SHELLS IN THE GLOBAL ISM

In recent years, kinematic feedback processes, especially
from massive stars, have been recognized as an essential influence
on galaxy formation and evolution.  As the stellar populations in
galaxies return mass and energy to the ISM, they propagate
interstellar shells which are evidently a principal interface
structure. 

This session will focus on understanding the role of shells in the global
ISM of galaxies.  Shells and superbubble activity often dominate the
kinematics and energy balance in the ISM, which in turn strongly
influences star formation activity and galaxy evolution.  How do
shells mediate and/or regulate the interaction of hot and cool 
gas, and the dispersion of heavy elements?  What mechanisms create
shells and structure in the ISM?  What are the relative
roles of the different types of shells in the multi-phase ISM of
different galactic types?  How and when does blowout occur, and does
material escape from galaxies? 

A great variety of objects can be classified as shells:  supergiant
shells (kpc-scale); OB superbubbles (10s--100s of pc); supernova
remnants; massive-star circumstellar bubbles; impacts from
high-velocity clouds; bow shocks; and other objects.  The existence of
this phenomenon on a range of scales and in different environments suggests
that a comparison of the various types and origins of interstellar
shells can provide important insights into their global properties and
consequences.  In this session, we will focus on phenomena
likely to have large-scale impact on interstellar processes.

The oral component of this session will take place during the morning
and early afternoon on Wednesday, June 2.  Time constraints restrict
the oral component to only invited presentations.  However, we welcome
contributions for the affiliated poster session, to be displayed on
the same day.  The second half of the afternoon will be free to view
the posters.