arXiv subjects

Thiem Hoang

Publications and source records attributed to Thiem Hoang.

At least 19 recordsLinked to original sources

arXiv2026

Time-Domain Dust Astrophysics. II. TransRAT: Time-Dependent Grain Alignment and Disruption by Cosmic Transients and Their Observational Signatures

We introduce {\it TransRAT}, a self-consistent time-domain framework that follows the coupled dynamical response of dust to transient irradiation and predicts its observable signatures. We apply {\it TransRAT} to a Type~IIP supernova illuminating a one-zone molecular cloud. Radiative heating raises the grain temperature, modifying the magnetic susceptibility and Larmor precession, while the enhanced radiation field accelerates radiative precession and can switch the alignment axis from the magnetic field (B-RAT) to the radiation direction (k-RAT). Simultaneously, strong RATs align grains faster than gas randomization, extending {\it fast alignment} to smaller grain sizes, and disrupt large grains through RAT disruption (RAT-D), irreversibly modifying the grain size distribution. As the transient fades, the alignment axis returns to ${\bf B}$ at a rate controlled by the magnetic susceptibility, whereas the enhanced aligned-grain population and RAT-D-modified grain size distribution can persist long after the radiation has faded- referred to as \emph{physical memory effects}. The time-dependent evolution of grain alignment and disruption produces distinctive observational signatures: a flare in extinction and thermal dust polarization followed by a RAT-D-induced dip; a blueward shift of the polarization peak $\lambda_{\max}$; a polarization-angle rotation equal to the projected ${\bf B}$--${\bf k}$ separation ($45^{\circ}$ for our adopted geometry) when RAT-D removes large high-$J$ aligned grains and leaves low-$J$ grains aligned with kRAT followed by angle reverberation as alignment returns to ${\bf B}$; and a non-monotonic evolution of $R_V$. The persistent observational manifestations of the transient irradiation, including enhanced polarization, blueshifted $\lambda_{\max}$, modified $R_V$, and polarization-angle evolution, constitute \emph{fossil imprints} of past cosmic transients.

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arXiv2026

Magnetic Fields in Massive Star-forming Regions (MagMaR). IX. Radiative Torque Alignment and Disruption in NGC6334I

Intense radiation from high-mass stars is expected to significantly affect dust grain alignment and evolution through RAdiative Torques (RATs). We investigate this effect in a massive star-forming region, NGC6334I, using 1.2 mm dust continuum polarization observations from the Atacama Large Millimeter/submillimeter Array. The polarization fraction spans from $\lesssim1\%$ to $\sim10\%$ and decreases with increasing column density, remaining below $2\%$ in dense cores despite high temperatures ($\sim100$ K), where efficient grain alignment by RATs is expected. We investigate how grain alignment, grain growth, grain disruption, B-field tangling, and local physical conditions affect the polarization properties of MM1, MM2, MM3, and their surroundings. Polarization angle dispersion shows that B-field tangling contributes to depolarization at moderate densities but cannot fully explain the lowest polarization fractions. Using RAT-based grain alignment and polarization modeling, we find that reduced alignment efficiency and high optical depth reproduce the low polarization in the densest regions. MM2 shows evidence of grain growth, with maximum grain sizes $a_{\max}\sim0.35-1.0~\mu$m, while MM1 exhibits smaller values of $\sim0.35-0.50~\mu$m. Accounting for optical depth increases the inferred grain sizes in MM1 to $\sim1.0-2.0~\mu$m. Analytical estimates of radiative torque disruption from the intense outburst suggest that micron-sized grains in high-temperature, moderate-density regions can fragment into submicron grains. Alternatively, high optical depth may also explain the low polarization in the densest regions even in the presence of micron-sized grains. Incorporating the B-field inclination effect indicates a transition from predominantly plane-of-sky fields at low densities to more line-of-sight-aligned configurations at high densities.

