J/MNRAS/503/4601 ALMA-IRDC from cloud to core scales (Barnes+, 2021)
ALMA-IRDC: dense gas mass distribution from cloud to core scales.
Barnes A.T., Henshaw J.D., Fontani F., Pineda J.E., Cosentino G., Tan J.C.,
Caselli P., Jimenez-serra I., Law C.Y., Avison A., Bigiel F., Feng S.,
Kong S., Longmore S.N., Moser L., Parker R.J., Sanchez-monge A., Wang K.
<Mon. Not. R. Astron. Soc., 503, 4601-4626 (2021)>
=2021MNRAS.503.4601B 2021MNRAS.503.4601B (SIMBAD/NED BibCode)
ADC_Keywords: Infrared sources; Millimetric/submm sources; Molecular clouds;
Photometry, millimetric/submm; Star Forming Region; Milky Way
Keywords: stars: formation - stars: massive - ISM: clouds
Abstract:
Infrared dark clouds (IRDCs) are potential hosts of the elusive early
phases of high mass star formation (HMSF). Here, we conduct an
in-depth analysis of the fragmentation properties of a sample of 10
IRDCs, which have been highlighted as some of the best candidates to
study HMSF within the Milky Way. To do so, we have obtained a set of
large mosaics covering these IRDCs with Atacama Large
Millimeter/submillimeter Array (ALMA) at Band 3 (or 3 mm). These
observations have a high angular resolution (∼3 arcsec;
∼0.05 pc), and high continuum and spectral line sensitivity
(∼0.15 mJy/beam and ∼0.2 K per 0.1 km/s^ channel at
the N2H+ (1 - 0) transition). From the dust continuum emission, we
identify 96 cores ranging from low to high mass (M = 3.4-50.9
M☉) that are gravitationally bound (αvir = 0.3-1.3) and
which would require magnetic field strengths of B = 0.3-1.0 mG to be
in virial equilibrium. We combine these results with a homogenized
catalogue of literature cores to recover the hierarchical structure
within these clouds over four orders of magnitude in spatial scale
(0.01-10 pc). Using supplementary observations at an even higher
angular resolution, we find that the smallest fragments (<0.02 pc)
within this hierarchy do not currently have the mass and-or the
density required to form high-mass stars. None the less, the new ALMA
observations presented in this paper have facilitated the
identification of 19 (6 quiescent and 13 star-forming) cores that
retain > 16 M☉ without further fragmentation. These high-mass
cores contain trans-sonic non-thermal motions, are kinematically
sub-virial, and require moderate magnetic field strengths for support
against collapse. The identification of these potential sites of HMSF
represents a key step in allowing us to test the predictions from
high-mass star and cluster formation theories.
Description:
To investigate the dense gas properties within the IRDC sample, we
have acquired high-angular resolution dust continuum and molecular
line observations with ALMA as part of the projects: 2017.1.00687.S
and 2018.1.00850.S (PI: A.T. Barnes). The observations used the Band 3
receiver, which was configured to obtain high spectral resolution
observations (0.1 km/s or 30.518 kHz) of N2H+ (1-0) centred
at ∼93 GHz, and a broad continuum bandwidth of ∼4 GHz.
Complementary observations were made in the C43-1 12 m array
configuration (baselines of 15-314 m) and 7 m (ACA) array
(baselines of 8-48 m).
In order to identify clump, core and core-fragmented structures, we
analyse these 10 clouds samples with the dendrogram analysis of the
core ID and name, the host cloud, the centre RA and Dec (see section
3). These methods were applied on 3mm dust continuum emission maps, 12
and 7m array continuum maps, N2H+ (1-0) integrated intensity maps.
Therefore these maps analysis give us integrated continuum fluxes,
lines intensities and effectives radius of cores cloud and underlying
structures. As a result, it allows us to compute a complete set of
observational and physical properties of the core population as
presented in the tablea12.dat.
For the purpose of testing our results, we aim to make a comparison
between the properties of the cores determined in this section to
those presented within the literature. Thus, we include and compute
properties of a large sample of cores and clumps from the literature
that also covers our 10 clouds sample as we show in the tablea3.dat.
