Characterising Tidal Features Around Galaxies in Cosmological Simulations

Abstract: Tidal features provide signatures of recent mergers and offer a unique insight into the assembly history of galaxies. The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will enable an unprecedentedly large survey of tidal features around millions of galaxies. To decipher the contributions of mergers to galaxy evolution it will be necessary to compare the observed tidal features with theoretical predictions. Therefore, we use cosmological hydrodynamical simulations NewHorizon, EAGLE, IllustrisTNG, and Magneticum to produce LSST-like mock images of $z\sim0$ galaxies ($z\sim0.2$ for NewHorizon) with $M_{\scriptstyle\star,\text{ 30 pkpc}}\geq10^{9.5}$ M${\scriptstyle\odot}$. We perform a visual classification to identify tidal features and classify their morphology. We find broadly good agreement between the simulations regarding their overall tidal feature fractions: $f{\text{NewHorizon}}=0.40\pm0.06$, $f_{\text{EAGLE}}=0.37\pm0.01$, $f_{\text{TNG}}=0.32\pm0.01$ and $f_{\text{Magneticum}}=0.32\pm0.01$, and their specific tidal feature fractions. Furthermore, we find excellent agreement regarding the trends of tidal feature fraction with stellar and halo mass. All simulations agree in predicting that the majority of central galaxies of groups and clusters exhibit at least one tidal feature, while the satellite members rarely show such features. This agreement suggests that gravity is the primary driver of the occurrence of visually-identifiable tidal features in cosmological simulations, rather than subgrid physics or hydrodynamics. All predictions can be verified directly with LSST observations.