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As part of the B -fields In Star-forming Region Observations survey, we present James Clerk Maxwell Telescope (JCMT) 850 μ m polarimetric observations toward the Orion integral-shaped filament (ISF) that covers three portions known as OMC-1, OMC-2, and OMC-3. The magnetic field threading the ISF seen in the JCMT POL-2 map appears as a tale of three: pinched for OMC-1, twisted for OMC-2, and nearly uniform for OMC-3. A multiscale analysis shows that the magnetic field structure in OMC-3 is very consistent at all the scales, whereas the field structure in OMC-2 shows no correlation across different scales. In OMC-1, the field retains its mean orientation from large to small scales but shows some deviations at small scales. Histograms of relative orientations between the magnetic field and filaments reveal a bimodal distribution for OMC-1, a relatively random distribution for OMC-2, and a distribution with a predominant peak at 90 ^∘ for OMC-3. Furthermore, the magnetic fields in OMC-1 and OMC-3 both appear to be aligned perpendicular to the fibers, which are denser structures within the filament, but the field in OMC-2 is aligned along with the fibers. All these suggest that gravity, turbulence, and magnetic field are each playing a leading role in OMC-1, 2, and 3, respectively. While OMC-2 and 3 have almost the same gas mass, density, and nonthermal velocity dispersion, there are on average younger and fewer young stellar objects in OMC-3, providing evidence that a stronger magnetic field will induce slower and less efficient star formation in molecular clouds.

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.

The electromagnetic field is a fundamental force in nature that regulates the formation of stars in the Universe. Despite decades of efforts, a reliable assessment of the importance of the magnetic fields in star formation relations remains missing. In star formation research, our acknowledgment of the importance of magnetic fields is best summarized by the R. M. Crutcher et al. B – ρ relation, \begin{eqnarray*}\mathrm{log}B(\rho )/\mathrm{Gauss}=\left\{\begin{array}{l}-5,\,\mathrm{if}\,\rho \,\lesssim \,{10}^{-20}\,{\rm{g}}\,{\mathrm{cm}}^{-3}\\ \displaystyle \frac{2}{3}\cdot \mathrm{log}\rho +\mathrm{log}{\rho }_{0},\,\mathrm{if}\,\rho \,\gtrsim \,{10}^{-20}\,{\rm{g}}\,{\mathrm{cm}}^{-3},\end{array}\right.\end{eqnarray*} whose interpretation remains controversial. The relation is either interpreted as proof of the importance of a magnetic field in gravitational collapse or as the result of self-similar collapse where the role of the magnetic field is secondary to gravity. Using simulations, we find a fundamental relation, ${{ \mathcal M }}_{{\rm{A}}}$ – k _B _− _ρ (the slope of the B – ρ relation): \begin{eqnarray*}\displaystyle \frac{{{ \mathcal M }}_{{\rm{A}}}}{{{ \mathcal M }}_{{\rm{A}},{\rm{c}}}}={{\rm{k}}}_{B-\rho }^{{ \mathcal K }}\approx \displaystyle \frac{{{ \mathcal M }}_{{\rm{A}}}}{7.5}\approx {{\rm{k}}}_{B-\rho }^{1.7\pm 0.15}.\end{eqnarray*} This fundamental B – ρ slope relation enables one to measure the Alfvénic Mach number, a direct indicator of the importance of the magnetic field, using the distribution of data in the B – ρ plane. It allows us to apply the following empirical B – ρ relation: \begin{eqnarray*}\displaystyle \frac{B}{{B}_{c}}=\exp \left({\left(\displaystyle \frac{\gamma }{{ \mathcal K }}\right)}^{-1}{\left(\displaystyle \frac{\rho }{{\rho }_{c}}\right)}^{\displaystyle \frac{\gamma }{{ \mathcal K }}}\right)\approx \displaystyle \frac{B}{{10}^{-6.3}{\rm{G}}}\approx \exp \left(9{\left(\displaystyle \frac{\rho }{{10}^{-16.1}{\rm{g}}\,{\mathrm{cm}}^{-3}}\right)}^{0.11}\right)\ ,\end{eqnarray*} which offers an excellent fit to the Crutcher et al. data, where we assume an ${{ \mathcal M }}_{{\rm{A}}}-\rho $ relation ( $\tfrac{{{ \mathcal M }}_{{\rm{A}}}}{{{ \mathcal M }}_{{\rm{A}},{\rm{c}}}}={\left(\tfrac{\rho }{{\rho }_{c}}\right)}^{\gamma }\approx {{ \mathcal M }}_{{\rm{A}}}/7.5\approx {\left(\rho /{10}^{-16.1}\,{\rm{g}}\,{{\rm{cm}}}^{-3}\right)}^{0.19}$ ). The foundational ${{ \mathcal M }}_{{\rm{A}}}-{{\rm{k}}}_{B-\rho }$ relation provides an independent way to measure the importance of the magnetic field against the kinematic motion using multiple magnetic-field measurements. Our approach offers a new interpretation of the classical B – ρ relation, where a gradual decrease in the importance of B at higher densities is implied.

