Morphological evolution in galaxy clusters a quantitative approach

Abstract

Galaxies form a beautiful part of our complex Universe. The study of this component gives invaluable information on the formation and evolution of the visible structures of the Universe. As in the case of other objects, the study of galaxies also started with their classification in the beginning of the 20th century. Using the largest telescope at that time, Edwin Hubble in the 1920s classified galaxies and his system forms the basis of galaxy classification even today. Astronomers interpreted the existence of the Hubble Tuning Fork diagram as one which reflects the sequence of formation and evolution of galaxies where ellipticals form first and flatten into disk systems as the Universe evolves. Modern telescopes can look back to very early stages of Universe and find that the Hubble system breaks down as these telescopes find more and more peculiar galaxies at high redshifts which cannot be accommodated into the Hubble system. These observations lead to another important era in modern astronomy. Modern telescopes produce deep images of the sky necessitating the analysis of millions of galaxy images. We develop an automated tool to perform such an analysis and use it to study the evolution of galaxies. It was found that the Hubble system correlates well with many physical properties of galaxies. For example, elliptical galaxies are redder, as these galaxies contain an old, low mass stellar population, compared to spiral galaxies. It can be seenth at a correlation exists between the bulge-to-total light ratio (B=T) and the Hubble type of galaxies where a disk galaxy can be identified with B=T _ 0 and an elliptical galaxy can be parameterized by B=T _ 1. The classification of galaxies on the basis of B=T has evolved as a powerful tool in the recent past since it needs considerably less human intervention. The two dimensional bulge disk decomposition technique is not only useful in finding B=T, but is also powerful enough to accurately estimate the structural parameters of both the bulge and the disk components