Issue |
A&A
Volume 440, Number 3, September IV 2005
|
|
---|---|---|
Page(s) | 909 - 919 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20041733 | |
Published online | 05 September 2005 |
Velocity field and star formation in the Horsehead nebula
1
LRA-LERMA, École normale supérieure et Observatoire de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France
2
Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France e-mail: hilyblan@iram.fr
3
Space Research Organization Netherlands, PO Box 800, 9700 AV Groningen, The Netherlands
4
Departamento de Astrofisica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain
5
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Received:
26
July
2004
Accepted:
4
May
2005
Using large scale maps in C18O(2-1) and in the
continuum at 1.2 mm obtained at the IRAM-30 m antenna with
the Heterodyne Receiver Array (HERA) and MAMBO2, we
investigated the morphology and the velocity field probed
in the inner layers of the Horsehead nebula. The data
reveal a non–self-gravitating () filament of dust and gas (the “neck”,
= 0.15-0.30 pc) connecting the Horsehead western ridge,
a Photon-Dominated Region illuminated by σOri, to
its parental cloud L1630. Several dense cores are embedded
in the ridge and the neck. One of these cores appears
particularly peaked in the 1.2 mm continuum map and
corresponds to a feature seen in absorption on ISO maps
around 7 μm. Its C18O emission drops at the
continuum peak, suggestive of molecular depletion onto
cold grains. The channel maps of the Horsehead exhibit an
overall north-east velocity gradient whose orientation
swivels east-west, showing a somewhat more complex
structure than was recently reported by Pound et al. (2003)
using BIMA CO(1-0) mapping. In both the neck and the
western ridge, the material is rotating around an axis
extending from the PDR to L1630 (angular velocity
=1.5-4.0 km s-1). Moreover, velocity gradients along the
filament appear to change sign regularly (3 km s-1 pc-1,
period = 0.30 pc) at the locations of embedded integrated
intensity peaks. The nodes of this oscillation are at the
same velocity. Similar transverse cuts across the filament
show a sharp variation of the angular velocity in the area
of the main dense core. The data also suggest that
differential rotation is occurring in parts of the
filament. We present a new scenario for the formation and
evolution of the nebula and discuss dense core formation
inside the filament.
Key words: ISM: clouds / ISM: kinematics and dynamics / ISM: individual objects: Horsehead nebula / stars: formation / radio lines: ISM
© ESO, 2005
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