We are currently analysing image data for a large sample of blue compact dwarf galaxies (BCDs), obtained in multiple optical broad- and narrow-band filters. We present preliminary results of a multi-band analysis of two typical BCDs, Mrk 5 and I Zw 123, for which surface-brightness profiles, colour profiles, colour maps and H_α equivalent-width

Based on the best observations of extragalactic H II regions of low metallicity available in the literature we redetermine the primordial helium abundance, Y[p], taking into account all the observed He I line intensities with the exception of those strongly affected by underlying absorption. We derive He/H, N[e](He II), T[e](He II), and τ (3889)

Dwarf galaxies may play a key role in the formation and evolution of bigger systems. This makes it a topic of major interest to know how they form and evolve and, in particular, how their star formation histories (SFHs) have proceeded since their birth. For nearby galaxies, the colour-magnitude diagram (CMD) contains stars formed over their full

A new photometric system suitable for deep, precise and quick metallicity mapping in galaxies is proposed. We find a linear correlation between our metallicity index and the Mg_2 index for stellar, globular-cluster, and early-type galaxy spectra, and model spectral energy distributions of the simple stellar populations.

We analyse spectral images across the full emission line in H_α of the discs of M100 and M101, extracting for each HII region its spectrum, and for the more luminous and extended, spectra over a range of circular apertures. The principal components of these spectra are presented in log-log plots of luminosity vs. turbulent line-width. These plots

We present a high-resolution kinematical study of the ionized gas in the circumnuclear region of NGC 4314. Our spectra reveal the presence of a central structure (apparently a ring or torus) located at ~ 2 arcsec from the nucleus, which we identify as the shocked interface between the nuclear bar and the gas inside the HII region ring.