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.

Context. It has been suggested that the escape fraction of hydrogen ionizing photons ( f esc ) from galaxies is evolving with time, but the picture is far from clear. While evidence for significant escape fractions has been found at high redshifts in several studies, the picture looks different in the closer universe. The lack of local detections could in principle be a combined effect of an evolving escape fraction, the low number galaxies observed, the selection criteria of these targets, and technical problems associated with the instrument best adapted for low redshift targets, the Far Ultraviolet Spectroscopic Explorer (FUSE). Aims. In an attempt to tackle the last of these effects, we apply a new background routine developed for FUSE data to study galaxies from the archive in search of possible Lyman continuum (LyC) leakage. In the process, for the first time a stacked spectrum in the LyC has been produced for local galaxies. With this small sample, we also make a more tentative approach to looking for possible correlations between f esc and physical parameters, such as internal absorption E(B − V) i , mass, H  mass, specific star formation rate (SSFR), metallicity, and Lyα emission. Methods. Eight star forming galaxies with redshifts z > 0.015 from the FUSE archive were re-examined. Also, a subsample of an additional four galaxies with lower redshifts were included, for which the escape fraction was estimated from residual flux in the low ionization interstellar C  λ1036 Å line. Results. Out of the eight galaxies, only one was found to have significant LyC leakage, Tol 1247-232 (S /N = 5.2). This is the second detection of a leaking galaxy in the local universe. From the first case, Haro 11, we derive an intrinsic Lyman break amplitude for starbursts at this young age of ( f 1500 Å / f 900 Å ) int = 1.5 +0.6 −0.5 , which gives an absolute escape fraction for Tol 1247−232 of f esc = 2.4 +0.9 −0.8 %. Tol 1247-232 exhibits an extremely blue far-UV slope reminiscent of high redshift LyC leaking galaxies, and although it does not classify as an AGN in the BPT diagram or by other available diagnostics, a minor AGN cannot be completely excluded. The stacked sample shows an excess in the LyC with f esc = 1.4 +0.6 −0.5 %, but we note that there might be important selection biases involved, since the galaxies were originally handpicked for their star forming qualities. With the small sample, we suggest a possible trend toward higher f esc with lower mass and with enhanced SSFR. None of the galaxies with high values of E(B − V) i were found to show any sign of leakage.

Context. The dominating reionization source in the young universe has not yet been identified. Possible candidates include metal poor dwarf galaxies with starburst properties. Aims. We selected an extreme starburst dwarf, the Blue Compact Galaxy Haro 11, with the aim of determining the Lyman continuum escape fraction from UV spectroscopy. Methods. Spectra of Haro 11 were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). A weak signal shortwards of the Lyman break is identified as Lyman continuum (LyC) emission escaping from the ongoing starburst. From profile fitting to weak metal lines we derive column densities of the low ionization species. Adopting a metallicity typical of the H II regions of Haro 11, these data correspond to a hydrogen column density of ∼10 19 cm −2 . This relatively high value indicates that most of the LyC photons escape through transparent holes in the interstellar medium. We then use spectral evolutionary models to constrain the escape fraction of the produced LyC photons. Results. Assuming a normal Salpeter initial mass function we obtain a Lyman continuum escape fraction of f esc ∼ 4-10%. We argue that in a hierarchical galaxy formation scenario, the upper limit we derive for the escape rate allows for a substantial contribution to cosmic reionization by starburst dwarf galaxies at high redshifts.

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