J/A+A/616/L10 RCW120 fragmentation at 0.01pc scale (Figueira+, 2018)
ALMA observations of RCW 120. Fragmentation at 0.01 pc scale.
Figueira M., Bronfman L., Zavagno A., Louvet F., Lo N., Finger R., Rodon J.
<Astron. Astrophys. 616, L10 (2018)>
=2018A&A...616L..10F 2018A&A...616L..10F (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Millimetric/submm sources ; Morphology
Keywords: HII region - ISM: bubbles - photon-dominated region
Abstract:
Little is known about how high-mass stars form. Around 30% of the
young high-mass stars in the Galaxy are observed at the edges of
ionized (HII) regions. Therefore these are places of choice to study
the earliest stages of high-mass star formation, especially towards
the most massive condensations. High-spatial resolution observations
in the millimeter range might reveal how these stars form and how they
assemble their mass.
We want to study the fragmentation process down to the 0.01pc scale
in the most massive condensation (1700M☉) observed at the
south-western edge of the HII region RCW 120 where the most massive
Herschel cores (∼124M☉ in average) could form high-mass stars.
Using ALMA 3mm continuum observations towards the densest and most
massive millimetric condensation (Condensation 1) of RCW 120, we used
the getimages and getsources algorithms to extract the sources
detected with ALMA and obtained their physical parameters. The
fragmentation of the Herschel cores is discussed through their Jeans
mass to understand the properties of the future stars.
We extracted 18 fragments from the ALMA continuum observation at 3mm
towards 8 cores detected with Herschel, whose mass and deconvolved
size range from 2M☉ to 32M☉ and from 1.6mpc to 28.8mpc,
respectively. The low degree of fragmentation observed, regarding to
the thermal Jeans fragmentation, suggests that the observed
fragmentation is inconsistent with ideal gravitational fragmentation
and other ingredients such as turbulence or magnetic fields should be
added in order to explain it. Finally, the range of fragments' mass
indicates that the densest condensation of RCW 120 is a favourable
place for the formation of high-mass stars with the presence of a
probable UCHII region associated with the 27M☉ Fragment 1 of
Core 2.
Description:
The observations of Condensation 1 were performed during Cycle 4 using
38 of the 40 12m ALMA antennas in nominal configuration C40-3 with
baselines ranging from 15m to 459m. We used a continuum bandwidth of
2.227GHz in Band 3 divided into 3x117.19MHz (122kHz-0.4km/s
resolution) + 1x1875MHz bandwidth. The spectral bands were centered on
93.17, 91.98, 104.02, and 102.5GHz allowing the observations of
N2H+, CH3CN, SO2 transition lines and 3mm continuum emission,
respectively. The primary beam at the sky representative frequency of
104.03GHz is 56". The total observing time was 27.8-min with a system
temperature between 46.7K and 69.9K and an average precipitable water
vapor of 1.6mm. For this work, we used the products delivered by ALMA.
The imaging was performed with the CLEAN algorithm of the Common
Astronomy Software Applications (CASA) package using a Briggs
weighting with a robust parameter of 0.5 and a primary beam limit of
20%.
File getimages.cfg contains the configuration file used by getimages
and file getsources.cfg contains the configuration file used by
getsources (see Men'shchikov (2012A&A...542A..81M 2012A&A...542A..81M) for an explanation
about the parameters).
File catalog.dat is the getsources catalog of the sources extracted
from the 3mm ALMA observation.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
catalog.dat 168 19 List of extracted sources
getimages.cfg 142 18 getimages configuration file
getsources.cfg 143 48 getsources configuration file
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See also:
J/A+A/472/835 : JHKs and GLIMPSE photometry of RCW 120 (Zavagno+, 2007)
J/A+A/496/177 : JHKs and GLIMPSE photometry of RCW 120 (Deharveng+, 2009)
J/A+A/600/A93 : Multiwavalenth fluxes of RCW120 (Figueira+, 2017)
Byte-by-byte Description of file: catalog.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Seq [1/19] Source's running number (NO)
4- 8 F5.1 pix Xpos X-coordinate of current source (relative to
the lower-left pixel (1,1)) (XCO_P)
10- 14 F5.1 pix Ypos Y-coordinate of current source (relative to
the lower-left pixel (1,1)) (YCO_P)
16- 26 F11.7 deg RAdeg WCS (J2000) right ascension of current
source (WCS_ACOOR)
28- 38 F11.7 deg DEdeg WCS (J2000) declination of current
source (WCS_DCOOR)
40- 48 E9.3 deg Signi Global detection significance over all
wavelengths (SIG_GLOB)
50 I1 --- FG Flag identifying global properties over all
wavelengths (FG)
52- 56 F5.2 --- Good Global goodness combining SIG_GLOB and
SNR_GLOB (GOOD)
58- 66 E9.3 --- Signi1 Detection significance from monochromatic
single scales (SIG_MONO1)
68 I1 --- FM01 Flag identifying monochromatic properties
(FM01)
70- 78 E9.3 Jy/beam Fpeak Estimate of 3mm peak flux for current source
(in Jy/beam_obs) (FXP_BEST01)
80- 88 E9.3 Jy/beam e_Fpeak Estimate of peak flux error for current
source (in Jy/beam_obs) (FXP_ERRO01)
90- 98 E9.3 Jy Ftot Estimate of total 3mm flux for current
source (FXT_BEST01)
100-108 E9.3 Jy e_Ftot Estimate of total flux error for current
source (FXT_ERRO01)
110-118 E9.3 arcsec AFWHM Major size estimate (FWHM) for current
source (AFWHM01)
120-128 E9.3 arcsec BFWHM Minor size estimate (FWHM) for current
source (BFWHM01)
130-138 E9.3 deg PA Major axis rotation angle (east of the
vertical axis) (THEPA01)
140-148 E9.3 arcsec Asize2 Major size estimate from full intensity
moments (ASIZE01)
150-158 E9.3 arcsec Bsize2 Minor size estimate from full intensity
moments (BSIZE01)
160-168 E9.3 deg PA2 Major axis rotation angle (east of the
vertical axis) (THETA01)
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Acknowledgements:
Miguel Figueira, miguel.figueira(at)lam.fr
(End) Patricia Vannier [CDS] 03-Aug-2018