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arXiv2026

Multiscale Synthetic observations of Polarized dust emission: On the origin of Depolarization effect from Molecular clouds to Starless cores and Constraints on Dust Physics

Submillimeter observations of polarized dust emission from molecular clouds to starless cores frequently report a decrease in polarization fraction (p) with increasing dust emission intensity (I). This feature is commonly attributed to the alignment loss of dust grains or the geometrical effects of magnetic fields, yet, the detailed contributions remain unclear. To investigate the mechanism responsible for the depolarization, we use POLARIS to perform the multiscale synthetic dust polarization observations at $850\mu m$ from magnetically aligned dust grains by RAdiative Torques (RATs) mechanism. We adopt three collapsing cloud models with different magnetic energy levels and explore the effects of grain magnetic properties and grain growth on dust polarization. The field geometrical effect is the dominant depolarization mechanism at $N_{\rm H}<10^{21}-10^{22}\rm cm^{-2}$. We find that if grains grow beyond $>0.5\mu m$ and are superparamagnetic (SPM) with large iron clusters, RATs remain effective at high column densities, and grain alignment loss contributes to depolarization only at $N_{\rm H} > 10^{23}\rm cm^{-2}$. If neither of these conditions is satisfied, the alignment loss (in cases of insufficient grain growth); or the reduced grain alignment efficiency by gaseous damping (for paramagnetic grains or SPM grains with small iron cluster sizes) can become the dominant depolarization mechanism at $N_{\rm H} > 10^{22}\rm cm^{-2}$, regardless of how tangled the magnetic field lines in our simulation. Finally, we show that the depolarization mechanism and the underlying dust physical properties inside starless cores may be identified through the $p-I$ slope and the mean p at the core center.

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arXiv2026

Time-Domain Dust Astrophysics. I. Polarization Flares, Polarization-Angle Reverberation, and Fossil Imprints in Supernova-Illuminated Clouds

Cosmic transients can dramatically enhance the local radiation field on timescales of days to months. Using the time-domain TransRAT framework, which self-consistently evolves grain heating, alignment, rotational disruption, and switching of the alignment axis between the magnetic field (B-RAT) and the radiation direction (k-RAT), we predict the time-dependent dust polarization of a dense cloud illuminated by a Type~IIP supernova at different distances. We identify four key signatures. First, for $D\lesssim1$ pc, a polarization flare develops within days to weeks, marked by sharp increases in both thermal dust polarization and extinction-polarization efficiency; this is followed by a polarization dip as radiative torque disruption (RAT-D) destroys the large aligned grains. Second, the peak wavelength of extinction polarization, $\lambda_{\rm max}$, shifts blueward as the minimum aligned-grain size decreases, providing a diagnostic largely independent of magnetic-field geometry. Third, the transition from B-RAT to k-RAT produces an abrupt polarization-angle rotation of $45^{\circ}$ in our fiducial geometry. Fourth, as the transient fades, the return to B-RAT generates a polarization-angle reverberation governed by Larmor precession. This reverberation is the most sensitive probe of grain magnetism, with superparamagnetic grains recovering more rapidly than paramagnetic grains. At $D>1$ pc, SN-induced polarization properties persist long after the radiation has faded, leaving a fossil imprint. This imprint offers the most practical near-term observational test: clouds near supernova remnants younger than the relaxation timescale of $\sim10\,t_{\rm gas}$ with $t_{\rm gas}$ gas damping time, should exhibit elevated polarization and blueshifted $\lambda_{\rm max}$ today.

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arXiv2026

Probing Anomalous Microwave Emission with the Square Kilometre Array

Anomalous microwave emission (AME) represents an excess of radiation in the 10-60 GHz range, distinct from synchrotron, free-free, or thermal dust emission. Although most commonly attributed to electric dipole radiation from rapidly rotating small dust grains (spinning dust), alternative mechanisms such as magnetic dipole emission (MDE) remain plausible. The detection of AME across diverse environments, from diffuse interstellar clouds to protoplanetary disks and external galaxies, suggests that multiple physical processes or carriers may contribute to its origin. Understanding AME is essential for both Galactic astrophysics and cosmology, as it constitutes a significant foreground for cosmic microwave background (CMB) studies, potentially biasing measurements. This chapter reviews current theoretical frameworks and observational evidence for AME, highlighting the key outstanding questions concerning its emission mechanisms, carriers, and polarization properties. We discuss how the Square Kilometre Array Observatory (SKAO), through its unprecedented sensitivity, angular resolution, and frequency coverage, will transform AME studies. SKA observations will enable detailed mapping of AME morphology, precise characterisation of its spectral energy distribution, and the identification of its carriers in Galactic and extragalactic environments. By combining SKA-mid data with higher-frequency observations from ALMA and other facilities such as SPHEREx, it will be possible to disentangle competing models and exploit AME as a diagnostic probe of interstellar grain physics and the small-scale structure of the interstellar medium.

