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

Free access article

Issue		A&A Volume 390, Number 3, August II 2002


Page(s)		891 - 915
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20020759

A&A 390, 891-915 (2002)
DOI: 10.1051/0004-6361:20020759

Optical/near-IR observations of 4 BCGs and their companions

N. Bergvall¹ and G. Östlin²

¹ Dept. of Astronomy and Space Physics, Box 515, S-75120 Uppsala, Sweden
e-mail: nils.bergvall@astro.uu.se
² Stockholm Observatory, SCFAB, SE-106 91 Stockholm, Sweden
e-mail: ostlin@astro.su.se

(Received 29 November 2001 / Accepted 15 May 2002 )

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 metal-rich stellar population of 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.

Key words: galaxies: evolution -- galaxies: formation -- galaxies: starburst -- galaxies: dwarfs

Offprint request: N. Bergvall, nils.bergvall@astro.uu.se

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