Star formation and environment of galaxies

Across cosmic time, stars have contributed most of the radiant energy found in the Universe and have created nearly all the chemical elements heavier than helium. Understanding the evolution of the Universe requires understanding the history of star formation. Stars form in galaxies, which are in essence huge aggregations of stars, dust and gas. Understanding star formation requires, among other things, measuring the rate at which interstellar gas is being converted into stars in a given galaxy. Star formation, a critical driver of galaxy evolution, responds both to external influences (local and global environment) and internal factors (e.g. dust).For several decades, the properties of star formation have been studied in galaxies residing in the dense environments of galaxy clusters and compared to those in the sparsely populated field. In this thesis we aim to bridge this gap in the study of the star formation-density relation by studying the evolution of galaxy properties, particularly their star formation rate (SFR) in the critical intermediate region on the periphery of rich galaxy clusters. Using photometric and spectroscopic data from the Sloan Digital Sky survey (SDSS) we show how common observables, such as colour, SFR, and SFR/M* are influenced when galaxies are assembled into clusters via large-scale filaments. We discover that complex galaxy populations (e.g. blue passive galaxies and [optically] red star-forming galaxies) are commonly found in and around rich clusters in the nearby (z ~ 0.1) universe. While the blue passive galaxies are the progenitors of passive red cluster galaxies, the (optically) red star-forming galaxies are a mix of at least two different populations. One set of red star-forming galaxies are dust obscured star-forming x galaxies, while the rest of them are normal star-forming galaxies whose colour is a result of metal-rich dominant stellar populations