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1. BICEP/Keck. XVI. Characterizing Dust Polarization through Correlations with Neutral Hydrogen

   https://doi.org/10.3847/1538-4357/acb64c  

   Ade, P. A. R. ; Ahmed, Z. ; Amiri, M. ; Barkats, D. ; Thakur, R. Basu ; Bischoff, C. A. ; Beck, D. ; Bock, J. J. ; Boenish, H. ; Bullock, E. ; et al ( March 2023 , The Astrophysical Journal)

   We characterize Galactic dust filaments by correlating BICEP/Keck and Planck data with polarization templates based on neutral hydrogen (Hi) observations. Dust polarization is important for both our understanding of astrophysical processes in the interstellar medium (ISM) and the search for primordial gravitational waves in the cosmic microwave background (CMB). In the diffuse ISM, Hiis strongly correlated with the dust and partly organized into filaments that are aligned with the local magnetic field. We analyze the deep BICEP/Keck data at 95, 150, and 220 GHz, over the low-column-density region of sky where BICEP/Keck has set the best limits on primordial gravitational waves. We separate the Hiemission into distinct velocity components and detect dust polarization correlated with the local Galactic Hibut not with the Hiassociated with Magellanic Streami. We present a robust, multifrequency detection of polarized dust emission correlated with the filamentary Himorphology template down to 95 GHz. For assessing its utility for foreground cleaning, we report that the Himorphology template correlates inBmodes at a ∼10%–65% level over the multipole range 20 <ℓ< 200 with the BICEP/Keck maps, which contain contributions from dust, CMB, and noise components. We measure the spectral index of the filamentary dust component spectral energy distribution to beβ= 1.54 ± 0.13. We find no evidence for decorrelation in this region between the filaments and the rest of the dust field or from the inclusion of dust associated with the intermediate velocity Hi. Finally, we explore the morphological parameter space in the Hi-based filamentary model.

    

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2. Magnetic Misalignment of Interstellar Dust Filaments

   https://doi.org/10.3847/1538-4357/acb0c4  

   Cukierman, Ari J. ; Clark, S. E. ; Halal, George ( April 2023 , The Astrophysical Journal)

   We present evidence for scale-independent misalignment of interstellar dust filaments and magnetic fields. We estimate the misalignment by comparing millimeter-wave dust-polarization measurements from Planck with filamentary structures identified in neutral-hydrogen (Hi) measurements from Hi4PI. We find that the misalignment angle displays a scale independence (harmonic coherence) for features larger than the Hi4PI beamwidth (16.′2). We additionally find a spatial coherence on angular scales of$\mathit{}(1°)$. We present several misalignment estimators formed from the auto- and cross-spectra of dust-polarization and Hi-based maps, and we also introduce a map-space estimator. Applied to large regions of the high-Galactic-latitude sky, we find a global misalignment angle of ∼2°, which is robust to a variety of masking choices. By dividing the sky into small regions, we show that the misalignment angle correlates with the parity-violatingTBcross-spectrum measured in the Planck dust maps. The misalignment paradigm also predicts a dustEBsignal, which is of relevance in the search for cosmic birefringence but as yet undetected; the measurements ofEBare noisier than those ofTB, and our correlations ofEBwith misalignment angle are found to be weaker and less robust to masking choices. We also introduce an Hi-based dust-polarization template constructed from the Hessian matrix of the Hiintensity, which is found to correlate more strongly than previous templates with Planck dustBmodes.

    

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3. 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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4. The kinematic structure of magnetically aligned H  i filaments

   https://doi.org/10.1093/mnras/stad2792  

   Kim, Doyeon A. ; Clark, S. E. ; Putman, M. E. ; Li, Larry ( September 2023 , Monthly Notices of the Royal Astronomical Society)

   We characterize the kinematic and magnetic properties of H i filaments located in a high Galactic latitude region (165° < α < 195° and 12° < δ < 24°). We extract three-dimensional filamentary structures using fil3d from the Galactic Arecibo L-Band Feed Array H i (GALFA-H i) survey 21-cm emission data. Our algorithm identifies coherent emission structures in neighbouring velocity channels. Based on the mean velocity, we identify a population of local and intermediate velocity cloud (IVC) filaments. We find the orientations of the local (but not the IVC) H i filaments are aligned with the magnetic field orientations inferred from Planck 353 GHz polarized dust emission. We analyse position–velocity diagrams of the velocity-coherent filaments, and find that only 15 per cent of filaments demonstrate significant major-axis velocity gradients with a median magnitude of 0.5 km s−1 pc−1, assuming a fiducial filament distance of 100 pc. We conclude that the typical diffuse H i filament does not exhibit a simple velocity gradient. The reported filament properties constrain future theoretical models of filament formation.

    

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5. Large-scale magnetic field in the Monoceros OB 1 east molecular cloud

   https://doi.org/10.1051/0004-6361/202039065  

   Alina, D. ; Montillaud, J. ; Hu, Y. ; Lazarian, A. ; Ristorcelli, I. ; Abdikamalov, E. ; Sagynbayeva, S. ; Juvela, M. ; Liu, T. ; Carrière, J.-S. ( February 2022 , Astronomy & Astrophysics)

   Context. The role of large-scale magnetic fields in the evolution of star-forming regions remains elusive. Its investigation requires the observational characterization of well-constrained molecular clouds. The Monoceros OB 1 molecular cloud is a large complex containing several structures that have been shown to be engaged in an active interaction and to have a rich star formation history. However, the magnetic fields in this region have only been studied on small scales. Aims. We study the large-scale magnetic field structure and its interplay with the gas dynamics in the Monoceros OB 1 east molecular cloud. Methods. We combined observations of dust polarized emission from the Planck telescope and CO molecular line emission observations from the Taeduk Radio Astronomy Observatory 14-metre telescope. We calculated the strength of the plane-of-sky magnetic field using a modified Chandrasekhar-Fermi method and estimated the mass-over-flux ratios in different regions of the cloud. We used the comparison of the velocity and intensity gradients of the molecular line observations with the polarimetric observations to trace dynamically active regions. Results. The molecular complex shows an ordered large-scale plane-of-sky magnetic field structure. In the northern part, it is mostly orientated along the filamentary structures, while the southern part shows at least two regions with distinct magnetic field orientations. Our analysis reveals a shock region in the northern part right between two filamentary clouds that, in previous studies, were suggested to be involved in a collision. The magnetic properties of the north-main and north-eastern filaments suggest that these filaments once formed a single one, and that the magnetic field evolved together with the material and did not undergo major changes during the evolution of the cloud. In the southern part, we find that either the magnetic field guides the accretion of interstellar matter towards the cloud or it is dragged by the matter falling towards the main cloud. Conclusions. The large-scale magnetic field in the Monoceros OB 1 east molecular cloud is tightly connected to the global structure of the complex. In the northern part, it seems to serve a dynamically important role by possibly providing support against gravity in the direction perpendicular to the field and to the filament. In the southern part, it is probably the most influential factor governing the morphological structure by guiding possible gas inflow. A study of the whole Monoceros OB 1 molecular complex at large scales is necessary to form a global picture of the formation and evolution of the Monoceros OB 1 east cloud and the role of the magnetic field in this process. 

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