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SgrA Reid

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Published on November 15, 2007

Author: Miguel

Source: authorstream.com

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Slide1:  Must Sgr A* be a Super-Massive Black Hole? Mark J. Reid Harvard-Smithsonian CfA Andreas Brunthaler MPIfR/JIVE Sgr A*:  Sgr A* Where is it? Does it move? Karl Menten Reinhard Genzel Thomas Ott Rainer Schoedel Andreas Eckart Andreas Brunthaler Discovery of Galactic Center:  Discovery of Galactic Center Shapley (1918): Globular Clusters “point” to Galactic Center Ro = 13 kpc Early Radio Observations:  Early Radio Observations Piddington & Minnett (1951); Haddock, Mayer & Sloanaker (1954); McGee & Bolton (1954) Sgr A History of Sgr A*:  History of Sgr A* Balick & Brown (1974) Discover Sgr A*: “Intense Sub-Arcsecond Structure” Lo et al (1985) Sgr A* < 20 AU Backer et al (1993) < 3 AU Rogers et al (1994) < 1 AU VLA Images of Sgr A:  VLA Images of Sgr A J-H Zhao Sgr A* IR Image of GC:  IR Image of GC 1-3 um image Where is Sgr A*? 6 Questions::  6 Questions: Is Sgr A* at the center of the stellar cluster? Is the stellar cluster tied to Sgr A*? Is Sgr A* at the dynamical center of the Galaxy? Does Sgr A* have a peculiar motion? Does Sgr A* have all the mass sensed by stars? Could exotic dark matter dominate the G. C. mass? Radio/IR frame alignment:  Radio/IR frame alignment Use stars visible in both Radio and IR Red Giants with masers Compare Radio and IR positions: Solve for IR plate scale & rotation Align IR with Radio to find Sgr A* VLA positions for stars:  VLA positions for stars 7 SiO masers <12” of SgrA* ~0.1 – 1 Jy Positions to ~ 3 mas mas/yr motions in few years VLBA proper motions:  VLBA proper motions VLBA proper motions (Reid et al 2003) Sub-mas positions mas/yr motions in 3 months Stellar positions & motions:  Stellar positions & motions 7 SiO maser stars positions ~ 3 mas motions ~ 100 km/s VLT with Adaptive Optics:  VLT with Adaptive Optics “3-color”: 1.5 - 3 um 8.2 m VLT telescope CONICA (IR camera) NAOS (adaptive optics) 60 mas resolution Where was Sgr A* in 1995:  Where was Sgr A* in 1995 15 mas accuracy Between stars: S1, S2 & S3 Sgr A* < 9 mJy Where was Sgr A* in 2002:  Where was Sgr A* in 2002 Sgr A* position: 10 mas Reid et al (2003) Star “S2” seen at pericenter passage V ~ 5000 km/s !! Orbit determined Schoedel et al (2002) S2’s orbit:  S2’s orbit 15 year period e = 0.87 Pericenter only 15 mas from Sgr A* ! (120 AU = 17 l-h) (Schoedel et al 2002) Stellar Orbits:  Stellar Orbits 6 stars with orbits Enclosed mass: 4 x 106 Msun < 100 AU radius Schoedel etal 02,03 Ghez et al 03 Sgr A* within 100 AU Reid et al 03 Question 1::  Question 1: Is Sgr A* at the center of the stellar cluster? Yes… to better than 10 mas Radio/IR frame alignment:  Radio/IR frame alignment Compare Radio(SiO) and IR positions: Solve for IR plate scale & rotation Align IR with Radio to find Sgr A* Compare Radio(SiO) and IR velocities: SiO velocities relative to Sgr A* Tie IR velocities to Sgr A* Velocity Alignment:  Velocity Alignment East,North proper motions in mas/yr Star Radio Infrared Difference IRS 9 +3.6,+2.4 +2.0,+0.5 +1.6 (0.7),+1.9 (1.2) IRS 7 -1.6,-4.5 -0.8,-3.6 -0.8 (1.0),-0.9 (3.5) IRS 12 -0.8,-2.8 -3.3,-0.8 +2.4 (0.5),-2.0 (0.8) IRS 10 +0.2,-2.1 +0.1,-2.2 +0.1 (0.4),+0.1 (1.0) Unweighted mean (sem) +0.8 (0.8),-0.25(1.0) 1 mas/yr ~ 40 km/s Central star cluster moves with Sgr A* to ~70 km/s Question 2::  Question 2: Is the stellar cluster tied to Sgr A*? Yes… to better than 70 km/s Proper Motion of Sgr A*:  Proper Motion of Sgr A* Sun’s Galactic Orbit: 225 Myr period 220 km/s @ 8.0 kpc = 6 mas/yr Sgr A*’s apparent motion:  Sgr A*’s apparent motion Relative to 2 Quasars Sun’s Galactic Orbit: 220 km/s at 8.0 kpc = 6 mas/yr in Gal plane (Kassim, Frail & Briggs) Project History:  Project History 1979: Proposal to US VLBI Network “To Study Feasibility of Detecting Proper Motion of the Galactic Center” 15 GHz; OVRO, HRAS, GB, Haystack Failed: Scatter broadened Sgr A* Limited sensitivity Needed VLBA ! Sgr A*’s Apparent Motion:  Sgr A*’s Apparent Motion Moves mostly along Galactic Plane Slight deviation from VSUN Gal Plane Best Fit Eastward Motion:  Eastward Motion Sgr A* drifts smoothly QSOs don’t move Northward Motion:  Northward Motion Sgr