AR_final file_2018-19

from these X-ray maps, we find evidence of feed- back from the active nuclei. We find that exclud- ing galaxies and AGNs, residing in group environ- ments, from our samples enhances the significance of our detection. Our results support the tenta- tive findings of Chatterjee et al., who use X-ray- selected AGNs for their analysis. We discuss the implications of these results in the context of quan- tifying AGN feedback, and show that the current method can be used to extract an X-ray source pop- ulation in high-redshift galaxies. This study has been done in collaboration with Sagnick Mukher- jee, Anirban Bhattacharjee, Jeffrey A. Newman, and Renbin Yan. Direct detection of quasar feedback via the Sunyaev- Zeldovich effect The nature and energetics of feedback from ther- mal winds in quasars can be constrained via obser- vations of the Sunyaev-Zeldovich Effect (SZE) in- duced by the bubble of thermal plasma blown into the intergalactic medium by the quasar wind. In this work, we present evidence that we have made the first detection of such a bubble, associated with the hyperluminous quasar HE 0515-4414. The SZE detection is corroborated by the presence of ex- tended emission line gas at the same position angle as the wind. Our detection appears on only one side of the quasar, consistent with the SZE signal arising from a combination of thermal and kinetic contri- butions. Estimates of the energy in the wind allow us to constrain the wind luminosity to the lower end of theoretical predictions, ∼ 0.01 per cent of the bolometric luminosity of the quasar. However, the age we estimate for the bubble, ∼ 0.1 Gyr, and the long cooling time, ∼ 0.6 Gyr, means that such bubbles may be effective at providing feedback be- tween bursts of quasar activity. This research work has been done in collaboration with Mark Lacy, Brian Mason. Kraign Sarazin, Kristina Nyland, Amy Kimball et al. Asis Kumar Chattopadhyay Clustering of gamma-ray bursts through kernel principal component analysis We considered clustering of gamma-ray bursts through kernel principal component analysis, in which our proposed kernel outperforms results of other competent kernels in terms of clustering accu- racy, and we obtain three physically interpretable groups of gamma-ray bursts. The electiveness of the suggested kernel in combination with the kernel principal component analysis in revealing natural clusters in noisy and non linear data while reduc- ing the dimension of the data is explored in two artificially created data sets. This work has been carried out in collaboration with Soumita Modak and Tanuka Chattopadhyay. Surajit Chattopadhyay A study of modified holographic Ricci dark energy in the framework of f ( T ) modified gravity and its statefinder hierarchy Inspired by the work of Bamba et al. 2012), the present study reports on the reconstruction of mod- ified holographic Ricci dark energy (MHRDE) in the framework of modified gravity taken as f ( T ) gravity. A correspondence between modified Chap- lygin gas (MCG) and MHRDE has also been con- sidered, and thereafter the f ( T ) gravity has been reconstructed via reconstruction of the Hubble pa- rameter. The reconstructed equation of state (EoS) parameter obtained this way has been found to be able to cross the phantom boundary. In the next phase of the work, a viable model of f ( T ) gravity has been considered and MHRDE has been discussed in this modified gravity frame. The EoS parameter due to the torsion contribution ob- tained this way has been found to behave like quintessence. The transition of the universe from the dark matter (DM) dominated to dark energy (DE) phase is apparent from this model. Also, the model is exhibiting DE domination of the cur- rent universe. Finally, the statefinder hierarchy has been discussed through the statefinder and snap parameters. The model has been found to be able to attain the Λ CDM fixed point in the statefinder trajectory. This work has been carried out in col- laboration with Arkaprabha Majumdar. Reconstruction of f ( T ) gravity in the context of standard Chaplygin gas as tachyon scalar field and study of the stability against gravitational perturba- tion The present work, carried out in collaboration with Soumyodipta Karmakar, reports a study on the f ( T ) gravity reconstruction scheme in the context of considering standard Chaplygin gas as tachyon scalar field model of dark energy. The solution for reconstructed f ( T ) gravity has been obtained from ( 181 )