Discovery of a Photoionized Bipolar Outflow toward the Massive Protostar G45.47+0.05

Zhang, Yichen; Tanaka, Kei E. I.; Rosero, Viviana; Tan, Jonathan C.; Marvil, Joshua; Cheng, Yu; Liu, Mengyao; Beltrán, M. T.; Garay, Guido

doi:10.3847/2041-8213/ab5309

Cited by 19 publications

(18 citation statements)

References 50 publications

(88 reference statements)

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“…The discovery of HC or UC Hii regions in which the ionized gas undergoes a global motion of infall or rotation suggests that mass accretion onto the star can also proceed after the onset of photoionization, in agreement with the models of "trapped" Hii regions (Keto 2003(Keto , 2007. Up to now, however, although clear cases of compact ionized rotating structures (size 100 au) have been reported in the literature (Zhang et al 2017;Jiménez-Serra et al 2020;Zhang et al 2019), the corresponding rotation in the molecular gas surrounding the HC or UC Hii region on scales of ∼1000 au has never been observed. The coexistence of both the outer molecular and inner ionized parts of the accretion disk is expected if the massive star inside the Hii region is still actively accret-Article number, page 2 of 10 L. Moscadelli et al: The ionized heart of a molecular disk ing from its parental molecular core, as predicted by the most complete models of massive star formation (Tanaka et al 2016;Kuiper & Hosokawa 2018).…”

Section: Introductionsupporting

confidence: 71%

The ionized heart of a molecular disk. ALMA observations of the hyper-compact HII region G24.78+0.08 A1

Moscadelli,

Cesaroni,

Beltrán

et al. 2021

Preprint

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Context. Hyper-compact (HC) or ultra-compact (UC) 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 (≥ 8 M ⊙ ) star formation. Aims. We employed Atacama Large Millimeter/submillimeter Array (ALMA) 1.4 mm Cycle 6 observations to investigate at high angular resolution (≈ 0. ′′ 050, corresponding to 330 au) the HC Hii region inside molecular core A1 of the high-mass star-forming cluster G24.78+0.08. Methods. We used the H30α emission and different molecular lines of CH 3 CN and 13 CH 3 CN to study the kinematics of the ionized and molecular gas, respectively. Results. At the center of the HC Hii region, at radii 500 au, 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 22 km s −1 mpc −1 , which is much larger than the other's, 3 km s −1 mpc −1 . 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 (≈ 20 M ⊙ ) responsible for the HC Hii region. Such a scenario is also supported by the position-velocity plots of the CH 3 CN and 13 CH 3 CN lines along the axis at PA = 133 • , which are consistent with Keplerian rotation around a 20 M ⊙ star. Conclusions. Toward the HC Hii region in G24.78+0.08, the coexistence of mass infall (at radii of ∼ 5000 au), an outer molecular disk (from 4000 au to 500 au), and an inner ionized disk ( 500 au) 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.

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Section: Introductionsupporting

confidence: 71%

The ionized heart of a molecular disk. ALMA observations of the hyper-compact HII region G24.78+0.08 A1

Moscadelli,

Cesaroni,

Beltrán

et al. 2021

Preprint

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“…Hence, we adopt the literature value as the systemic velocity of the source and used through this work. The ratio between H30α integrated intensity and freefree continuum intensity for optically thin Local Thermodynamic Equilibrium (LTE) conditions is (see, e.g., Zhang et al 2019c)…”

Section: H30α Emissionmentioning

confidence: 99%

“…Figure 10 bottom right panel presents a map of the ratio of H30α integrated intensity to 1.3 mm continuum.The ratio between H30α integrated intensity and freefree continuum intensity for optically thin Local Thermodynamic Equilibrium (LTE) conditions is (see, e.g.,Zhang et al 2019c) …”

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confidence: 99%

Isolated Massive Star Formation in G28.20-0.05

Law¹,

Tan²,

Gorai³

et al. 2022

Preprint

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We report high-resolution 1.3mm continuum and molecular line observations of the massive protostar G28.20-0.05 with ALMA. The continuum image reveals a ring-like structure with 2,000 au radius, similar to morphology seen in archival 1.3cm VLA observations. Based on its spectral index and associated H30α emission, this structure mainly traces ionized gas. However, there is evidence for ∼ 30 M of dusty gas near the main mm continuum peak on one side of the ring, as well as in adjacent regions within 3,000 au. A virial analysis on scales of ∼2,000 au from hot core line emission yields a dynamical mass of ∼ 80M . A strong velocity gradient in the H30α emission is evidence for a rotating, ionized disk wind, which drives a larger-scale molecular outflow. An infrared SED analysis indicates a current protostellar mass of m * ∼ 24 M forming from a core with initial mass M c ∼ 400 M in a clump with mass surface density of Σ cl ∼ 3 g cm −2 . Thus the SED and other properties of the system can be understood in the context of core accretion models. Structure-finding analysis on the largerscale continuum image indicates G28.20-0.05 is forming in a relatively isolated environment, with no other concentrated sources, i.e., protostellar cores, above ∼ 1 M found from ∼0.1 to 0.4 pc around the source. This implies that a massive star is able to form in relative isolation and the dearth of other protostellar companions within the ∼ 1 pc environs is a strong constraint on massive star formation theories that predict the presence of a surrounding protocluster.

