The Two Young Star Disks in the Central Parsec of the Galaxy: Properties, Dynamics, and Formation

We report the definite spectroscopic identification of ≃40 OB supergiants, giants, and main-sequence stars in the central parsec of the Galaxy. Detection of their absorption lines has become possible with the high spatial and spectral resolution and sensitivity of the adaptive optics integral field spectrometer SPIFFI/SINFONI on the ESO VLT. Several of these OB stars appear to be helium- and nitrogen-rich. Almost all of the ≃80 massive stars now known in the central parsec (central arcsecond excluded) reside in one of two somewhat thick (⟨ /R⟩ ≃ 0.14) rotating disks. These stellar disks have fairly sharp inner edges (R ≃ 1′′) and surface density profiles that scale as R-2. We do not detect any OB stars outside the central 0.5 pc. The majority of the stars in the clockwise system appear to be on almost circular orbits, whereas most of those in the "counterclockwise" disk appear to be on eccentric orbits. Based on its stellar surface density distribution and dynamics, we propose that IRS 13E is an extremely dense cluster (ρcore ≳ 3 × 108 M☉ pc-3) that has formed in the counterclockwise disk. The stellar contents of both systems are remarkably similar, indicating a common age of ≃6 ± 2 Myr. The K-band luminosity function of the massive stars suggests a top-heavy mass function and limits the total stellar mass contained in both disks to ≃1.5 × 104 M☉. Our data strongly favor in situ star formation from dense gas accretion disks for the two stellar disks. This conclusion is very clear for the clockwise disk and highly plausible for the counterclockwise system.

[1]  H Germany,et al.  GCIRS34W : an irregular variable in the Galactic Centre , 2005, astro-ph/0510478.

[2]  James E. Larkin,et al.  High Spectral Resolution Observations of the Massive Stars in the Galactic Center , 2005, astro-ph/0510028.

[3]  Reinhard Genzel,et al.  Weighing the young stellar discs around Sgr A , 2005 .

[4]  T. Alexander,et al.  Stellar Processes Near the Massive Black Hole in the Galactic Center , 2005, astro-ph/0508106.

[5]  Norbert Hubin,et al.  SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month , 2005 .

[6]  R. Kudritzki,et al.  A Medium Resolution Near-Infrared Spectral Atlas of O and Early-B Stars , 2005, astro-ph/0506705.

[7]  Wolfgang Brandner,et al.  The Arches Cluster: Evidence for a Truncated Mass Function? , 2005, astro-ph/0506575.

[8]  A. Eckart,et al.  A Black Hole in the Galactic Center Complex IRS 13E , 2005 .

[9]  IRS 16 SW: A New Comoving Group of Young Stars in the Central Parsec of the Milky Way , 2005, astro-ph/0504276.

[10]  R. Kudritzki,et al.  The Physical Properties and Effective Temperature Scale of O-Type Stars as a Function of Metallicity. II. Analysis of 20 More Magellanic Cloud Stars and Results from the Complete Sample , 2005, astro-ph/0503464.

[11]  F. Martins,et al.  A new calibration of stellar parameters of Galactic O stars , 2005, astro-ph/0503346.

[12]  E. Quataert,et al.  Radiation Pressure-supported Starburst Disks and Active Galactic Nucleus Fueling , 2005, astro-ph/0503027.

[13]  MIT,et al.  An Overabundance of Transient X-Ray Binaries within 1 Parsec of the Galactic Center , 2004, astro-ph/0412492.

[14]  F. Rasio,et al.  The Disruption of Stellar Clusters Containing Massive Black Holes near the Galactic Center , 2004, astro-ph/0412452.

[15]  Jessica R. Lu,et al.  Stellar Orbits around the Galactic Center Black Hole , 2003, astro-ph/0306130.

[16]  Bernard Delabre,et al.  First light of SINFONI at the VLT , 2004 .

[17]  Cambridge,et al.  Hard X-ray view of the past activity of Sgr A in a natural Compton mirror , 2004, astro-ph/0408190.

