Parallel and perpendicular alignments of velocity gradient and magnetic field observed in the molecular clouds L1478 and L1482

Star formation is a complex process that typically occurs in dense regions of molecular clouds mainly regulated by magnetic fields, magnetohydrodynamic (MHD) turbulence, and self-gravity. However, it remains a challenging endeavour to trace the magnetic field and determine regions of gravitational collapse, where the star is forming. Based on the anisotropic properties of MHD turbulence, a new technique termed velocity gradient technique (VGT) has been proposed to address these challenges. In this study, we apply the VGT to two regions of the giant California Molecular Cloud (CMC), namely, L1478 and L1482, and analyse the difference in their physical properties. We use the (CO)-C-12 (J = 2-1), (CO)-C-13 (J = 2-1), and (CO)-O-18 (J = 2-1) emission lines observed with the Heinrich Hertz Submillimeter Telescope. We compare VGT results calculated in the resolutions of 3.3 and 10 arcmin to Planck polarization at 353 GHz and 10 arcmin to determine areas of MHD turbulence dominance and self-gravity dominance. We show that the resolution difference can introduce misalignment between the two measurements. We find the VGT-measured magnetic fields globally agree with those from Planck in L1478, suggesting self-gravity's effect is insignificant. The best agreement appears in VGT-(CO)-C-12. As for L1482, the VGT measurements are statistically perpendicular to the Planck polarization indicating the dominance of self-gravity. This perpendicular alignment is more significant in VGT-(CO)-C-13 and VGT-(CO)-O-18.

Automated summary

Star formation is a complex process that occurs in dense regions of molecular clouds, and is regulated by magnetic fields, MHD turbulence, and self-gravity. The velocity gradient technique (VGT), based on the anisotropic properties of MHD turbulence, is proposed to trace the magnetic field and determine regions of gravitational collapse. In this study, the VGT is applied to two regions of the giant California Molecular Cloud (CMC) and the physical properties are analyzed.