Title: Molecular Cloud Decoupling and Magnetic Binding during Strong Ram Pressure Stripping 
of the Coma Spiral NGC 4921

Abstract:
Remarkable dust extinction features in deep HST images of the face-on Coma cluster spiral 
galaxy NGC 4921 show in unprecedented ways how ram pressure strips the ISM from the disk 
of a spiral galaxy.  On one side of the disk, there is a well-defined, continuous front of dust that 
extends over 90 degrees and 20 kpc that separates the dusty from dust-free regions of the 
galaxy, and which we interpret as galaxy ISM swept up near the leading side of the ICM-ISM 
interaction. We identify and characterize substructure within this dust front caused by ram 
pressure, including V-shaped, Y-shaped and linear head-tail filaments, as well as C-shaped 
features and long smooth dust fronts.  The morphology of these features strongly suggests that 
dense gas clouds partially decouple from surrounding lower density gas during stripping, but 
decoupling is inhibited, possibly by magnetic fields which link and bind distant parts of the ISM. 
 The decoupling clouds are probably predominantly molecular. Studies like this one are 
necessary to quantify the efficiency of ram pressure stripping in a real multiphase substructured 
ISM, which in turn is necessary to understand the importance of stripping as a star formation 
quenching mechanism throughout the universe.