arXiv subjects

Dalei Li

Publications and source records attributed to Dalei Li.

At least 19 recordsLinked to original sources

arXiv2026

ALMA Reveals an Explosive Outflow Candidate in IRAS 16119--5048

We present a multiwavelength study of the massive star formation region IRAS 16119-5048 (I16119) using ALMA ATOMS Band 3 and QUARKS Band 6 observations, complemented by archival ATCA radio continuum and Spitzer mid-infrared data. The CO (2-1) emission reveals a system of high-velocity streamer-like structures around the central region. Using dendrogram analysis of velocity-channel maps followed by linking in position-position-velocity space, we identify 16 approximately radially distributed streamers whose projected trajectories converge toward a common central region. The kinetic energy of the outflows is at least an order of magnitude lower than those of most known explosive outflows, while their mass entrainment and momentum rates are high compared with typical protostellar outflows, suggesting that I16119 may represent a low-energy explosive outflow candidate. Dense-gas and photodissociation-region tracers reveal shell-like structures associated with the 8 $\mu$m emission, indicating that feedback from the H II region may influence the streamer morphology. The 1.3 mm continuum resolves 27 dense cores along a fragmented filamentary structure. Their separations are consistent with thermal Jeans or cylindrical fragmentation, while the collect-and-collapse scenario is unsupported. The dense cores also show evidence of mass segregation, with the most massive cores concentrated near the inferred explosive centre. We suggest that I16119 is a plausible low-energy explosive outflow candidate, possibly triggered by dynamical interactions among centrally concentrated massive cores. However, the complex velocity structure and possible contamination from individual core-driven outflows prevent a definitive classification. More sensitive, higher angular-resolution observations are required to confirm the nature of the outflow.

astro-ph.GA↗

arXiv2026

ALOHA IRDCs Molecular Line Follow-up: I. Gas properties and kinematics

Infrared Dark Clouds 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 (JCMT) Large Program, has mapped nearby IRDCs with SCUBA-2. Complementary molecular line observations are needed to characterise the physical, kinematic, and chemical properties of the dense gas. 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. We performed single-pointing K-band and W-band observations towards 56 ALOHA IRDCs clumps using the Effelsberg 100-m and Yebes 40-m telescopes, respectively. We derived NH3 kinetic temperatures using the hyperfine group ratio (HFGR) method and identified infall and shock signatures from HCO+, H13CO+, SiO, and HNCO profiles. Water masers and NH2D emission were used as complementary tracers of chemical evolution and star formation. The clumps exhibit kinetic temperatures of 15-29 K. We detect NH2D emission towards 18 sources, with NH2D centroid velocities consistent with NH3, indicating both 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 are detected in 22 sources, with prominent velocity ranges and variability. Broad SiO emission (>~20 km/s) indicates strong shocks, while narrower extents (<~6km/s) likely trace large-scale interactions or low-velocity shocks. The widespread infall signatures, shock tracers, masers, and NH2D 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.

astro-ph.GA↗

arXiv2026

The TOP-SCOPE Survey of Planck Galactic Cold Clumps: Molecular gas properties

We surveyed 2008 Planck Galactic Cold Clumps (PGCCs) in $^{12}\mathrm{CO}$ and $^{13}\mathrm{CO}$ $J=1$--0 lines using the Taeduk Radio Astronomy Observatory (TRAO) 14 m telescope's multi-beam receiver. We detected 2784 ($^{12}\mathrm{CO}$) and 2291 ($^{13}\mathrm{CO}$) velocity components, their closely correlated centroid velocities suggest that $^{12}$CO and $^{13}$CO generally trace kinematically associated gas. PGCCs have low excitation temperatures (mean $\sim$10 K), mean $^{13}\mathrm{CO}$ optical depth $\sim$0.5, and mean $^{13}\mathrm{CO}$-derived H$_2$ column density $4.3\times10^{21}$~cm$^{-2}$. Gas--dust correlations are moderate, with $N_{^{13}\mathrm{CO}}$ more tightly correlated with the dust-derived H$_2$ column density from the PGCC catalog than $I_{^{12}\mathrm{CO}}$. Colder PGCCs tend to have higher CO-to-H$_2$ conversion factor ($X_{\mathrm{CO}}$) and $[\mathrm{H_{2}}]/[^{13}\mathrm{CO}]$ ratio. $X_{\mathrm{CO}}$ increases clearly with the dust-derived H$_2$ column density, consistent with enhanced CO freeze-out in high-column-density gas. Supersonic non-thermal motions are widespread: the Mach number derived from $^{13}\mathrm{CO}$ has a mean of 4.3 and a median of 3.6, increasing slightly with dust-derived H$_2$ column density. Overall, PGCCs are cold but dynamically active, serving as a valuable laboratory for studying the initial conditions of star formation.

