MS. RAJESHWARA DUTTA

Understanding the physical conditions and volume filling factor of the cold neutral medium (CNM) phase, which is closely related to the molecular gas, is essential to understand the processes through which gas gets converted to stars and the star formation history of galaxies. HI 21-cm absorption allows us to probe the thermal state of the HI gas as well as the parsec- to kpc-scale structures in the gas and relate them to the in-situ star formation. Using 250 hrs of GMRT and VLA time, we have conducted a systematic HI 21-cm absorption survey of radio-loud quasars whose sightlines happen to pass through the gas disks/halos of nearby galaxies (referred as quasar-galaxy pairs or QGPs). Our sample of low-z (z<0.4) QGPs spans a wide range of impact parameter (0