Fig. 1. H I surface brightness map of IC 2574. The greyscale is a linear representation of the H I surface brightness. The beamsize (6.4" × 5.9") is indicated in the lower left. Forty-eight holes were detected whose outlines are indicated by ellipses

Fig. 2. Location of the H I holes found in DDO 47 (with numbers). The greyscale is a linear representation of the H I surface brightness. Nineteen holes were detected whose outlines are indicated by ellipses

Fig. 3. H I surface brightness map of IC 10. The greyscale is a linear representation of the H I surface brightness. Eight holes were detected whose outlines are indicated by ellipses

Fig. 4. Comparison of the relative distribution, in percentage, of the absent masses of the H I holes in IC 2574, M 31, M 33 and Ho II (left panel)
Fig. 5 Comparison of the relative distribution, in percentage, of the energies required to produce the H I holes in IC 2574, M 31, M 33 and Ho II (right panel)

Fig. 6. Comparison of the relative distribution, in percentage, of the diameters of the H I holes in IC 2574, M 31, M 33 and Ho II (left panel)
Fig. 7. Comparison of the relative distribution, in percentage, of the ages of the H I holes in IC 2574, M 31, M 33 and Ho II (right panel)

Fig. 8. Comparison of the relative distribution, in percentage, of the expansion velocities of the H I holes in IC 2574, M 31, M 33 and Ho II (left panel)
Fig. 9. The relation between expansion velocity and diameter in each of the four galaxies. Crosses represent observed values. The plotted curves are lines of constant energy (based on Chevalier 1974) at levels of 10⁴⁹, 10⁵⁰, 10⁵¹ and 10⁵² ergs (from left to right). The straight lines correspond to constant age and are drawn at 10⁷ years (steepest slope), 5·10⁷ years and 10⁸ years (right panel)