On the flaring of thick discs of galaxies: insights from simulations

The merger history of a galaxy has a direct impact on the structure of its geometrically defined thick disc. Among other effects, mergers induce flaring in the stellar populations in the disc, which can be reflected on the thick disc's age structure. As we are studying the age structure of thick discs in the MW and nearby galaxies with an unprecedented level of detail, it is important to use simulations in order to have a more comprehensible picture of the diversity of thick disc age structures, and their connection to the galaxies' merger histories. In this talk, I will present the results of an analysis performed on a sample of 27 simulated MW mass galaxies in their cosmological context, where we explore the connection between the flaring of mono-age populations (MAPs), thick disc flaring, thin/thick disc separation, and thick disc's age structure. I will explain under which conditions MAPs create flat thick discs, and how these galaxies form a continuum thin/thick structure, have radial age gradients, and tend to have quiescent recent merger histories, similar to our understanding of the Galaxy. Conversely, I will show the different scenarios we find where MAPs can create flared thick discs, with these galaxies showing a wider variety of the aforementioned features. In conclusion, the results presented in this talk are in agreement with the emerging picture of thick discs being diverse and complex components of external galaxies, which when studied in detail, can provide vital constrains for the formation and evolution of disc galaxies.