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G. V. Vijayagovindan

Publications and source records attributed to G. V. Vijayagovindan.

8 recordsLinked to original sources
arXiv2010

PyMorph: Automated Galaxy Structural Parameter Estimation using Python

We present a new software pipeline -- PyMorph -- for automated estimation of structural parameters of galaxies. Both parametric fits through a two dimensional bulge disk decomposition as well as structural parameter measurements like concentration, asymmetry etc. are supported. The pipeline is designed to be easy to use yet flexible; individual software modules can be replaced with ease. A find-and-fit mode is available so that all galaxies in a image can be measured with a simple command. A parallel version of the Pymorph pipeline runs on computer clusters and a Virtual Observatory compatible web enabled interface is under development.

astro-ph.IM↗
arXiv2009

A Cosmological Model with Fermionic Field

In this work, a cosmological model inspired by string/M- theory with fermionic field is taken into consideration. Here it is investigated whether the introduction of a non-Dirac fermionic field--characterized by an \textit{interaction term}--affects the cosmological evolution. The self-interaction potential is considered as a combination of the scalar and pseudo-scalar invariants. It is observed that the fermionic field under consideration behaves like an inflation field for the early Universe and later on, as a dark energy field. The late time acceleration becomes more prominent by the addition of the interaction term. There is a slight decrease for the inflation peak as well as for the energy density. We see that addition of higher order terms to the fermionic part of Lagrangian does not significantly change either the inflation or the late time acceleration behavior.

gr-qc↗
arXiv2009

Quantitative measure of evolution of bright cluster galaxies at moderate redshifts

Using archival data from the Hubble Space Telescope, we study the quantitative morphological evolution of spectroscopically confirmed bright galaxies in the core regions of nine clusters ranging in redshift from $z = 0.31$ to $z = 0.84$. We use morphological parameters derived from two dimensional bulge-disk decomposition to study the evolution. We find an increase in the mean bulge-to-total luminosity ratio $B/T$ as the Universe evolves. We also find a corresponding increase in the fraction of early type galaxies and in the mean Sérsic index. We discuss these results and their implications to physical mechanisms for evolution of galaxy morphology.

astro-ph.CO↗
arXiv2009

A Cosmological Model with Fermionic Field and Gauss-Bonnet Term

In this work, a cosmological model inspired by string theory with Gauss-Bonnet term coupled to the fermionic field is taken into consideration. The self-interaction potential is considered as a combination of the scalar and pseudo-scalar invariants. Here the cosmological contribution of the coupling of Gauss-Bonnet term with a non-Dirac fermionic field--characterized by an \textit{interaction term}$L_{DG} ^2$-- is investigated. It is observed that the new type of coupling plays a significant role in the accelerating behavior of the universe. Specifically, in addition to the late time acceleration for the universe, $L_{DG} ^2$ produces an early decelerating behavior. The behavior of the equation-of-state parameter $(w)$ is such that it guarantees the stability of the theory.

hep-ph↗
arXiv2006

Brane World Dynamics and Adiabatic Matter creation

We have treated the adiabatic matter creation process in various three-brane models by applying thermodynamics of open systems. The matter creation rate is found to affect the evolution of scale factor and energy density of the universe. We find modification at early stages of cosmic dynamics. In GB and RS brane worlds, by chosing appropriate parameters we obtain standard scenario, while the warped DGP model has different Friedmann equations. During later stages, since the matter creation is negligible the evolution reduces to FRW expansion, in RS and GB models.

astro-ph↗
arXiv2001

Dissipative Collapse of a Spherical Cluster of Gas Clouds

With a view to understand the galaxy/star formation scenario, we investigate the dissipative collapse of a spherical cluster of gas clouds with an isotropic velocity distribution. The time scale for collapse to one tenth radius is studied as a function of the collision time in the system. The scalar virial equation is used to investigate the evolution of the size of the cluster. This is supplemented with an evolution equation for the random kinetic energy. The above system is numerically solved and the results analyzed. For large values of the collision time we find that the time scale for collapse is proportional to the collision time as expected. However for large values of the dissipation, i.e. for small collision times, the collapse time shows a nonlinear dependence on the collision time.

astro-ph↗
arXiv1999

Super-reflection of light from a random amplifying medium with disorder in the complex refractive index : Statistics of fluctuations

The probability distribution of the reflection coefficient for light reflected from a one-dimensional random amplifying medium with {\it cross-correlated} spatial disorder in the real and the imaginary parts of the refractive index is derived using the method of invariant imbedding. The statistics of fluctuations have been obtained for both the correlated telegraph noise and the Gaussian white-noise models for the disorder. In both cases, an enhanced backscattering (super-reflection with reflection coefficient greater than unity) results because of coherent feedback due to Anderson localization and coherent amplification in the medium. The results show that the effect of randomness in the imaginary part of the refractive index on localization and super-reflection is qualitatively different.

cond-mat.dis-nn↗