Massive (?) starburst hosts of blue compact galaxies (BCGs)

TL;DR

This study investigates luminous, metal-poor blue compact galaxies and their companions, revealing that their host structures resemble massive ellipticals with old, metal-rich populations, suggesting a merger-driven formation history involving dark matter and complex chemical evolution.

Contribution

It provides new insights into the structure, stellar populations, and formation processes of BCGs, emphasizing the role of mergers and dark matter in their evolution.

Findings

Hosts have elliptical-like luminosity profiles and red colors.

Metallicity differences challenge the recurrent burst scenario.

Evidence supports merger origins involving early-type and gas-rich galaxies.

Abstract

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.