Rudrapriya Das

Our planet is in the Milky way galaxy which is just one of billions of galaxies in the Universe. Galaxies preferentially found in groups are called clusters. Galaxy clusters consist of hundreds to thousands of galaxies which are bound together by gravity. Galaxy clusters act as remarkable laboratories to know more about Astrophysics, dark matter, baryons and also plasma and high-energy physics. Mergers of galaxy cluster, non-thermal diffuse radio emissions have been discovered. Structures such as cold fronts and shock waves have also been found in many clusters of galaxies by using the Chandra X-ray Observatory. NASA's Chandra X-ray Observatory is a telescope specially designed to detect X-ray emission from very hot regions of the universe such as clusters of galaxies, exploded stars, and matter around black holes.

In this work I have studied the thermodynamic structure of Galaxy Cluster Abell 2069 and Abell 1995 with Chandra X-ray Observation. I have analyzed Chandra X-ray archival data of A2069 and A1995 and created thermodynamics maps (temperature, flux-density, pseudo-pressure, pseudo-entropy).
A systematic calibration and analysis pipeline ClusterPyXT has been used along with Chandra Interactive Analysis of Observations (CIAO) and Chandra Calibration Database (CALDB). CIAO is the software package developed by the Chandra X-Ray Center for analysing the data of Chandra X-ray Telescope. The CALDB is the directory and indexing structure that stores and provides access to all calibration files that are required for standard processing and analysis.
Methodology-
First I have noted the basic information of galaxy clusters from the website of Chandra X-ray Observatory. The used pipeline calculates the circular bin using Adaptive Circular Binning Method to create a scale map. APEC (Astrophysical Plasma Emission Code) and PHABS (photoelectric absorption) models are used to fit the spectra. The temperature corresponding to each pixel gives the high resolution temperature map. From the surface brightness we can map the projected density of the cluster, and combining that with a temperature map, we have also computed the pseudo pressure and entropy maps. Pseudo-pressure is calculated by using the relation, P∝√ST where S is the surface brightness and T is the temperature. We get the entropy (K) from the relation K∝TЅˉ¹/³.

Result- Both of the clusters have different morphology. A2069 has experienced cluster merger. Based on the temperature map of A2069 we can conclude that there are two hot regions near the center, one at northwest from the center, another at southeast of the center and two subclusters are colliding. Temperature decreases gradually as the distance increases from the centre of the galaxy cluster. The colour index describing the temperature is also shown in the map. Flux density is higher in the core region and at an extended region and decreases gradually moving outwards from the central region. We have found that pressure drops down around the core. At one edge of the galaxy cluster, the value of pseudo pressure is the same as it’s value around the core. From the entropy map it seems that entropy is higher around the centre of galaxy and gradually decreasing outside the core.

From all the maps of Abell 1995, it is observed that the core of the galaxy cluster is more ordered and no merging event is going on. We have found out from the Pseudo-pressure map that the pseudo pressure is maximum in the centre of galaxy cluster and pressure fall down with increasing distance from the centre. The temperature and flux-density are highest at the core whereas entropy is greater in the outer region of the core.