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arXiv2026

The magnetic field in the Milky Way Galaxy: from large to small scales

The Milky Way is the galaxy in which we can study its magnetic field to the finest details, providing an ideal laboratory to understand the fundamental questions: how magnetic field is generated and evolves, and how it influences other components in the Galaxy. An SKA-Mid polarization survey will produce an all-sky rotation measure (RM) grid with a density of about 100 per square degree, which is approximately two orders of magnitude larger than what is currently available, and produce total intensity, polarized intensity, and RM all-sky images of diffuse emission covering scales from about 10 arcseconds upward after combination with single-dish observations. The dense RM grid and images of diffuse emission will allow us to determine the most complete picture of the magnetic field in the southern Galactic hemisphere from large to small scales.

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arXiv2026

Grain alignment and dust evolution physics with polarisation (GRADE-POL). II. On the physical basis of Serkowski and super-Serkowski polarisation spectra

Optical-to-near-infrared interstellar polarisation, induced by aligned dust grains, generally follows a convex wavelength dependence, known as the Serkowski relation. However, observations in the ultraviolet (UV) and at [mid-]infrared wavelengths have indicated that some of the spectra do not follow this relation. Specifically, about 25% show an excess in the degree of polarisation at mid-UV wavelengths ($\lambda^{-1} > 3\,\rm \mu m^{-1}$), referred to as the super-Serkowski polarisation. For this study, we re-examined both the Serkowski and super-Serkowski spectra based on the joint effect of paramagnetic relaxation, known as the Davis-Greenstein (DG) and radiative torque (RAT) alignment. We used the observational data for HD 30614, HD 204827, HD 37903 and HD 161056 to constrain our modelling. We examined two types of radiation fields: one derived from the scaled interstellar radiation field and the other originating from a B-type star. For the super-Serkowski spectra of HD 30614 and HD 204827, our model demonstrates that RAT alignment enhanced by radiation produced from a B-type star below the Lyman limit ($\lambda=912\r{A}$) can reasonably explain the observations and that a combination with the DG alignments results in a better fit for $\lambda^{-1}\geq 5.5\,\rm \mu m^{-1}$. For the Serkowski spectra in HD 37903 and HD 161056, only the RAT alignment by itself under the typical interstellar radiation field above the Lyman limit, within a typical cold neutral medium, can account for the observed spectra, with a combination of a very inefficient DG alignment. The capacity of our model to predict the starlight polarisation spectrum from infrared to far-UV is thus a promising tool for interpreting future missions that observe spectrophotometry in the UV bands.

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arXiv2026

BISTRO Survey: Gravity-Dominated and Magnetically Regulated Star Formation in M17 SW

We present high-resolution magnetic field maps of the M17 SW molecular cloud using JCMT 850 $\mu$m dust polarization at a scale of 14$''$. The magnetic field exhibits a distinct arc-like structure that encircles three dense clumps (C1, C2, and C3). By combining polarization data with ammonia line observations, the plane-of-sky magnetic field strength, measured using the Skalidis-Tassis method to minimize angle dispersion errors, ranges from 0.1 to 2.4 mG (mean: 0.54 mG). Energy budget analysis reveals a hierarchy dominated by gravity ($e_G \approx 10^{-7.8}$ erg cm$^{-3}$), which exceeds both magnetic ($e_B \approx 10^{-8.3}$ erg cm$^{-3}$) and turbulent ($e_k \approx 10^{-8.7}$ erg cm$^{-3}$) energies. Since all three energy densities lie within one order of magnitude, gravitational dominance acts primarily as the global driver, while the system remains in a state of near-equipartition. Structurally, the northeastern boundary shows magnetic field lines perpendicular to the shock front, consistent with compression from the adjacent HII region. Within the cloud, magnetic field lines generally align with gravity to assist collapse, but turn perpendicular to gravity within curved accretion bridges. This configuration provides support against radial collapse while guiding gas flow. Kinematic evidence suggests that these channels transport material from Clump C3 onto the massive Clump C2. Star formation in M17 SW is globally driven by gravity but locally regulated by the magnetic field structure.

