Thermal Sunyaev-Zeldovich Effect in the CGM of low-redshift L* galaxies.

Phase structure of the highly ionized circumgalactic medium (CGM) of the Milky Way; Neutral CGM of local galaxies.

All-sky dispersion measure mapping in the local group

We are searching for faint emission signature of neutral Hydrogen (HI) in the halo of galaxies using deep Radio spectroscopic observations. Result: We have detected large scale diffuse HI out to a significant fraction of the virial radii of our target galaxies. The mass of this gas is larger by an order of magnitude compared to earlier studies.

I am doing the X-ray background analysis around an extragalactic sightline to extract the contribution of the ISM/CGM of Milky Way/Local Group medium along this direction. By combining this with the absorption studies done in our previous project, we will be able to break the degeneracy between the mass parameters. This would tell us the spatial extent and the density structure of the warm-hot/hot gas in the circumgalactic region. Update: Interestingly, we found that the temperature of the warm-hot and hot phase observed in emission and absorption are not consistent with each other, unlike the previous single-temperature analyses. Taking into account the measurements of past two decades, we consider several possibilities objectively, and rule out the picture of single-temperature CGM in hydrostatic equilibrium. Most likely, we are observing different phases in emission and absorption.

I worked on a very high S/N X-ray absorption spectrum of a quasar to determine the multi-phase metallicity of the circumgalactic medium of Milky way. We discovered the hottest component of the Milky Way's CGM (10^7 K), coexisting with the well-known warm-hot phase at ~10^6 K. In conjunction, we found that the chemical composition of the gas is significantly (~99.73%) non-solar, with a paucity of Iron with respect to Nitrogen, Oxygen and Neon. Also, Oxygen is sub-solar with respect to Nitrogen and Neon, such that the latter two are in solar mixture. This provides important information about the thermal and chemical evolution of the CGM of Milky Way.

I worked on the diffuse soft X-ray emission from the warm-hot circumgalactic medium(CGM) of a Milky-way type galaxy (NGC 3221). After subtracting the dominant foreground and background emissions, we were able to extract the faint emission from an extended region out to 150 kpc with ~99.988% confidence, for the first time. For a reasonable metallicity of 0.3solar, we found that the baryons do meet the cosmological allotment. This is the first external L* spiral galaxy, after Milky Way found to be baryon sufficient.

Core-collapse Supernovae - explodability, parametrization and effect of immediate circumstellar medium.

Detection of Short Gamma-ray Bursts: We analysed the photometric calibration data of GRB160119A from CZTI, Astrosat (http://astrosat.iucaa.in/?q=node/10) to extract traces of SGBs by distinguishing it from cosmic ray, stellar flare or high intensity gamma-ray background. We used the standard methods of peak detection and detector-plane histogram. My main contribution was to chalk out an algorithm by combining spatial and temporal information of the pixels to efface the detection process.

Application of Atomic and Molecular Physics in Observational Astronomy

Studying HI-H2 Transition in the ISM of Local Galaxies: Here I had explored the dependence of HI-H2 transition on the quantities regulating the production of molecular hydrogen (no. density of neutral hydrogen, temperature, radiation intensity, and dust abundance) using photo-ionization code CLOUDY (http://www.nublado.org/wiki). The intention was to scale this transition to obtain a unified curve of growth. We had also studied how the bimodality of molecular hydrogen column density, and the forbidden range of physical state between WNM and CNM vary with respect to the regulating quantities aforementioned. The motivation behind the study was a striking similarity in the value of neutral hydrogen column density where efficient star formation starts and also interstellar atomic cloud turns into a molecular one. A glitch in temperature estimation of CLOUDY was found and reported. Later, these simulations were utilized to model the DLA systems identified in the absorption spectrum of J0925+4004 obtained from Cosmic Origin Spectrograph (HST) and HIRES. The data was analysed using IDL and VPFIT. Interestingly, we found two clouds very close to each other with considerably different thermodynamic properties and environment, which had earlier been studied as a single cloud in literature.

Detection of Sickle -Cell Disease by Optical (scattering and absorption) Method

Testing of new receiver systems and comparing the performance of GWB with GSB : The stability of cross-correlation amplitude and phase of complex visibility with respect to frequency as well as time had been studied from the interferometric test observations in four different bands for all possible combinations of the polarization channels and modes of recording signals. The major findings were detecting RFI in one of the antennas in western array and reporting malfunction of synthesizer receivers in one of the bands.

Detection of extra-solar planet using transit method: I had studied all direct and indirect detection processes, their novelty and limitations to infer presence of orbiting objects around stars. Then I focused on transit method only, and derived the one-to-one relations between the observable quantities and the physical properties of the planetary system from scratch.