J/A+A/622/A99 Starless MDCs of NGC6334 molecular spectra (Louvet+, 2019)
Lack of high-mass pre-stellar cores in the starless MDCs of NGC 6334.
Louvet F., Neupane S., Garay G., Russeil D., Zavagno A., Gomez L.,
Guzman A., Bronfman L., Nony T.
<Astron. Astrophys. 622, A99 (2019)>
=2019A&A...622A..99L 2019A&A...622A..99L (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Spectroscopy
Keywords: stars: formation - stars: massive - ISM: clouds - ISM: structure -
methods: observational - techniques: interferometric
Abstract:
The formation of high-mass stars remains unknown in many aspects. Two
families of models compete to explain the formation of high-mass
stars. On the one hand, quasi-static models predict the existence of
high-mass pre-stellar cores sustained by a high degree of turbulence.
On the other hand competitive accretion models predict that high-mass
proto-stellar cores evolve from low/intermediate mass proto-stellar
cores in dynamic environments.
The aim of the present work is to bring observational constraints at
the scale of high-mass cores (∼0.03pc).
We targeted with ALMA and MOPRA a sample of 9 starless massive dense
cores (MDCs) discovered in a recent Herschel/HOBYS study. Their mass
and size (∼110M☉ and r=0.1pc, respectively) are similar to the
initial conditions used in the quasi-static family of models
explaining for the formation of high-mass stars.We present ALMA 1.4mm
continuum observations that resolve the Jeans length
(λJeans∼0.03pc) and that are sensitive to the Jeans mass
(MJeans∼0.65M☉) in the 9 starless MDCs, together with
ALMA-12CO(2-1) emission line observations. We also present
HCO+(1-0), H13CO+(1-0) and N2H+(1-0) molecular lines from the
MOPRA telescope for 8 of the 9 MDCs.
The 9 starless MDCs have the mass reservoir to form high-mass stars
according to the criteria by Baldeschi et al. (2017MNRAS.466.3682B 2017MNRAS.466.3682B).
Three of the starless MDCs are subvirialized with αvir∼0.35,
and 4 MDCs show sign of collapse from their molecular emission lines.
ALMA observations show very little fragmentation within the MDCs. Only
two of the starless MDCs host compact continuum sources, whose fluxes
correspond to <3M☉ fragments. Therefore the mass reservoir of
the MDCs has not yet been accreted onto compact objects, and most of
the emission is filtered out by the interferometer.
These observations do not support the quasi-static models for
high-mass star formation since no high-mass pre-stellar core is found
in NGC6334. The competitive accretion models, on the other hand,
predict a level of fragmentation much higher than what we observe
Description:
These observations were performed in September 2008 with the ATNF
MOPRA 22-m telescope with the 3mm receiver and the MOPRA spectrometer
(MOPS) in the "zoom mode" that allows to observe simultaneously up
to 16 different frequencies, among them the HCO+(1-0) at 89.18GHz,
the H13CO+(1-0) at 86.75GHz, and the N2H+(1-0) at 93.17GHz
emission lines.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 75 9 Physical parameters of the MDCs
table2.dat 65 8 Physical parameters of the fragments
tablea1.dat 74 9 Additional parameters of the MDCs
tablea2.dat 56 9 Integration parameters of the CO line in the MDCs
list.dat 149 15 List of fits spctra
fits/* . 15 Individual fits spectra
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See also:
J/A+A/602/A77 : HOBYS: 46 MDCs found in NGC 6334 (Tige+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- MDC MDC name (NGC6334-MDC NN)
16- 21 F6.4 pc Rad Radius (Mean value 0.090)
22- 24 I3 Msun Mass Mass (Mean value 116)
26- 29 F4.1 km/s vN2H+ ?=- N2H+ velocity
31- 34 F4.2 km/s sigmaN2H+ ?=- N2H+ velocity dispersion
(Mean value 1.12)
36- 39 F4.1 km/s vHCO+ ?=- HCO+ velocity
41- 44 F4.1 km/s vH13CO+ ?=- H13CO+ velocity
46- 49 F4.1 --- deltaV ?=- Asymmetry parameter,
δV=(Vthick-Vthin))/σVthin)
(1)
51- 53 I3 Msun Mvir ?=- Virial mass (Mean value 71)
55- 58 F4.2 --- alphavir ?=- Virial parameter alpha (Mean value 0.60)
60- 63 F4.1 Msun Mthr Threshold mass (Mean value 40.0)
