Jia-Wei Wang, Patrick M. Koch, Hauyu Baobab Liu, Shih-Ping Lai
How filaments form from molecular clouds and evolves to stars is a key question in the field of star formation. Hub-filament system (HFS) is a transition stage connecting parsec-scale filaments and forming protocluster, and hence understanding the origin of HFS is crucial to reveal how star formation proceeds between the clouds to core scales. In this work, we report the JCMT POL-2 850 micron polarization observations and the IRAM 30-m C18O (2-1) observations toward the approximately face-on, massive, HFS G33.92+0.11. The 850 micron continuum map shows four major filaments converging to the massive center of G33.92+0.11 with numerous short filaments converging to the major filaments. We estimate the direction/orientation of filaments, magnetic fields, local gravitational force, and local velocity from the observed data, and systematically examine their cross correlation. In the high-density areas, our analysis shows that filaments tend to align with magnetic fields and local gravity in the high-density areas. In the low-density areas, we found that the local velocity gradient tends to perpendicular to both magnetic fields and the local gravity, although filaments still tend to align with the local gravity. In addition, our virial analysis suggests that the gravitational energy dominates the magnetic and kinematic energy. Based on these results, we interpret that the formation of the G33.92+0.11 HFS was predominately driven by gravity, which captures and drags both the major filaments and the magnetic fields accreting into the massive center. In the diffuse areas, the ambient gas might be accreted onto the major filaments directly or via short filaments, and this kinematic is traced by the observed local velocity gradient.