J/A+A/650/A142 G24.78+0.08 A1 ALMA images and datacubes (Moscadelli+, 2021)
The ionized heart of a molecular disk. ALMA observations of the hyper-compact
HII region G24.78+0.08 A1.
Moscadelli L., Cesaroni R., Beltran M.T., Rivilla V.M.
<Astron. Astrophys. 650, A142 (2021)>
=2021A&A...650A.142M 2021A&A...650A.142M (SIMBAD/NED BibCode)
ADC_Keywords: H II regions ; Masers ; Millimetric/submm sources ;
Interstellar medium
Keywords: ISM: individual objects: G24.78+0.08 - HII regions -
ISM: molecules - masers - techniques: interferometric
Abstract:
Hyper-compact (HC) or ultra-compact HII regions are the first
manifestations of the radiation feedback from a newly born massive
star. Therefore, their study is fundamental to understanding the
process of massive (≥8M☉) star formation.
We employed Atacama Large Millimeter/submillimeter Array (ALMA) 1.4mm
Cycle 6 observations to investigate at high angular resolution
(∼0.050, corresponding to 330au) the HC HII region inside molecular
core A1 of the high-mass star-forming cluster G24.78+0.08.
We used the H30α emission and different molecular lines of
CH3CN and 13CH3CN to study the kinematics of the ionized and
molecular gas, respectively.
At the center of the HC HII region, at radii ≲500au, we observe two
mutually perpendicular velocity gradients, which are directed along
the axes at PA=39° and PA=133°, respectively. The velocity
gradient directed along the axis at PA=39° has an amplitude of
22km/s/mpc, which is much larger than the other;s, 3km/s/mpc. We
interpret these velocity gradients as rotation around, and expansion
along, the axis at PA=39°. We propose a scenario where the
H30α line traces the ionized heart of a disk-jet system that
drives the formation of the massive star (∼20M☉) responsible for
the HC HII region. Such a scenario is also supported by the
position-velocity plots of the CH3CN and 13CH3CN lines along the
axis at PA=133°, which are consistent with Keplerian rotation
around a 20M☉ star.
Toward the HC HII region in G24.78+0.08, the coexistence of mass
infall (at radii of ∼5000au), an outer molecular disk (from ≲4000 au
to ≳500au), and an inner ionized disk (≲500au) indicates that the
massive ionizing star is still actively accreting from its parental
molecular core. To our knowledge, this is the first example of a
molecular disk around a high-mass forming star that, while becoming
internally ionized after the onset of the HII region, continues to
accrete mass onto the ionizing star.
Description:
We performed ALMA Cycle 6 continuum and line observations at 1.4mm
(using the C43-8 configuration) towards the hyper-compact HII region
G24.78+0.08. We provide the ALMA Cycle 6, calibrated channel maps of
the data presented in the article.
Objects:
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RA (2000) DE Designation(s)
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18 36 12.661 -07 12 10.15 G024.78+0.08 = GAL 024.78+00.08
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 200 13 List of fits images and datacubes
fits/* . 13 List of fits images and datacubes
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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 slices for the datacubes
34- 59 A26 "datime" Obs.date Observation date
61- 67 F7.3 GHz bFreq ? Lower value of frequency interval
for the datacubes
69- 75 F7.3 GHz BFreq ? Upper value of frequency interval
for the datacubes
77- 82 I6 Hz dFreq ? Frequency resolution for the datacubes
84- 94 E11.6 m/s bVel ? Lower value of velocity interval
96-106 E11.6 m/s BVel ? Upper value of velocity interval
108-114 F7.3 m/s dVel ? Velocity resolution
116-121 I6 Kibyte size Size of FITS file
123-160 A38 --- FileName Name of FITS file, in subdirectory fits
162-200 A39 --- Title Title of the FITS file
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Acknowledgements:
Luca Moscadelli, luca.moscadelli(at)inaf.it
(End) Luca Moscadelli [Arcetri], Patricia Vannier [CDS] 03-May-2021