One of the most obvious global tests of mechanical feedback is to
identify the parent stellar populations, or their remains, with the
superbubbles. M31
(Brinks & Bajaja 1986)
and M33
(Deul & den Hartog 1990)
both show correlations of OB assocations with
H i holes. However,
Ho II shows contradictory results, based on the
H i hole catalog compiled by
Puche et al. (1992).
Tongue & Westpfahl (1995)
found that the SN rate implied by radio continuum emission is
consistent with the hole energetics in that galaxy. However,
Rhode et al. (1999)
carried out a direct, BVR search for remnant stellar
populations within the H i
holes, and found little evidence for the expected stars. But
Stewart et al. (2000)
used far-UV data from the Ultraviolet Imaging Telescope and
H
images to conclude
that a significant correlation between the
H i holes and recent star
formation does indeed support a feedback origin for the holes.
It is perhaps unsurprising that studies of Ho II yield these confusing
results in view of that galaxy's distance of 3 Mpc. The LMC, which
is 60 times closer, presents much better spatial resolution and
should therefore yield less ambiguous results.
Kim et al. (1999)
examined the correspondence between their
H i shell catalog, catalogued
H ii regions
(Davies et al. 1976),
and H imaging. Not only
do they find a correspondence, but they
are also able to identify an evolutionary sequence with respect to the
relative sizes, expansion velocities, and
H emission.
Further investigation of the Magellanic Clouds should confirm and
reveal more quantitative details of the mechanical feedback
process (Oey, Gerken, & Walterbos, in preparation).