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Iron inclusions embedded inside dust grains play a crucial role in both internal alignment (IA) via Barnett relaxation and external alignment via the MAgnetically Enhanced RAdiative Torque (MRAT) mechanism. Moreover, inelastic relaxation is predicted to dominate over Barnett relaxation in driving the IA of micron-sized grains and very large grains (VLGs) above 10 μ m. Yet, a detailed modeling of polarized thermal dust emission from Class 0/I young stellar objects (YSOs) taking into account these effects and their observational constraints is still lacking. In this paper, we update the POLARIS code and use it to perform synthetic dust polarization modeling for MHD simulations of an intermediate-mass YSOs. Results will be post-processed with CASA to confront Atacama Large Millimeter/submillimeter Array (ALMA) polarimetric observations. We found that to reproduce the high polarization degree of p ∼ 5%–30% observed in protostellar envelopes by ALMA, micron-sized grains and VLGs must contain iron inclusions with N _cl ∼ 5–10 ^3 iron atoms per cluster, assuming 30% of iron abundance locked inside dust grains under the cluster form. Inside the inner ∼500 au region, inelastic relaxation must participate in driving the grain IA, and grains must contain larger iron inclusions of N _cl ∼ 10 ^2 –10 ^4 and grow beyond ≥10 μ m to reproduce ∼3%–10% of dust polarization observed by ALMA. But given such a combination, the IA and MRAT efficiency acting on VLGs still decreases toward the center, inducing the decrease of p (%) with increasing gas density, reaching p ∼ 1% inside the disk.

We present 850 μ m polarization observations of the IC 348 star-forming region in the Perseus molecular cloud as part of the B-fields In STar-forming Region Observation survey. We study the magnetic properties of two cores (HH 211 MMS and IC 348 MMS) and a filamentary structure of IC 348. We find that the overall field tends to be more perpendicular than parallel to the filamentary structure of the region. The polarization fraction decreases with intensity, and we estimate the trend by power law and the mean of the Rice distribution fittings. The power indices for the cores are much smaller than 1, indicative of possible grain growth to micron size in the cores. We also measure the magnetic field strengths of the two cores and the filamentary area separately by applying the Davis–Chandrasekhar–Fermi method and its alternative version for compressed medium. The estimated mass-to-flux ratios are 0.45–2.20 and 0.63–2.76 for HH 211 MMS and IC 348 MMS, respectively, while the ratios for the filament are 0.33–1.50. This result may suggest that the transition from subcritical to supercritical conditions occurs at the core scale (∼0.05 pc) in the region. In addition, we study the energy balance of the cores and find that the relative strength of turbulence to the magnetic field tends to be stronger for IC 348 MMS than for HH 211 MMS. The result could potentially explain the different configurations inside the two cores: a single protostellar system in HH 211 MMS and multiple protostars in IC 348 MMS.

We report 850 μ m continuum polarization observations toward the filamentary high-mass star-forming region NGC 2264, taken as part of the B -fields In STar forming Regions Observations large program on the James Clerk Maxwell Telescope. These data reveal a well-structured nonuniform magnetic field in the NGC 2264C and 2264D regions with a prevailing orientation around 30° from north to east. Field strength estimates and a virial analysis of the major clumps indicate that NGC 2264C is globally dominated by gravity, while in 2264D, magnetic, gravitational, and kinetic energies are roughly balanced. We present an analysis scheme that utilizes the locally resolved magnetic field structures, together with the locally measured gravitational vector field and the extracted filamentary network. From this, we infer statistical trends showing that this network consists of two main groups of filaments oriented approximately perpendicular to one another. Additionally, gravity shows one dominating converging direction that is roughly perpendicular to one of the filament orientations, which is suggestive of mass accretion along this direction. Beyond these statistical trends, we identify two types of filaments. The type I filament is perpendicular to the magnetic field with local gravity transitioning from parallel to perpendicular to the magnetic field from the outside to the filament ridge. The type II filament is parallel to the magnetic field and local gravity. We interpret these two types of filaments as originating from the competition between radial collapsing, driven by filament self-gravity, and longitudinal collapsing, driven by the region's global gravity.

