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 centralparsecoftheGalaxy.Detection oftheirabsorption lineshasbecomepossible withthehighspatialandspectral resolution and sensitivity of the adaptive optics integral field spectrometer SPIFFI/SINFONI on the ESO VLT. Sev- eral 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 (h h jj /R i' 0:14) rotating disks. These stellar disks have fairly sharp inner edges (R ' 100) 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,whereasmostof thoseinthe''counterclockwise''diskappeartobeoneccentricorbits.Basedonitsstellarsurface densitydistributionanddynamics,weproposethatIRS13Eisanextremelydensecluster( core k 3 ;108 Mpc 3)that has formed in the counterclockwise disk. The stellar contents of both systems are remarkably similar, indicating a common age of '6 2M yr.TheK-band luminosity functionof the massive stars suggests a top-heavy mass function and limitsthe totalstellar masscontained in both disks to '1:5 ; 104 M . Our datastrongly favor insitu starformation 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. Subject headings: Galaxy: center — stars: early-type — stars: formation — stars: luminosity function, mass function — stellar dynamics