J/A+A/595/A27 JVLA images of W51A (Ginsburg+, 2016)
Toward gas exhaustion in the W51 high-mass proto clusters.
Ginsburg A., Goss W.M., Goddi C., Galvan-Madrid R., Dale J., Bally J.,
Battersby C., Youngblood A., Sankrit R., Smith R., Darling J.,
Kruijssen J.M.D., Liu H.-Y.B.
<Astron. Astrophys. 595, A27 (2016)>
=2016A&A...595A..27G 2016A&A...595A..27G (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; H II regions ; Radio sources
Keywords: HII regions - circumstellar matter - radio continuum: ISM -
radio lines: ISM - stars: massive - stars: protostars
Abstract:
We present new JVLA observations of the high-mass cluster-forming
region W51A from 2 to 16GHz with resolution θfwhm≈0.3-0.5".
The data reveal a wealth of observational results: (1)
Currently-forming, very massive (proto-O) stars are traced by
o-H2CO 21,1-21,2 emission, suggesting that this line can be used
efficiently as a massive protostar tracer. (2) There is a spatially
distributed population of ≲mJy continuum sources, including
hypercompact HII regions and candidate colliding wind binaries, in and
around the W51 proto-clusters. (3) There are two clearly detected
protoclusters, W51e and W51 IRS2, that are gas-rich but may have most
of their mass in stars within their inner ≲0.05pc. The majority of
the bolometric luminosity in W51 most likely comes from a third
population of OB stars between these clusters. The presence of a
substantial population of exposed O-stars coincident with a population
of still-forming massive stars, along with a direct measurement of the
low mass loss rate via ionized gas outflow from W51 IRS2, together
imply that feedback is ineffective at halting star formation in
massive protoclusters. Instead, feedback may shut off the large-scale
accretion of diffuse gas onto the W51 protoclusters, implying that
they are evolving towards a state of gas exhaustion rather than gas
expulsion. Recent theoretical models predict gas exhaustion to be a
necessary step in the formation of gravitationally bound stellar
clusters, and our results provide an observational validation of this
process.
Description:
We used the Karl G. Jansky Very Large Array (JVLA) in multiple bands
and configurations.
In project 12B-365, we observed in A-array in S and C bands (3 and
5GHz, approximately) with 2GHz total bandwidth. In project 13A-064, we
observed in C-band in C (1h) and A (5h) arrays and in Ku-band in D
(1h) and B (5h) arrays. We also include continuum data from project
12A-274 (Goddi et al., 2015A&A...573A.109G 2015A&A...573A.109G, 2016, Cat. J/A+A/589/A44)
covering the range 25-36GHz using the JVLA B array configuration.
Our spectral coverage included o-H2CO 11,01-1,1_ at 4.82966GHz and
21,1-21,2 at 14.488GHz with 0.3km/s resolution and the radio
recombination lines (RRLs) H77α (14.1286GHz) and H110α
(4.8741GHz) at 1km/s resolution. The H110α line had lower S/N
than the H77α line but was otherwise similar; it is not
discussed further in this paper.
Objects:
-----------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------
19 23 50 +14 06.0 W51 = 3C 400
-----------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
phot.dat 318 496 EVLA VLA point source photometry
list.dat 255 3 List of fits files
fits/* . 3 Individual fits files
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See also:
J/ApJ/706/83 : Embedded YSO candidates in W51 (Kang+, 2009)
J/ApJ/720/1055 : VBLA observations of W51 Main/South (Sato+, 2010)
J/ApJS/191/232 : CO survey of W51 molecular cloud (Bieging+, 2010)
J/MNRAS/424/1658 : Molecular clumps in W51 giant mol. cloud (Parsons+, 2013)
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)
Byte-by-byte Description of file: phot.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Object name (SourceName)
12- 27 A16 --- Label Label for the frequency + epoch
(FrequencyName)
29- 54 A26 --- Obs.date Date of the observation
(YYYY-MM-DDThh:mm:ss.ssssss)
(ObservationDate)
56- 59 F4.1 GHz Freq Observed central frequency (Frequency)
61 I1 --- Ep [1/3] Epoch ID of the observation
(1, 2, or 3) (Epoch)
63- 76 F14.12 arcsec Bmaj Beam major axis (BMAJ)
78- 91 F14.12 arcsec Bmin Beam minor axis (BMIN)
93-110 E18.13 Jy/beam FluxAp ? Average intensity over an aperture
(aperture_flux)
112-129 E18.13 Jy/beam FluxPk ? Peak intensity of the source (peak_flux)
131-141 E11.7 Jy/beam rms ? Noise estimated from a small area around
the source (localrmsnoise)
143-160 E18.13 Jy/beam cutfluxm ? Lowest measured intensity in the source
cutout (cutoutminflux)
163-180 E18.13 Jy/beam Gbckg ? Fitted Gaussian background (gbackground)
182-199 E18.13 Jy/beam Gamp ? Fitted Gaussian amplitude (gamplitude)
201-213 F13.9 deg GRAdeg ? Fitted Gaussian RA centroid (gracen)
215-227 F13.10 deg GDEdeg ? Fitted Gaussian Dec centroid (gdeccen)
229-245 E17.12 deg GXw ? Fitted Gaussian x width (gxwidth)
247-263 E17.12 deg GYw ? Fitted Gaussian y width (gywidth)
265-281 E17.12 deg GPA ? Fitted position angle (gpositionangle)
283-299 F17.10 --- Gchi2 ? Gaussian fit chi2 (gfit_chi2)
301-318 F18.13 --- Gchi2r ? Gaussian fit reduced chi2
(gfitchi2reduced)
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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- 28 I4 --- Ny Number of pixels along Y-axis
30- 32 I3 --- Nz ? Number of slices, for the datacube
34- 54 A21 --- Obs.Date Observation date (YYYY-MM-DDThh:mm:ss.s)
56- 62 F7.4 GHz Freq Observed frequency
64- 71 F8.3 km/s bVel ? Lower value of velocity interval,
for the datacube
73- 79 F7.3 km/s BVel ? Upper value of velocity interval,
for the datacube
81- 87 F7.5 km/s dVel ? Velocity resolution, for the datacube
89- 95 I7 Kibyte size Size of FITS file
97-125 A29 --- FileName Name of FITS file, in subdirectory fits
127-255 A129 --- Title Title of the FITS file
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Acknowledgements:
Adam Ginsburg, adam.g.ginsburg(at)gmail.com
(End) Patricia Vannier [CDS] 11-Jul-2016