Galaxy Mergers Moulding The CGM
Maan Hani (University of Victoria)
July 05, 2017
Abstract: Galaxy evolution is primarily driven by the life cycle of gas. The circumgalactic medium is a key part in this cycle, viz. the CGM is a major gas reservoir where inflowing cold gas mixes with outflowing metal enhanced gas and ultimately settles onto the ISM. Galaxy-galaxy mergers have been hypothesized to play a critical role in shaping the CGM’s chemical and physical structure. In addition to being a fundamental evolutionary path for galaxies to grow their stellar mass and trigger star formation and AGN activity, galaxy mergers are known to vigorously reshuffle the gas reservoir due to the strong tidal torques and feedback processes which are induced by the interaction. However, detailed predictions for the effect of galaxy mergers on the CGM are currently lacking. In this talk, I will present a new analysis of the CGM of major mergers using cosmological zoom-in hydrodynamical simulations. This analysis provides the first constraints on the interplay between mergers and the CGM in a self-consistent cosmological framework. I will demonstrate the long lasting effects of mergers on the metal content of the CGM and its ionization, specifically highlighting the importance of mergers in moulding the CGM of galaxies: increasing its metal content by factors of 2-3, preferentially increasing the covering fractions of the high ionization species, and the large radial extent of such enhancements. Finally, I will use these simulations to make predictions of absorption line column densities and associated impact parameters in the CGM of post-merger galaxies, that can be directly tested with observations (i.e. with HST-COS).