AR_final file_2018-19

clusters are not a viable option due to the attractive nature of gravity, but the repulsive and outward pe- culiar gravitational acceleration at the voids makes it easier to stretch them at an accelerated rate. We argue that this accelerated expansion of the voids inside the cosmic web may mimic the behaviour of dark energy. Mahadev B. Pandge A combined X-ray, optical and radio view of the merging galaxy cluster MACS J0417.5-1154 We present a comprehensive multi-wavelength analysis of the merging galaxy cluster MACS J0417.5-1154 at a redshift of z = 0 . 44, using available images red obtained with Chandra in X-ray, Subaru , Hubble Space Telescope (HST) in optical, Giant Metrewave Radio Telescope (GMRT) in radio and Bolocam at 2.1 mm wavelength. This is an example of a complex merging galaxy cluster, also hosting a steep-spectrum Mpc scale radio halo. The mass distribution obtained by weak lensing reconstruction shows that MACS J0417.5-1154 belongs to the dissociative class of mergers, where one of its sub structures has had its gas content detached after the pericentric passage. The overall structure, surface brightness profile, temperature, and metal abundance of the intra-cluster medium (ICM) all point towards the presence of a cold front and merger induced gas-sloshing motion near the core. We detect a surface brightness edge to the south − east direction at a projected distance of ∼ 45 arcsec ( ∼ 255 kpc) from the centre of this cluster. The X-ray spectral analysis across the inner and outer edge allows us to confirm the detected edge as a cold front. The GMRT 235MHz observation shows a comet − like extended sychrotron radio halo emission trailing behind the cold front. The peak of the Sunyaev-Zel’dovich decrement is found displaced from the centre of X-ray emission, which is interpreted as conse- quence of the merger dynamics. The optical HST imaging analysis of the cluster reveals the complex morphology of the BCG, with three surrounding ring-shaped structures with bright knots, which appear to be images of a multiply-imaged strongly lensed background galaxy. In addition two pre- viously unknown giant arcs are found, which are all indications of strong gravitational lensing in this massive system. This study has been done in collaboration with Rogrio Monteiro de Oliveira, Joydeep Bagchi, A. Simionescu, Marceau Limousin, and Somak Raychaudhury. AGN Feedback in galaxy groups: A detailed study of X-ray features and diffuse radio emission in IC1262 We report a systematic search of X-ray cavities, density jumps, and shocks in the inter-galactic en- vironment of the galaxy group IC 1262 using Chan- dra , GMRT and VLA archival observations. The X-ray imaging analysis reveals a pair of X-ray cav- ities on the north and south of the X-ray peak, at projected distances of 6.48 kpc and 6.30 kpc re- spectively. Total mechanical power contained in both these cavities is found to be ∼ 12.37 × 10 42 erg s − 1 , and compares well with the X-ray lumi- nosity, within the cooling radius, measured to be ∼ 3 . 29 × 10 42 erg s − 1 , suggesting that the mechan- ical power injected by the central AGN efficiently balances the radiative loss. We detect a previously unknown X-ray cavity at the position of southern radio lobe in the intra-group medium, and find a loop of excess X-ray emission extending ∼ 100 kpc southwest from the central galaxy. The X-ray cav- ity at the position of southern radio lobe probably represents a first generation X-ray cavity. Two sur- face brightness edges are evident to the west and east − north of the centre of this group. The radio galaxy at the core of the IC 1262 group is a rare low- redshift ultra-steep radio galaxy, its spectral index being α ∼− 1 . 73 (including the central AGN), and α ∼− 2 . 08 (excluding the central AGN). We detect a radio phoenix embedded within the southern ra- dio lobe, for the first time in a poor group, with a spectral index ( α ≤− 1 . 92). The spectral index dis- tribution across the phoenix steepens with increas- ing distance from its intensity peak. This study has been done in collaboration with S. S. Sonkamble, Viral Parekh, Pratik Dabhade, Avni Parmar, M. K. Patil, and Somak Raychaudhury. Amit Pathak DFT study of five-membered ring PAHs This work reports a Density Functional Theory (DFT) calculation of PAH molecules with a five- member ring to determine the expected region of infrared features. It is highly possible that fullerene molecule might be originated from five-membered ring PAH molecules in the ISM. Effect of ioniza- tion and protonation on five-membered ring PAH molecule is also discussed. A detail vibrational ( 205 )