Sun-like stars are thought to accrete most of their final mass during the protostellar phase, during which the stellar embryo is surrounded by an infalling dense envelope. We present an analysis of 26 K -band spectra of Class 0 protostars, which are the youngest protostars. Of these, 18 are new observations made with the Keck MOSFIRE instrument. H i Br γ , several H _2 , and CO Δ v = 2 features are detected and analyzed. We detect Br γ emission in 62%, CO overtone emission in 50%, and H _2 emission in 90% of sources. The H i and CO emission is associated with accretion, while the H _2 lines are consistent with shock excitation indicating jets/outflows. Six objects exhibit photospheric absorption features, with almost no outflow activity and no detection of the accretion-related Br γ emission line. Comparing these results with an archival sample of Class I K -band spectra, we find that the CO and Br γ emission lines are systematically more luminous in Class 0s, suggesting that the accretion is on average more vigorous in the Class 0 phase. Typically associated with the heated inner accretion disk, the much higher detection rate of CO overtone emission in Class 0s indicates also that episodes of high accretion activity are more frequent in Class 0 systems. The kinematics of the Class 0 CO overtone emission suggest either an accretion-heated inner disk or material directly infalling onto the central region. This could point toward an accretion mechanism of different nature in Class 0 systems than the typical picture of magnetospheric accretion.

We report the discovery of jets emanating from pre-main-sequence objects exclusively at mid-infrared wavelengths, enabled by the superb sensitivity of JWST’s Mid-Infrared Instrument Medium-Resolution Spectrometer. These jets are observed only in lines of [Ni ii ], [Fe ii ], [Ar ii ], and [Ne ii ]. The H _2 emission, imaged in eight distinct transitions, has a completely different morphology, exhibiting a wide-angled, biconical shape, symmetrically distributed about the jet axes. Synergistic high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations resolve a pair of side-by-side edge-on accretion disks lying at the origin of the twin mid-infrared jets. Assuming coevality of the components of the young multiple system under investigation, the system age is at least (2–2.5) × 10 ^6 yr, despite the discrepantly younger age inferred from the spectral energy distribution of the combined edge-on disk sources. The later system evolutionary stage is corroborated by ALMA observations of CO(2−1), ^13 CO(2−1), and C ^18 O(2−1), which show no traces of molecular outflows or remnant cavity walls. Consequently, the observed H _2 structures must have their origins in wide-angled disk winds, in the absence of any ambient, swept-up gas. In the context of recent studies of protostars, we propose an outflow evolutionary scenario in which the molecular gas component dominates in the youngest sources, whereas the fast, ionized jets dominate in the oldest sources, as is the case for the twin jets discovered in the WL 20 system.

Mapping stars and gas in nearby galaxies is fundamental for understanding their growth and the impact of their environment. This issue is addressed by comparing the stellar “edges” of galaxies D _stellar , defined as the outermost diameter where in situ star formation significantly drops, with the gaseous distribution parameterized by the neutral atomic hydrogen diameter measured at 1 M _⊙ pc ^−2 , D _HI . By sampling a broad H i mass range 10 ^5 M _⊙ < M _HI < 10 ^11 M _⊙ , we find several dwarf galaxies with M _HI < 10 ^9 M _⊙ from the field and Fornax Cluster that are distinguished by D _stellar ≫ D _HI . For the cluster dwarfs, the average H i surface density near D _stellar is ∼0.3 M _⊙ pc ^−2 , reflecting the impact of quenching and outside-in gas removal from ram pressure and tidal interactions. In comparison, D _stellar / D _HI ranges between 0.5 and 2 in dwarf field galaxies, consistent with the expectations from stellar feedback. Only more massive disk galaxies in the field can thus be characterized by the common assumption that D _stellar ≲ D _HI . We discover a break in the D _stellar – M _⋆ relation at m _break ∼ 4 × 10 ^8 M _⊙ that potentially differentiates the low-mass regime, where the influence of stellar feedback and environmental processes more prominently regulates the sizes of nearby galaxies. Our results highlight the importance of combining deep optical and H i imaging for understanding galaxy evolution.

We present BISTRO Survey 850 μ m dust emission polarization observations of the L1495A-B10 region of the Taurus molecular cloud, taken at the James Clerk Maxwell Telescope (JCMT). We observe a roughly triangular network of dense filaments. We detect nine of the dense starless cores embedded within these filaments in polarization, finding that the plane-of-sky orientation of the core-scale magnetic field lies roughly perpendicular to the filaments in almost all cases. We also find that the large-scale magnetic field orientation measured by Planck is not correlated with any of the core or filament structures, except in the case of the lowest-density core. We propose a scenario for early prestellar evolution that is both an extension to, and consistent with, previous models, introducing an additional evolutionary transitional stage between field-dominated and matter-dominated evolution, observed here for the first time. In this scenario, the cloud collapses first to a sheet-like structure. Uniquely, we appear to be seeing this sheet almost face on. The sheet fragments into filaments, which in turn form cores. However, the material must reach a certain critical density before the evolution changes from being field dominated to being matter dominated. We measure the sheet surface density and the magnetic field strength at that transition for the first time and show consistency with an analytical prediction that had previously gone untested for over 50 yr.

