J/A+A/672/A133 Orion B molecular cloud CO and HCO datacubes (Shimajiri+, 2023)
Witnessing the fragmentation of a filament into prestellar cores in
Orion B/NGC 2024.
Shimajiri Y., Andre P., Peretto N., Arzoumanian D., Ntormousi E., Konyves V.
<Astron. Astrophys. 672, A133 (2023)>
=2023A&A...672A.133S 2023A&A...672A.133S (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Radio lines ; Carbon monoxide
Keywords: stars: formation - molecular data - ISM: clouds
Abstract:
Recent Herschel observations of nearby molecular clouds have shown
that filamentary structures are ubiquitous and that most prestellar
cores form in dense filaments. Probing the detailed density and
velocity structure of molecular filaments is therefore crucial for
improving our observational understanding of the star formation
process.
We aim to characterize both the density and the velocity field of a
typical molecular filament in the process of fragmenting into cores.
We mapped a portion of the NGC 2024 region in the Orion B molecular
cloud with the Nobeyama 45m telescope, in the 12CO (J=1-0),
13CO (J=1-0), C18O (J=1-0), and H13CO+ (J=1-0) lines, and the
southwestern part of NGC 2024, corresponding to the NGC 2024S
filament, with the NOEMA interferometer in H13CO+ (J=1-0).
The maps of 13CO, C18O, and H13CO+ emission trace at least part
of the filamentary structure seen in the 800-resolution
ArTeMiS+Herschel data. The median radial column density profile of the
NGC 2024S filament as derived from ArTeMiS+Herschel dust emission data
is well fitted by a Plummer profile with a half-power diameter
DPlummerHP=0.081±0.014pc, which is similar to the findings of
previous studies of nearby molecular filaments with Herschel. On the
other hand, the half-power diameters of NGC 2024S as measured from the
Nobeyama 13CO and C18O data are broader, while the half-power
diameter derived from the H13CO+ data is narrower, than the filament
diameter measured with Herschel. These results suggest that the 13CO
and C18O data trace only the (low-density) outer part of the
Herschel filament and the H13CO+ data only the (dense) inner part.
We identified four cores in the portion of the Herschel map covered by
NOEMA and found that each Herschel core corresponds to a single core
detected in the combined NOEMA+45m H13CO+ data cube. The Nobeyama
H13CO+ centroid velocity map reveals velocity gradients along both
the major and the minor axis of the NGC 2024S filament, as well as
velocity oscillations with a period ∼0.2pc along the major axis.
Comparison between the centroid velocity and the column density
distribution shows a tentative λ/4 phase shift in H13CO+ or
C18O. This λ/4 shift is not simultaneously observed for all
cores in any single tracer but is tentatively seen for each core in
either H13CO+ or C18O. The difference between the H13CO+ and
C18O velocity patterns may arise from differences in the range of
densities probed by H13CO+ and C18O. We produced a toy model
taking into account the three velocity-field components: a transverse
velocity gradient, a longitudinal velocity gradient, and a
longitudinal oscillation mode caused by fragmentation. Examination of
synthetic data shows that the longitudinal oscillation component
produces an oscillation pattern in the velocity structure function of
the model. Since the velocity structure function of the Nobeyama
H13CO+ centroid velocity data does show an oscillation pattern, we
suggest that our observations are partly tracing core-forming motions
and fragmentation of the NGC 2024S filament into cores. We also found
that the mean core mass in NGC 2024S corresponds to the effective
Bonnor-Ebert mass in the filament. This is consistent with a scenario
in which higher-mass cores form in higher line-mass filaments.
We revealed that (1) the widths of filaments vary among tracers, (2)
filaments a re breaking into cores, and (3) cores with higher mass
form in filaments with a higher line-mass.
Description:
We mapped a portion of the NGC 2024 region in the Orion B molecular
cloud with the Nobeyama 45m telescope, in the 12CO (J=1-0),
13CO (J=1-0), C18O (J=1-0), and H13CO+ (J=1-0) lines, and the
southwestern part of NGC 2024, corresponding to the NGC 2024S
filament, with the NOrthern Extended Millimeter Array (NOEMA)
interferometer in H13CO+ (J=1-0).
Objects:
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RA (2000) DE Designation(s)
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05 41 43.00 -01 50 30.0 NGC 2024 = [BDB2003] G206.47-16.32
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 162 5 List of fits datacubes
fits/* . 5 Individual fits datacubes
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See also:
J/AJ/126/1665 : NICMOS observations of NGC 2024 (Liu+, 2003)
J/ApJ/598/375 : Chandra X-ray observations of NGC 2024 (Skinner+, 2003)
J/ApJ/646/1215 : Low-mass stars and brown dwarfs in NGC 2024 (Levine+, 2006)
J/ApJ/787/109 : Age estimates for NGC 2024 and ONC stars (Getman+, 2014)
J/ApJ/802/77 : Protoplanetary disk masses in NGC 2024 cluster (Mann+, 2015)
J/A+A/640/A27 : Protoplanetary disk masses in NGC 2024 (van Terwisga+, 2020)
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- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 30 I3 --- Nz Number of pixels along Z-axis
32- 52 A21 "datime" Obs.date Observation date
54- 65 E12.6 m/s bVELO-LSR Lower value of VELO_LSR velocity
67- 77 E11.6 m/s BVELO-LSR Upper value of VELO_LSR velocity
78- 83 I6 m/s dVELO-LSR VELO_LSR resolution
85- 89 I5 Kibyte size Size of FITS file
91-119 A29 --- FileName Name of FITS file, in subdirectory fits
121-162 A42 --- Title Title of the FITS file
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Acknowledgements:
Yoshito Shimajiri, y-shimajiri(at)fains.jp
(End) Patricia Vannier [CDS] 13-Feb-2023