Merger histories of galaxies in the GECKOS survey

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This project will examine the connection between a galaxy's merger history and the structure of its disc, and will take advantage of GECKOS, a new VLT/MUSE survey of 35 nearby edge-on galaxies.To recover merger histories, a range of techniques exist (see for instance Martig et al 2021, Boecker et al 2020, Zhu et al 2022). The technique presented in Martig et al (2021) is based on the idea that for a given age, accreted stars are more metal-poor than those formed in situ. This technique needs to be tested and refined, and it will be the first step of the project: to use simulations to assess how well we can recover past merger events based on the age-metallicity relation: which mergers can be identified that way? How much can we trust mass ratio and merger time derived? We will use the ARTEMIS simulations for this project, and will create mock GECKOS-like observations to test the method.The second step will be to use what we have learnt, and characterize the merger histories of all GECKOS galaxies (we will also produce maps of where accreted stars currently lie).The final step will be to gather all the results obtained within the course of the survey on the structure of discs (mass in thin and thick discs, age-velocity relation, scale-heights of mono-age populations, flaring in the outer disc, radial age gradients). Can we link merger events with particular signatures such as jumps in velocity dispersion at a given age, or increased scale-height? Which mergers produce massive thick discs? Do we confirm results from Garcia de la Cruz et al (2021) on the influence of mergers on flaring and age gradients? Are there thick discs that seem to have formed in the absence of mergers?