Issue |
A&A
Volume 426, Number 1, October IV 2004
|
|
---|---|---|
Page(s) | 81 - 96 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20034209 | |
Published online | 05 October 2004 |
Kinematic and structural analysis of the Minispiral in the Galactic Center from BEAR spectro-imagery
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
Integral field spectroscopy of the inner region of the Galactic
Center, over a field of roughly was obtained at
2.06 μm (
) and 2.16 μm (Brγ) 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
. 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.
Key words: Galaxy: center / ISM: individual objects: Sgr A West / ISM: kinematics and dynamics / infrared: ISM / Instrumentation: interferometers / line: profiles
© ESO, 2004
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