Annual Report_Abridged - Second Version - FINAL

18 centers with a larger CO-to-HI abundance ratio, and another with lower molecular abundance in the outer regions of the galaxy. The comparison of interferometric and single dish observations shows that the detection of absorption requires sufficient spatial resolution to overcome the dilution by emission, and will be an important criterion for mm follow-up of 21-cm absorbers fromongoing large-scale surveys. Reference: Cold molecules in HI 21cm absorbers across redshifts 0.1-4; F. Combes and N. Gupta, 2023, A&A, 683, 20 Forecasting Gravitational Wave merger candidates The research group led by Shasvath Kapadia and his collaborators is trying to forecast the kind of massive binary black hole mergers that will be observed by future space based detectors like LISA and DECIGO, using large-scale cosmological hydrodynamical simulation data. It also attempts to come up with a preliminary estimate of the electromagnetic luminosities of these mergers, since such massive black holes will have matter surrounding them, and their mergers will enable electromagnetic counterparts. Another project in that group involves probing line-of-sight acceleration of the centre of mass of merging compact objects as a means to identify their provenance and the environments in which they merge. A third project concerns probing the abundance of compact objects in our Milky Way galaxy using the non-detection of continuous gravitational waves from these spinning compact objects. And finally, the group is also constructing sophisticated methods to identify gravitationally lensed gravitational waves in LIGO-Virgo data, where lensing will result in multiple, time- separated copies of the original signal. New techniques in Gravitational Wave data searches In the past year Sanjit Mitra worked on various aspect of gravitational wave (GW) data analysis. Kanchan Soni, Sanjeev Dhurandhar and Sanjit