Deuterated molecules are valuable probes for investigating the evolution and the kinematics in the earliest stages of star formation. In this study, we conduct a comprehensive investigation by performing a single-point survey of 101 starless clump candidates, and carrying out on-the-fly (OTF) observations of 11 selected sources, focusing on deuterated molecular lines using the IRAM 30 m telescope. In the single-point observation, we make 46 detections for DCO ^+ J = 1−0, 12 for DCN J = 1−0, 51 for DNC J = 1−0, 7 for N _2 D ^+ J = 1−0, 20 for DCO ^+ J = 2−1, and 10 for DCN J = 2−1. The starless clump candidates with deuterated molecule detections exhibit lower median kinetic temperatures and a narrower H _2 CO (1 _(0,1) −0 _(0,0) ) median full width at half maximum compared to those without such detections, while simultaneously displaying similar median values of 1.1 mm intensity, mass, and distance. Furthermore, our OTF observations reveal that deuterated molecules predominantly have peaks near the 1.1 mm continuum peaks, with the DCO ^+ J = 1−0 emission demonstrating higher intensity in the deuterated peak region compared to the DCN and DNC J = 1−0 emissions. Additionally, the majority of emissions from deuterated molecules and ^13 C isotopologues exhibit peak positions close to those of the 1.1 mm continuum peaks. By analyzing the 20″ × 20″ regions with strongest deuterated emissions in the OTF observations, we estimated deuterated abundances of 0.004−0.045, 0.011−0.040, and 0.004−0.038 for D _frac (HCN), D _frac (HCO ^+ ), and D _frac (HNC), respectively. The differential detection of deuterated molecular lines in our OTF observations could be attributed to variations in critical densities and formation pathways.

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.

We have comprehensively studied the multiscale physical properties of the massive infrared dark cloud G28.34 (the Dragon cloud) with dust polarization and molecular line data from Planck, FCRAO-14 m, James Clerk Maxwell Telescope, and Atacama Large Millimeter/submillimeter Array. We find that the averaged magnetic fields of clumps tend to be either parallel with or perpendicular to the cloud-scale magnetic fields, while the cores in clump MM4 tend to have magnetic fields aligned with the clump fields. Implementing the relative orientation analysis (for magnetic fields, column density gradients, and local gravity), velocity gradient technique, and modified Davis–Chandrasekhar–Fermi analysis, we find that G28.34 is located in a trans-to-sub-Alfvénic environment; the magnetic field is effectively resisting gravitational collapse in large-scale diffuse gas, but is distorted by gravity within the cloud and affected by star formation activities in high-density regions, and the normalized mass-to-flux ratio tends to increase with increasing density and decreasing radius. Considering the thermal, magnetic, and turbulent supports, we find that the environmental gas of G28.34 is in a supervirial (supported) state, the infrared dark clumps may be in a near-equilibrium state, and core MM4-core4 is in a subvirial (gravity-dominant) state. In summary, we suggest that magnetic fields dominate gravity and turbulence in the cloud environment at large scales, resulting in relatively slow cloud formation and evolution processes. Within the cloud, gravity could overwhelm both magnetic fields and turbulence, allowing local dynamical star formation to happen.

