A New Class of X-Ray Tails of Early-Type Galaxies and Subclusters in
  Galaxy Clusters - Slingshot Tails vs Ram Pressure Stripped Tails
  We show that there is a new class of gas tails - slingshot tails - which form
as a subhalo (i.e. a subcluster or early-type cluster galaxy) moves away from
the cluster center towards the apocenter of its orbit. These tails can point
perpendicular or even opposite to the subhalo direction of motion, not tracing
the recent orbital path. Thus, the observed tail direction can be misleading,
and we caution against naive conclusions regarding the subhalo's direction of
motion based on the tail direction. A head-tail morphology of a galaxy's or
subcluster's gaseous atmosphere is usually attributed to ram pressure stripping
and the widely applied conclusion is that gas stripped tail traces the most
recent orbit. However, during the slingshot tail stage, the subhalo is not
being ram pressure stripped (RPS) and the tail is shaped by tidal forces more
than just the ram pressure. Thus, applying a classic RPS scenario to a
slingshot tail leads not only to an incorrect conclusion regarding the
direction of motion, but also to incorrect conclusions in regard to the subhalo
velocity, expected locations of shear flows, instabilities and mixing. We
describe the genesis and morphology of slingshot tails using data from binary
cluster merger simulations, discuss their observable features and how to
distinguish them from classic RPS tails. We identify three examples from the
literature that are not RPS tails but slingshot tails and discuss other
potential candidates.
