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1. Magnetic Fields in the Bones of the Milky Way

   https://doi.org/10.3847/1538-4357/ae08a8  

   Stephens, Ian W; Coudé, Simon; Myers, Philip C; Zucker, Catherine; Jackson, James M; Andersson, B-G; Smith, Rowan; Soam, Archana; Sanhueza, Patricio; Hogge, Taylor; et al (December 2025, The Astrophysical Journal)

   Abstract Stars primarily form in galactic spiral arms within dense, filamentary molecular clouds. The largest and most elongated of these molecular clouds are referred to as “bones,” which are massive, velocity-coherent filaments (lengths ∼20 to >100 pc, widths ∼1–2 pc) that run approximately parallel and in close proximity to the Galactic plane. While these bones have been generally well characterized, the importance and structure of their magnetic fields (B-fields) remain largely unconstrained. Through the Stratospheric Observatory for Infrared Astronomy Legacy program FIlaments Extremely Long and Dark: a Magnetic Polarization Survey (FIELDMAPS), we mapped the B-fields of 10 bones in the Milky Way. We found that their B-fields are varied, with no single preferred alignment along the entire spine of the bones. At higher column densities, the spines of the bones are more likely to align perpendicularly to the B-fields, although this is not ubiquitous, and the alignment shows no strong correlation with the locations of identified young stellar objects. We estimated the B-field strengths across the bones and found them to be ∼30–150μG at parsec scales. Despite the generally low virial parameters, the B-fields are strong compared to the local gravity, suggesting that B-fields play a significant role in resisting global collapse. Moreover, the B-fields may slow and guide gas flow during dissipation. Recent star formation within the bones may be due to high-density pockets at smaller scales, which could have formed before or simultaneously with the bones. 

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2. FIELDMAPS Data Release: Far-infrared Polarization in the “Bones” of the Milky Way

   https://doi.org/10.3847/1538-4365/ae0e61  

   Coudé, Simon; Stephens, Ian W; Myers, Philip C; Karnath, Nicole; Smith, Howard A; Guzmán, Andrés E; Marin, Jessy; Zucker, Catherine; Andersson, B-G; Li, Zhi-Yun; et al (December 2025, The Astrophysical Journal Supplement Series)

   Abstract Polarization observations of the Milky Way and many other spiral galaxies have found a close correspondence between the orientation of spiral arms and magnetic field lines on scales of hundreds of parsecs. This paper presents polarization measurements at 214μm toward 10 filamentary candidate “bones” in the Milky Way using the High-resolution Airborne Wide-band Camera on the Stratospheric Observatory for Infrared Astronomy. These data were taken as part of the Filaments Extremely Long and Dark: A Magnetic Polarization Survey and represent the first study to resolve the magnetic field in spiral arms at parsec scales. We describe the complex yet well-defined polarization structure of all 10 candidate bones, and we find a mean difference and standard deviation of −74° ± 32° between their filament axis and the plane-of-sky magnetic field, closer to a field perpendicular to their length rather than parallel. By contrast, the 850μm polarization data from Planck on scales greater than 10 pc show a nearly parallel mean difference of 3° ± 21°. These findings provide further evidence that magnetic fields can change orientation at the scale of dense molecular clouds, even along spiral arms. Finally, we use a power law to fit the dust polarization fraction as a function of total intensity on a cloud-by-cloud basis and find indices between −0.6 and −0.9, with a mean and standard deviation of −0.7 ± 0.1. The polarization, dust temperature, and column density data presented in this work are publicly available online. 

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3. Dense gas in a giant molecular filament

   https://doi.org/10.1051/0004-6361/202037928  

   Wang, Y.; Beuther, H.; Schneider, N.; Meidt, S. E.; Linz, H.; Ragan, S.; Zucker, C.; Battersby, C.; Soler, J. D.; Schinnerer, E.; et al (September 2020, Astronomy & Astrophysics)

   null (Ed.)

   Context. Recent surveys of the Galactic plane in the dust continuum and CO emission lines reveal that large (≳50 pc) and massive (≳10 5 M ⊙ ) filaments, know as giant molecular filaments (GMFs), may be linked to Galactic dynamics and trace the mid-plane of the gravitational potential in the Milky Way. Yet our physical understanding of GMFs is still poor. Aims. We investigate the dense gas properties of one GMF, with the ultimate goal of connecting these dense gas tracers with star formation processes in the GMF. Methods. We imaged one entire GMF located at l ~ 52–54° longitude, GMF54 (~68 pc long), in the empirical dense gas tracers using the HCN(1–0), HNC(1–0), and HCO + (1–0) lines, and their 13 C isotopologue transitions, as well as the N 2 H + (1–0) line. We studied the dense gas distribution, the column density probability density functions (N-PDFs), and the line ratios within the GMF. Results. The dense gas molecular transitions follow the extended structure of the filament with area filling factors between 0.06 and 0.28 with respect to 13 CO(1–0). We constructed the N-PDFs of H 2 for each of the dense gas tracers based on their column densities and assumed uniform abundance. The N-PDFs of the dense gas tracers appear curved in log–log representation, and the HCO + N-PDF has the flattest power-law slope index. Studying the N-PDFs for sub-regions of GMF54, we found an evolutionary trend in the N-PDFs that high-mass star-forming and photon-dominated regions have flatter power-law indices. The integrated intensity ratios of the molecular lines in GMF54 are comparable to those in nearby galaxies. In particular, the N 2 H + / 13 CO ratio, which traces the dense gas fraction, has similar values in GMF54 and all nearby galaxies except Ultraluminous Infrared Galaxies. Conclusions. As the largest coherent cold gaseous structure in our Milky Way, GMFs, are outstanding candidates for connecting studies of star formation on Galactic and extragalactic scales. By analyzing a complete map of the dense gas in a GMF we have found that: (1) the dense gas N-PDFs appear flatter in more evolved regions and steeper in younger regions, and (2) its integrated dense gas intensity ratios are similar to those of nearby galaxies. 

