Imaging of mbg starbursts - I. Morphological analysis

Abstract

We present, in detail, the morphological analysis of a sample of 15 galaxies of the Montreal blue galaxy (MBG) survey, based on BVRI imaging. The sample consists of starburst nucleus galaxies, mostly with early-type morphologies. We fit elliptical isophotes to the images, and analyse the parameters derived from the fitting procedure, the luminosity profiles, the B - I colour profiles and B- I colour maps. Circumnuclear regions of star . formation are identified, corresponding well to the extended H a emission measured spectroscopically. The dimensions of these extended regions are of the arder of kiloparsecs. For barred galaxies, the star formation is more concentrated than for unbarred ones, which tend to have extended starbursts. A high interaction rate for the objects studied is indicated by the frequency of dust, twisted isophotes, anda wide dispersion of colours (similar to Arp-Madore galaxies), which is not correlated with the morphological type. The observed isophotal twists in our sample are related to the presence of bars, for SBa and later types, or to geometrical decoupling, for SO and E galaxies. The level of 'boxiness' and 'discyness' is larger than that of normal early-type galaxies, reflecting the disturbed morphology of these objects. The connection of these morphological characteristics with the observed starbursts is highly probable.