EDP Sciences
Free access
Issue
A&A
Volume 426, Number 1, October IV 2004
Page(s) 81 - 96
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20034209


A&A 426, 81-96 (2004)
DOI: 10.1051/0004-6361:20034209

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

T. Paumard1, J.-P. Maillard1 and M. Morris2

1  Institut d'astrophysique de Paris (CNRS), 98b Bd. Arago, 75014 Paris, France
    e-mail: paumard@mpe.mpg.de
2  University of California, Los Angeles, Div. of Astronomy, Dept of Physics and Astronomy, Los Angeles, CA 90095-1562, USA

(Received 19 August 2003 / Accepted 23 April 2004)

Abstract
Integral field spectroscopy of the inner region of the Galactic Center, over a field of roughly $40\arcsec\times40\arcsec$ was obtained at 2.06  $\mu$m ( $\ion{He}{i}$) and 2.16  $\mu$m (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 $\simeq$ $0.5\arcsec$. 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 $^{\star}$ . 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 $^{\star}$ 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 $^{\star}$ . 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.


Key words: Galaxy: center -- ISM: individual objects: Sgr A West -- ISM: kinematics and dynamics -- infrared: ISM -- Instrumentation: interferometers -- line: profiles

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