Kinematic and structural analysis of the Minispiral in the Galactic Center from BEAR spectro-imagery

Thibaut Paumard1, & Jean-Pierre Maillard1, & Mark Morris2

(1) Institut d'astrophysique de Paris (CNRS), 98b Blvd Arago, 75014 Paris, France
(2) University of California, Los Angeles, Div. of Astronomy, Dept of Physics and Astronomy, Los Angeles, CA 90095-1562, USA

Paper: A&A, 2004, in press

EPrint Server: astro-ph/0405197


Integral field spectroscopy of the inner region of the Galactic Center, over a field of roughly 40''*40'' was obtained at 2.06 micron (HeI) and 2.16 micron (Br gamma ) using BEAR, an imaging Fourier Transform Spectrometer, at spectral resolutions respectively of 52.9 km s-1 and 21.3 km s-1, and a spatial resolution of 0.5''. The analysis of the data was focused on the kinematics of the gas flows, traditionally called the ``Minispiral'', concentrated in the neighborhood of the central black hole, Sgr A*. From the decomposition into several velocity components (up to four) of the line profile extracted at each point of the field, velocity features were identified. Nine distinguishable structures are described: the standard Northern Arm, Eastern Arm, Bar, Western Arc, and five additional, coherently-moving patches of gas. From this analysis, the Northern Arm appears not limited, as usually thought, to the bright, narrow North-South lane seen on intensity images, but it consists instead of a weak, continuous, triangular-shaped surface, drawn out into a narrow stream in the vicinity of Sgr A* where it shows a strong velocity gradient, and a bright western rim. The Eastern Arm is split into three components (a Ribbon and a Tip, separated by a cavity, and an elongated feature parallel to the Ribbon: the Eastern Bridge). We also report extinction of some interstellar structures by other components, providing information on their relative position along the line of sight. A system of Keplerian orbits can be fitted to most of the Northern Arm, and the bright rim of this feature can be interpreted in terms of line-of-sight orbit crowding caused by the warping of the flowing surface at the western edge facing Sgr A*. These results lead to a new picture of the gas structures in Sgr A West, in which large-scale gas flows and isolated gas patches coexist in the gravitational field of the central Black Hole. The question of the origin of the ionized gas is addressed and a discussion of the lifetime of these features is presented.

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