The James Clerk Maxwell Telescope (JCMT) Transient Survey has been monitoring eight Gould Belt low-mass star-forming regions since 2015 December and six somewhat more distant intermediate-mass star-forming regions since 2020 February with the Submillimeter Common User Bolometer Array 2 on board JCMT at 450 and 850 μ m and with an approximately monthly cadence. We introduce our pipeline v2 relative calibration procedures for image alignment and flux calibration across epochs, improving on our previous pipeline v1 by decreasing measurement uncertainties and providing additional robustness. These new techniques work at both 850 and 450 μ m, where version 1 only allowed investigation of the 850 μ m data. Pipeline v2 achieves better than 0.″5 relative image alignment, less than a tenth of the submillimeter beam widths. The version 2 relative flux calibration is found to be 1% at 850 μ m and

We present a comprehensive analysis of young stellar object (YSO) variability within the M17 Southwest Extension (M17 SWex), using 3.5 yr of monitoring data from the James Clerk Maxwell Telescope (JCMT) Transient Survey at submillimeter and 9 yr from the NEOWISE mission at mid-infrared (mid-IR). Our study encompasses observations of 147 bright submillimeter peaks identified within our deep JCMT coadded map as well as 156 YSOs in NEOWISE W1 and 179 in W2 that were previously identified in Spitzer surveys. We find three robust submillimeter variables: two are candidate YSOs and one is a likely extragalactic source. At mid-IR wavelengths, our analysis reveals secular and stochastic variability in 47 YSOs, with the highest fraction of secular variability occurring at the earliest evolutionary stage. This is similar to what has previously been observed for low-mass YSO variability within the Gould Belt. However, we observe less overall variability in M17 SWex at both the submillimeter and mid-IR. We suspect that this lower fraction is due to the greater distance to M17 SWex. Our findings showcase the utility of multiwavelength observations to better capture the complex variability phenomena inherent to star formation processes and demonstrate the importance of years-long monitoring of a diverse selection of star-forming environments.

We report the first arcsecond-resolution observations of the magnetic field in the ministarburst complex Sgr B2. SMA polarization observations revealed magnetic field morphology in three dense cores of Sgr B2 N(orth), M(ain), and S(outh). The total plane-of-sky magnetic field strengths in these cores are estimated to be 4.3–10.0 mG, 6.2–14.7 mG, and 1.9–4.5 mG derived from the angular dispersion function method after applying the correction factors of 0.21 and 0.5. Combining with analyses of the parsec-scale polarization data from Stratospheric Observatory for Infrared Astronomy, we found that a magnetically supercritical condition is present from the cloud scale (∼10 pc) to core scale (∼0.2 pc) in Sgr B2, which is consistent with the burst of star formation activities in the region likely resulting from a multiscale gravitational collapse from the cloud to dense cores.

Using the H i self-absorption data from the Five-hundred-meter Aperture Spherical radio Telescope, we perform a study of the cold atomic gas in the Cygnus X North region. The most remarkable H i cloud is characterized by a filamentary structure, associated in space and in velocity with the principal molecular filament in the Cygnus X North region. We investigate the transition from atomic filament to molecular filament. We find that the H ii regions Cygnus OB2 and G081.920+00.138 play a critical role in compressing and shaping the atomic Cygnus X North filament, where the molecular filament subsequently forms. The cold H i in the DR21 filament has a much larger column density ( N (H i ) ∼1 × 10 ^20 cm ^−2 ) than the theoretical value of the residual atomic gas (∼1 × 10 ^19 cm ^−2 ), suggesting that the H i -to-H _2 transition is still in progress. The timescale of the H i -to-H _2 transition is estimated to be 3 × 10 ^5 yr, which approximates the ages of massive protostars in the Cygnus X North region. This implies that the formation of molecular clouds and massive stars may occur almost simultaneously in the DR21 filament, in accord with a picture of rapid and dynamic cloud evolution.

The Davis–Chandrasekhar–Fermi (DCF) method is widely used to indirectly estimate the strength of magnetic fields in star-forming regions. However, recent developments in this method have primarily focused on improving the measurement of angular dispersion of the field, neglecting other physical quantities, especially turbulence velocity. Most DCF studies tend to overlook or fail to acknowledge the influence of bulk motions on the linewidth, and directly obtain the turbulence velocity based on the non-thermal linewidth. Therefore, to explore the contributions of bulk motions to the linewidth, we conducted radiative transfer simulations using a rotating and infalling envelope–disk model to a high-mass star formation region, IRAS18360-0537. The main conclusion from our work is that the bulk motions contribute significantly to the linewidth and cannot be fully eliminated by simply deducing velocity gradients. Hence, fully attributing the observed non-thermal velocity dispersion derived from fitting a spectral line profile to the turbulence can result in significantly overestimated magnetic field strength and may yield unscientific results of star-forming regions.

