Sample of minor merger of galaxies: Optical CCD surface photometry and HII region propertie

Abstract

We present the results of the B, V and I photometry of eleven southern minor mergers. The total apparent B magnitude, integrated B-V and V-I colours were measured. We built B, V, and I equivalent profiles for each galaxy and decomposed them into bulge and disk components when possible. From H$α$+N[II] images we have estimated the basic photometric parameters of the HII regions, such as position, size, B-V and V-I colours, H$α$+[NII] luminosity and $EW(Hα+[NII])$ equivalent width. We found a linear correlation between the luminosity ratios of the components and their ratio of major diameters, leading to mass ratios between 0.04 $<$ $\cal M$ $_{secondary} / \cal M$ $_{primary}$ $<$ 0.2, suggesting indeed that our sample is formed by minor mergers. Most of the HII regions and evolved star-forming regions of the sample were formed between 3.6 to 13.7 Myr ago with an average of (6.3$\pm$0.7) Myr. The HII region properties, luminosity, sizes and ages are similar in both components. The HII regions have log(H$α$+[NII]) luminosity between 38.6 and 41.7. The HII region luminosity function for the whole sample fits a power law of index $α$ = --1.33. The linear correlation between the luminosity $\cal L$(H$α$+[NII]) and the size of the HII regions has slope of 2.12$\pm$0.06. We found that the disk of the primary component is more luminous than those of Lu's sample, while the disk of the secondary is smaller and fainter.