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arXiv2026

B-fields And dust in interstelLar fiLAments using Dust POLarization (BALLAD-POL): VI. Grain alignment mechanisms in the massive quiescent filament G16.96+0.27 using dust polarization observations from JCMT/POL-2

Dust polarization induced by aligned non-spherical grains acts as an important tool to trace the magnetic field (B-field) morphologies and strengths in molecular clouds and constrain grain properties and their alignment mechanisms. The widely accepted grain alignment theory is the alignment induced by RAdiative Torques (RATs). In this work, we investigate grain alignment mechanisms in a massive, quiescent and filamentary Infrared Dark Cloud G16.96+0.27 using thermal dust polarization observation with JCMT/POL-2 at 850 $\mu$m. We observe the so-called phenomenon of polarization hole attributed to the decrease in polarization fraction in denser regions of higher total intensity and gas density. Our study finds that B-field tangling effect is minimal to cause the polarization hole, and the dominant factor is the reduction in grain alignment efficiency in denser regions, consistent with RAT mechanism. To test RAT theory, we calculate various quantities describing grain alignment, including minimum size of aligned grains, magnetic and magnetic relaxation parameter, and show that RAT mechanism can explain observational data. Our study also reveals evidence for magnetically-enhanced RAT (M-RAT) mechanism required to explain the observed high polarization fractions of above 10 % in the outer regions of the filament. Finally, we perform detailed modeling of thermal dust polarization using $\mathrm{DustPOL\_py}$ based on M-RAT theory and find that the modeling could successfully reproduce the observational data when maximum grain size is around 0.45 $\mu$m accompanied by an increase in grain axial ratio, along with the consideration of variations in the magnetic field's inclination angle with the line of sight.

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arXiv2026

Effective Magnetic Susceptibility of Dust Grains with Superparamagnetic Inclusions and Implications

Magnetic properties of dust grains play a fundamental role in their alignment with ambient magnetic fields and magnetic dipole emission. In the radiative torque (RAT) paradigm, superparamagnetic inclusions (SPIs) embedded within dust grains are expected to significantly enhance magnetic susceptibility and alignment efficiency. Previous studies have generally assumed SPIs of a single characteristic size. In this work, we develop an effective superparamagnetism model that explicitly accounts for a power-law size distribution of SPIs. We show that the effective zero-frequency susceptibility can be described by the superparamagnetic susceptibility of uniform-sized inclusions evaluated at the critical blocking size, reduced by a factor $F_{\rm eff}\sim 0.1$. It exhibits a slight increase with dust temperature $T_{d}$, in contrast to the rapid decrease for the case of single-size SPIs. For rotating grains at angular frequency $\omega$, we identify a characteristic resonance size of SPIs that dominates the magnetic response, $N_{\rm res} = (T_{d}/T_{\rm act}) \ln (\nu_{0}/\omega)$ with $T_{\rm act}$ activation temperature and $\nu_{0}$ the characteristic attempt frequency of SPIs. The frequency-dependent effective susceptibility is well described by the maximum susceptibility $\chi_{\rm eff}^{\rm max}(\omega)$ at $N_{\rm res}$, reduced by a factor $G_{\rm eff}\sim 0.1$. Unlike models assuming uniform-sized inclusions, we find that the effective susceptibility exhibits a nearly flat spectrum for frequency below $\nu_{0}$, arising from the progressive activation of larger inclusions at lower frequencies. This effective superparamagnetism model based on the SPI size distrbution has important implications for magnetic grain alignment, dust polarization, and magnetic dipole emission across diverse environments.

