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 ≳ 3 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, that is, a return to parallel alignment at A_V ≳ 21 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 ≳ 21 mag, allowing gravitational collapse and star cluster formation to occur even in the presence of relatively strong magnetic fields.