ALMA Polarization Study of the Magnetic Fields in Two Massive Clumps in the 20 km s$^{-1}$ Cloud of the Central Molecular Zone

Abstract

We present the Atacama Large Millimeter/submillimeter Array (ALMA) observations of linearly polarized 870 $\mu$m continuum emission at a resolution of $\sim$0.2$^{\prime\prime}$ (2000 au) toward the two massive clumps, Clump 1 and Clump 4, in the 20 km s$^{-1}$ cloud. The derived magnetic field strengths for both clumps range from $\sim$0.3 to 3.1 mG using the Angular Dispersion Function (ADF) method. The magnetic field orientations across multiple scales suggests that the magnetic field dominates at the cloud scale, whereas gravity likely governs the structures at the core (0.01$-$0.1 pc) and condensation ($\le$ 0.01 pc) scales. Furthermore, the study on the angular difference between the orientations of the local gravity gradient and the magnetic field suggests that the magnetic field predominantly governs the dynamics in the diffuse regions, while gravity and star formation feedback become increasingly significant within the dense regions. The ratio of the magnetic field tension force $F_\textrm{B}$ to the gravitational force $F_\textrm{G}$ suggests that the magnetic field may provide some support against gravity, but it is insufficient to prevent gas from infalling toward the dense cores.