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4. Dust polarized emission observations of NGC 6334: BISTRO reveals the details of the complex but organized magnetic field structure of the high-mass star-forming hub-filament network

   https://doi.org/10.1051/0004-6361/202038624  

   Arzoumanian, D.; Furuya, R. S.; Hasegawa, T.; Tahani, M.; Sadavoy, S.; Hull, C. L.; Johnstone, D.; Koch, P. M.; Inutsuka, S.; Doi, Y.; et al (March 2021, Astronomy & Astrophysics)

   Context. Molecular filaments and hubs have received special attention recently thanks to new studies showing their key role in star formation. While the (column) density and velocity structures of both filaments and hubs have been carefully studied, their magnetic field (B-field) properties have yet to be characterized. Consequently, the role of B-fields in the formation and evolution of hub-filament systems is not well constrained. Aims. We aim to understand the role of the B-field and its interplay with turbulence and gravity in the dynamical evolution of the NGC 6334 filament network that harbours cluster-forming hubs and high-mass star formation. Methods. We present new observations of the dust polarized emission at 850 μ m toward the 2 pc × 10 pc map of NGC 6334 at a spatial resolution of 0.09 pc obtained with the James Clerk Maxwell Telescope (JCMT) as part of the B-field In STar-forming Region Observations (BISTRO) survey. We study the distribution and dispersion of the polarized intensity ( PI ), the polarization fraction ( PF ), and the plane-of-the-sky B-field angle ( χ B_POS ) toward the whole region, along the 10 pc-long ridge and along the sub-filaments connected to the ridge and the hubs. We derived the power spectra of the intensity and χ B POS along the ridge crest and compared them with the results obtained from simulated filaments. Results. The observations span ~3 orders of magnitude in Stokes I and PI and ~2 orders of magnitude in PF (from ~0.2 to ~ 20%). A large scatter in PI and PF is observed for a given value of I . Our analyses show a complex B-field structure when observed over the whole region (~ 10 pc); however, at smaller scales (~1 pc), χ B POS varies coherently along the crests of the filament network. The observed power spectrum of χ B POS can be well represented with a power law function with a slope of − 1.33 ± 0.23, which is ~20% shallower than that of I . We find that this result is compatible with the properties of simulated filaments and may indicate the physical processes at play in the formation and evolution of star-forming filaments. Along the sub-filaments, χ B POS rotates frombeing mostly perpendicular or randomly oriented with respect to the crests to mostly parallel as the sub-filaments merge with the ridge and hubs. This variation of the B-field structure along the sub-filaments may be tracing local velocity flows of infalling matter in the ridge and hubs. Our analysis also suggests a variation in the energy balance along the crests of these sub-filaments, from magnetically critical or supercritical at their far ends to magnetically subcritical near the ridge and hubs. We also detect an increase in PF toward the high-column density ( N H 2 ≳ 10 23  cm −2 ) star cluster-forming hubs. These latter large PF values may be explained by the increase in grain alignment efficiency due to stellar radiation from the newborn stars, combined with an ordered B-field structure. Conclusions. These observational results reveal for the first time the characteristics of the small-scale (down to ~ 0.1 pc) B-field structure of a 10 pc-long hub-filament system. Our analyses show variations in the polarization properties along the sub-filaments that may be tracing the evolution of their physical properties during their interaction with the ridge and hubs. We also detect an impact of feedback from young high-mass stars on the local B-field structure and the polarization properties, which could put constraints on possible models for dust grain alignment and provide important hints as to the interplay between the star formation activity and interstellar B-fields. 

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5. Parallel Alignments between Magnetic Fields and Dense Structures in the Central Molecular Zone

   https://doi.org/10.3847/1538-4357/adf8c7  

   Pan, Xing; Zhang, Qizhou; Qiu, Keping; Paré, Dylan M; Chuss, David T; Butterfield, Natalie O; Tress, Robin G; Sormani, Mattia C; Tang, Yuping; Longmore, Steven N; et al (September 2025, The Astrophysical Journal)

   Abstract The recent Far-Infrared Polarimetric Large-Area Central Molecular Zone Exploration (FIREPLACE) survey with SOFIA has mapped plane-of-sky magnetic field orientations within the Central Molecular Zone (CMZ) of the Milky Way. Applying the Histogram of Relative Orientations analysis to the FIREPLACE data, we find that the relative orientation between magnetic fields and column density structures is random in low-density regions ( $2\times 10^{22}\lesssim N_{{\mathrm{H}}_2}\lesssim 10^{23}{\mathrm{cm}}^{-2}$) but becomes preferentially parallel in high-density regions (≳10²³cm⁻²). This trend is in contrast with that of the nearby molecular clouds, where the relative orientation transitions from parallel to perpendicular with increasing column densities. However, the relative orientation varies between individual CMZ clouds. Comparisons with magnetohydrodynamic simulations specific to the CMZ conditions suggest that the observed parallel alignment is intrinsic, rather than artifacts caused by the projection effect. The origin of this parallel configuration may arise from the fact that most dense structures in the CMZ are not self-gravitating, as they are in supervirial states, except for the ministarburst region Sgr B2. These findings are consistent with the low star formation efficiency observed in the CMZ compared to that in the Galactic disk. 

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