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“…There is observational evidence that these outflows and jets are linked with magnetic fields. First, synchrotron emission has been associated with jets in observations of massive protostellar sources (Carrasco-González et al 2010;Sanna et al 2019b;Zhang et al 2019b). Second, observations of an alignment between outflows and the magnetic field direction inferred from spectral-line linear polarisation have also been reported in massive star forming regions (Cortes et al 2006;Beuther et al 2010;Girart et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Discs and outflows in the early phases of massive star formation: Influence of magnetic fields and ambipolar diffusion

Commerçon

González

Mignon-Risse

et al. 2022

A&A

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Context. Massive star formation remains one of the most challenging problems in astrophysics, as illustrated by the fundamental issues of the radiative pressure barrier and the initial fragmentation. The wide variety of physical processes involved, in particular the protostellar radiative feedback, increase the complexity of massive star formation in comparison with its low-mass counterpart. Aims. We aim to study the details of mass accretion and ejection in the vicinity of massive star forming cores using high-resolution (5 au) three-dimensional numerical simulations. We investigated the mechanisms at the origin of outflows (radiative force versus magnetic acceleration). We characterised the properties of the disc forming around massive protostars depending on the physics included: hydrodynamics, magnetic fields, and ambipolar diffusion. Methods. We used state-of-the-art three-dimensional adaptive-mesh-refinement models of massive dense core collapse, which integrate the equations of (resistive) grey radiation magnetohydrodynamics, and include sink particle evolution. For the first time, we include both protostellar radiative feedback via pre-main-sequence evolutionary tracks and magnetic ambipolar diffusion. To determine the role of magnetic fields and ambipolar diffusion play in the formation of outflows and discs, we studied three different cases: a purely hydrodynamical run, a magnetised simulation under the ideal approximation (perfect coupling), and a calculation with ambipolar diffusion (resistive case). In the most micro-physically complex model (resistive MHD), we also investigated the effect the initial amplitude of both magnetic field and solid body rotation have on the final properties of the massive protostellar system. We used simple criteria to identify the outflow and disc material and follow their evolution as the central star accretes mass up to 20 M⊙ in most of our models. The radiative, magnetic, and hydrodynamical properties of the outflows and discs are quantitatively measured and cross-compared between models. Results. Massive stars form in all our models, together with outflows and discs. The outflow is completely different when magnetic fields are introduced, so magneto-centrifugal processes are the main driver of the outflow up to stellar masses of 20 M⊙. Then, the disc properties heavily depend on the physics included. In particular, the disc formed in the ideal and resistive runs show opposite properties in terms of plasma beta; that is, the ratio of thermal-to-magnetic pressures and of magnetic field topology. While the disc in the ideal case is dominated by the magnetic pressure and the toroidal magnetic fields, the one formed in the resistive runs is dominated by the thermal pressure and essentially has a vertical magnetic field in the inner regions (R < 100−200 au). Conclusions. We find that magnetic processes dominate the early evolution of massive protostellar systems (M⋆ < 20 M⊙) and shapes the accretion and ejection as well as the disc formation. Ambipolar diffusion is mainly at work at disc scales and regulates its properties. We predict magnetic field’s topology within the disc and outflows, as well as disc masses and radii to be compared with observations. Lastly, our finding for the outflow and disc properties are reminiscent of the low-mass star formation framework, suggesting that accretion and ejection in young massive and low-mass protostars are regulated by the same physical processes in the early stages.

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Discovery of a Photoionized Bipolar Outflow toward the Massive Protostar G45.47+0.05

Cited by 19 publications

References 50 publications

The ionized heart of a molecular disk. ALMA observations of the hyper-compact HII region G24.78+0.08 A1

The ionized heart of a molecular disk. ALMA observations of the hyper-compact HII region G24.78+0.08 A1

Isolated Massive Star Formation in G28.20-0.05

Discs and outflows in the early phases of massive star formation: Influence of magnetic fields and ambipolar diffusion

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