A study of H I-selected galaxies in the Hercules cluster

The present study focuses on a sample of 22 galaxies detected in the blind VLA H I survey of the Hercules cluster by Dickey (1997), 18 of which were selected on an H I line width smaller than 270 km s -1 and 4 others with only tentative optical counterparts in the Palomar Sky Survey. Sensitive single-dish H I line spectra were obtained for 20 of them, and for one the VLA detection was not confirmed. Optical surface photometry has been carried out for 10 objects, for 8 of which optical spectroscopy was obtained as well. Based on various criteria, we classify two sample galaxies (ce143 and ne-204) as genuine dwarfs whereas the remaining sample objects are found to be intrinsically luminous galaxies. For those objects investigated in optical wavelengths we determine properties similar to those of actively star-forming galaxies, and find that approximately one half of them has properties intermediate between those of dwarf galaxies and low-luminosity disc galaxies. No optical redshifts could be determined for two of the galaxies (sw-103 and sw-194) and their physical association with the H I clouds detected at their positions therefore remains uncertain. A particularly interesting object in our sample is the Tidal Dwarf Galaxy candidate ce-061 in the galaxy merger IC 1182.