Recent Star Formation in the Leading Arm of the Magellanic Stream
  Strongly interacting galaxies undergo a short-lived but dramatic phase of
evolution characterized by enhanced star formation, tidal tails, bridges and
other morphological peculiarities. The nearest example of a pair of interacting
galaxies is the Magellanic Clouds, whose dynamical interaction produced the
gaseous features known as the Magellanic Stream trailing the pair's orbit about
the Galaxy, the Bridge between the Clouds, and the Leading Arm, a wide and
irregular feature leading the orbit. Young, newly formed stars in the Bridge
are known to exist, giving witness to the recent interaction between the
Clouds. However, the interaction of the Clouds with the Milky Way is less well
understood. In particular, the Leading Arm must have a tidal origin, however no
purely gravitational model is able to reproduce its morphology and kinematics.
A hydrodynamical interaction with the gaseous hot halo and disk of the Galaxy
is plausible as suggested by some models and supporting neutral hydrogen
observations. Here we show for the first time that young, recently formed stars
exist in the Leading Arm, indicating that the interaction between the Clouds
and our Galaxy is strong enough to trigger star formation in certain regions of
the Leading Arm --- regions in the outskirts of the Milky Way disk (R ~ 18
kpc), far away from the Clouds and the Bridge.
