| dc.description.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. | en_US |
