A MORPHOLOGICAL AND COLOR STUDY OF FORNAX LOW SURFACE BRIGHTNESS GALAXIES IN THE WASHINGTON SYSTEM

We present Washington CCD surface photometry of a sample of low surface brightness dwarf galaxies in the Fornax Cluster. Their surface brightness profiles are not always well fitted by ''pure'' exponential models; instead, the introduction of a shape parameter in the model profile produces very good fits. This shape parameter corre lates with total magnitude; however, there may be selection effects involving the average surface brightness of the galaxies which lead to this correlation. The color profiles of these galaxies show no meaningful gradient, except for the brightest dwarf, which shows evidence of recent or current star-forming activity at its center. Integrated colors show a dissimilar behavior: the (M - T1) index is almost constant for the whole sample, while (C - T1), which is known to be a good metallicity indicator, correlates with the structural parameters, evidencing the existence of a luminosity-metal abundance relation among these dwarfs. This relation is consistent with that already known for Local Group early-type dwarfs. No difference is found between the colors of nucleated and nonnucleated galaxies of the same luminosity. Since total magnitudes correlate with central surface brightnesses and diameters, the more metal-rich dwarfs are also the largest and those of higher surface brightness. However, as the correlations between the different structural parameters are affected by selection effects, it is still not clear which of these parameters determines a galaxy's integrated colors, and hence its metallicity.