Magnetized filamentary gas flows feeding the young embedded cluster in
  Serpens South
  Observations indicate that molecular clouds are strongly magnetized, and that
magnetic fields influence the formation of stars. A key observation supporting
the conclusion that molecular clouds are significantly magnetized is that the
orientation of their internal structure is closely related to that of the
magnetic field. At low column densities the structure aligns parallel with the
field, whereas at higher column densities, the gas structure is typically
oriented perpendicular to magnetic fields, with a transition at visual
extinctions $A_V\gtrsim{}3~\rm{}mag$. Here we use far-infrared polarimetric
observations from the HAWC+ polarimeter on SOFIA to report the discovery of a
further transition in relative orientation, i.e., a return to parallel
alignment at $A_V\gtrsim{}21~\rm{}mag$ in parts of the Serpens South cloud.
This transition appears to be caused by gas flow and indicates that magnetic
supercriticality sets in near $A_V\gtrsim{}21~\rm{}mag$, allowing gravitational
collapse and star cluster formation to occur even in the presence of relatively
strong magnetic fields.
