A holistic perspective on the dynamics of G035.39-00.33: the interplay between gas and magnetic fields (1803.09457v4)

Abstract: Magnetic field is one of the key agents that play a crucial role in shaping molecular clouds and regulating star formation, yet the complete information on the magnetic field is not well constrained due to the limitations in observations. We study the magnetic field in the massive infrared dark cloud G035.39-00.33 from dust continuum polarization observations at 850 $\micron$ with SCUBA-2/POL-2 at JCMT. The magnetic field tends to be perpendicular to the densest part of the main filament (F${M}$), whereas it has a less defined relative orientation in the rest of the structure, where it tends to be parallel to some diffuse regions. A mean plane-of-the-sky magnetic field strength of $\sim$50 $\mu$G for F${M}$ is obtained using Davis-Chandrasekhar-Fermi method. Based on $^{13}$CO (1-0) line observations, we suggest a formation scenario of F${M}$ due to large-scale ($\sim$10 pc) cloud-cloud collision. Using additional NH$_3$ line data, we estimate that F${M}$ will be gravitationally unstable if it is only supported by thermal pressure and turbulence. The northern part of F${M}$, however, can be stabilized by a modest additional support from the local magnetic field. The middle and southern parts of F${M}$ are likely unstable even if the magnetic field support is taken into account. We claim that the clumps in F${M}$ may be supported by turbulence and magnetic fields against gravitational collapse. Finally, we identified for the first time a massive ($\sim$200 M${\sun}$), collapsing starless clump candidate, "c8", in G035.39-00.33. The magnetic field surrounding "c8" is likely pinched, hinting at an accretion flow along the filament.

Dynamics of G035.39-00.33: Interaction of Gas and Magnetic Fields

The paper by Liu et al. offers a comprehensive examination of the massive infrared dark cloud, G035.39-00.33, with an emphasis on the interaction between gas and magnetic fields. Utilizing dust continuum polarization observations at 850 μm obtained via SCUBA-2/POL-2 at the JCMT, this research aims to elucidate the role of magnetic fields in shaping molecular clouds and facilitating star formation.

Key Findings

1. Magnetic Field Orientation: The paper reveals that the magnetic field tends to be perpendicular to the densest segments of the main filament, while demonstrating a less clear orientation in the filament's peripheral areas, where it aligns parallel to some diffuse regions. A mean magnetic field strength of approximately 50 μG was determined using the Davis-Chandrasekhar-Fermi method.
2. Cloud-Cloud Collision: Using $^{13}$CO (1-0) line observations, the authors propose that the fragmenting and shaping of the main filament may be attributed to a large-scale cloud-cloud collision spanning approximately 10 parsecs. This hypothesis provides a framework for understanding the velocity gradients and multiple velocity components observed within G035.39-00.33.
3. Gravitational Stability: Analysis using NH$_3$ line data suggests varied stability across the filament regions. The northern part of F$_M$ could be stabilized by local magnetic field support, while the middle and southern parts appear gravitationally unstable, even when considering magnetic field support.
4. Sub-Structure and Fragmentation: The filament exhibits clustering into dense clumps potentially supported by turbulence and magnetic fields. The paper introduces a significant candidate for a massive, starless, collapsing clump (approximately 200 M$_{\odot}$), denoted as "c8," with indications of accretion flow suggested by the pinched magnetic field.

Implications

The findings from this investigation suggest that magnetic fields may play a critical role in organizing and supporting molecular clouds against gravitational collapse, which is essential for star formation processes. The inferred presence of large-scale cloud-cloud collision processes contributing to the formation of massive filaments like G035.39-00.33 expands our understanding of dynamic interactions within the interstellar medium.

Future Prospects

Further studies are warranted to explore the magnetic field structure at higher resolutions, utilizing facilities such as ALMA to resolve finer details and investigate sub-filamentary structures. Such investigations could provide critical insights into the dynamics at play in massive star-forming regions. Additionally, advancing our understanding of these interactions may promote theoretical developments in simulations of molecular cloud evolution and star formation theories.

In summary, Liu et al.'s paper sheds light on the complex interactions between magnetic fields and molecular dynamics within G035.39-00.33, contributing valuable information to the field of astrophysics and expanding our comprehension of star formation processes associated with massive filaments.