OBSERVATIONS

The MBG survey (Montreal Blue Galaxy) is a spin-off project of the Montreal Cambridge Tololo (MCT) survey of southern subluminous blue stars (Demers et al. 1986). Using a subset of the plate material covering 7000 deg2, with b ≤ -40∘, we pick up all extended UV-bright objects. The analysis of our follow-up spectroscopy has shown that the bulk of our UV-bright candidates consists of H II galaxies or starbursts; the fraction of AGNs being somewhat less than 10% (Coziol et al. 1993). We expect to find ∼ 500 such galaxies, with magnitude B ≤ 15.5.

Recently, we undertook an imaging follow-up of our candidates to determine their morphology and search for clues to the origin of their activity. Our first sample consist of 11 MBG galaxies with strong H II-region like spectra suggesting an intense phase of star formation. Usually, these galaxies also possess relatively hot IRAS color typical of starburst galaxies (Sekiguchi 1987). Using our 1.6m telescope, located on mont Mégantic in Québec, Canada, we obtained CCD images, with BVRI filters. Details of the observations, reductions and analysis will be published elsewhere (Coziol, Barth, and Demers 1993). Following, is a summary of our first results.

We find mostly spiral galaxies with bright nuclear regions. There is a strong tendency to find early type galaxies. Further analysis of the surface photometry reveals that the bursts are located, preferentially, in the circumnuclear region prolonging far into the nucleus. This confirms the earlier spectral classification of our objects, using the excitation diagnostic diagram of [O III]λ5007/Hβ versus [N II]λ6584/Hα, which suggested that MBG objects are mostly starburst nuclei galaxies (see Salzer et al. 1989 for a definition).