J/A+A/632/A83 NGC 6334 filament with ALMA (Shimajiri+, 2019)
Probing fragmentation and velocity sub-structure in the massive NGC 6334
filament with ALMA.
Shimajiri Y., Andre P., Ntormousi E., Men'shchikov A., Arzoumanian D.,
Palmeirim P.
<Astron. Astrophys. 632, A83 (2019)>
=2019A&A...632A..83S 2019A&A...632A..83S
ADC_Keywords: Interstellar medium ; Radio lines
Keywords: ISM: clouds - ISM: structure - stars: formation
Abstract:
Herschel imaging surveys of galactic interstellar clouds support a
paradigm for low-mass star formation in which dense molecular
filaments play a crucial role. The detailed fragmentation properties
of star-forming filaments remain poorly understood, however, and the
validity of the filament paradigm in the intermediate- to high-mass
regime is still unclear.
Here, following up on an earlier 350um dust continuum study with the
ArTeMiS camera on the APEX telescope, we investigate the detailed
density and velocity structure of the main filament in the high-mass
star-forming region NGC 6334.
We conducted ALMA Band 3 observations in the 3.1mm continuum and of
the N2H+(1-0), HC5N(36-35), HNC(1-0), HC3N(10-9),
CH3CCH(6-5), and H2CS(3-2) lines at an angular resolution of 300,
corresponding to 0.025 pc at a distance of 1.7kpc.
The NGC 6334 filament was detected in both the 3.1mm continuum and the
N2H+, HC3N, HC5N, CH3CCH, and H2CS lines with ALMA. We
identified twenty-six compact (<0.03pc) dense cores at 3.1mm and five
velocity-coherent fiber-like features in N2H+ within the main
filament. The typical length (∼0.5pc) of, and velocity difference
(∼0.8km/s) between, the fiber-like features of the NGC 6334 filament
are reminiscent of the properties for the fibers of the low-mass
star-forming filament B211/B213 in the Taurus cloud. Only two or three
of the five velocity-coherent features are well aligned with the
NGC 6334 filament and may represent genuine, fiber sub-structures; the
other two features may trace accretion flows onto the main filament.
The mass distribution of the ALMA 3.1mm continuum cores has a peak at
10 M, which is an order of magnitude higher than the peak of the
prestellar core mass function in nearby, low-mass star-forming clouds.
The cores can be divided into seven groups, closely associated with
dense clumps seen in the ArTeMiS 350um data. The projected separation
between ALMA dense cores (0.03-0.1pc) and the projected spacing
between ArTeMiS clumps (0.2-0.3pc) are roughly consistent with the
effective Jeans length (0.08±0.03pc) in the filament and a physical
scale of about four times the filament width, respectively, if the
inclination angle of the filament to line of sight is ∼30°. These
two distinct separation scales are suggestive of a bimodal
fragmentation process in the filament.
Despite being one order of magnitude denser and more massive than the
Taurus B211/B213 filament, the NGC 6334 filament has a density and
velocity structure that is qualitatively very similar. The main
difference is that the dense cores embedded in the NGC 6334 filament
appear to be an order of magnitude denser and more massive than the
cores in the Taurus filament. This suggests that dense molecular
filaments may evolve and fragment in a similar manner in low- and
high-mass star-forming regions, and that the filament paradigm may
hold in the intermediate-mass (if not high-mass) star formation
regime.
Description:
We conducted ALMA Band3 observations in the 3.1mm continuum and of
the N2H+(1-0) line at an angular resolution of ∼3 arcsec toward
NGC6334.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
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17 20 51 -36 06.9 NGC6334 = NGC 6334
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 141 40 Results of compact source extractions on the
ALMA 12m-only 3.1mm continuum map
list.dat 238 3 List of fits files
fits/* . 3 Individual fits files
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See also:
J/A+A/481/169 : ATCA 3mm obs. of NGC 6334I and NGC 6334I(N) (Beuther+, 2008)
J/A+A/587/A135 : Halpha images of NGC 6334 and NGC 6357 (Russeil+, 2016)
J/A+A/592/A54 : Combined ArTeMiS+SPIRE 350um image of NGC6334 (Andre+, 2016)
J/A+A/593/A37 : Spectral cube toward NGC 6334 I & I(N) (van der Wiel+, 2016)
J/ApJ/866/87 : VLA 22GHz water masers obs. in NGC6334I-MM1 (Brogan+, 2018)
J/A+A/622/A99 : Starless MDCs of NGC6334 molecular spectra (Louvet+, 2019)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- ID ID numbers of 3.1 mm compact sources
4- 5 I2 h RAh Right ascension (J2000)
7- 8 I2 min RAm Right ascension (J2000)
10- 14 F5.2 s RAs Right ascension (J2000)
16 A1 --- DE- Declination sign (J2000)
17- 18 I2 deg DEd Declination (J2000)
20- 21 I2 arcmin DEm Declination (J2000)
23- 26 F4.1 arcsec DEs Declination (J2000)
28- 30 F3.1 arcsec Rmaj Deconvolved FWHM source diameter along the
major axis, in arcsec (1)
32- 34 F3.1 arcsec Rmin Deconvolved FWHM source diameter along the
minor axis, in arcsec (1)
36- 39 F4.2 pc Rmajpc Deconvolved FWHM source diameter along the
major axis, in pc (1)
41- 44 F4.2 pc Rminpc Deconvolved FWHM source diameter along the
minor axis, in pc (1)
46- 48 I3 deg PA [] Position angle (1)
50- 52 F3.1 mJy/beam Speak 3.1mm peak flux (1)
54- 56 F3.1 mJy/beam e_Speak rms uncertainty on Speak
58- 61 F4.1 --- S/N Signa-to-noise ratio f 3.1mm peak flux
63- 66 F4.1 mJy Stot Integrated 3.1mm flux density (1)
68- 71 F4.1 Msun Mtot Total mass (2)
73- 77 F5.1 10+6cm-3 nH2 Volume-averaged gas density derived assuming
spheroidal cores as in Eq. (2) of the paper
79-109 A31 --- Vch Velocity channel at which source is detected
in N2H+, in km/s unit (3)
111-141 A31 ---- Feature Association with N2H+ features
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Note (1): Results of the 2D Gaussian fitting on the 12m+7m map.
For IDs 21, 29, 32, 35, the 12m map was used since the 3.1mm continuum
emission is not detected with a >3σ on the 12m+7m map.
Note (2): We adopted Tdust=20K for all sources, except for source ID 2 for which
we assumed Tdust=50K (see Sect. 3.3.1).
Note (3): When only one value, marginal N2H+ detection since it is detected
in only one channel for this source
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
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 slices for the datacube
32- 54 A23 "datime" Obs.date Observation date
56- 61 I6 Kibyte size Size of FITS file
63- 75 A13 --- FileName Name of FITS file, in subdirectory fits
77-238 A162 --- Title Title of the FITS file
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Acknowledgements:
Yoshito Shimajiri, yoshito.shimajiri(at)nao.ac.jp
(End) Patricia Vannier [CDS] 22-Nov-2019