A Comprehensive study of star formation in blue compact dwarf galaxies a thesis submitted for the degree of Doctor of Philosophy in The Faculty of Science, Bangalore University, Bangalore S. Ramya [Ph.D Thesis]

Thesis Supervisor T. P. Prabhu

Doctor of Philosophy Bangalore University , Bangalore 2011

By definition, dwarf galaxies are low surface brightness, low luminosity galaxies that are smaller and less massive than ordinary galaxies. Dwarf galaxies are the most abundant in the universe and are proposed to be the building blocks from which larger systems have been created by merging. Some of the dwarf galaxies appear bluer due to the presence of young, blue stars. These are low luminosity, compact systems, spectroscopically characterized by a faint, blue optical continuum accompanied in most cases, by intense emission lines. UV spectra of these galaxies show a continuum steeply rising towards blue. These systems are called Blue Compact Dwarf (BCDs) Galaxies. The blue rest frame colour and strong emission line spectra in BCDs indicate current star formation activity. Typical star formation rate lies between 0.1 1.0 M⊙ yr. −1. They are rich in neutral hydrogen and show significant underabundancce of elements heavier than Helium. This indicates that either the systems are young, undergoing their first phase of star formation or that they have experienced an episodic star formation history. Deep CCD images of these galaxies have revealed an underlying old stellar population on which the starburst is superimposed, implying that these are not actually young systems. There is growing evidence that most BCDs undergo a few or several bursts of star formation followed by a longer more quiescent period and what we are seeing as a BCD is an intense young burst of star formation in an older galaxy.The Low Surface Brightness Galaxies (LSB) resemble normal late type spirals, usually with a few well-defined spiral arms. There are usually a few H II regions (ionized gas surrounding young, hot stars) present, sitting often towards the edge of the galaxy. The lack of major star formation in the LSBs suggests that they are relatively unperturbed and
have not suffered from the mergers or interactions. The study of these types of galaxies is of current interest and there is considerable scope for further research in the optical and infrared region. Introduction to the BCDs is given in Chapter 1.