Revealing Gravitational Collapse in Serpens G3-G6 Molecular Cloud using
  Velocity Gradients
  The relative role of turbulence, magnetic fields, self-gravity in star
formation is a subject of intensive debate. We present IRAM 30m telescope
observations of the $^{13}$CO (1-0) emission in the Serpens G3-G6 molecular
cloud and apply to the data a set of statistical methods. Those include the
probability density functions (PDFs) of column density and the Velocity
Gradients Technique (VGT). We combine our data with the Planck 353 GHz
polarized dust emission observations, Hershel H$_2$ 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
$n\ge10^3$ $\rm cm^{-3}$. We estimate the plane-of-the-sky magnetic field
strength of approximately 120 $\mu G$ using the traditional
Davis-Chandrasekhar-Fermi method and 100 $\mu G$ using a new technique proposed
in Lazarian et al.(2020). We find 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-Alfv\'{e}nic cloud.
