Ram Pressure and Anomalous Shell Formation in HoII

Neutral hydrogen VLA D-array observations of the dwarf irregular galaxy HoII, a prototype galaxy for studies of shell formation, are presented. The large-scale HI morphology is reminiscent of ram pressure and is unlikely caused by interactions. A case is made for intragroup gas in poor and compact groups like the M81 group, to which HoII belongs. Numerous shortcomings of the supernova explosions and stellar winds scenario to create the shells in HoII are highlighted, and it is suggested that ram pressure may be able to reconcile the observations available.