Astronomy and Astrophysics, volume 584A, 2-2 (2015/12-1)
KMOS view of the Galactic centre. I. Young stars are centrally concentrated.
FELDMEIER-KRAUSE A., NEUMAYER N., SCHOEDEL R., SETH A., HILKER M., DE ZEEUW P.T., KUNTSCHNER H., WALCHER C.J., LUETZGENDORF N. and KISSLER-PATIG M.
Abstract (from CDS):
The Galactic centre hosts a crowded, dense nuclear star cluster with a half-light radius of 4pc. Most of the stars in the Galactic centre are cool late-type stars, but there are also >100 hot early-type stars in the central parsec of the Milky Way. These stars are only 3-8Myr old. Our knowledge of the number and distribution of early-type stars in the Galactic centre is incomplete. Only a few spectroscopic observations have been made beyond a projected distance of 0.5pc of the Galactic centre. The distribution and kinematics of early-type stars are essential to understand the formation and growth of the nuclear star cluster. We cover the central 4pc2 (0.75arcmin2) of the Galactic centre using the integral-field spectrograph KMOS (VLT). We extracted more than 1000 spectra from individual stars and identified early-type stars based on their spectra. Our data set contains 114 bright early-type stars: 6 have narrow emission lines, 23 are Wolf-Rayet stars, 9 stars have featureless spectra, and 76 are O/B type stars. Our wide-field spectroscopic data confirm that the distribution of young stars is compact, with 90% of the young stars identified within 0.5pc of the nucleus. We identify 24 new O/B stars primarily at large radii. We estimate photometric masses of the O/B stars and show that the total mass in the young population is >12000M☉. The O/B stars all appear to be bound to the Milky Way nuclear star cluster, while less than 30% belong to the clockwise rotating disk. We add one new star to the sample of stars affiliated with this disk. The central concentration of the early-type stars is a strong argument that they have formed in situ. An alternative scenario, in which the stars formed outside the Galactic centre in a cluster that migrated to the centre, is refuted. A large part of the young O/B stars is not on the disk, which either means that the early-type stars did not all form on the same disk or that the disk is dissolving rapidly.
Galaxy: center - stars: early-type - stars: emission-line, Be - stars: Wolf-Rayet
VizieR on-line data:
<Available at CDS (J/A+A/584/A2): table2.dat table3.dat tableb1.dat tableb2.dat tableb3.dat sp/* spectra.fits>
Table 2: [FNS2015] NNNNN N=29 among (Nos 9-25346). Table 3: [FNS2015] NNNNN N=9 among (Nos 88-25347). Tables B1-B3 : [FNS2015] NNNNN N=29 among (Nos 64-11652).
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