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We present HI synthesis observations of the nearby dwarf galaxy IC 2574 (amember of the M81 group of galaxies) made with the NRAO Very Large Array athigh spatial and velocity resolution (95 pc x 2.6 km/s). The VLA HIobservations show a stunning amount of detail in the form of 48 mostlyexpanding HI shells and holes in its neutral interstellar medium. Thesefeatures range in size from about 100 (a limit set by the size of the beam) toabout 1000 pc dominating the appearance of the HI surface brightness map. Theirdynamics clearly influence the velocity field of IC 2574. Current starformation, as traced by H-alpha emission, is predominantly found along the rimsof the larger HI holes, suggesting propagating star formation. On linear scalesof about 95 pc, star formation occurs if the HI surface density reaches valueshigher than 10^21 cm^-2. The scaleheight of the HI layer is found to be about350 pc, considerably thicker than that in massive disk galaxies. This is due toa lower gravitational potential (for the same observed onedimensional velocitydispersion of about 7 km/s). A comparison with other galaxies shows that theenergies needed to create the expanding HI structures are the same for alltypes of galaxies, at least to first order. The overall statistical propertiesof the HI holes and shells in galaxies show clear trends with Hubble type (orrather mass), such as in their diameter distribution, expansion velocities andages.Comment: 37 pages, 20 figures, accepted for publication in the Astronomical  Journa

Holes and Shells in the Interstellar Medium of the Nearby Dwarf Galaxy IC 2574