Kartick C. Sarkar

Introduction

I am an astrophysicist, working in various directions of theoretical (analytical + numerical) galaxy formation and evolution.  My research interest lies in understanding the SN-driven bubbles/superbubbles, galactic outflows, and different physical processes in the interstellar and circumgalactic medium (ISM/CGM) that affect galaxy evolution. 

A frequent assumption in modeling the ISM/CGM is that the plasma is in collisional or photo-ionization equilibrium. While this is, in general, a good assumption in modeling the dynamics of the system, it is not a good assumption in modeling the emission/absorption properties of the system. I have shown in a few of my works that such assumptions of ionization equilibrium may result in misleading interpretations of the observing system.

Another aspect is the radiation field produced due to the radiative cooling of plasma in the ISM/CGM. The media themselves are assumed to be optically thin, i.e., radiation can escape the system without suffering from serious absorption or scattering, which diminishes the number of photons traveling toward the observer. However, we generally disregard the effect of the radiation on the plasma itself. One can imagine that if the absorbed number of photons (despite being a small fraction of the total number of photons) is comparable to the particles that absorb them, the plasma will be significantly affected. As a part of understanding the ISM/CGM properly, I built a frequency-dependent radiative transfer that is coupled to the ionization network and the fluid dynamics.

One of my favorite topics related to the study of bubbles and outflows is the study of Fermi/eROSITA Bubbles and other nearby large-scale features seen in X-rays or UV lines. I built a star-formation model for the Fermi Bubbles that could explain the gamma-rays, x-rays, UV absorbing clouds, and even be consistent with radio emission from the bubbles and the surrounding area. The recently discovered eROSITA bubbles perfectly match the theoretical model that my colleagues and I put forward. 

In this respect, I am also investigating the effects of active galactic nuclei (AGN) due to supermassive black holes in Milky Way-type galaxies. It is believed that the evolution of galaxies lighter than the Milky Way is affected by the energy feedback from supernovae, while galaxies heavier are affected by the AGN activities at the galactic center. For Milky Way-type galaxies, both supernova feedback and AGN feedback are equally important in dictating the evolution of the galaxy. Interestingly, both of these feedback processes are contradictory to each other - the presence of one energy source can suppress the other. It is, therefore, important to understand how the energy feedback process works in such galaxies. My recent efforts are to understand the inner workings of these processes. 

Other activities

I am a volunteer at the Padakshep which supports meritorious but under-privileged students in West Bengal for their education. Every year just after the results of board exams, Padakshep volunteers scout through different news articles, personal connections, and best-wishers to reach the students who need our help. Students can also apply through the official application portal of Padakshep for a scholarship.