David J. Eden

We present a resolved far-infrared/sub-millimetre study of dust in the nearby spiral galaxy M 81 using Herschel PACS/SPIRE and JCMT SCUBA-2 observations from 70 to 850 μm. We model the dust emission using both single-temperature modified blackbody (SMBB) fits and point process mapping (PPMAP), comparing pixel-by-pixel SED-fitting with image cubes of dust surface density as a function of position and temperature. For fixed β = 1.9 and a dust opacity of κ350μm = 1.92 cm2 g−1, SMBB gives an integrated dust mass of (1.77 ± 0.09) × 107M⊙, while PPMAP gives (2.65 ± 0.13) × 107M⊙. The higher PPMAP mass is expected because real lines of sight contain dust over a range of temperatures, whereas SMBB assumes a single effective temperature and can underestimate the dust mass. Both methods show enhanced dust surface densities along the spiral arms and a radially declining dust temperature, with the warmest dust in the central region. Variable-β fits indicate only moderate spatial variation in β for well-constrained pixels, but the strong T–β degeneracy motivates a fixed emissivity index for the main analysis. Combining the dust maps with H i data, we find a positive radial gas-to-dust ratio gradient, with dlog10(GDR)/dR = 0.065 dex kpc−1. Comparison with M 81’s metallicity gradient implies a declining dust-to-metals ratio, potentially consistent with more efficient grain growth in the inner disc. The star formation rate is modest, ~0.27 M⊙ yr−1, and is strongly concentrated along the spiral arms. These results suggest that the dust, gas, and star-forming structures of M 81 are strongly shaped by its spiral arms, while the central region hosts the warmest dust in the disc.

Context . Infrared-dark clouds (IRDCs) are ideal sites for investigating the initial conditions of massive star and cluster formation. The A Lei Of the Habitat and Assembly of Infrared Dark Clouds (ALOHA IRDCs), a James Clerk Maxwell Telescope Large Program, has mapped nearby IRDCs utilising the SCUBA-2 continuum camera at the highest achievable sensitivity. Complementary molecular line observations are needed to characterise the physical, kinematic, and chemical properties of the dense gas. Aims . We aim to determine the thermal, kinematic, and chemical properties of clumps identified in the ALOHA IRDCs, and to assess their evolutionary status and level of star-forming activity. Methods . We performed single-pointing K -band and W -band observations towards 56 clumps pf ALOHA IRDCs using the Effelsberg 100 m and Yebes 40 m telescopes, respectively. We derived NH ₃ kinetic temperatures using the hyperfine group ratio method and identified infall and shock signatures from HCO ⁺ , H ¹³ CO ⁺ , SiO, and HNCO profiles. Water masers and NH ₂ D emission were used as complementary tracers of chemical evolution and star formation. Results . The clumps exhibit kinetic temperatures of 15–29 K. We detect NH ₂ D emission towards 18 sources; the NH ₂ D centroid velocities are consistent with those of NH ₃ , indicating the two species trace the same dense gas component. More than half of the clumps display blue-asymmetric HCO ⁺ profiles, identifying them as infall candidates. Water masers with prominent velocity ranges and variability are detected in 22 sources. Broad SiO emission (≳20 km s ⁻¹ ) indicates strong shocks, while narrower emission (≲6 km s ⁻¹ ) likely traces large-scale interactions or low-velocity shocks. Conclusions . The widespread infall signatures, shock tracers, masers, and NH ₂ D emission suggest that relatively quiescent, chemically young material can coexist with dynamically active gas affected by early protostellar feedback, providing insight into the coupled physical and chemical evolution of massive IRDC clumps.

We present high-resolution magnetic field maps of the M17 SW molecular cloud using JCMT 850 μ m dust polarization at 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 ≈ 10 ^−7.8 erg cm ⁻³ ), which exceeds both magnetic ( e _B ≈ 10 ^−8.3 erg cm ⁻³ ) and turbulent ( e _k ≈ 10 ^−8.7 erg cm ⁻³ ) energies. Since all three energy densities lie within 1 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 H II 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.