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arXiv2026

Galactic Dust Polarization in Turbulent Multiphase ISM: On the Origin of the $EE/BB$ Asymmetry

Polarized thermal emission from Galactic dust is the dominant foreground for CMB polarization measurements at high frequencies, with its statistical properties shaped by the interplay between turbulence and magnetic fields in the multiphase interstellar medium (ISM). Variations in turbulence regime and density-magnetic-field alignment across the warm (WNM), unstable (UNM), and cold (CNM) neutral media should imprint distinct signatures on the power spectra and $EE/BB$ power ratio, yet the relative contributions of these phases remain poorly constrained. Using high-resolution 3D magnetohydrodynamic simulations of a turbulent multiphase ISM coupled with synthetic dust polarization maps, we quantify phase-dependent turbulence, anisotropy, and alignment properties. We find that the trans-Alfv\'enic and transonic WNM and UNM are strongly anisotropic, exhibiting tight alignment of density and velocity structures with the local magnetic field. In contrast, the super-Alfv\'enic and supersonic CNM displays reduced anisotropy and weak alignment. These dynamical differences are reflected in the statistical scaling of fluctuations: the square root of the second-order velocity structure function exhibits a slope near $1/3$ in the WNM, near $1/2$ in the CNM, and intermediate in the UNM. Comparing our synthetic polarization power spectra with \textit{Planck} measurements, we find that polarization from UNM dust yields spectral slopes closest to the \textit{Planck}-inferred values, whereas WNM and CNM dust produce steeper and shallower spectra, respectively. The WNM yields $EE/BB>2$, the UNM gives $EE/BB\sim2$, and the CNM yields $EE/BB\approx1$. These results suggest that UNM dust may be an important contributor to the polarized foreground under typical high-latitude ISM conditions. We present predictions at 150 GHz to inform foreground modeling and separation.

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arXiv2026

One-dimensional and time-dependent modelling of complex organic molecules in protostars

Complex organic molecules (COMs), the building blocks of life, have been extensively detected under various physical conditions, from quiescent clouds to star-forming regions. They therefore serve as excellent tracers for the local physical and chemical properties of these environments. Proper models that are capable of grasping the formation and destruction of COMs are crucial to understanding observations. However, given that distinct COMs may be detected from different locations and at varying times, we improve UCLCHEM - a gas-grain chemical code - to a one-dimensional, time-dependent model, tailored to protostars. In this update, we examine two stages of a protostar: the prestellar and heating stages, incorporating a simple radiative mechanism for both the internal and external radiation fields of the cloud. This approach relies on the key assumption that the dust and gas temperatures are completely coupled. Ultimately, we implement an updated version of our model to interpret observations obtained through both single-dish and interferometry under varying conditions, including a SgrB2(N1) hot core, massive Galactic clumps and a hot core in Orion. We show that our model could reproduce these observations well, highlighting that some COMs are positioned at a higher temperature in the envelope, whereas others are from the lower temperature, potentially leading to misinterpretation when using a single-point model. In a particular case of SgrB2(N1), the best model indicates that the cosmic-ray ionisation rate significantly exceeds the value typically used for the standard interstellar medium. Our model shows as an efficient computational tool particularly useful for better insights into observations of COMs.

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arXiv2025

Grain alignment and dust evolution physics with polarisation (GRADE-POL). I. Dust polarisation modelling for isolated starless cores

The polarisation of light induced by aligned interstellar dust serves as a significant tool in investigating cosmic magnetic fields, dust properties, and poses a challenge in characterising the polarisation of the cosmic microwave background and other sources. To establish dust polarisation as a reliable tool, the physics of the grain alignment process needs to be studied thoroughly. The Magnetically enhanced Radiative Torque (MRAT) alignment is the only mechanism that can induce highly efficient alignment of grains with magnetic fields required by polarisation observations of the diffuse interstellar medium. Our numerical modelling of dust polarisation using the MRAT theory demonstrated that the alignment efficiency of starlight polarisation ($p_{\rm ext}/A_{\rm V}$) and the degree of thermal dust polarisation ($p_{\rm em}$) first decrease slowly with increasing visual extinction ($A_{\rm V}$) and then falls steeply as $\propto A^{-1}_{\rm V}$ at large $A_{\rm V}$ due to the loss of grain alignment, which explains the phenomenon known as polarisation holes. Visual extinction at the transition from shallow to steep slope ($A^{\rm loss}_{\rm V}$) increases with the maximum grain size. By applying physical profiles suitable for a starless core 109 in the Pipe Nebula (Pipe-109), our model successfully reproduces the existing observations of starlight polarisation at R-band ($0.65\,μ$m) and H-band ($1.65\,μ$m), as well as emission polarisation at submillimetre ($870\,μ$m). Successful modelling of observational data requires perfect alignment of large grains as evidence of the MRAT mechanism, and larger maximum size with higher elongation at higher $A_{\rm V}$. The latter reveals the first evidence for the new model of anisotropic grain growth induced by magnetic grain alignment.