[18]  M. F. Radioastronomie,et al.  The Proper Motion of Sagittarius A*. II. The Mass of Sagittarius A* , 2004, astro-ph/0408107.

[19]  Y. Levin,et al.  Orbital Roulette: A New Method of Gravity Estimation from Observed Motions , 2004, astro-ph/0405533.

[20]  M. Morris,et al.  Kinematic and structural analysis of the Minispiral in the Galactic Center from BEAR spectro-imagery , 2004, astro-ph/0405197.

[21]  M. Morris,et al.  Dynamical Friction on Galactic Center Star Clusters with an Intermediate-Mass Black Hole , 2004, astro-ph/0405164.

[22]  T. Paumard,et al.  The nature of the Galactic Center source IRS 13 revealed by high spatial resolution in the infrared , 2004 .

[23]  G. Meynet,et al.  Stellar evolution with rotation and magnetic fields II. General equations for the transport by Tayler-Spruit dynamo , 2004, astro-ph/0404417.

[24]  Mario Livio,et al.  Orbital Capture of Stars by a Massive Black Hole via Exchanges with Compact Remnants , 2004, astro-ph/0403425.

[25]  First results from SPIFFI. I: The Galactic Center , 2004 .

[26]  Milos Milosavljevic,et al.  The Link between Warm Molecular Disks in Maser Nuclei and Star Formation near the Black Hole at the Galactic Center , 2004, astro-ph/0401221.

[27]  J. Goodman,et al.  Supermassive Stars in Quasar Disks , 2003, astro-ph/0307361.

[28]  J. Puls,et al.  Bright OB stars in the Galaxy I. Mass-loss and wind-momentum rates of O-type stars: A pure Hα analysis accounting for line-blanketing , 2004 .

[29]  A. Sternberg,et al.  Ionizing Photon Emission Rates from O- and Early B-Type Stars and Clusters , 2003, astro-ph/0312232.

[30]  Onera,et al.  The infrared L'-band view of the Galactic Center with NAOS-CONICA at VLT , 2003, astro-ph/0312108.

[31]  M. Questier.  Rethinking Catholicism in Reformation England. By Lucy E. C. Wooding. Oxford Historical Monographs. Edited by, R. R. Davies et al. Oxford: Oxford University Press, Clarendon Press, 2000. Pp. viii+305. $35.00. , 2003 .

[32]  Harvey S. Liszt,et al.  The velocity field of ionized gas near Sgr A$^{\ast}$ , 2003 .

[33]  Ralf Bender,et al.  The universe in 3D : First observations with SPIFFI, the infrared integral field spectrometer for the VLT , 2003 .

[34]  Marcia J. Rieke,et al.  Hubble Space Telescope Paα and 1.9 Micron Imaging of Sagittarius A West , 2003 .

[35]  K. Sellgren,et al.  Really Cool Stars and the Star Formation History at the Galactic Center , 2003, astro-ph/0307291.

[36]  Mark Morris,et al.  Dynamical Friction on Star Clusters near the Galactic Center , 2003, astro-ph/0307271.

[37]  A. Eckart,et al.  Stellar Dynamics in the Central Arcsecond of Our Galaxy , 2003, astro-ph/0306214.

[38]  Milos Milosavljevic,et al.  The Need for a Second Black Hole at the Galactic Center , 2003, astro-ph/0306074.

[39]  D. Rouan,et al.  The Stellar Cusp around the Supermassive Black Hole in the Galactic Center , 2003, astro-ph/0305423.

[40]  M. Rieke,et al.  HST Paschen alpha and 1.9 micron imaging of Sgr A West , 2003, astro-ph/0305350.

[41]  G. Meynet,et al.  Stellar evolution with rotation X. Wolf-Rayet star populations at solar metallicity , 2022 .

[42]  Simon Portegies Zwart,et al.  The Fate of Star Clusters near the Galactic Center. I. Analytic Considerations , 2003, astro-ph/0304022.