astro-ph.GA↗

arXiv2026

A 1.3 cm spectral line study of the W33 region

At a distance of 2.4kpc, W33 is one of the most prolific sources of molecular line emission, and it is an excellent research target for a centimeter spectral line search. We carried out a 1.3cm spectral line survey in the frequency range 18-26GHz. The lines we identified include 44 radio recombination lines (RRLs) and 24 molecular lines, excluding transitions from the main isotopolog of NH3. The RRLs are associated with the ionized gas from W33Main. Intensity ratios between RRL pairs with varying differences in the principal quantum number $n$ (i.e., $\Delta n$) from the same element at adjacent frequencies agree with ratios expected under conditions of local thermodynamical equilibrium. In spite of a resulting helium-to-hydrogen abundance ratio (equal emitting volumes assumed) of (10.7$\pm$1.8)\%, which is consistent with expectations, helium shows broader turbulent line widths than hydrogen. The difference amounts to a few kilometers per second, hinting that the spatial distributions are slightly different. The molecular lines are attributed to nine different species (CH3OH, HC3N, SiS, c-C3H2, CH3CN, NH2D, HNCO, H2O and CCS). Rotation temperatures and column densities were derived from CH3OH transitions using rotational temperature diagram analysis. Maser emission produced by water vapor and methanol have been observed in W33Main, W33A, and W33B. Our survey discovered a CH3OH(10$_{2,8}$-10$_{1,9}$E) maser in W33Main. Toward W33B1, the fractionated deuterium-to-hydrogen ratio (D/H) deduced from para-NH2D/NH3 is estimated to be $\lesssim$(1.0$\pm$0.2)$\times$10$^{-3}$. For the other molecular W33-hotspots, 3$\sigma$ upper limits are (5.0$\pm$0.4)$\times$10$^{-3}$. At linear scales of (0.5pc), fractional abundances and excitation temperatures do not reach values close to those in well-established hot cores, but higher-resolution measurements may alter this picture.

astro-ph.GA↗

arXiv2026

The ALMA-QUARKS survey: Investigating Thermal Feedback of Massive Protostars in Hot Molecular Cores

We identify a sample of 83 spatially resolved hot molecular cores (HMCs) in the QUARKS survey, aiming at investigating thermal feedback from massive stars. Using CH$_3$CN\,(12--11) line emission together with 1.3\,mm continuum data we derive the radial temperature, volume density and \ch3cn{} abundance profiles for the 83 HMCs. Based on the envelope temperature and density profiles, we compute the luminosities of the embedded massive protostars with \radmc{} radiation transfer model. The derived luminosities are comparable (within $\sim1$ dex) to the bolometric luminosities of their natal clumps and show strong correlations with several core-scale properties, including the HMC mass ($Log[ M_\mathrm{env}] = 1.01\,Log [L_\star] - 4.80$), the inner core radius (the flat radius of Plummer-like volume density profile) ($Log[a] = 0.46\,Log[L_\star] + 0.52$) and the central density $ (Log[n_c] = -0.55 Log[L_\star] +10.47) $. These empirical relations provide useful observational constraints for physical models of protostellar objects. Importantly, we find a strong positive correlation between the massive protostellar luminosity and the local thermal Jeans mass. The derived Jeans masses, $M_\mathrm{Jeans}$, exceed the HMC masses $M_\mathrm{env}$, with the average $M_\mathrm{Jeans}$ being two times larger than the average $M_\mathrm{env}$. This provides observational evidence that thermal feedback from massive protostars can effectively suppress further fragmentation of HMCs, thereby promoting massive star formation. In addition, the positive correlation between massive protostellar luminosity and natal clump mass suggests that more massive clumps preferentially host more luminous protostars, leading to stronger thermal feedback.

astro-ph.GA↗

arXiv2025

The ALMA-QUARKS survey: Hot Molecular Cores are a long-standing phenomenon in the evolution of massive protostars

We present an analysis of the QUARKS survey sample, focusing on protoclusters where Hot Molecular Cores (HMCs, traced by CH3CN(12--11)) and UC HII regions (traced by H30\alpha/H40\alpha) coexist. Using the high-resolution, high-sensitivity 1.3 mm data from the QUARKS survey, we identify 125 Hot Molecular Fragments (HMFs), which represent the substructures of HMCs at higher resolution. From line integrated intensity maps of CH3CN(12--11) and H30\alpha, we resolve the spatial distribution of HMFs and UC HII regions. By combining with observations of CO outflows and 1.3 mm continuum, we classify HMFs into four types: HMFs associated with jet-like outflow, with wide-angle outflow, with non-detectable outflow, and shell-like HMFs near UC HII regions. This diversity possibly indicates that the hot core could be polymorphic and long-standing phenomenon in the evolution of massive protostars. The separation between HMFs and H30\alpha/H40\alpha emission suggests that sequential high-mass star formation within young protoclusters is not likely related to feedback mechanisms.