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arXiv2025

3D B-fieLds in the InterStellar medium and Star-forming regions (3D-BLISS): I. Using Starlight Polarization in the Massive IRDC Filament G11.11-0.12

Measuring three-dimensional magnetic fields (3D B-fields) is essential to understand the formation and evolution of the interstellar medium and multi-scale star formation; however, the accurate measurement of 3D B-fields is still challenging. The dust polarization angles by magnetically aligned grains provide the projected B-fields onto the plane-of-sky, while the dust polarization degree provides the B-field's inclination angle with respect to the line-of-sight. Our previous theoretical studies proposed a new method of probing 3D B-fields using dust polarization combined with the Radiative Torque (RAT) alignment theory and demonstrated the accurate inference of B-field inclination angles using synthetic polarization data. In this paper, we report the first application of the new technique to study 3D B-fields and dust properties in the G11.11-0.12 filament (hereafter G11) from starlight polarization observations taken by ISRF/SIRPOL at $2.19\,\rm\mu m$. Using both observed starlight polarization and optical dust extinction curves from the Gaia mission, we constrained the maximum grain size of $0.25\,\rm\mu m$ and the grain elongation with an axial ratio of $s\gtrsim 1.4$ in the outer regions of G11. We calculated the alignment properties in G11 by using the \textsc{DustPOL\_py} code. The B-field's inclination angles in G11 are then inferred from the observed starlight polarization efficiency when the grain alignment is included, with a mean angle of $\sim 48$ degrees. From these inferred inclination angles, we found evidence of the local 3D arc-shaped B-field structure toward the sightline. These findings are important for understanding 3D B-field's roles in the formation and evolution of massive filamentary clouds.

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arXiv2025

Toward A General Theory of Grain Alignment and Disruption by Radiative Torques and Magnetic Relaxation

We generalize the magnetically enhanced radiative torque (MRAT) alignment theory for general astrophysical environments described by a dimensionless parameter $U/(n_{1}T_{2})$ with $U$ local radiation strength, $n_{1}=n_{\rm H}/(10{\rm cm}^{-3})$ the hydrogen density, and $T_{2}=T_{\rm gas}/100{\rm K}$ the gas temperature. We first derive the critical magnetic relaxation $δ_{\rm mag,cri}$ required to produce high-J attractors for different RAT models and local conditions and find that $δ_{\rm mag,cri}$ must be larger for stronger radiation fields. We then numerically study the grain alignment and rotational disruption by the MRAT mechanism taking into account gas collisions and magnetic fluctuations. We find that, for the collision-dominated (CD) regime ($U/(n_{1}T_{2})\leq 1$), collisional and magnetic excitations can slowly transport large grains from low-J rotation to high-J attractors, leading to the perfect {\it slow alignment} within $\sim 10-100$ damping times due to MRATs. However, for the radiation-dominated (RD) regime ($U/(n_{1}T_{2})>1$), only a fraction of grains can be fast aligned at high-J attractors by MRATs, and the majority of grains are trapped at low-J rotation due to strong radiative torques, a new effect we term {\it radiative torque (RAT) trapping}. For extreme radiation fields of $U/(n_{1}T_{2})>10^{4}$, the efficiency of magnetic relaxation on grain alignment is suppressed, and grains only have fast alignment and disruption purely determined by RATs. We quantified the fraction of grains with fast alignment at high-J attractors, $f_{\rm high-J}^{\rm fast}$, for different RAT models, magnetic relaxation, and $U/(n_{1}T_{2})$, and found that the maximum $f_{\rm high-J}^{\rm fast}$ can reach $45\%$ by MRATs and $22\%$ by RATs.

