) Hipparcos data (black) Excellent agreement between Hipparcos and VLBA

24 Solar Motion V Gal. Rot. Asymmetric Drift: V appears larger when measured against older stars with higher dispersion Maser π & p.m. Late B-type Dehnen & Binney (1998) Hipparcos data in black Massive stars born rotating ~13 km/s slower than Galaxy spins; as they age, first speed up and then slow down again.

25 Possible Sequence: 1. Molecular l cloud in circular orbit 2. Hit by Spiral shock 3. Goes into elliptical orbit (near apocenter) 4. Compression triggers star formation Massive Star Birth

26 Extreme Supergiants Extreme red supergiants with L 10 6 L sun Fabulous 4 : NML Cyg, S Per, VY CMa, VX Sgr H 2 O and SiO masers in circumstellar envelopes VY CMa 0.4 < D < 1.8 kpc Association with NGC 2362 D = 1.5 kpc (M-S fitting) Parallax measured to be 1.1 kpc... L = 3 x 10 5 L sun (quite reasonable) NGC 2362 cluster closer than thought

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

28 Extragalactic Proper Motions Parallax accuracy: M33 σ D ~ 10% at 10 kpc can t do galaxies yet Proper motion: same techniques, but σ μ ~ T -3/2 M33 & IC10 1) see spin (van Maanen) 2) see galaxy s motion Andreas Brunthaler s PhD Thesis

29 Extragalactic Proper Motions M33/IC133 M33/19 masers VLBA: Δμ x = 30 +/- 2, Δμ y = 10 +/- 5 μas/yr HI: Δv x = 106 +/-20, Δv y = 35 +/- 20 km/s D = 750 +/- 50 +/- 140 kpc σ μ σ v Improvements in Rotation Model & 3 rd maser source: σ D < 10% possible Brunthaler, Reid & Falcke

30 Extragalactic Proper Motions M31 s motion unknown Critical for L.G. dynamics

31 Try M31 proper motions; then calculate l orbits Tidal Heating of M33 Tidal heating of M33 for trial proper motions of M31: μ M31 = (100,-100) 100) km/s ( -50, -50) km/s ( 0, 0) km/s μ Μ31 ~ 0 km/s M33 destroyed μ Μ31 ~100 km/s M33 OK Loeb, Reid, Brunthaler & Falcke (2005)

32 NGC 4258 Seyfert galaxy H 2 O masers in an edge-on, sub-parsec disk Rotation speed ~1000 km/s M ~ 3 x 10 7 M sun Geometric model D = 7.2 +/- 0.5 Mpc Used by Hubble Key Project to re-calibrate Cepheid PL relation Herrnstein, Moran, Greenhill et al (1999)

33 AGN Maser Distance Measurements Red highvelocity masers V R = D θ Blue high- velocity masers A = V 2 / R R = D θ D = V 2 / A θ High Velocity Maser Map Drift of systemic masers over time Systemic velocity masers

34 Maser Distance Measurements (2) D = V 2 / A θ V θ

35 Maser Cosmology Project Braatz, Condon, Greenhill, Henkel, Lo & Reid Goal: H o accurate to 3%; constain Dark Energy Eq. of State How: Geometric Distances to H 2 O masers in Hubble Flow GBT finds masers VLBA maps them

36 UGC 3789 J. Braatz: GBT V CMB = 3385 km/s D ~ 50 Mpc

37 UGC 3789: VLBA + GBT Interferometer spectrum: rms noise ~1 mjy

38 Similar to NGC 4258 Edge-on disk Systemic vel. masers between red and blue high vel. masers ~7 times smaller angle ~7 times more distant UGC 3789 map

39 UGC 3789 Position-Velocity Diagram Keplerian high vel. masers ~10 7 M sun SMBH Systemic maser P-V ~ linear (slight bend changing R) V θ V = 625 km/s, θ = 0.52 mas

40 UGC 3789 Accelerations ~ 3.4 km/s/year D=V 2 / A θ Preliminary Analysis V ~ 625 km/s θ ~ 0.52 km/s/yr}d mas }D = 47 Mpc +/- 5 A ~ 3.4 H o = V cmb /D = 3385 km/s / 47 Mpc = 72 +/- 7 +/- 4 from σ D σ Vcmb ~200 km/s Comparable to Hubble Key Project!

41 The Next 5 Years R o & Θ o from parallax & p.m. data with 3% accuracy Map of Milky Way spiral structure Proper motions of ~4 Local Group Galaxies H o with 3% accuracy from 5 to 10 AGN H 2 O masers