2003A&A...406..453I

The present study focuses on a sample of 22 galaxies detected in the blind VLA HI survey of the Hercules cluster by Dickey (1997AJ....113.1939D), 18 of which were selected on an HI line width smaller than 270km/s and 4 others with only tentative optical counterparts in the Palomar Sky Survey. Sensitive single-dish HI 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 (ce-143 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 HI 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.