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arXiv2025

Optical design and polarimetric performance of a SmallSat UV polarimeter to study interstellar dust: PUFFINS

The Polarimetry in the Ultraviolet to Find Features in INterStellar dust (PUFFINS) is a SmallSat mission concept designed to obtain ultraviolet (UV) spectropolarimetric observations to probe the interstellar dust grain properties and to understand wavelength-dependent extinction and star formation. PUFFINS plans to observe 70 UV bright target stars at varying distances within a 180-320 nm wavelength range with 0.02% polarimetric accuracy. PUFFINS uses a simple telescope design with all reflective optics coated with protected aluminum to enhance reflectivity in the UV. The telescope and the spectropolarimeter, which consists of a Wollaston prism and a half-wave retarder, have been carefully selected to be greater than Technology Readiness Level 6 (TRL6). The telescope is designed to exhibit negligible instrumental polarization and crosstalk, significantly reducing the time needed for polarimetric calibration in orbit. The optimum and careful selection of the target stars will enable PUFFINS to observe an expanded and well-defined sample to test the predictions by interstellar grain alignment theory in the observation phase of 9 months. This paper outlines the details of the optical and optomechanical design and evaluates the polarimetric performance of PUFFINS.

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arXiv2025

B-fields And dust in interstelLar fiLAments using Dust POLarization (BALLAD-POL): IV. Grain alignment mechanisms in Cocoon Nebula (IC 5146) using polarization observations from JCMT/POL-2

The polarization of starlight and thermal dust emission from aligned non-spherical grains provides a powerful tool for tracing magnetic field morphologies and strengths in diffuse interstellar medium to star-forming regions, and constraining dust grain properties and their alignment mechanisms. However, the physics of grain alignment is not yet fully understood. The alignment based on RAdiative Torques (RATs), known as RAT Alignment or RAT-A mechanism is the most acceptable mechanism. In this work, we investigate the grain alignment mechanisms in F13 (F13N and F13C) and F13S filamentary regions of the Cocoon Nebula (IC 5146) using polarized thermal dust emission observations from JCMT/POL-2 at 850 $μ$m. We find that the polarization fraction decreases with increasing total intensity and gas column density in each region, termed as polarization hole. We investigate for any role of magnetic field tangling on the observed polarization hole by estimating the polarization angle dispersion function. Our study finds that the polarization hole is not significantly influenced by magnetic field tangling, but majorly due to decrease in RAT alignment efficiency of grains in denser regions. To test whether RAT-A mechanism can reproduce the observational results, we estimate minimum alignment size of grains using RAT theory. Our study finds strong evidence for RAT-A mechanism that can explain the polarization hole. We also find potential hints that the observed higher polarization fractions in some regions of F13 filament can be due to combined effects of both suprathermal rotation by RATs and enhanced magnetic relaxation, supporting the Magnetically-Enhanced RAT (M-RAT) mechanism.

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arXiv2025

The JCMT BISTRO-3 Survey: Variation of magnetic field orientations on parsec and sub-parsec scales in the massive star-forming region G28.34+0.06

Magnetic fields play a significant role in star-forming processes on core to clump scales. We investigate magnetic field orientations and strengths in the massive star-forming clump P2 within the filamentary infrared dark cloud G28.34+0.06 using dust polarization observations made using SCUBA-2/POL-2 on the James Clerk Maxwell Telescope as part of the B-field In STar-forming Region Observations (BISTRO) survey. We compare the magnetic field orientations at the clump scale of ~2 parsecs from these JCMT observations with those at the core scale of ~0.2 parsecs from archival ALMA data, finding that the magnetic field orientations on these two different scales are perpendicular to one another. We estimate the distribution of magnetic field strengths, which range from 50 to 430 μG over the clump. The region forming the core shows the highest magnetic field strength. We also obtain the distribution of mass-to-flux ratios across the clump. In the region surrounding the core, the mass-to-flux ratio is larger than 1, which indicates the magnetic field strength is insufficient to support the region against gravitational collapse. Therefore, the change in the magnetic field orientation from clump to core scales may be the result of gravitational collapse, with the field being pulled inward along with the flow of material under gravity.

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