A* drifts smoothly QSO don’t move NB: error bars larger than eastward positions Sgr A* motion Galactic Coords::  Sgr A* motion Galactic Coords: Motion in Galactic Plane: Qo/Ro = 29.4 +/- 0.9 km/s/kpc Compare to (A-B)/Ro= 27.2 +/- 0.9 km/s/kpc (Feast & Whitelock 1997) Motion out of Galactic Plane: Very small… Question 3::  Question 3: Is Sgr A* at the dynamical center of the Galaxy? Yes… to within our knowledge of Qo/Ro Sgr A* motion toward Galactic Pole:  Sgr A* motion toward Galactic Pole Solar Motion 7 km/s Sgr A*s peculiar motion -0.4 +/- 0.8 km/s Question 4::  Question 4: Does Sgr A* have a peculiar motion? No … less than 1.6 km/s (out of Plane) Estimating Sgr A*’s Mass:  Estimating Sgr A*’s Mass Chatterjee, Hernquist & Loeb (2002) mass estimator: a <energy> Mlim ~ G M(R) m / R V2 Set M(R) = 4 x 106 for R = 100 AU m = 3 Msun V < 1.6 km/s get M > 3.5 x 106 Msun If Sgr A* is not a SMBH…:  If Sgr A* is not a SMBH… 1) Tight binary black hole Decays by Grav Radiation 2) Theoretically “flexible” eg, density power law: r ~ 1/rb If Sgr A* is not a SMBH…:  If Sgr A* is not a SMBH… V >> 1 km/s for any dark matter distribution, unless Mdark ~ 0 Would be easily observed, except… If Sgr A* is not a SMBH…:  If Sgr A* is not a SMBH… Accel >> 10-2 cm/s2 Would be easily observed, EXCEPT… Sgr A* “orbital period”:  Sgr A* “orbital period” Measured V (& A) not sensitive to P<16 yrs Essentially all dark mass distributions give P<16 yrs But still detectable … Sgr A* orbital excursions:  Sgr A* orbital excursions Would easily see excursions > 4 AU Sgr A* either i) ~4 x 106 Msun ii) “bound” within 4 AU 4 AU 2 AU Stars orbiting Sgr A*:  Stars orbiting Sgr A* Consider star orbiting a massive object: MV = mv Add in large number of stars & random fluctuations give: MV2 ~ mv2 Effect of Bound Stars on Sgr A*:  Effect of Bound Stars on Sgr A* Recipe: Put 4 x 106 stars in computer Place SMBH/dark mass at center of mass of system Solve Kepler’s Eq for each star Calculate COM after 8 years Determine position & then velocity of SMBH Repeat as needed to get Vrms Standard IMF eccentricities from 0 to 0.99 Sgra A* must be massive…:  Sgra A* must be massive… Compare simulated systems with trial measurements Sgr A*’s mass (Msun) Best est.: 2 x 106 90% conf.: 0.3 x 106 Very conservative calc.: Ignored effects of DM, clumping, stars > 4 pc Sgra A* must be massive…:  Sgra A* must be massive… Compare simulated systems with trial measurements Sgr A*’s mass (Msun) Maximum liklihood lower limit: 1.2 x 106 90% confidence lower limit: 0.2 x 106 Very conservative calculation; ignored effects of… Possible dark cluster of stellar remnants, Stellar clumping/collective effects, Stars beyond 2 pc Effects of Stellar Remnants:  Effects of Stellar Remnants 10% of mass <100 AU in stellar remnants Plummer distribution of Mouawad et al 2004 Vz(SgrA*) > 0.3 km/s for 0.01 < a < 2 pc Question 5::  Question 5: Does Sgr A* have all the gravitational mass? Yes … well, more than ~30% of mass Exotic Dark Matter ?:  Exotic Dark Matter ? Could exotic dark matter dominate the G.C. mass? Not likely … less than 30% of mass & dropping Tied radiative source to the mass… “Fermion ball” can’t give Sgr A*’s SED First time ~106 Msun tied directly to an AGN 6 Questions: 6 Answers:  6 Questions: 6 Answers Is Sgr A* at the center of the stellar cluster? Yes … to within 10 milli-arcsec Is the stellar cluster tied to Sgr A*? Yes … to within 70 km/s Is Sgr A* at the dynamical center of the Galaxy? Yes … to within our knowledge of Qo/Ro Does Sgr A* have a peculiar motion? No … less than 2 km/s Does Sgr A* have all the mass sensed by stars? Yes … (>30%) Could exotic dark matter dominate the G. C. mass? No … (<70% and dropping; can’t give observed SED) Must Sgr A* be a SMBH?:  Must Sgr A* be a SMBH? Object Density Method Mass & Radius (Msun/pc3) M 87 2 x 106 HST: 3x109 Msun in 7 pc NGC 4258 7 x 109 VLBA : H2O 3x107 Msun in 0.1 pc Sgr A* 8 x 1015 S2’s orbit 4x106 Msun in 0.001 pc Sgr A* 2 x 1022 Sgr A*s p.m. 1x106 Msun in 0.5 AU SMBH 2 x 1025 Rsch 4x106 Msun in 0.08 AU VLBI (eg, SMA-ALMA-LMT-CARMA…) @ 1 mm -> 20 uas 10 uas @ 8 kpc The Utimate Proof/Prize:  The Utimate Proof/Prize Image SMBH with resolution ~RSch Show all of the mass is contained within ~3RSch See how accretion disk, black hole, and jets work

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