The dwarf galaxy population in nearby groups: The data

We used V and ICCD photometry to search for low surface brightness dwarf galaxies in the central (< 0.5 h(-1) Mpc) region of the groups NGC 6868, NGC 5846, HCG 42, and the poor cluster IC 4765. We used the exponential profile fit parameters to identify 80 low surface brightness dwarf galaxy candidates with 17 mag < V < 22 mag (-16.7 > M-V > -11.4), V - I < 1.5 mag, mu(0) > 22.5 V mag arcsec(-2), h > 1.5, and diameters larger than 1.2 h(-1) kpc. Twenty of these galaxies are extended low surface brightness galaxies that were detected only on smoothed images, after masking all high surface brightness objects. The completeness in the sample detection is similar to 80% for V less than or similar to 20 and 22.5 V mag arcsec(-2) < mu(0) < 24.5 V mag arcsec(-2). For galaxies with V > 20 mag and mu(0) > 24.5 V mag arcsec(-2), the completeness is below 50% but increases to similar to 80% when we search for galaxies in smoothed images. The detected galaxies are highly concentrated toward the center of the groups (inner 250 h(-1) kpc). The best-fit power-law slope of the surface density distribution is, on average, beta similar to -1.5, in agreement with the values found for satellite dwarfs around isolated E/S0 galaxies and in X-ray-bright groups. The selected dwarf galaxies do not show a clear correlation in the M-V-mu(0) plane, suggesting that the correlation noted by other studies could be produced by selection effects. We also find that these galaxies follow a well-defined color-magnitude relation, extending for more than 10 mag (from bright elliptical galaxies to faint dwarfs). A similar relation is known to be valid for galaxy clusters, but it is the first time that it has been demonstrated in the sparse environments of groups. The spectroscopic follow-up shows that only 78 of the 409 galaxies with measured velocities are group members. Of these, five are low surface brightness dwarf galaxies. In addition, new structures along the groups' lines of sight were discovered. These new structures are groups and poor clusters that extend to similar to 0.3 in redshift space.