THE PECULIAR VELOCITY-FIELD IN THE HERCULES REGION

We examine the three-dimensional distribution of galaxies in the Hercules region (14h less-than-or-equal-to alpha less-than-or-equal-to 17h, 0-degrees less-than-or-equal-to delta less-than-or-equal-to 60-degrees) which contains the Hercules supercluster and an underdense region in front of the supercluster, the Hercules void. With the aid of the Tully-Fisher relation, we search for deviations from a smooth Hubble flow in that region. New I-band CCD images have been obtained for 86 galaxies in the Hercules region. The sample was selected to minimize any bias in derived distances. The selection criteria are discussed in detail. Magnitudes and inclinations measured from those images are presented. The total magnitudes in combination with the inclination-corrected H I line widths are used to estimate redshift-independent distances. The comparison of those distances with the redshifts are used lo estimate peculiar velocities of the galaxies. A much bigger sample of 2165 galaxies for which only redshifts are known is used to model the gravitationally induced deviations from a smooth Hubble flow using the linear theory of gravitational perturbations. For the galaxies with redshift-independent distances, a comparison of the predicted velocities with those measured indicates a marginal correlation or a firm upper limit on the value for the density parameter-OMEGA of 0.7.