astro-ph.GA↗

arXiv2025

Rethinking Habitability using Biogenic Precursors: Formaldehyde in Millimeter Molecular Clouds of the Inner Galaxy

We present a comprehensive study of formaldehyde (H2CO) absorption and radio recombination line (H110a) emission in 215 molecular clouds from the Bolocam Galactic Plane Survey (BGPS), observed using the Nanshan 25-m radio telescope. H2CO was detected in 88 sources (40.93 percent) with 59 being new detections, while H110a emission was found in only 11 sources (5.12 percent), all coincident with H2CO absorption. There exists a correlation of H2CO fluxes with millimeter fluxes below a 3 Jy threshold and an increased dispersion above it, suggesting the sub-CMB cooling of H2CO. Cross-matching with kinematic distance catalogs revealed H2CO spanning galactocentric distances from 0.216 to 10.769 kpc, with column densities ranging from 7.82 x 10^11 to 6.69 x 10^14 cm-2. A significant inverse correlation was observed between H2CO detection fraction and galactocentric distance, suggesting enhanced star forming activity closer to the Galactic Center. These findings challenge traditional Galactic Habitable Zone (GHZ) models by demonstrating the presence of biogenic precursors in the inner Galaxy, shielded within dense molecular clouds. Our results underscore the importance of incorporating chemical tracers like H2CO, alongside physical constraints, to refine the boundaries of the GHZ and advance the research of prebiotic chemistry in the Milky Way.

astro-ph.GA↗

arXiv2025

Evidence for Core-Core Collision in Barnard 68

The prestellar core Barnard 68 (B68) is a prototypical source to study the initial conditions and chemical processes of star formation. A previous numerical simulation suggested the southeastern bullet is impacting on the main body of B68. In order to obtain more observational evidence, mapping observations of the ground state SO ($1_0-0_1$) emission line at 30 GHz were made with the Effelsberg 100 m telescope. Based on the velocity field and channel maps derived from SO, three velocity components were clearly detected. The velocity field of the main body indicates rotation and is well fitted by a solid-body rotation model. The measured radial velocity difference between the bullet and the main core is about 0.4 km s$^{-1}$, which is almost equal to the velocity obtained by the previous numerical simulation. Therefore, the bullet is most likely impacting onto the rotating main body of B68. A 1D spherical non-LTE Monte-Carlo radiation transfer RATRAN code is performed to derive the radial abundance profile of SO by analyzing the observed velocity-integrated intensity. SO is depleted inside a 60$^{\prime\prime}$ (0.02 pc) radius from the core. The abundance stays constant at 2.0$\times$10$^{-9}$ for radii larger than 60$^{\prime\prime}$ from the center of the main core. The abundance is enhanced at the interface of the bullet and the main core indicating that shock waves were produced by the collision between the bullet and the main core. In conclusion, based on the kinematical and chemical analysis, our observational results support the previously proposed core-core collision scenario in B68.

astro-ph.GA↗

arXiv2025

Cloud-cloud collision and star formation in G013.313+0.193

We study the G013.313+0.193 G013.313 region, a complex environment characterized by molecular cloud interactions indicative of cloud-cloud collision (CCC). Observations of the NH3(1,1) and (2,2) inversion transitions were obtained using the Nanshan 26 m radio telescope, while HCO+ (1-0), 12CO, 13CO, and C18O(1-0) transitions from the Purple Mountain Observatory Delingha 14 m telescope. Archival data are also included. We identified key observational signatures of CCC, including complementary spatial distributions, U-shaped structures, bridge features, and V-shaped velocity distributions. The position-velocity diagrams (P-V) reveal clear indications of gas interaction between two velocity components, suggesting an ongoing collision at an estimated angle of approximately 45 degree to the line of sight. The estimated collision timescale is 0.35-1.03 Myr, aligned with the inferred ages of young stellar objects (YSOs) in the region, supporting the hypothesis of collision-induced star formation. Hub-filament system (HFS) are identified in the compressed gas region, where filaments converge toward a dense hub, suggesting the CCC as a potential driver of HFS formation and massive star formation. The high column density suggests favorable conditions for the formation of massive stars. Although alternative kinematic drivers such as longitudinal collapse and shear motion are considered, CCC remains the most plausible explanation for the observed features. Our findings contribute to our understanding of the mechanisms of cloud dynamics and massive star formation in turbulent molecular environments.