Complex organic molecules (COMs) in young stellar objects have attracted significant attention in recent years due to their potential connection to prebiotic chemistry and their utility as tracers of warm or shocked gas components. Proto-binary and multiple systems with close separations are particularly valuable targets for investigating chemical inheritance and reaction, as their members are expected to form from similar material in their parental cloud. We present Atacama Large Millimeter/submillimeter Array observations of the hierarchical proto-triple system HOPS-288, focusing on the physical structure, kinematics, and COM compositions. The system is treated as a proto-binary system consisting of HOPS-288-A and HOPS-288-B due to the limited spatial resolutions, with a separation of 200 au. Three COM-rich features are revealed: two hot corinos associated with the two members, rich in a variety of COMs, and an intervening component between the two members traced by CH ₃ OH and tentatively by CH ₃ CHO. The hot corino in HOPS-288-A exhibits rotational features and might trace a disk. The hot corino in HOPS-288-B is also possibly exhibiting rotational motion. The intervening component could possibly trace a shocked region in the circumbinary disk or a bridge between the two members. The column densities of COMs, including ¹³ CH ₃ OH, CH ₂ DOH, CH ₃ CHO, HCOOCH ₃ , C ₂ H ₅ OH, ¹³ CH ₃ CN, and NH ₂ CHO, are broadly similar between the two sources, possibly suggesting the complex organic similarities among proto-binary/multiple systems. Given the complexity of the studied physical structures, further detailed investigations will be essential to confirm this result.

Protostellar jets provide valuable insight into the evolutionary stage and formation history of star-forming cores in their earliest phases. We investigated the inner envelope structures of three extremely young protostars, selected for having the shortest dynamical timescales in their outflows and jets. Our analysis is based on Atacama Large Millimeter/submillimeter Array observations of the N ₂ D ⁺ , DCO ⁺ , DCN, C ¹⁸ O, CH ₃ OH, and H ₂ CO lines, along with 1.3 mm continuum data, obtained at two spatial resolutions of ∼500 and 150 au. By examining molecular depletion and sublimation patterns and emission extents at core-scale and outflow rotational temperatures, we assessed the relative evolutionary stages of the three sources. In G208.68–19.20N1, the absence of N ₂ D ⁺ toward the core—despite a semi-ringlike distribution—and the presence of bright DCN and DCO ⁺ emission cospatial with C ¹⁸ O indicate a warmer envelope, possibly suggesting a more advanced evolutionary state. In contrast, G208.68–19.20N3 shows no dense central structures in C ¹⁸ O, DCN, DCO ⁺ , or N ₂ D ⁺ , with emission instead appearing scattered around the continuum and along large-scale filaments, consistent with a likely younger stage than G208.68–19.20N1. The third source, G215M, exhibits compact C ¹⁸ O emission at the continuum peak but spatially extended N ₂ D ⁺ , DCN, and DCO ⁺ along the continuum, pointing to a cooler envelope and likely the youngest stage among the three. This comparative analysis across three protostars demonstrates the effectiveness of molecular tracers for evolutionary staging, though variations in luminosity or accretion may also shape chemical morphologies. These results highlight the promise of broader surveys for advancing our understanding of early protostellar evolution.

Stars form in dense, cold regions of interstellar clouds where gravity, turbulence, and magnetic fields interact. Magnetic fields are expected to regulate how gas contracts, but their role at the earliest, prestellar stage is poorly constrained, because polarized dust emission from the coldest cores is faint. Here we report submillimeter dust polarization observations of the well-studied prestellar core L1544, obtained with the James Clerk Maxwell Telescope SCUBA-2/POL-2 instrument as part of the BISTRO (B-fields in Star-forming Region Observations) survey. The data resolve a clearly pinched, hourglass-shaped magnetic field at the core center, representing the first detection in a prestellar core. The plane-of-sky field morphology matches classical predictions for magnetically regulated contraction and is consistent with previously reported slow infall and filament-fed accretion flows that deliver material into the core. From the polarization angle dispersion, we infer a magnetic field strength that implies an Alfvén speed above the measured infall speed and well below the free-fall velocity, indicating sub-Alfvénic, magnetically moderated contraction. These results show that the hourglass-shaped field geometry reported in some protostellar envelopes can already be present before a protostar forms, thereby bridging a key observational gap in the timeline of magnetically regulated star formation. As a nearby, representative core on the verge of star formation, L1544 now serves as a benchmark for testing theoretical models that couple gravity and magnetic fields in dense cores.