J/A+A/616/A111 Integral-shaped filament NH3 observations (Wu+, 2018)
Extended ammonia observations towards the integral-shaped filament.
Wu G., Qiu K., Esimbek J., Zheng X., Henkel C., Li D., Han X.H.
<Astron. Astrophys. 616, A111 (2018)>
=2018A&A...616A.111W 2018A&A...616A.111W (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Morphology
Keywords: ISM: clouds - ISM: structure - ISM: kinematics and dynamics -
stars: formation - ISM: individual objects: ISF
Abstract:
Recent observations suggest a scenario in which filamentary structures
in the interstellar medium represent the first step towards
clumps/cores and eventually star formation. The densest filaments
would then fragment into prestellar cores owing to gravitational
instability.
We seek to understand the roles filamentary structures play in
high-mass star formation.
We mapped the integral-shaped filament (ISF) located at the northern
end of the Orion A molecular cloud in NH3 (1, 1) and (2, 2). The
observations were made using the 25m radio telescope operated by the
Xinjiang Astronomical Observatory, Chinese Academy of Sciences. The
whole filamentary structure, about 1.2°x0.6°, is uniformly and
fully sampled. We investigate the morphology, fragmentation,
kinematics, and temperature properties in this region.
We find that the morphology revealed by the map of velocity-integrated
intensity of the NH3 (1, 1) line is closely associated with the dust
ridge revealed by the Herschel Space Observatory. We identify 6
"lumps" related to the well known OMC-1 to 5 and 11 "sub-clumps"
within the map. The clumps and sub-clumps are separated not randomly
but in roughly equal intervals along the ISF. The average spacing of
clumps is 11.30'±1.31' (1.36±0.16pc) and the average spacing of
sub-clumps is 7.18'±1.19' (0.86±0.14pc). These spacings agree well
with the predicted values of the thermal (0.86 pc) and turbulent
sausage instability (1.43pc) by adopting a cylindric geometry of the
ISF with an inclination of 60° with respect to the line of sight.
We also find a velocity gradient of about 0.6km/s/pc that runs along
the ISF which likely arises from an overall rotation of the Orion A
molecular cloud. The inferred ratio between rotational and
gravitational energy is well below unity. Furthermore, fluctuations
are seen in the centroid velocity diagram along the ISF. The OMC-1 to
5 clouds are located close to the local extrema of the fluctuations,
which suggests that there exist gas flows associated with these clumps
in the ISF. The derived NH3 (1, 1) and (2, 2) rotation temperatures in
the OMC-1 are about 30-40K while lower temperatures (below 20K)
are obtained in the northern and southern parts of the ISF. In OMC-2,
OMC-3, and the northern part of OMC-4, we find higher and lower
temperatures at the boundaries and in the interior, respectively.
Description:
The 25m radio telescope, operated by the Xinjiang Astronomical
Observatory, Chinese Academy of Sciences, was used for all the
NH3 (1, 1) and (2, 2) observations presented here. The rest
frequency was set at 23.708564 GHz for observing NH3 (1, 1) at
23.694495GHz and NH3 (2, 2) at 23.722633GHz, simultaneously. At
this frequency, the telescope has a primary beam width (FWHM) of
125" obtained from point-like continuum calibrators and a velocity
resolution of 0.098km/s provided by an 8192 channel Digital
Filter Bank in a 64MHz bandwidth mode.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 126 2 List of fits datacubes
fits/* . 2 Individual fits datacubes
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 21 I2 --- Nx Number of pixels along X-axis
23- 24 I2 --- Ny Number of pixels along Y-axis
26- 28 I3 --- Nz Number of pixels along Z-axis
30- 35 I6 m/s bVRAD Lower value of VRAD interval
37- 43 F7.1 m/s BVRAD Upper value of VRAD interval
45- 51 F7.3 m/s dVRAD VRAD resolution
53- 56 I4 Kibyte size Size of FITS file
58- 72 A15 --- FileName Name of FITS file, in subdirectory fits
74-126 A53 --- Title Title of the FITS file
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Acknowledgements:
Gang Wu, wug(at)xao.ac.cn
(End) Patricia Vannier [CDS] 04-Sep-2018