astro-ph.GA↗

arXiv2025

The Impact of Expanding HII Regions on Filament G37:Curved Magnetic Field and Multiple Direction Material Flows

Filament G37 exhibits a distinctive "caterpillar" shape, characterized by two semicircular structures within its 40\,pc-long body, providing an ideal target to investigate the formation and evolution of filaments. By analyzing multiple observational data, such as CO spectral line, the H$\alpha$\,RRL, and multi-wavelength continuum, we find that the expanding H\,{\scriptsize II} regions surrounding filament G37 exert pressure on the structure of the filament body, which kinetic process present as the gas flows in multiple directions along its skeleton. The curved magnetic field structure of filament G37 derived by employing the Velocity Gradient Technique with CO is found to be parallel to the filament body and keeps against the pressure from expanded H\,{\scriptsize II} regions. The multi-directional flows in the filament G37 could cause the accumulation and subsequent collapse of gas, resulting in the formation of massive clumps. The curved structure and star formation observed in filament G37 are likely a result of the filament body being squeezed by the expanding H\,{\scriptsize II} region. This physical process occurs over a timescale of approximately 5\,Myr. The filament G37 provides a potential candidate for end-dominated collapse.

astro-ph.GA↗

arXiv2024

A Tale of Three: Magnetic Fields along the Orion Integral-Shaped Filament as Revealed by JCMT BISTRO survey

As part of the BISTRO survey, we present JCMT 850 $\mu$m polarimetric observations towards 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 multi-scale 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$^\circ$ 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 non-thermal 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.

astro-ph.GA↗

arXiv2024

The JCMT BISTRO Survey: The Magnetic Fields of the IC 348 Star-forming Region

We present 850 $\mu$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 (BISTRO) 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 is 0.33-1.50. This result may suggest that the transition from subcritical to supercritical conditions occurs at the core scale ($\sim$ 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 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.

astro-ph.GA↗

arXiv2024

Chemical models of interstellar glycine and adenine precursor aminoacetonitrile (NH2CH2CN)

Aminoacetonitrile (AAN), also known as glycinenitrile, has been suggested as a possible precursor of glycine and adenine in the interstellar medium. Here we present the chemical modeling of AAN and its isomers in hot cores using the three-phase chemical model NAUTILUS with the addition of over 300 chemical reactions of the three AAN isomers and related species. Our models predicted a peak gas phase abundance of AAN reaching the order of 10-8, which is consistent with observation towards Sgr B2(N). Regarding the reaction pathways of AAN and its isomers, we found that AAN is primarily formed via free radical reactions on grain surfaces during the early evolutionary stages. Subsequently, it is thermally desorbed into the gas phase as the temperature rises and is then destroyed by positive ions and radicals in gas phase. The isomers of AAN are formed through the hydrogenation reaction of CH3NCN on the grain surface and via electron recombination reactions of ion C2H5N2+ in gas phase. We speculate that there is a possibility for NCCN and AAN to react with each other, eventually leading to the formation of adenine in hot cores. However, further investigation is required to understand the efficiency of grain surfaces in adenine formation, through theoretical calculations or laboratory experiments in future research.

astro-ph.GA↗

arXiv2024

Kinematics and star formation of hub-filament systems in W49A

W49A is a prominent giant molecular cloud (GMC) that exhibits strong star formation activities, yet its structural and kinematic properties remain uncertain. Our study aims to investigate the large-scale structure and kinematics of W49A, and elucidate the role of filaments and hub-filament systems (HFSs) in its star formation activity. We utilized continuum data from Herschel and the James Clerk Maxwell Telescope (JCMT) as well as the molecular lines 12CO (3-2), 13CO (3-2), and C18O (3-2) to identify filaments and HFS structures within W49A. Further analysis focused on the physical properties, kinematics, and mass transport within these structures. Additionally, recombination line emission from the H I/OH/Recombination (THOR) line survey was employed to trace the central H II region and ionized gas. Our findings reveal that W49A comprises one blue-shifted (B-S) HFS and one red-shifted (R-S) HFS, each with multiple filaments and dense hubs. Notably, significant velocity gradients were detected along these filaments, indicative of material transport toward the hubs. High mass accretion rates along the filaments facilitate the formation of massive stars in the HFSs. Furthermore, the presence of V-shaped structures around clumps in position-velocity diagrams suggests ongoing gravitational collapse and local star formation within the filaments. Our results indicate that W49A consists of one R-S HFS and one B-S HFS, and that the material transport from filaments to the hub promotes the formation of massive stars in the hub. These findings underscore the significance of HFSs in shaping the star formation history of W49A.

