Understanding Polarized Dust Emission from ρ Ophiuchi A in Light of Grain Alignment and Disruption by Radiative Torques

Tram, Le Ngoc; Hoang, Thiem; Lee, Hyeseung; Santos, Fábio P.; Soam, Archana; Lesaffre, Pierre; Reach, W. T.

doi:10.3847/1538-4357/abc6fe

Cited by 20 publications

(10 citation statements)

References 54 publications

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“…This selective disruption by RAT-D decreases the degree of dust polarization (Lee et al 2020) and may change the polarization pattern. The former was observationally tested (Tram et al 2021a(Tram et al , 2021b(Tram et al , 2021c.…”

Section: Selective Effect Of Rat-d and Increase In The K-rat Alignmentmentioning

confidence: 99%

On Internal and External Alignment of Dust Grains in Protostellar Environments

Hoang

Tram

Giang

et al. 2022

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Multiwavelength observations toward protostars reveal complex properties of dust polarization, which are challenging to interpret. Here we study the physical processes inducing the alignment of the grain axis of the maximum inertia moment with the angular momentum ( J ; i.e., internal alignment) and of J with the magnetic field (i.e., external alignment) of very large grains (VLGs; of radius a > 10 μm) using the alignment framework based on radiative torques (RATs) and mechanical torques (METs). We derive analytical formulae for critical sizes of grain alignment, assuming grains aligned at low-J and high-J attractors by RATs (METs). For protostellar cores, we find that super-Barnett relaxation induces efficient internal alignment for VLGs with large iron inclusions, but inelastic relaxation is efficient for VLGs regardless of composition aligned at high-J attractors by RATs (METs). For external alignment, VLGs with iron inclusions aligned at high-J attractors have magnetic alignment by RATs (B-RAT) or METs (B-MET), enabling dust polarization as a reliable tracer of magnetic fields in dense regions. Still, grains at low-J attractors or without iron inclusions have alignment with J along the radiation direction (k-RAT) or gas flow (v-MET). For protostellar disks, we find that super-Barnett relaxation is efficient for grains with large iron inclusions in the outer disk thanks to spin-up by METs, but inelastic relaxation is inefficient. VLGs aligned at low-J attractors can have k-RAT (v-MET) alignment, but grains aligned at high-J attractors likely exhibit B-RAT (B-MET) alignment. We also find that grain alignment by METs is more important than that by RATs in protostellar disks.

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Section: Selective Effect Of Rat-d and Increase In The K-rat Alignmentmentioning

confidence: 99%

On Internal and External Alignment of Dust Grains in Protostellar Environments

Hoang

Tram

Giang

et al. 2022

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“…The variation of B-fields along the line of sight is neglected by assuming the uniform magnetic field (the field tangling effect is discussed in Section 4.5). The detailed description of this model was presented in Lee et al (2020) and Tram et al (2021a).…”

Section: Assumptions and Basic Equationsmentioning

confidence: 99%

“…Top: gas column density (A) and dust temperature (B) constructed from Herschel data (figure adopted from Santos et al, 2019 andTram et al, 2021a). A star symbol locates the radiation source Oph-S1.…”

Section: Figurementioning

confidence: 99%

“…The RAT paradigm (RAT-A and RAT-D) successfully reproduces both the increase and decrease part of the data. Figures adopted from Tram et al (2021a).…”

Section: Figurementioning

confidence: 99%

“…They showed that the polarization at 850 μm first increases and then decreases with T d , which could reproduce the p − T d trend observed by Planck (Planck Collaboration et al, 2020). Tram et al (2021a) carried out a detailed modeling to interpret the p − T d of Ophiuchus, a cloud observed by SOFIA/HAWC+ with higher resolution than Planck. The authors demonstrated that the combination of the RAT-A and RAT-D effects could successfully reproduce the observational data.…”

Section: Introductionmentioning

confidence: 99%

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Recent progress in theory and observational study of dust grain alignment and rotational disruption in star-forming regions

Tram

Hoang²

2022

Front. Astron. Space Sci.

