SURFACE PHOTOMETRY OF GALAXIES IN LOW-DENSITY REGIONS

We perform detailed surface photometry, based on B- and/or R-band CCD images of 92 faint galaxies. They are a subsample of those galaxies wh ich were studied by Hopp et al. (1994) in the direction of three nearb y voids. We derive integral photometric parameters and radial surface brightness profiles and compare them to those of several faint galaxy samples, located in different environments, and of a bright field gala xy sample. According to the obtained photometric characteristics, our sample is a mixture of intrinsically bright and faint galaxies, about 60% of them belonging to the bright subsample (M(B) < -19.0). These br ight ones show mean characteristics of typical Freeman's disks and are mainly located in the background of the observed voids. The faint sub sample (M(B) greater than or equal to -19.0) has parameters typical fo r the low-surface-brightness (LSB) galaxies. There are a few well isol ated galaxies both among the bright and faint subsamples. About 40% of studied galaxies reveal ellipticity and position angle variations alo ng of the radius. The (B - R) colour indices of the observed galaxies span over a wide range of 0.5-1.8 mag with a median value at 1.11 mag, rather blue. About 30% of the observed galaxies reveal radial colour gradients at a 5 sigma significance level. These galaxies show typical ly red centers and are getting bluer towards the periphery. The most i solated galaxies in our sample show relatively blue colours (B-T - R(T ) similar or equal to 0.8). About 40% of the studied galaxies have sur face brightness profiles which can be described by the model of single exponential disk. 38% of our galaxies have more complicated profiles and either can be approximated by two exponentials or show the presenc e of a small bulge. 20% of the observed galaxies have central light de pression and outer irregularities - typical for some dwarf galaxies. T hese profile type frequencies are similar to those of faint field gala xy sample. The evolutionary history of both the isolated and clustered galaxies obviously results in similar photometric and structural char acteristics. Thus the photometric methods alone are inadequate for sel ecting galaxies with different isolation properties.