astro-ph.GA↗

arXiv2024

Investigating Sulfur Chemistry in the HD 163296 disk

Sulfur chemistry in the formation process of low-mass stars and planets remains poorly understood. The protoplanetary disks (PPDs) are the birthplace of planets and its distinctive environment provides an intriguing platform for investigating models of sulfur chemistry. We analyzed the ALMA observations of CS 7-6 transitions in the HD 163296 disk and perform astrochemical modeling to explore its sulfur chemistry. We simulated the distribution of sulfur-containing molecules and compared it with observationally deduced fractional column densities. We have found that the simulated column density of CS is consistent with the observationally deduced fractional column densities, while the simulated column density of C$_2$S is lower than the observationally deduced upper limits on column densities. This results indicate that we have a good understanding of the chemical properties of CS and C$_2$S in the disk. We also investigated the influence of the C/O ratio on sulfur-containing molecules and found that the column densities of SO, SO$_2$, and H$_2$S near the central star are dependent on the C/O ratio. Additionally, we found that the $N$[CS]/$N$[SO] ratio can serve as a promising indicator of the disk's C/O ratio in the HD 163296. Overall, the disk of HD 163296 provides a favorable environment for the detection of sulfur-containing molecules.

astro-ph.EP↗

arXiv2024

Magnetic Field of Molecular Gas Measured with the Velocity Gradient Technique II: Curved Magnetic Field in kpc-Scale Bubble of NGC\,628

We report the detection of the ordered alignment between the magnetic field and kpc-scale bubbles in the nearby spiral galaxy, NGC\,628. Applying the Velocity Gradient Technique (VGT) on CO spectroscopic data from the ALMA-PHANGS, the magnetic field of NGC\,628 is measured at the scale of 191\,pc ($\sim$ 4\,$''$). The large-scale magnetic field is oriented parallel to the spiral arms and curves around the galactic bubble structures in the mid-infrared emission observed by the James Webb Space Telescope (JWST). Twenty-one bubble structures have been identified at the edges of spiral arms with scales over 300\,pc, which includes two kpc-scale structures. These bubbles are caused by supernova remnants and prolonged star formation and are similar to the outflow chimneys found in neutral hydrogen in galactic disks. At the edge of the bubbles, the shocks traced by the OIII emission present a curved magnetic field that parallels the bubble's shell. The magnetic field follows the bubble expansion and binds the gas in the shell to trigger further star formation. By analyzing the larger sample of 1694 bubbles, we found a distinct radial-size distribution of bubbles in NGC\,628 indicating the star formation history in the galaxy.

astro-ph.GA↗

arXiv2024

Filamentary Network and Magnetic Field Structures Revealed with BISTRO in the High-Mass Star-Forming Region NGC2264 : Global Properties and Local Magnetogravitational Configurations

We report 850 $\mu$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 (BISTRO) large program on the James Clerk Maxwell Telescope (JCMT). These data reveal a well-structured non-uniform magnetic field in the NGC 2264C and 2264D regions with a prevailing orientation around 30 deg from north to east. Field strengths estimates and a virial analysis for 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 the longitudinal collapsing, driven by the region's global gravity.

astro-ph.SR↗

arXiv2023

Magnetic Fields in Giant Filaments Probed by the Velocity Gradient Technique: Regular Magnetic Field interrupted by Magnetization Gaps

We study the magnetic field structures in six giant filaments associated with the spiral arms of the Milky Way by applying the Velocity Gradient technique (VGT) to the 13CO spectroscopic data from GRS, Fugin, and SEDIGSM surveys. Compared to dust polarized emission, the VGT allows us to separate the foreground and background using the velocity information, from which the orientation of the magnetic field can be reliably determined. We find that in most cases, the magnetic fields stay aligned with the filament bodies, which are parallel to the disk midplane. Among these, G29, G47, and G51 exhibit smooth magnetic fields, and G24, G339, and G349 exhibit discontinuities. The fact that most filaments have magnetic fields that stay aligned with the Galactic disk midplane suggests that Galactic shear can be responsible for shaping the filaments. The fact that the magnetic field can stay regular at the resolution of our analysis (<= 10 pc) where the turbulence crossing time is short compared to the shear time suggests that turbulent motion can not effectively disrupt the regular orientation of the magnetic field. The discontinuities found in some filaments can be caused by processes including filament reassembly, gravitational collapse, and stellar feedback.

astro-ph.GA↗