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Modern understanding of dust astrophysics reveals that radiative torques (RATs) arising from the radiation–dust interaction can induce two fundamental effects: grain alignment and rotational disruption. Here, we review the recent progress in the theoretical development and observational testing of these effects using dust polarization observed toward star-forming regions (SFRs). We first review the basic theory of the RAT alignment and RAT disruption, which are referred to as RAT-A and RAT-D effects, respectively. We then briefly describe the numerical method used to model polarized thermal dust emission by accounting for both RAT-A and RAT-D and theoretical predictions of dust polarization for observations. Next, we review our observational efforts to search for observational evidence of the RAT-A and RAT-D effects using thermal dust polarization toward SFRs. Finally, we discuss magnetic fields inferred from dust polarization observed toward these SFRs and implications of the RAT paradigm for different astrophysical conditions, including protostellar environments, dust evolution, and time-domain astrophysics.

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Physical conditions for dust grain alignment in Class 0 protostellar cores

Gouellec¹,

Maury²,

Hull³

et al. 2023

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Context. The polarized dust emission observed in Class 0 protostellar cores at high angular resolution with ALMA has raised several concerns about the grain alignment conditions in these regions. Aims. We aim to study the role of the radiation field in grain alignment mechanisms that occur in the interior (≤1000 au) of Class 0 protostars. Methods. We produced synthetic observations of the polarized dust emission from a magnetohydrodynamic model of protostellar formation using the POLARIS dust radiative transfer tool, which includes dust alignment with radiative torque alignment (RAT). We tested how the polarized dust emission from the model core depends on the irradiation conditions in the protostellar envelope by varying the radiation due to accretion luminosity propagating from the central protostellar embryo throughout the envelope. The level of grain alignment efficiency obtained in the radiative transfer models was then compared to (sub)millimeter ALMA dust polarization observations of Class 0 protostars. Results. Our radiative transfer calculations have a central irradiation that reproduces the protostellar luminosities typically observed toward low- to intermediate-mass protostars, as well as super-paramagnetic grains and grains ≥10 µm, which are required to bring the dust grain alignment efficiencies of the synthetic observations up to the observed levels. We discuss the characteristics timescales of the grain alignment physics together with the radiative torque disruption (RATD) of grains and the typical time variability of accretion occurring in Class 0 protostellar cores. In our model, during an accretion burst or a steady-state phase of high luminosity from the protostellar embryo, RATD could have enough time to disrupt the largest grains in irradiated regions. Finally, in high-luminosity conditions (with L★ ≥ 20 L⊙ in our model), we find that the alignment of grains with respect to the anisotropic component of the radiation field (k-RAT) could drive inefficient alignment for grains ≳10 µm. However, given the high grain alignment efficiency observed in protostellar envelopes, large grains are most likely aligned with the magnetic field and thus potentially subject to rotational disruption, depending on their tensile strength. Conclusions. Our radiative transfer calculations show that irradiation plays an important role in the mechanisms that dictate the size range of aligned grains in Class 0 protostars. Regions of the envelope that are preferentially irradiated harbor strong polarized dust emission but can be affected by the rotational disruption of dust grains, thus controlling the population of the largest aligned grains. Episodes of high luminosity could affect grain alignment and trigger grain disruption mechanisms.

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Understanding Polarized Dust Emission from ρ Ophiuchi A in Light of Grain Alignment and Disruption by Radiative Torques

Cited by 20 publications

References 54 publications

On Internal and External Alignment of Dust Grains in Protostellar Environments

On Internal and External Alignment of Dust Grains in Protostellar Environments

Recent progress in theory and observational study of dust grain alignment and rotational disruption in star-forming regions

Physical conditions for dust grain alignment in Class 0 protostellar cores

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