Revealing Gravitational Collapse in the Serpens G3-G6 Molecular Cloud Using Velocity Gradients

Abstract

The relative role of turbulence, magnetic fields, and self-gravity in star formation is a subject of intensive debate. We present IRAM 30 m telescope observations of the ¹³CO (1-0) emission in the Serpens G3-G6 molecular cloud and apply to the data a set of statistical methods. These include the probability density functions of column density and the velocity gradients technique. We combine our data with the Planck 353 GHz polarized dust emission observations and Hershel H₂ column density. We suggest that the Serpens G3-G6 south clump is undergoing a gravitational collapse. Our analysis reveals that the gravitational collapse happens at volume density n ≥ 10³ cm^-3. We estimate the plane-of-the-sky magnetic field strength to be approximately 120 μG using the traditional Davis-Chandrasekhar-Fermi method and 100 μG using a new technique proposed in Lazarian et al (2020). We find that the Serpens G3-G6 south clump's total magnetic field energy significantly surpasses kinetic energy and gravitational energy. We conclude that the gravitational collapse could be successfully triggered in a supersonic and sub-Alfvénic cloud.