B-fields in Star-forming Region Observations (BISTRO): Magnetic Fields in the Filamentary Structures of Serpens Main

Abstract

We present 850 μm polarimetric observations toward the Serpens Main molecular cloud obtained using the POL-2 polarimeter on the James Clerk Maxwell Telescope as part of the B-fields In STar-forming Region Observations survey. These observations probe the magnetic field morphology of the Serpens Main molecular cloud on about 6000 au scales, which consists of cores and six filaments with different physical properties such as density and star formation activity. Using the histogram of relative orientation (HRO) technique, we find that magnetic fields are parallel to filaments in less-dense filamentary structures where N H 2 < 0.93 × 10 22 cm−2 (magnetic fields perpendicular to density gradients), while they are perpendicular to filaments (magnetic fields parallel to density gradients) in dense filamentary structures with star formation activity. Moreover, applying the HRO technique to denser core regions, we find that magnetic field orientations change to become perpendicular to density gradients again at N H 2 ≈ 4.6 × 10 22 cm−2. This can be interpreted as a signature of core formation. At N H 2 ≈ 16 × 10 22 cm−2, magnetic fields change back to being parallel to density gradients once again, which can be understood to be due to magnetic fields being dragged in by infalling material. In addition, we estimate the magnetic field strengths of the filaments (B POS = 60–300 μG)) using the Davis–Chandrasekhar–Fermi method and discuss whether the filaments are gravitationally unstable based on magnetic field and turbulence energy densities.

Magnetic field properties in star formation: A review of their analysis methods and interpretation

“…Li et al (2022) compared the inferred magnetic field from HAWC+ with the Herschel column density map in Taurus/B211 and found that the magnetic field is more likely perpendicular to the column density structures in B211. Kwon et al (2022) found negative ξ values in the Serpens Main cloud with JCMT observations at a resolution of 14′′ (~0.03 pc), where they suggested that the first column density bin at N H_{2} ~9.3 × 10 21 cm −2 is approximately the transition column density. In Kwon et al (2022), the ξ decreases from 0 to negative values from N H_{2} ~9.3 × 10 21 cm −2 to ~4.6 × 10 22 cm −2 , which mainly corresponds 9 A significant amount of the diffuse ISM is in the atomic phase, while molecular clouds are in the molecular phase.…”

Magnetic field properties in star formation: a review of their analysis methods and interpretation

“…Kwon et al found negative ξ values in the Serpens Main cloud with JCMT observations at a resolution of 14 ′′ (∼0.03 pc), where they suggested that the first column density bin at N H 2 ∼ 9.3 × 10 21 cm −2 is approximately the transition column density. In Kwon et al (2022), the ξ decreases from 0 to negative values from N H 2 ∼ 9.3 × 10 21 cm −2 to ∼ 4.6 × 10 22 cm −2 , which mainly corresponds to the filamentary structures. Between N H 2 ∼ 4.6 × 10 22 cm −2 to ∼ 10 23 cm −2 , ξ increases back to 0, suggesting that the magnetic fields are trending parallel to elongated structures.…”

Three-dimensional magnetic fields of molecular clouds

“…Numerous observatories, including the James Clark Maxwell Telescope (JCMT; e.g., Eswaraiah et al, 2021;Ngoc et al, 2021;Hwang et al, 2021;Kwon et al, 2022), Planck Space Observatory (e.g., Planck Collaboration et al, 2016;Alina et al, 2019), Atacama Large Millimeter/sub-millimeter Array (ALMA; e.g., Pattle et al, 2021;Cortés et al, 2021), Sub-Millimeter Array (SMA; e.g., Zhang et al, 2014), and Stratospheric Observatory for Infrared Astronomy (SOFIA; e.g., Chuss et al, 2019) have observed B POS of numerous star-forming regions. However, the number of B LOS observations of molecular clouds are still limited.…”