J/A+A/603/A10 ALMA view of G351.77-0.54 (Beuther+, 2017)
Fragmentation and disk formation in high-mass star formation:
The ALMA view of G351.77-0.54 at 0.06'' resolution.
Beuther H., Walsh A.J., Johnston K.G., Henning T., Kuiper R.,
Longmore S.N., Walmsley S.M.
<Astron. Astrophys. 603, A10 (2017)>
=2017A&A...603A..10B 2017A&A...603A..10B (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Interferometry
Keywords: stars: formation - stars: massive - stars: individual: G351.77-0.54 -
stars: winds, outflows - instrumentation: interferometers
Abstract:
The fragmentation of high-mass gas clumps and the formation of the
accompanying accretion disks lie at the heart of high-mass star
formation research.
We resolve the small-scale structure around the high-mass hot core
G351.77-0.54 to investigate its disk and fragmentation properties.
Using the Atacama Large Millimeter Array at 690GHz with baselines
exceeding 1.5km, we study the dense gas, dust, and outflow emission
at an unprecedented spatial resolution of 0.06" (130AU at 2.2kpc).
Within the inner few 1000AU, G351.77 is fragmenting into at least four
cores (brightness temperatures between 58 and 201K). The central
structure around the main submm source #1 with a diameter of ∼0.5"
does not show additional fragmentation. While the CO(6-5) line wing
emission shows an outflow lobe in the northwestern direction emanating
from source #1, the dense gas tracer CH3CN shows a velocity gradient
perpendicular to the outflow that is indicative of rotational motions.
Absorption profile measurements against the submm source #2 indicate
infall rates on the order of 10-4 to 10-3M☉/yr, which can
be considered as an upper limit of the mean accretion rates. The
position-velocity diagrams are consistent with a central rotating
disk-like structure embedded in an infalling envelope, but they may
also be influenced by the outflow. Using the CH3CN(37k-36k)
k-ladder with excitation temperatures up to 1300K, we derive a gas
temperature map for source #1 exhibiting temperatures often in excess
of 1000K. Brightness temperatures of the submm continuum barely exceed
200K. This discrepancy between gas temperatures and submm dust
brightness temperatures (in the optically thick limit) indicates that
the dust may trace the disk mid-plane, whereas the gas could trace a
hotter gaseous disk surface layer. We conduct a pixel-by-pixel Toomre
gravitational stability analysis of the central rotating structure.
The derived high Q values throughout the structure confirm that this
central region appears stable against gravitational instability.
Resolving for the first time a high-mass hot core at 0.06
resolution at submm wavelengths in the dense gas and dust emission
allowed us to trace the fragmenting core and the gravitationally
stable inner rotating disk-like structure. A temperature analysis
reveals hot gas and comparably colder dust that may be attributed to
different disk locations traced by dust emission and gas lines. The
kinematics of the central structure #1 reveal contributions from a
rotating disk, an infalling envelope, and potentially an outflow as
well, whereas the spectral profile toward source #2 can be attributed
to infall.
Description:
The target region G351.77-0.54 was observed with ALMA in cycle 2 in
the 690GHz band with 42 antennas in the array. One noisy antenna
and very short baselines have been flagged because of outlying
amplitudes. This results in a baseline length coverage from 40m to
almost ∼1.6km. The total duration of that one execution of one
scheduling block was 1h40min with an on-target time of
35min. Because of the large number of antennas, even in such a
short time, ALMA achieves an excellent uv-plane coverage.
This results in an almost circular beam and allows us to recover
spatial scales between approximately 0.06" and 2.7". The phase center
of the observations was
RA (J2000.0) 17:26:42.568 and Dec (J2000.0) -36:09:17.6.
Objects:
-------------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------------
17 26 42.8 -36 09 17 G351.77-0.54 = IRAS 17233-360
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 162 26 List of fits files
fits/* . 26 Individual fits files
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See also:
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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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- 52 A23 "date" Obs.date Observation date (YYYY-MM-DDThh:mm:ss.sss)
54- 58 F5.2 --- offsetX ? Offset in X
60- 63 F4.2 --- offsetY ? Offset in Y
65- 68 F4.2 --- doffset ? Offset resolution
70- 72 I3 km/s bVel ? Lower value of velocity interval or velocity
74- 77 F4.1 km/s BVel ? Upper value of velocity interval
79- 81 F3.1 km/s dVel ? Velocity resolution
83- 87 I5 Kibyte size Size of FITS file
89-111 A23 --- FileName Name of FITS file, in subdirectory fits
113-162 A50 --- Title Title of the FITS file
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Acknowledgements:
Henrik Beuther, beuther(at)mpia.de
(End) Patricia Vannier [CDS] 04-Apr-2017