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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⁻¹cloud, CO 0.02−0.02, theStone, and theSticksandStrawamong 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 Hiiregions 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.

 

We present 250 GHz continuum and H29α line data toward W 49 N:A2, a hypercompact H ii region ionized by an O9 star. The data obtained with ALMA at a resolution of ∼0${_{.}^{\prime\prime}}$05 (600 au) confirmed the presence of an ionized ring with a radius of ∼700 au inclined by ∼50° (0° for pole-on). It has a width of ∼1000 au and is relatively flat with a scale height of less than several hundred au. The tilted ring, or the apparent ellipse, has a prominent velocity difference between its NW and SE ridges along the minor axis, suggesting that it is expanding in the equatorial plane at a velocity of 13.2 km s−1. The ring also shows a hint of rotation at 2.7 km s−1, which is significantly (2.5 σ) smaller than the Kepler velocity of 5.2 km s−1 at its radius around the 20 M⊙ star. This can be interpreted as that the ring gas has been transported from the radius of ∼170 au by conserving its original specific angular momentum that it had there. The ionized ring may thus be a remnant of the accretion disk that fed the O9 star, the radiation or magnetic activities of which became so strong that the disk accretion was reversed due to the intense thermal or magneto-hydrodynamic pressure around the star. The data has revealed a rare example of how a massive star terminates its accretion at the end of its formation, transforming a hypercompact H ii region into an ultracompact H ii region.

 

Abstract We have obtained sensitive dust continuum polarization observations at 850 μ m in the B213 region of Taurus using POL-2 on SCUBA-2 at the James Clerk Maxwell Telescope as part of the B -fields in STar-forming Region Observations (BISTRO) survey. These observations allow us to probe magnetic field ( B -field) at high spatial resolution (∼2000 au or ∼0.01 pc at 140 pc) in two protostellar cores (K04166 and K04169) and one prestellar core (Miz-8b) that lie within the B213 filament. Using the Davis–Chandrasekhar–Fermi method, we estimate the B -field strengths in K04166, K04169, and Miz-8b to be 38 ± 14, 44 ± 16, and 12 ± 5 μ G, respectively. These cores show distinct mean B -field orientations. The B -field in K04166 is well ordered and aligned parallel to the orientations of the core minor axis, outflows, core rotation axis, and large-scale uniform B -field, in accordance with magnetically regulated star formation via ambipolar diffusion taking place in K04166. The B -field in K04169 is found to be ordered but oriented nearly perpendicular to the core minor axis and large-scale B -field and not well correlated with other axes. In contrast, Miz-8b exhibits a disordered B -field that shows no preferred alignment with the core minor axis or large-scale field. We found that only one core, K04166, retains a memory of the large-scale uniform B -field. The other two cores, K04169 and Miz-8b, are decoupled from the large-scale field. Such a complex B -field configuration could be caused by gas inflow onto the filament, even in the presence of a substantial magnetic flux.