Linearly polarized emission from dust grains and molecular spectroscopy is an effective probe of the magnetic field topology in the interstellar medium and molecular clouds. The longstanding Davis-Chandrasekhar-Fermi (DCF) method and the recently developed Histogram of Relative Orientations (HRO) analysis and the polarization-intensity gradient (KTH) method are widely used to assess the dynamic role of magnetic fields in star formation based on the plane-of-sky component of field orientations inferred from the observations. We review the advances and limitations of these methods and summarize their applications to observations. Numerical tests of the DCF method, including its various variants, indicate that its largest uncertainty may come from the assumption of energy equipartition, which should be further calibrated with simulations and observations. We suggest that the ordered and turbulent magnetic fields of particular observations are local properties of the considered region. An analysis of the polarization observations using DCF estimations suggests that magnetically trans-to-super-critical and averagely trans-to-super-Alfvénic clumps/cores form in sub-critical clouds. High-mass star-forming regions may be more gravity-dominant than their low-mass counterparts due to higher column density. The observational HRO studies clearly reveal that the preferential relative orientation between the magnetic field and density structures changes from parallel to perpendicular with increasing column densities, which, in conjunction with simulations, suggests that star formation is ongoing in trans-to-sub-Alfvénic clouds. There is a possible transition back from perpendicular to random alignment at higher column densities. Results from observational studies using the KTH method broadly agree with those of the HRO and DCF studies.

We present ALMA dust polarization and molecular line observations toward four clumps (I(N), I, IV, and V) in the massive star-forming region NGC 6334. In conjunction with large-scale dust polarization and molecular line data from JCMT, Planck, and NANTEN2, we make a synergistic analysis of relative orientations between magnetic fields ( θ _B ), column density gradients ( θ _NG ), local gravity ( θ _LG ), and velocity gradients ( θ _VG ) to investigate the multi-scale (from ∼30 to 0.003 pc) physical properties in NGC 6334. We find that the relative orientation between θ _B and θ _NG changes from statistically more perpendicular to parallel as column density ( ${N}_{{{\rm{H}}}_{2}}$ ) increases, which is a signature of trans-to-sub-Alfvénic turbulence at complex/cloud scales as revealed by previous numerical studies. Because θ _NG and θ _LG are preferentially aligned within the NGC 6334 cloud, we suggest that the more parallel alignment between θ _B and θ _NG at higher ${N}_{{{\rm{H}}}_{2}}$ is because the magnetic field line is dragged by gravity. At even higher ${N}_{{{\rm{H}}}_{2}}$ , the angle between θ _B and θ _NG or θ _LG transits back to having no preferred orientation, or statistically slightly more perpendicular, suggesting that the magnetic field structure is impacted by star formation activities. A statistically more perpendicular alignment is found between θ _B and θ _VG throughout our studied ${N}_{{{\rm{H}}}_{2}}$ range, which indicates a trans-to-sub-Alfvénic state at small scales as well, and this signifies that magnetic field has an important role in the star formation process in NGC 6334. The normalized mass-to-flux ratio derived from the polarization-intensity gradient (KTH) method increases with ${N}_{{{\rm{H}}}_{2}}$ , but the KTH method may fail at high ${N}_{{{\rm{H}}}_{2}}$ due to the impact of star formation feedback.

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.

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.

We use molecular line data from the Atacama Large Millimeter/submillimeter Array, Submillimeter Array, James Clerk Maxwell Telescope, and NANTEN2 to study the multiscale (∼15–0.005 pc) velocity statistics in the massive star formation region NGC 6334. We find that the nonthermal motions revealed by the velocity dispersion function (VDF) stay supersonic over scales of several orders of magnitude. The multiscale nonthermal motions revealed by different instruments do not follow the same continuous power law, which is because the massive star formation activities near central young stellar objects have increased the nonthermal motions in small-scale and high-density regions. The magnitudes of VDFs vary in different gas materials at the same scale, where the infrared dark clump N6334S in an early evolutionary stage shows a lower level of nonthermal motions than other more evolved clumps due to its more quiescent star formation activity. We find possible signs of small-scale-driven (e.g., by gravitational accretion or outflows) supersonic turbulence in clump N6334IV with a three-point VDF analysis. Our results clearly show that the scaling relation of velocity fields in NGC 6334 deviates from a continuous and universal turbulence cascade due to massive star formation activities.