Study of Morphology - Density relation in Groups of Galaxies
at Medium Redshift (0.3 < z < 0.8)
'Morphology' refers to the general appearance of an object. In the case of those patches of light in the sky we understand to be galaxies like the Milky Way galaxy, morphology would mean the nature of the distribution of the light. Based on their appearance galaxies fall into three major types -elliptical spiral and irregular (Look up the Hubble tuning fork diagram). More than thirty years ago it was noticed that if the number of galaxies in a particular region of the sky was large, more of them are ellipticals and in regions were there was no clustering of galaxies more of them were spirals. A quantitative way of expressing this would be to find out what fraction of galaxies are ellipticals in a region having a particular number density (number of galaxies per unit volume, or number of galaxy images per unit area in the sky) of galaxies. This is called the
Morphology-Density relation. We can by analyzing images of the sky taken by various telescopes, study this relation and so try to come to an understanding of how such a situation came to be. This second part comes under the study of galaxy evolution.
The Morphology-Density Relation
Study of Morphology - Density relation (MDR) is an important tool to understand the formation and evolution of galaxies. MDR is simply the relation between the morphological population and the projected density of the galaxies in that region. Dressler (1980) showed that in clusters of galaxies, early type galaxies (Elliptical, S0) are dominating while field galaxies are mostly late type galaxies (Spirals, irregulars). More recent works confirm the result. With MDR, we will be able to figure out the physical process which is responsible for the formation of different morphological types. For example, the larger abundance of elliptical galaxies in higher density
environments, points to the fact that these are the results of merger events.
In this project, we are planning to quantify the morphology of group galaxies (Groups have less than or about a hundred galaxies. Clusters can have up to thousands of galaxies ) at moderate redshift (look up Doppler shift, cosmological redshift and Hubble law) using HST (look up Hubble Space Telescope) or other optical observational data. We will use bulge-disk (look up galaxy bulge, galaxy disk) decomposition technique, with the aid of a computer, to estimate the
morphology of the galaxies instead of visual classification. This has an added advantage that it enable us to quantify the structural parameters of the galaxies. The results from this project can be used to compare the group MDR's at nearly the same redshift. This is an important step to check whether groups are scaled versions of clusters of galaxies.
This project needs a basic knowledge of fits images, galaxy photometry and galaxy classification. It is expected that the students know the de Vaucouleurs law, Sersic law and other empirical laws which describes galaxy light profiles and also have a basic knowledge in linux Operating System. It will be highly beneficial if the students familiarize themselves with the study materials on the above which will be added to this soon.