SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month
Abstract
We report on 75 mas resolution, near-IR imaging spectroscopy within the central 30 lt-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 μm He I 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 three-dimensional 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 Sgr A*. 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 inward 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 Msolar. We happened to catch two smaller flaring events from Sgr A* during our spectral observations. The 1.7-2.45 μm spectral energy distributions of these flares are fit by a featureless, ``red'' power law of spectral index α'=-4+/-1 (Sν~να'). The observed spectral slope is in good agreement with synchrotron models in which the infrared emission comes from accelerated, nonthermal, high-energy electrons in a radiatively inefficient accretion flow in the central R~10RS region.
Based on observations obtained at the Very Large Telescope of the European Southern Observatory, Chile.- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2005
- DOI:
- 10.1086/430667
- arXiv:
- arXiv:astro-ph/0502129
- Bibcode:
- 2005ApJ...628..246E
- Keywords:
-
- Black Hole Physics;
- Galaxy: Center;
- Galaxy: Structure;
- Infrared: Stars;
- Techniques: Spectroscopic;
- Astrophysics
- E-Print:
- 50 pages, 10 figures, 2 tables, submitted to ApJ, February 6th, 2005, abstract abridged