J/A+A/592/A21 Are infrared dark clouds really quiescent? (Feng+, 2016)
Are infrared dark clouds really quiescent?
Feng S., Beuther H., Zhang Q., Henning T., Linz H., Ragan S., Smith R.
<Astron. Astrophys. 592, A21 (2016)>
=2016A&A...592A..21F 2016A&A...592A..21F (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Molecular clouds ; Spectroscopy
Keywords: stars: formation - stars: massive - ISM: lines and bands -
ISM: molecules - submillimeter: ISM - ISM: abundance
Abstract:
The dense, cold regions where high-mass stars form are poorly
characterised, yet they represent an ideal opportunity to learn more
about the initial conditions of high-mass star formation (HMSF), since
high-mass starless cores (HMSCs) lack the violent feedback seen at
later evolutionary stages.
We present continuum maps obtained from the Submillimeter Array (SMA)
interferometry at 1.1mm for four infrared dark clouds (IRDCs,
G28.34S, IRDC 18530, IRDC 18306, and IRDC 18308). We also present
1mm/3mm line surveys using IRAM 30m single-dish observations.
Our results are: (1) At a spatial resolution of 104AU, the 1.1mm SMA
observations resolve each source into several fragments. The mass of
each fragment is on average >10M☉, which exceeds the predicted
thermal Jeans mass of the whole clump by a factor of up to 60,
indicating that thermal pressure does not dominate the fragmentation
process. Our measured velocity dispersions in the 30m lines imply that
non-thermal motions provides the extra support against gravity in the
fragments. (2) Both non-detection of high-J transitions and the
hyperfine multiplet fit of N2H+(1-0), C2H(1-0), HCN(1-0), and
H13CN(1-0) indicate that our sources are cold and young. However,
obvious detection of SiO and the asymmetric line profile of
HCO+(1-0) in G28.34S indicate a potential protostellar object and
probable infall motion. (3) With a large number of N-bearing species,
the existence of carbon rings and molecular ions, and the
anti-correlated spatial distributions between N2H+/NH2D and CO,
our large-scale high-mass clumps exhibit similar chemical features as
small-scale low-mass prestellar objects. This study of a small sample
of IRDCs illustrates that thermal Jeans instability alone cannot
explain the fragmentation of the clump into cold (∼15K), dense
(>105cm-3) cores and that these IRDCs are not completely
quiescent.
Description:
All fits files are molecular line integrated intensity maps in
G28.34S, IRDC18530, IRDC18306, and IRDC 18308 (Fig.3 in the paper).
The maps unit is the intensity integrations (Kkm/s) over the velocity
dispersion of each line. For the lines with <4σ detections, we
only integrate a total of three channels around the system Vlsr at
their rest frequencies.
Files are named as "source"+"species"+".fits". G28.34S is abbreviated
as "28", IRDC18306 is abbreviated as "06", IRDC18308 is abbreviated as
"08", and IRDC18530 is abbreviated as "30".
Objects:
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RA (2000) DE Designation(s)
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18 33 32 -08 32 27 IRDC18306 = SDC G23.296+0.055
18 33 35 -08 35 53 IRDC18308 = SDC G23.252+0.017
18 42 47 -04 04 07 G28.34S
18 55 30 +02 17 06 IRDC18530 = SDC G35.429+0.138
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 63 76 List of fits images
fits/* . 76 Individual fits images
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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- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 29 I2 Kibyte size Size of FITS file
31- 43 A13 --- FileName Name of FITS file, in subdirectory fits
45- 63 A19 --- Title Title of the FITS file
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Acknowledgements:
Siyi Feng, syfeng(at)mpe.mpg.de
(End) Siyi Feng [SAO, Russia], Patricia Vannier [CDS] 23-May-2016