\hi shells, supershells, shell-like objects, and 'worms'
C. Heiles;
ApJS, 1984, 55, 585
ABSTRACT:The present photographic representations of the combinations of two H I surveys and high contrast photographs for particular
velocities (made in order to exhibit weak H I features) have been used to prepare a
list of H I shells, supershells, and shell-like objects.
Attention is
given to the structure of three shell-like objects associated with high
velocity gas, as well as with gas at all velocities that is associated with radio
continuum loops I, II, and III.
The gas filaments or 'worms' found by spatial
filtering to be crawling away from the galactic plane in the inner Galaxy are
probably parts of shells that are open at the top.
An assessment of
observational data on shells and supershells indicates no unique relationship
between shells and any other type of astronomical object.
Stellar winds and
supernovas in stellar associations are inadequate energy supplies for the
largest observed supershells, unless star formation activity is unusually
great.
An alternative energy source, high velocity cloud collisions with the
galactic disk, is consistent with several aspects of the data.
KEYWORDS: astronomical photography, hydrogen clouds, interstellar gas, milky way galaxy, radio sources (astronomy), centimeter waves, nebulae, spatial distribution, spatial filtering, supernova remnants
PERSOKEY:21 cm, h_i, supershell, ,
CODE: heiles84