OPTICAL STRUCTURE AND STAR-FORMATION IN BLUE COMPACT DWARF GALAXIES .2. RELATIONS BETWEEN PHOTOMETRIC COMPONENTS AND EVOLUTIONARY IMPLICATIONS

In a preceding paper, we have derived the structural parameters of the young high-surface-brightness stellar component formed in starbursts and that of the old underlying low-surface-brightness component, by ap plying a 3-component decomposition scheme to the surface brightness pr ofiles of 12 blue compact dwarf galaxies (BCDs) and 2 starburst galaxi es. Here we compare the various properties of these two components. We find that the size of the starburst component depends on the size and luminosity of the underlying component, as well as on the HI mass of the BCD. Furthermore? the fractional surface occupied by the star-form ing regions decreases with increasing luminosity of the underlying hos t galaxy. We compare the structural properties of BCDs with those of o ther types of dwarf galaxies. We find that, at equal B luminosity, the underlying component of a BCD has a central surface brightness bright er by similar to 1.5 mag and an exponential scale length smaller by a factor of similar to 2 than that of dwarf irregulars (dIs) and dwarf e llipticals (dEs). Thus there can be evolutionary connections between B CDs and dEs and dIs only if the B CD underlying component can modify i ts structural properties. This may occur in response to changes in the global gravitational potential of the dwarf galaxy, caused by such ev ents as mass infall from the outer gas halo and/or mass loss in starbu rst-driven galactic winds.