[43]  Matthew Bierbaum,et al.  Formation of Massive Black Holes in Dense Star Clusters. I. Mass Segregation and Core Collapse , 2003, astro-ph/0308449.

[44]  Simon Portegies Zwart,et al.  The Origin of IRS 16: Dynamically Driven In-Spiral of a Dense Star Cluster to the Galactic Center? , 2003, astro-ph/0303599.

[45]  Yuri Levin,et al.  Stellar Disk in the Galactic Center: A Remnant of a Dense Accretion Disk? , 2003, astro-ph/0303436.

[46]  Jeremy Goodman,et al.  Self-gravity and quasi-stellar object discs , 2003 .

[47]  Norbert N. Hubin,et al.  SINFONI - Integral field spectroscopy at 50 milli-arcsecond resolution with the ESO VLT , 2003, SPIE Astronomical Telescopes + Instrumentation.

[48]  Anne-Marie Lagrange,et al.  NAOS-CONICA first on sky results in a variety of observing modes , 2003, SPIE Astronomical Telescopes + Instrumentation.

[49]  A. Gould,et al.  Sagittarius A* Companion S0-2: A Probe of Very High Mass Star Formation , 2003, astro-ph/0302437.

[50]  G. Neugebauer,et al.  The First Measurement of Spectral Lines in a Short-Period Star Bound to the Galaxy’s Central Black Hole: A Paradox of Youth , 2003 .

[51]  Norbert N. Hubin,et al.  Implementation of MACAO for SINFONI at the VLT, in NGS and LGS modes , 2003, SPIE Astronomical Telescopes + Instrumentation.

[52]  David Mouillet,et al.  NAOS, the first AO system of the VLT: on-sky performance , 2003, SPIE Astronomical Telescopes + Instrumentation.

[53]  D. Figer.  Massive stars and the creation of our Galactic Center , 2002, astro-ph/0207300.

[54]  C. McKee,et al.  The Formation of Massive Stars from Turbulent Cores , 2002, astro-ph/0206037.

[55]  R. Sari,et al.  Eccentricity Evolution for Planets in Gaseous Disks , 2002, astro-ph/0202462.

[56]  H. Falcke,et al.  The Galactic Black Hole : Lectures on General Relativity and Astrophysics , 2002 .

[57]  C. Evans,et al.  Revised Stellar Temperatures for Magellanic Cloud O Supergiants from Far Ultraviolet Spectroscopic Explorer and Very Large Telescope UV-Visual Echelle Spectrograph Spectroscopy , 2002 .

[58]  K. Menten,et al.  A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way , 2002, Nature.

[59]  C. Evans,et al.  Revised Stellar Temperatures for Magellanic Cloud O Supergiants from FUSE and VLT-UVES Spectroscopy , 2002, astro-ph/0206257.

[60]  Simon F. Portegies Zwart,et al.  The Runaway Growth of Intermediate-Mass Black Holes in Dense Star Clusters , 2002, astro-ph/0201055.

[61]  Jeremy Goodman,et al.  Selfgravity and QSO disks , 2002, astro-ph/0201001.

[62]  On the effective temperature scale of O stars , 2001, astro-ph/0111233.

[63]  UCLA,et al.  Chandra X-Ray Spectroscopic Imaging of Sagittarius A* and the Central Parsec of the Galaxy , 2001, astro-ph/0102151.

[64]  Charles F. Gammie,et al.  Nonlinear Outcome of Gravitational Instability in Cooling, Gaseous Disks , 2001, astro-ph/0101501.

[65]  T. Paumard,et al.  New results on the helium stars in the galactic center using BEAR spectro-imagery , 2000, astro-ph/0011215.

[66]  Laird M. Close,et al.  Analysis of isoplanatic high resolution stellar fields by the StarFinder code , 2000 .

[67]  Thibault Lejeune,et al.  Database of Geneva stellar evolution tracks and isochrones for (UBV) J (RI) C JHKLL'M, HST-WFPC2, Geneva and Washington photometric systems , 2000 .

[68]  C. Pichon,et al.  Stellar dynamics in the Galactic centre: Proper motions and anisotropy , 2000, astro-ph/0001428.