We identify 96 cores across the 10 clouds within the ALMA continuum
maps which we compute properties such as their masses. Finally, we
study the phases of high mass star formation by an in-depth analysis
of the hierarchical structure present within these molecular clouds,
and assess the high-mass star-forming potential across fragmentation
scales from clouds (∼1 pc), to clumps (∼0.5 pc), to cores
(∼0.1 pc), and finally to core fragments (∼0.01 pc) (see
conclusion section).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea12.dat 753 96 Observational properties of the core population
tablea3.dat 166 430 Properties of the homogenized
literature core sample
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Byte-by-byte Description of file: tablea12.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- ID Core cloud ID (ID)
4- 11 A8 --- Core Core cloud name, ANcNN (Name)
13- 18 A6 --- Cloud Host infrared dark cloud name, cloudN,
[BT2009] N in Simbad (Cloud)
20- 37 F18.14 deg RAdeg Right ascension of the core center (J2000)
(RA_cen)
40- 59 F20.16 deg DEdeg Declination of the core center (J2000)
(Dec_cen)
61- 78 F18.16 arcsec Reff Effective radius (radius_eff)
80- 99 F20.16 arcsec2 AreaExact Exact area defined by π*Reff2
(AreaExact)
102-120 F19.16 arcsec2 AreaEllipse Core cloud ellipse area computed from
major_sigma, minor_sigma and
position_angle (AreaEllipse)
123-140 F18.16 arcsec majorSigma parameter linked to semi-major axis of the
Ellipse area parameter AreaEllipse
(majorSigma)
142-160 F19.17 arcsec minorSigma Parameter linked to the semi-minor axis of
the Ellipse area parameter AreaEllipse
(minorSigma)
163-182 F20.15 deg PA [] Position angle defining the Core cloud
ellipse inclination (PositionAngle)
184-205 F22.20 Jy Sv The total continuum flux density (Sv)
207-228 E22.20 Jy Svb The background-subtracted flux density
(Svb)
230-251 F22.20 Jy Ivmax The peak continuum intensity from Sv
(Ivmax)
253-270 F18.16 K Tmax Temperature (Tmax) (1)
272-289 F18.15 km/s v0 Centroid velocity (v0) (1)
291-309 F19.17 km/s e_v0 velocity dispersion (sigmav) (1)
311-314 A4 --- MMcore Millimetre core region label (MM) (2)
316 I1 --- f_SF [0/1] Binary number 0 or 1 (SF) (3)
318 A1 --- SF [y/n] Yes or No (SF)
320-325 F6.1 pc Distance Core cloud distance in parsec units
(Distance_parsec)
327-346 F20.18 pc Reffpc Effective radius in untis of parsecs
(Reff)
348-366 F19.17 pc Smin The minimum separation or nearest
neighbour distance (Smin)
368-385 F18.15 K Tdust The mean dust temperature (Tdust)
387-407 F21.16 Msun M The mass determined using the mean dust
temperature (M)
409-430 F22.17 Msun Mb The background-subtracted mass using
the mean dust temperature (Mb)
432-452 F21.16 Msun M18K The mass determined using a constant
temperature of 18K (M18K)
454-475 F22.17 Msun Mb18K The background-subtracted mass using a
constant temperature of 18K (Mb18K)
477-496 F20.17 Msun Mext ? The extinction mass (Mext) (4)
498-510 F13.6 uJy S70um ? The flux density at 70um (S70um) (5)
512-529 F18.15 K T70um ? Estimated temperature associated
to S70um flux density (T70um)
531-549 F19.16 Msun M70um ? The mass estimates using a temperature
determined from 70 um emission (M70um)
551-569 F19.11 cm-3 nH2 The mean density of H2 into the core
cloud (nH2)
571-590 F20.12 cm-3 nH2bgsub The background-subtracted mean density
(nH2_bgsub)
592-611 F20.18 Myr tff the free-fall time (tff)
613-632 F20.18 Myr tffbgsub The background-subtracted free-fall time
(tff_bgsub)
634-652 F19.17 --- alphavir The virial parameter (αvir)
654-673 F20.17 --- alphavirb The background-subtracted virial paramete
(alphavirb)
675-693 F19.17 km/s sigmavrsub The residual velocity substracted
(sigmavelressub)
695-715 F21.19 km/s sigmaNT ? The non-thermal velocity dispersion
(sigmaNT)
716-733 F18.16 --- Machvrsub ? The residual sonic substracted
Mach number (Mach_velressub)
735-753 F19.17 --- Machs ? The sonic non thermal Mach number
(Machs_nonthermal)
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Note (1): The results of the N2H+ Gaussian fits of peak brightness
(See the dynamical properties section 3.3).
Note (2): We show the millimetre (MM) core in which each core is contained
(Rathborne et al.2006ApJ...641..389R, Cat. J/ApJ/641/389).
Note (3): If the core contains an embedded (Spitzer or Herschel 70 um) infrared
point source.
Note (4): The mass determined from the near- and mid- infrared extinction maps
(Mext; Kainulainen & Tan 2013A&A...549A..53K 2013A&A...549A..53K)
Note (5): The flux density of any associated 70 um point sources
(S70m; Molinari et al. 2016A&A...591A.149M 2016A&A...591A.149M Cat. J/A+A/591/A149 ;
Marton et al. 2017 preprint (arXiv:1705.05693)).
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Byte-by-byte Description of file: tablea3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Cloud Host cloud name, cloudN, [BT2009] N in Simbad
(cloud)
8- 20 A13 --- CloudID Host cloud ID, GLLL.ll+BB.bb,
MSXDC GLLL.ll+BB.bb, in Simbad) (cloudID)
22- 29 A8 --- Core Core cloud name, ANcNN (Name)
31- 48 F18.14 deg RAdeg Core cloud right ascension (J2000) (RAdeg)
50- 69 F20.16 deg DEdeg Core cloud declination (J2000) (DEdeg)
71- 90 F20.17 arcsec Reff Effective radius in arsec unit (Reff)
92-112 F21.19 pc Reffpc Effective radius in parsec unit (Reffpc)
114-135 F22.17 Jy Slambda The total flux density at the observed
frequency (Slambda)
137-158 F22.17 Msun M18K The mass assuming a constant temperature
of 18 K (M18K)
160-162 A3 --- Ref Literature reference (ref) (1)
164-166 F3.1 mm lambda the wavelength of the observations (lambda)
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Note (1): References as follows:
B21 = This work, Barnes et al. 2021MNRAS.503.4601B 2021MNRAS.503.4601B
H16 = Henshaw et al. 2017MNRAS.464L..31H 2017MNRAS.464L..31H
H17 = Henshaw et al. 2016MNRAS.463..146H 2016MNRAS.463..146H
L18 = Liu et al. 2018ApJ...862..105L 2018ApJ...862..105L, Cat. J/ApJ/862/105
R06 = Rathborne et al. 2006ApJ...641..389R 2006ApJ...641..389R, Cat. J/ApJ/641/389
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 16-Apr-2024