AR-2019-2020

colour map is constructed showing the variation of the colour-index through the coma. Changes ap- pear at the transition between the coma and the tail with a low colour-index ( < 0.3 mag) close to the optocentre and further away increasing up in the tail direction (about 0.45 mag at 10 000 km). We interpret these changes in terms of dust prop- erties, and we compare our results to other remote observations of 67P including in situ Rosetta ob- servations This work has been done in collabora- tion with Edith Hadamcik, Robert Botet, Jeremie Lasue, Saumyadeep Roy Choudhury, and Ranjan Gupta. T. R. Seshadri Probing magnetic field in high-redshift galaxies us- ing background quasars We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (rrm) for quasar sight- lines with intervening Mg ii absorbers. For this purpose, archival data for 1,132 quasars have been used and the spread in the rrm has been com- puted. The lines-of-sight to the quasar could pass through intermediate galaxies. If this happens, one also expected to see an absorption in MgII. If there are more than one such intermediate systems, one expects such absorption features at different red- shifts. We have found the spread to be 17.1 ± 0 . 7 rad m − 2 for 352 sightlines having Mg ii interven- ing absorbers in comparison to its value of 15 . 1 ± 0 . 6 rad m − 2 for 780 sightlines without such absorbers, resulting in an excess broadening ( σ ex rrm ) of 8 . 0 ± 1 . 9 rad m − 2 among these two subsamples. This value of σ ex rrm , has allowed us to constrain the average strength of magnetic field (rest frame) in high red- shift galaxies responsible for these Mg ii absorbers, to be ∼ 1 . 3 ± 0 . 3 μG at a median redshift of 0.92. A similar analysis was done on subsample split based on the radio spectral index, α , (with F ν ∝ ν α ). The spectral index α was found to be greater than or equal to − 0 . 3 for 315 sources and ≤ − 0 . 7 for 476 sources. The former shows a significant σ ex rrm (at 3.5 σ level) and is absent in latter. An anti- correlation found between the σ md rrm and percentage polarisation ( p ) with similar Pearson correlation of − 0 . 62 and − 0 . 87 for subsample with and without Mg ii , respectively, suggests main contribution for decrements in the p value to be intrinsic to the lo- cal environment of quasars. This work has been done in collaboration with Sunil Malik, and Hum Chand. Constraining the spectral index of density perturba- tions from primordial black holes Primordial Black Holes (PBHs) could be formed due to the collapse of the inhomogeneities that were generated during inflation in the early universe. Their evaporation can lead to energy injection in the universe. By using the current results of the baryon-photon ratio obtained from BBN and CMB observations, we impose constraints on the spec- tral index of perturbations on those small scales that cannot be estimated through CMB anisotropy and CMB distortions. The masses of the PBHs constrained in this study lie in the range of 10 9 and 10 11 g, which corresponds to those PBHs whose maximal evaporation took place during the red- shifts 10 6 < z < 10 9 . It is shown that the up- per bound on the scalar spectral index, n s can be constrained for a given threshold value, ζ th , of the curvature perturbations for PBHs formation. Us- ing Planck results, We obtained constraints on the scalar spectral index, n s to be less than 1 . 309 for ζ th = 0 . 7 and n s < 1 . 334 for ζ th = 1 . 2, respectively. We have also estimated the the density fraction that has contributed to the formation of PBH. This work is carried out in collaboration with Gaveshna Gupta, and Ramkishor Sharma. Mohit Kumar Sharma Transfer of radiation in the formic acid - A precur- sor for amino acids Formic acid (HCOOH), a simplest carboxylic acid, has great importance as it is a precursor for amino acids (constituents of life). It has two rotameric isomers: trans-HCOOH and cis-HCOOH, each of which lies in a plane due to the delocalization of π - electrons over the heavy atom chain. In each of the isomers, the electric dipole moment is aligned such that there are both a and b type rotational tran- sitions. Further, the energy levels in each type of transitions can be classified into two groups. Thus, there are 8 groups in which the rotational transi- tions of formic acid may be classified. The trans- HCOOH is detected in Sgr B2, cold dark cloud L134N, Sgr A, comet Hale-Bopp, Orion KL, W51, IRAS 16293-2422 through its a -type transitions. Because of very small value of b -component of elec- tric dipole moment, the b -type transitions of trans-

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