  We present optical spectroscopy and deep optical/near-IR photometry of 4
luminous metal-poor blue compact galaxies (BCGs) and two of their companions.
With the aid of spectral evolutionary models (SEMs) and structural parameters
derived from the surface photometry we discuss the properties of the central
starbursts and the halo populations of the galaxies. Special attention is paid
to the effects of dust, chemical inhomogeneities and contamination of nebular
emission to the halo light. The optical/near-IR colour index profiles show a
sharp distinction between the starburst and the host. The hosts have luminosity
profiles characteristic of massive ellipticals and remarkably red colours,
typical of a relatively {\it metal-rich} stellar population of {\it old age}.
These properties are in conflict with the relatively low luminosities. The
situation can best be explained if the hosts have an unusually large amount of
dark matter that can hinder the outflow of metals from the system. The
indicated difference in metallicity between the halo and the young starburst
disproves the recurrent burst scenario and supports different origins of the
two populations. We conclude that these BCGs are undergoing mergers between
early type galaxies/thick disks and gas-rich galaxies or intergalactic HI
clouds, in many respects reminiscent of a retarded formation of massive
ellipticals.