65- 68 F4.2 Msun MJeans Jeans mass (Mean value 0.64)
70- 71 I2 pc lambdaJeans Jeans scale, λJeans (Mean value 32)
73- 75 F3.1 mgauss Bfield ?=- Magnetic field (Mean value 1.2)
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Note (1): A negative deltaV value is indicative of infall, and
a positive value of deltaV is indicative of expansion motions.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Source Source name (1)
15- 16 I2 h RAh Right ascension (J2000)
18- 19 I2 min RAm Right ascension (J2000)
21- 25 F5.2 s RAs Right ascension (J2000)
27 A1 --- DE- Declination sign (J2000)
28- 29 I2 deg DEd Declination (J2000)
31- 32 I2 arcmin DEm Declination (J2000)
34- 38 F5.2 arcsec DEs Declination (J2000)
40- 43 F4.1 mJy Flux Integrated flux (Mean value 9.0±0.4)
45- 47 F3.1 mJy e_Flux rms uncertainty on Flux
49- 51 F3.1 arcsec Size1 Size (Mean value 1.0x0.8)
52 A1 --- --- [x]
53- 55 F3.1 arcsec Size2 Size (Mean value 1.0x0.8)
57- 60 F4.2 Msun Mass Mass (method to derive the mass follows
eq. (2)) (Mean value 0.90±0.03)
62- 65 F4.2 Msun e_Mass rms uncertainty on Mass
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Note (1): The label of the source is defined as the name of the nearest MDC,
plus the Getsources extraction number MDC NN-almaNN
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- MDC Source name, NGC6334-MDC NN (1)
16- 17 I2 h RAh Right ascension (J2000)
19- 20 I2 min RAm Right ascension (J2000)
22- 26 F5.2 s RAs Right ascension (J2000)
28 A1 --- DE- Declination sign (J2000)
29- 30 I2 deg DEd Declination (J2000)
32- 33 I2 arcmin DEm Declination (J2000)
35- 39 F5.2 arcsec DEs Declination (J2000)
40- 42 I3 Lsun Lbol Bolometric luminosity (Meand value 203) (1)
44- 48 F5.2 Msun/Lsun M/L Mass to light ratio
50- 55 E6.2 cm-3 <nH2> Mean H2 density number
(Mean value 2.0E+6) (1)
57- 60 F4.1 K T Temperature (Mean value 15.5) (1)
62- 65 F4.1 mJy/beam sigma12CO 1CO velocity dispersion
(Mean value 16.6) (2)
67- 69 I3 uJy/beam sigmacont Continuum velocity dispersion
(Mean value 336) (3)
71- 74 F4.2 Msun MassSen Mass sensitivity at 5σ
(Mean value 0.11) (4)
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Note (1): Data set from Tige et al., 2017, Cat. J/A+A/602/A77.
Note (2): ALMA-cycle 3 observations. The 1σ rms noise level is given per
channel, where the channel width is of 0.7km/s.
Note (3): ALMA-cycle 3 observations
Note (4): ALMA-cycle 3 observations. The method to estimate the mass from the
5σ value follows the equation (2).
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- MDC MDC name
16 A1 --- ---
17- 21 F5.1 km/s bVelBS Lower value of blue-shifted 12CO(2-1)
emission velocity range
23 A1 --- --- [;]
25- 29 F5.1 km/s BVelBS Upper value of blue-shifted 12CO(2-1)
emission velocity range
31 A1 --- ---
33- 36 F4.1 mJy/beam*km/s sigmaB 1σ value for blue-shifted 12CO(2-1)
38 A1 --- ---
39- 42 F4.1 km/s bVelRS Lower value of red-shifted 12CO(2-1)
emission velocity range
44 A1 --- --- [;]
46- 49 F4.1 km/s BVelRS Upper value of red-shifted 12CO(2-1)
emission velocity range
51 A1 --- ---
53- 56 F4.1 mJy/beam*km/s sigmaR 1σ value for red-shifted 12CO(2-1)
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right Ascension (J2000)
4- 5 I2 min RAm Right Ascension (J2000)
7- 11 F5.2 s RAs Right Ascension (J2000)
13 A1 --- DE- Declination sign (J2000)
14- 15 I2 deg DEd Declination (J2000)
17- 18 I2 arcmin DEm Declination (J2000)
20- 23 F4.1 arcsec DEs Declination (J2000)
25- 28 I4 --- Nx Number of pixels along X-axis
30- 52 A23 "datime" Obs.date Observation date (YYYY-MM-DDThh:mm:ss.sss"
54- 65 E12.6 Hz bFreq Lower value of relative frequency interval
67- 77 E11.6 Hz BFreq Upper value of relative frequency interval
79- 85 F7.1 Hz dFreq Frequency resolution
87- 88 I2 Kibyte size Size of FITS file
90-101 A12 --- FileName Name of FITS file, in subdirectory fits
103-149 A47 --- Title Title of the FITS file
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Acknowledgements:
Fabien Louvet, fabien.louvet(at)cea.fr
(End) Patricia Vannier [CDS] 13-Dec-2018