Detection limits of galaxy shells in cosmological simulations and observations
Creators: name: Bazkiaei, Amir Ebadati
Publisher: name: Macquarie University
Year: 2023
Subjects: classificationCode: 510103
subject: Cosmology and extragalactic astronomy

description: According to galaxy evolution models, galaxies assemble their stellar mass through star formation and accreting stars in galaxy-galaxy merger events. It is believed that low surface brightness structures, such as shells, around galaxies are likely traces of merger events. Looking for these features in optical images or (and) cosmological simulations are two popular methods of investigating galaxy evolution. However, the detection of these features is restricted by observational and resolution limits of observations and simulations, respectively. The limits on low surface brightness structures may result in missing a range of structures that exist in the Universe but lie beyond the detection limits. Ignoring the detection limits and assuming that the lack of a missing structure is a natural phenomenon might result in biased conclusions. Therefore, determining the detection limits of low surface brightness structures is necessary to make realistic and unbiased conclusions. This thesis is focused on determining detection limits on galaxy shells, as an interesting tidal feature, in cosmological simulations and observations. I present analytical methods to determine the limits on the stellar mass of detectable shells in cosmological simulations such as Illustris and TNG. I find limits are greater for wide opening shells and shells around massive galaxies compared to narrow opening shells and shells around low mass galaxies. I show the limits on shells correlate with the stellar particle mass resolution of simulations. The higher the resolution, the smaller the limits on the stellar mass of detectable shells. I use the derived limits to estimate the limits on detectable merger ratios in Illustris simulation. My estimations indicate that the detection of galaxy shells in Illustris can reveal shell-forming mergers with ratios greater than 1:50-100. Studying mock images of simulated galaxies is common when making comparisons between observations and the theory. Smoothing simulated particles is crucial to minimize the sparse sampling of stars in mock images of simulated galaxies. In this thesis, I introduce an analytical method to investigate the impacts of smoothing particles on the profiles of simulated galaxies. Applying this method on a sample of Sérsic profiles shows that the smoothing process deflects the profiles to the greater values in the outskirts of galaxies. The magnitude of this deflection increases by the stellar particle mass resolution and radius while it decreases with the total stellar mass and the Sérsic index of the galaxy. Then, I use the smoothed profiles to find the impact of smoothing on the limits of detectable shells. I find the smoothing process has no considerable impact on the stellar mass limits of detectable shells in cosmological simulations. The surface brightness that observations of telescopes reach limits the observation of shells around galaxies. In this thesis, I introduce an analytical method to estimate the surface brightness limits of visible shells in observations of the Huntsman Telescope and Vera Rubin Observatory. I convert the stellar mass limits on shells in cosmological simulations into the surface brightness limits by using simple stellar population (SSP) models. I find detecting the same shells at small (large) radii is more likely in observations (simulations) compared to simulations (observations). I also find the surface brightness limits on simulated shells can be about two mag arcsec<sup>−2</sup> brighter for simulated shells around massive galaxies compared to that of simulated shells around low mass galaxies. I estimate the stellar mass limits on the visible shells in observations. These estimates show that shells further from the center of their host galaxy should have a more stellar mass for being visible in observations compared to shells closer to the center of their host galaxy. I also estimate the ratio of detectable shell-forming mergers in observations. I find the range of detectable merger ratios depends on the characteristics of the shell. Large (wide opening) radii shells are more likely the result of greater merger ratios compared to small radii (narrow opening) shells.