Velocity Gradient in the Presence of Self-Gravity: Identifying Gravity-induced Inflow and Determining Collapsing Stage

Yue Hu, Alex Lazarian, Ka Ho Yuen

Published 2020-02-17Version 1

Understanding how star formation is regulated requires studying the energy balance between turbulence, magnetic fields, feedback, and gravity within molecular clouds. However, identifying the transition region where the gravity takes over and collapse occurs remains elusive. Recent studies of the Velocity Gradient Technique (VGT), which is an advanced tool for magnetic field studies, reveal that the velocity gradient changes its direction by 90 degrees with respect to the magnetic field in the regions of gravitational collapse. In this study, we confirm that the self-gravity induces the change of orientation and high gradient amplitude for both the velocity gradient and intensity gradient. We explore two ways of identifying self-gravitating regions through the double-peak feature in the histogram of gradients' orientation and the curvature of gradients. We show that velocity gradients' morphology and amplitude can be synthetically used to trace the convergent inflows. By comparing with the column density Probability Density Functions method, we show that VGT is a powerful new tool for studying the gas dynamics and tracing magnetic field in star-forming regions. By analogy with VGT, we extend the Intensity Gradient Technique (IGT) to locate the gravitational collapsing region and shock. We show that the synergy of VGT and IGT can determine the collapsing stages in a star-forming region. We conclude that star formation can happen very successfully in strongly magnetized and fully ionized media.