We present observations of polarized dust emission at 850 μ m from the L43 molecular cloud, which sits in the Ophiuchus cloud complex. The data were taken using SCUBA-2/POL-2 on the James Clerk Maxwell Telescope as a part of the BISTRO large program. L43 is a dense ( ${N}_{{{\rm{H}}}_{2}}\sim {10}^{22}$ –10 ^23 cm ^−2 ) complex molecular cloud with a submillimeter-bright starless core and two protostellar sources. There appears to be an evolutionary gradient along the isolated filament that L43 is embedded within, with the most evolved source closest to the Sco OB2 association. One of the protostars drives a CO outflow that has created a cavity to the southeast. We see a magnetic field that appears to be aligned with the cavity walls of the outflow, suggesting interaction with the outflow. We also find a magnetic field strength of up to ∼160 ± 30 μ G in the main starless core and up to ∼90 ± 40 μ G in the more diffuse, extended region. These field strengths give magnetically super- and subcritical values, respectively, and both are found to be roughly trans-Alfvénic. We also present a new method of data reduction for these denser but fainter objects like starless cores.

The linear polarization of thermal dust emission provides a powerful tool to probe interstellar and circumstellar magnetic fields, because aspherical grains tend to align themselves with magnetic field lines. While the Radiative Alignment Torque (RAT) mechanism provides a theoretical framework for this phenomenon, some aspects of this alignment mechanism still need to be quantitatively tested. One such aspect is the possibility that the reference alignment direction changes from the magnetic field (“ B -RAT”) to the radiation field k-vector (“ k -RAT”) in areas of strong radiation fields. We investigate this transition toward the Orion Bar PDR, using multiwavelength SOFIA HAWC+ dust polarization observations. The polarization angle maps show that the radiation field direction is on average not the preferred grain alignment axis. We constrain the grain sizes for which the transition from B -RAT to k -RAT occurs in the Orion Bar (grains ≥ 0.1 μ m toward the most irradiated locations), and explore the radiatively driven rotational disruption that may take place in the high-radiation environment of the Bar for large grains. While the grains susceptible to rotational disruption should be in suprathermal rotation and aligned with the magnetic field, k -RAT aligned grains would rotate at thermal velocities. We find that the grain size at which the alignment shifts from B -RAT to k -RAT corresponds to grains too large to survive the rotational disruption. Therefore, we expect a large fraction of grains to be aligned at suprathermal rotation with the magnetic field, and to potentially be subject to rotational disruption, depending on their tensile strength.

We present new Very Large Array observations, between 6.8 and 66 mm, of the edge-on Class I disk IRAS04302+2247. Observations at 6.8 mm and 9.2 mm lead to the detection of thermal emission from the disk, while shallow observations at the other wavelengths are used to correct for emission from other processes. The disk radial brightness profile transitions from broadly extended in previous Atacama Large Millimeter/submillimeter Array 0.9 mm and 2.1 mm observations to much more centrally brightened at 6.8 mm and 9.2 mm, which can be explained by optical depth effects. The radiative transfer modeling of the 0.9 mm, 2.1 mm, and 9.2 mm data suggests that the grains are smaller than 1 cm in the outer regions of the disk, allowing us to obtain the first lower limit for the scale height of grains emitting at millimeter wavelengths in a protoplanetary disk. We find that the millimeter dust scale height is between 1 au and 6 au at a radius 100 au from the central star, while the gas scale height is estimated to be about 7 au, indicating a modest level of settling. The estimated dust height is intermediate between less evolved Class 0 sources, which are found to be vertically thick, and more evolved Class II sources, which show a significant level of settling. This suggests that we are witnessing an intermediate stage of dust settling.

We study the H ii regions associated with the NGC 6334 molecular cloud observed in the submillimeter and taken as part of the B -fields In STar-forming Region Observations Survey. In particular, we investigate the polarization patterns and magnetic field morphologies associated with these H ii regions. Through polarization pattern and pressure calculation analyses, several of these bubbles indicate that the gas and magnetic field lines have been pushed away from the bubble, toward an almost tangential (to the bubble) magnetic field morphology. In the densest part of NGC 6334, where the magnetic field morphology is similar to an hourglass, the polarization observations do not exhibit observable impact from H ii regions. We detect two nested radial polarization patterns in a bubble to the south of NGC 6334 that correspond to the previously observed bipolar structure in this bubble. Finally, using the results of this study, we present steps (incorporating computer vision; circular Hough transform) that can be used in future studies to identify bubbles that have physically impacted magnetic field lines.