Multi wavelength analysis of morphology and evolution of galaxies/

Abstract

Galaxies are considered as building blocks of our Universe and the studies on morphology and evolution of galaxies provide vital information about the evolution scenario of the Universe. The morphological and star-forming features of galaxies are crucial to the present knowledge of galaxy formation. Most of the massive galaxies harbor supermassive black holes (SMBH) at their centers and this central region plays a vital role in the evolution scenario of host galaxies. The relationship between the origin and evolution of SMBHs with their host galaxies is a hot topic. The accretion of matter towards the SMBH is the prime reason for the origin and growth of active galactic nuclei (AGN) in the nuclear region of galaxies. The dynamics of gas in the interstellar medium (ISM) of galaxies also share significant information regarding the galaxy's evolution. In order to comprehend the evolution of these kinds of galaxies, it may be crucial for determining correlations between different parameters for a set of galaxies with comparable morphology. In this thesis, we investigate the central region of AGN host galaxies as well as the early-type galaxies (ETGs) by using simple photometry and exploring various correlations between galaxy properties. We determined the Central Intensity Ratio (CIR) at the optical center of the archival images of the nearby (z < 0.02) Seyfert galaxies observed by HST. We find that CIR shows a strong correlation with the mass of the supermassive black hole residing at the center of the galaxy. The removal of cold gas by the active black hole might be suppressing the star formation near the central region of the galaxies, which is responsible for the decrease in CIR. We identified the large discrepancy that occurred in the estimation of central velocity dispersion (σ) due to the extra luminous feature of AGN. Thus, we propose that CIR can be utilized as a fast and reliable tool to estimate the SMBH mass of AGNs instead of σ. Most ETGs are known to be strong X-ray emitters. The contribution from various sources (like hot gas, AGNs, SMBH, and X-ray binaries) to this X-ray emission of ETGs has been a hot topic. In this context, optical CIR is used to investigate the centers of nearby (D < 30 Mpc) ETGs. We find new scaling relations, CIR − L X,GAS and CIR − T GAS , that strongly suggests the role of central gas temperature on the star formation process and evolution scenario of early-type galaxies. To measure X-ray gas luminosity from ISM with greater accuracy, it is necessary to subtract various contributors to the X-ray emission in galaxies using rigorous spectroscopic modeling. Thus, we propose the simple photometric parameter CIR can be used instead of employing spectroscopy for determining the L X,GAS of ETGs. Moreover, total stellar mass is a fundamental parameter in understanding the formation and evolution of galaxies. Recent studies have reported that the Mid-infrared band is an excellent tracer of the stellar mass of galaxies. In this light, we estimated mid-infrared CIR for a representative sample of ETGs by using Spitzer/IRAC 3.6 μm data. Mid-IR CIR found to be significantly correlated with the total stellar mass, SMBH mass, σ, and absolute B band magnitude. Since mid-IR emission mainly comes from the old stars, CIR can be utilized as a better tracer of stellar mass and used to study the variation of the old stellar population at the central region of galaxies.