[69]  Hubble Space Telescope/NICMOS Observations of Massive Stellar Clusters near the Galactic Center , 1999, astro-ph/9906299.

[70]  Landolt-Börnstein. Numerical data and functional relationships in science and technology. New Series. Group VI: Astronomy and astrophysics. Volume 3: Astronomy and astrophysics. Extension and supplement to Volume 2. Subvolume c: Interstellar matter, Galaxy, universe. , 1999 .

[71]  A. Sternberg.  The Initial Mass Functions in the Super-Star Clusters NGC 1569A and NGC 1705-1 , 1998, astro-ph/9805240.

[72]  W. Goss,et al.  Radio Continuum Structure of IRS 13 and Proper Motions of Compact H II Components at the Galactic Center , 1998 .

[73]  William D. Vacca,et al.  New Models for Wolf-Rayet and O Star Populations in Young Starbursts , 1997, astro-ph/9711140.

[74]  Reinhard Genzel,et al.  On the nature of the dark mass in the centre of the Milky Way , 1997 .

[75]  I. McLean,et al.  A K-Band Spectral Atlas of Wolf-Rayet Stars , 1997 .

[76]  L. Wallace,et al.  Medium-Resolution Spectra of Normal Stars in the K Band , 1997 .

[77]  D. Martinez-Delgado,et al.  Luminous Red Stars in Local Group Dwarf Elliptical Galaxies: An Intermediate-Age Population? , 1997, astro-ph/9704013.

[78]  Alfred Krabbe,et al.  The Dark Mass Concentration in the Central Parsec of the Milky Way , 1996 .

[79]  M. Rieke,et al.  A spectral atlas of hot, luminous stars at 2 microns , 1996 .

[80]  P. Conti,et al.  Infrared Spectra of Massive Stars in Transition: WNL, Of, Of/WN, Be, B[e], and Luminous Blue Variable Stars , 1996 .

[81]  Eugene Serabyn,et al.  THE GALACTIC CENTER ENVIRONMENT , 1996 .

[82]  Really Cool Stars at the Galactic Center , 1996, astro-ph/9608107.

[83]  Laird M. Close,et al.  The peculiar population of hot stars at the galactic center , 1996 .

[84]  Alfred Krabbe,et al.  The Nuclear Cluster of the Milky Way: Star Formation and Velocity Dispersion in the Central 0.5 Parsec , 1995 .

[85]  K. Sellgren,et al.  Discovery of a possible Wolf-Rayet star at the galactic center , 1995 .

[86]  A. Zdziarski,et al.  Black hole accretion disks with coronae , 1994 .

[87]  G. Rieke,et al.  IRS 16: The Galaxy's Central Wimp? , 1993 .

[88]  Mark R. Morris,et al.  Massive star formation near the Galactic center and the fate of the stellar remnants , 1993 .

[89]  Gordon J. Stacey,et al.  Neutral gas in the central 2 parsecs of the Galaxy , 1993 .

[90]  W. Vacca,et al.  Optical spectrophotometry of Wolf-Rayet galaxies , 1992 .

[91]  Alfred Krabbe,et al.  A cluster of He I emission-line stars in the Galactic center , 1991 .

[92]  D. Allen,et al.  The source of luminosity at the Galactic Centre , 1990 .

[93]  J. E. Pringle,et al.  A viscosity prescription for a self-gravitating accretion disc⋆ , 1987 .

[94]  R. Genzel,et al.  Physical conditions, dynamics, and mass distribution in the center of the galaxy , 1987 .

[95]  Jack J. Lissauer,et al.  Timescales for planetary accretion and the structure of the protoplanetary disk , 1986 .

[96]  S. G. Kleinmann,et al.  Broad helium emission in the galactic center , 1982 .

[97]  G. Neugebauer,et al.  High-resolution maps of the galactic center at 2.2 and 10 microns , 1975 .

[98]  A. Toomre,et al.  On the gravitational stability of a disk of stars , 1964 .