High Resolution H I Distributions and Multi-Wavelength Analyses of
  Magellanic Spirals NGC 4618 and NGC 4625
  We present a detailed analysis of high resolution H I observations of the
Magellanic spiral galaxies NGC 4618 and NGC 4625. While the H I disk of NGC
4625 is remarkably quiescent with a nearly uniform velocity dispersion and no
evidence of H I holes, there is a dynamic interplay between star formation and
the distribution of neutral hydrogen in NGC 4618. We calculate the critical
density for widespread star formation in each galaxy and find that star
formation proceeds even where the surface density of the atomic gas is well
below the critical density necessary for global star formation. There are
strong spatial correlations in NGC 4618 between UV emission, 1.4 GHz radio
continuum emission, and peaks in the H I column density. Despite the apparent
overlap of the outer disks of the two galaxies, we find that they are
kinematically distinct, indicating that NGC 4618 and NGC 4625 are not
interacting. The structure of NGC 4618 and, in particular, the nature of its
outer ring, are highly suggestive of an interaction, but the timing and nature
of such an interaction remain unclear.
