2025 Seminars

Abstract:

We present 850 μm 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 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 are 0.33–1.50. This result may suggest that the transition from subcritical to supercritical conditions occurs at the core scale (∼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 for 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.

Abstract:

We present JCMT POL-2 850μm dust polarization and Mimir H band stellar polarization observations toward the starless core L 1512. The POL-2 data reveal a highly ordered core-scale magnetic field, of which the field orientation is consistent with the parsec-scale magnetic fields traced by Planck data. The Mimir data indicate a wider variation in field orientation in the surrounding region, suggesting a transition in magnetic field morphology at the intermediate cloud/envelope scale. Using the Davis–Chandrasekhar–Fermi method, we derived a plane-of-sky magnetic field strength of 18+/-7 μG and a mass-to-flux ratio of 3.5+/-2.4, indicating a magnetically supercritical core. However, our earlier time-dependent chemical study suggested that L1512 is a long-lived starless core, implying that the magnetic field could be strong enough to slow the core collapse under subcritical conditions, which aligns with the absence of significant infall motion and the presence of an oscillating envelope. Using a Virial analysis, we suggest the presence of a hitherto hidden line-of-sight magnetic field of ~27 μG, in which case both magnetic and kinetic pressures are important in supporting the core. On the other hand, L1512 may have just reached supercriticality and will collapse at any time.

Abstract:

Magnetic fields of molecular clouds in the central molecular zone (CMZ) have been relatively under-observed at sub-parsec resolution. Here, we report JCMT/POL2 observations of polarized dust emission in the CMZ, which reveal magnetic field structures in dense gas at ~0.5 pc resolution. The 11 molecular clouds in our sample include two in the western part of the CMZ (Sgr C and a farside cloud candidate), four around the Galactic longitude 0 (the 50 km s-1 cloud, CO 0.02-0.02, the Stone, and the Sticks and Straw among the Three Little Pigs), and five along the Dust Ridge (G0.253+0.016, clouds b, c, d, and e/f), for each of which we estimate the magnetic field strength using the angular dispersion function method. The morphologies of magnetic fields in the clouds suggest potential imprints of feedback from expanding H II regions and young massive star clusters. A moderate correlation between the total viral parameter versus the star formation rate (SFR) and the dense gas fraction of the clouds is found. A weak correlation between the mass-to-flux ratio and the SFR, and a weak anticorrelation between the magnetic field and the dense gas fraction are also found. Comparisons between magnetic fields and other dynamic components in clouds suggest a more dominant role of self-gravity and turbulence in determining the dynamical states of the clouds and affecting star formation at the studied scales. Finally, I will also introduce preliminary results from our ALMA polarization observations toward four representative fields in this cloud sample, which reveal magnetic fields inside dense cores at a resolution of 2000 au.