J/A+A/657/A30 W51 North ALMA 1.3 and 3mm images (Tang+, 2022)
W51 North: a protocluster emerging out of a thermally inhibited fragmenting
cloud?
Tang M., Palau A., Zapata L., Qin S.L.
<Astron. Astrophys. 657, A30 (2022)>
=2022A&A...657A..30T 2022A&A...657A..30T (SIMBAD/NED BibCode)
ADC_Keywords: Star Forming Region ; Radio sources
Keywords: instrumentation: high angular resolution - methods: observational -
stars: formation - stars: massive - radio continuum: ISM -
ISM: individual objects: W51 North
Abstract:
The fragmentation process in massive star-forming regions is one of
the contemporary problems in astrophysics, and several physical
processes have been proposed to control the fragmentation including
turbulence, magnetic field, rotation, stellar feedback, and gravity.
However, the fragmentation process has been poorly studied at small
spatial scales well below 1000AU.
W51 IRS2 is a well known massive star-forming region whose
fragmentation properties have not been well investigated yet. We aim
to use ALMA (Atacama Large Millimeter and Submillimeter Array) high
angular resolution data to identify the fragments in W51 IRS2 and to
study the fragmentation properties on a spatial scale of 0.04"
(200AU).
We used ALMA data of W51 IRS2 from three projects, which give an
angular resolution of 0.028" (144AU) at millimeter wavelengths. The
continuum images reveal significant substructure in an east-west
ridge, where both W51 North and W51d2 are embedded. A spectral index
map has been generated from the 3 and 1.3mm high-resolution continuum
images.We identified compact fragments by using uv-range constrained
1.3mm continuum data. A Mean Surface Density of Companions (MSDC)
analysis has been performed to study the separations between
fragments.
A total number of 33 continuum sources are identified and 29 out of
them are defined as fragments in the surveyed region.The MSDC analysis
reveals two breaks corresponding to spatial sales of 1845AU and
7346AU, indicative of a two-level clustering phenomenon, along with a
linear regime below 1845AU, mostly associated with W51 North, whose
slope is consistent with the slope for the clustering regime of other
cluster-like regions in the Galaxy.
The typical masses and separations of the fragments as well as the
relation between density and number of fragments can be explained
through a thermal Jeans process operating at high temperatures of
200-400K, consistent with previous measurements of the temperature
in the region, and produced by the nearby massive stars. Therefore,
although W51 IRS2 seems to be undergoing a thermally inhibited
fragmentation phase, this does not seem to prevent the formation of a
protocluster associated with W51 North.
Description:
We used three ALMA datasets of W51 IRS2 from the projects:
2017.1.00293.S, 2015.1.01596.S, and 2013.1.00994.S.
Band 3 (3mm) observations were carried out with ALMA in
2017 October 6 to 15 as part of Cycle 5 program 2017.1.00293.S.
Band 6 (1.3mm) high angular resolution observations were carried out
with ALMA in 2015 October 30 and 31 as part of Cycle 3 program
2015.1.01596.S.
Band 6 (1.3mm) low angular resolution observations were carried out
with ALMA in 2013 July 18 as part of Cycle 2 program 2013.1.00994.S.
33 continuum sources are identified by the 1.3mm uv-range constrained
continuum image, their basic parameter are estimated and listed in
this table. It should be noted that the flux density and intensity are
also estimated from the 1.3mm uv-range constrained continuum image.
Objects:
---------------------------------------------------------
RA (2000) DE Designation(s)
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19 23 40.05 +14 31 07.1 W 51 IRS 2 = NAME W 51 IRS 2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 117 33 Catalogue of identified continuum sources
list.dat 194 5 List of fits images
fits/* . 5 Individual fits images
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See also:
J/ApJS/191/232 : CO survey of W51 molecular cloud (Bieging+, 2010)
J/A+A/582/A64 : W51/e2 and G34.3+0.2 IRAM spectra (Lykke+, 2015)
J/A+A/589/A44 : W51 Main NH3 and CH3OH data cubes (Goddi+, 2016)
J/A+A/595/A27 : JVLA images of W51A (Ginsburg+, 2016)
J/A+A/597/A45 : W51 line of sight deuterium fractionation (Vastel+, 2017)
J/ApJ/845/116 : 3mm mapping spectral line survey toward W51 (Watanabe+, 2018)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Name Name of identified source
5 A1 --- n_Name [+] + for isolated and point-like sources (1)
7- 8 I2 h RAh Right ascension (J2000.0)
10- 11 I2 min RAm Right ascension (J2000.0)
13- 20 F8.5 s RAs Right ascension (J2000.0)
22 A1 --- DE- Declination sign (J2000)
23- 24 I2 deg DEd Declination (J2000.0)
26- 27 I2 arcmin DEm Declination (J2000.0)
29- 35 F7.4 arcsec DEs Declination (J2000.0)
37- 41 F5.3 arcsec Major Major axis of source size
43- 47 F5.3 arcsec e_Major Major axis of source size error
49- 53 F5.3 arcsec Minor Minor axis of source size
55- 59 F5.3 arcsec e_Minor Minor axis of source size error
61- 65 F5.1 deg PA Position angle of source size
67- 71 F5.2 mJy/beam Int 1.3mm continuum peak intensity of source
73- 76 F4.2 mJy/beam e_Int 1.3mm continuum peak intensity of source error
78- 82 F5.2 mJy S Integrated intensity of identified source
84- 87 F4.2 mJy e_S Integrated intensity of identified source
error
89- 92 F4.2 Msun Mass Mass estimated from the 1.3mm continuum
94- 97 F4.2 Msun e_Mass Mass estimated from the 1.3mm continuum error
99-102 F4.2 Msun Masst Mass estimated by optically thick assumption
104-107 F4.2 Msun e_Masst Mass estimated by optically thick assumption
error
109-112 F4.2 --- SpIndex Spectral index estimated for continuum source
114-117 F4.2 --- e_SpIndex Spectral index estimated for continuum source
error
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Note (1): + for isolated and point-like sources. They are not defined as a
fragments and are excluded from further analysis.
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
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- 23 I4 --- Nx Number of pixels along X-axis
25- 27 I3 --- Ny Number of pixels along Y-axis
29- 54 A26 "datime" Obs.date Observation date
56- 63 F8.4 GHz Freq Observed frequency
65- 68 I4 Kibyte size Size of FITS file
70- 95 A26 --- FileName Name of FITS file, in subdirectory fits
97-194 A98 --- Title Title of the FITS file
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Acknowledgements:
Mengyao Tang, mengyao_tang(at)yeah.net
(End) Patricia Vannier [CDS] 20-Sep-2021