SEAGLE- Simulating EAGle LEnses: Deciphering the galaxy formation via strong lens simulations

Strong gravitational lensing is a robust tool for studying the mass structure and evolution of early type galaxies (ETGs). In this
thesis, I introduce the SEAGLE (i.e. Simulating EAGLE LEnses) pipeline, that approaches the study of galaxy formation through
strong gravitational lensing, using a suite of high-resolution hydrodynamic simulations, Evolution, and Assembly of GaLaxies and
their Environments (EAGLE) project. I showed that the galaxy evolution models with either too weak or too strong stellar and/or
AGN feedback fail to explain the distribution of observed mass-density slopes. On the other hand, models with constant stellar
feedback, or AGN feedback with a higher duty cycle but milder temperature increases of their surrounding gas, produce strong
lenses with total mass density slopes close to isothermal. For the first time, I discovered a major discrepancy between simulations
and strong lensing observations in their projected dark matter fraction within half of the effective radius. This discrepancy is however
lifted when a variable bottom heavy stellar initial mass function (IMF) is used in the simulation. This could also indicate a yet
unaccounted dependency of the properties of ETGs on stellar and AGN feedback and the assumed stellar IMF. In this thesis, I
have investigated some of the key but open questions related to galaxy formation via strong lensing and opened up some new
thought-provoking questions for future.