SINFONI in the Galactic Center: young stars and IR flares in the central light month

F.Eisenhauer, R.Genzel, T.Alexander, R.Abuter, T.Paumard, T.Ott, A.Gilbert, S.Gillessen, M.Horrobin, S.Trippe, H.Bonnet, C.Dumas, N.Hubin, A.Kaufer, M.Kissler-Patig, G.Monnet, S.Ströbele, T.Szeifert, A.Eckart, R.Schödel & S.Zucker

EPrint Server: astro-ph/0502129


We report 75 milli-arcsec resolution, near-IR imaging spectroscopy within the central 30 light days of the Galactic Center, taken with the new adaptive optics assisted, integral field spectrometer SINFONI on the ESO-VLT. To a limiting magnitude of K 16, 9 of 10 stars in the central 0.4'', and 13 of 17 stars out to 0.7'' from the central black hole have spectral properties of B0-B9, main sequence stars. Based on the 2.1127 micron HeI line width all brighter early type stars have normal rotation velocities, similar to solar neighborhood stars. We combine the new radial velocities with SHARP/NACO astrometry to derive improved 3d stellar orbits for six of these 'S'-stars in the central 0.5''. Their orientations in space appear random. Their orbital planes are not co-aligned with those of the two disks of massive young stars 1-10'' from SgrA*. We can thus exclude the hypothesis that the S-stars as a group inhabit the inner regions of these disks. They also cannot have been located/formed in these disks and then migrated inwards within their planes. From the combination of their normal rotation and random orbital orientations we conclude that the S-stars were most likely brought into the central light month by strong individual scattering events. The updated estimate of distance to the Galactic center from the S2 orbit fit is R0=7.62+/-0.32 kpc, resulting in a central mass value of 3.61+/-0.32*106 Mo. We happened to catch two smaller flaring events from SgrA* during our spectral observations. The 1.7-2.45 micron spectral energy distributions of these flares are fit by a featureless, 'red' power law of spectral index alpha '=-4+/-1(S nu nu alpha ') . The observed spectral slope is in good agreement with synchrotron models in which the infrared emission comes from accelerated non-thermal, high energy electrons in a radiative inefficient accretion flow in the central R 10 Rs region.

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