J/A+A/617/A89 G328.2551-0.5321 ALMA images (Csengeri+, 2018)
The search for high-mass protostars with ALMA revealed up to kilo-parsec scales
(SPARKS).
I. Indication for a centrifugal barrier in the environment of a single
high-mass protostar.
Csengeri T., Bontemps S., Wyrowski F., Belloche A., Menten K.M.,
Leurini S., Beuther H., Bronfman L., Commercon B., Chapillon E.,
Longmore S., Palau A., Tan J.C., Urquhart J.S.
<Astron. Astrophys. 617, A89 (2018)>
=2018A&A...617A..89C 2018A&A...617A..89C (SIMBAD/NED BibCode)
ADC_Keywords: Radio sources ; YSOs ; Interstellar medium
Keywords: accretion, accretion disks - stars: massive - stars: formation -
submillimeter: ISM
Abstract:
The conditions leading to the formation of the most massive O-type
stars, are still an enigma in modern astrophysics. To assess the
physical conditions of high-mass protostars in their main accretion
phase, here we present a case study of a young massive clump selected
from the ATLASGAL survey, G328.2551-0.5321. The source exhibits a
bolometric luminosity of 1.3x104L☉, which allows us to
estimate its current protostellar mass to be between ∼11 and 16
M☉. We show high angular-resolution observations with ALMA
reaching a physical scale of ∼400au. To reveal the structure of this
high-mass protostellar envelope in detail at a ∼0.17" resolution, we
use the thermal dust continuum emission and spectroscopic information,
amongst others from the CO (J=3-2) line, which is sensitive to the
high velocity molecular outflow, the SiO (J=8-7), and SO2
(J=82,6-71,7) lines tracing shocks along the outflow, as well as
several CH3OH and HC3N lines that probe the gas of the inner
envelope in the closest vicinity of the protostar. The dust continuum
emission reveals a single high-mass protostellar envelope, down to our
resolution limit. We find evidence for a compact, marginally resolved
continuum source, which is surrounded by azimuthal elongations that
could be consistent with a spiral pattern. We also report on the
detection of a rotational line of CH3OH within its vt=1
torsionally excited state. This shows two bright peaks of emission
spatially offset from the dust continuum peak, and exhibiting a
distinct velocity component ±4.5km/s offset compared to the source
Vlsr. Rotational diagram analysis and models based on local
thermodynamic equilibrium (LTE) assumption require high CH3OH column
densities reaching N(CH3OH)=1.2-2x1019cm-2, and kinetic
temperatures of the order of 160-200K at the position of these peaks.
A comparison of their morphology and kinematics with those of the
outflow component of the CO line, and the SO2 line suggests that the
high excitation CH3OH spots are associated with the innermost regions
of the envelope. While the HC3N v7=0 (J=37-36) line is also
detected in the outflow, the HC3N v7=1e (J=38-37) rotational
transition within the molecule's vibrationally excited state shows a
compact morphology. We find that the velocity shifts at the position
of the observed high excitation CH3OH spots correspond well to the
expected Keplerian velocity around a central object with 15M☉
consistent with the mass estimate based on the source's bolometric
luminosity. We propose a picture where the CH3OH emission peaks
trace the accretion shocks around the centrifugal barrier, pinpointing
the interaction region between the collapsing envelope and an
accretion disk. The physical properties of the accretion disk inferred
from these observations suggest a specific angular momentum several
times larger than typically observed towards low-mass protostars. This
is consistent with a scenario of global collapse setting on at larger
scales that could carry a more significant amount of kinetic energy
compared to the core collapse models of low-mass star formation.
Furthermore, our results suggest that vibrationally exited HC3N
emission could be a new tracer for compact accretion disks around
high-mass protostars.
Description:
These are the corresponding continuum data published in the paper.
G328.2551-0.5321 has been observed with ALMA in Cycle 2, and the phase
center was (RA,DE)J2000=(15:58:00.05, -53:57:57.8). We used 11 of the
7m antennas on the 2014 July 8 and 16, as well as 34 and 35 of the 12m
antennas on 2015 May 3, and 2015 September 1, respectively. The 7m
array observations are discussed in detail in Csengeri et al. (2017,
Cat. J/A+A/600/L10). Here we also present the 12m array observations,
for which the baseline range is 15m (17kλ) to 1574m
(1809kλ). The total time on source was 7.4 minutes, and the
system temperature (Tsys) varies between 120 and 200K.
Objects:
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RA (2000) DE Designation(s)
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15 58 00.05 -53 57 57.8 G328.2551-0.5321
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 234 16 List of fits files
fits/* . 16 Individual fits files
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See also:
J/A+A/600/L10 : Massive cluster progenitors from ATLASGAL (Csengeri+, 2017)
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- 32 I3 --- Nz ? Number of pixels along Z-axis
34- 56 A23 --- Obs.Date Observation date
58- 64 F7.3 GHz Freq ? Observed frequency
66- 74 F9.1 m/s bVRAD ? Lower value of VRAD interval
76- 85 F10.3 m/s BVRAD ? Upper value of VRAD interval
87- 94 F8.3 m/s dVRAD ? VRAD resolution
96-101 I6 Kibyte size Size of FITS file
103-140 A38 --- FileName Name of FITS file, in subdirectory fits
142-234 A93 --- Title Title of the FITS file
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Acknowledgements:
Timea Csengeri, csengeri(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 25-Jun-2018