Probing the merger history of red early-type galaxies with their faint stellar substructures

Abstract

Several detailed observations, such as those carried out at the Canada-France-Hawaii Telescope (CFHT), have revealed prominent Low Surface Brightness (LSB) fine structures that lead to a change in the apparent morphology of galaxies. Previous photometry surveys have developed observational techniques which make use of the diffuse light detected in the external regions of galaxies. In these studies, the outer perturbations have been identified and classified. These include tidal tails, stellar streams, and shells. These structures serve as tracers for interacting events and merging events and retain some memory of the mass assembly of galaxies. Cosmological numerical simulations are required to estimate their visibility timescale, among other properties, in order to reconstruct the merger history of galaxies. In the present work, we analyze a hydrodynamical cosmological simulation to build up a comprehensive interpretation of the properties of fine structures. We present a census of several types of LSB fine structures compiled using a visual inspection of individual snapshots at various points in time. We reconstruct the evolution of the number of fine structures detected around an early-type galaxy and we compare it with the merger history of the galaxy. We find that most fine structures are associated with major and intermediate mass merger events. Their survival timescale ranges between 0.7 and 4 Gyr. Shells and streams remain visible for a longer time, while tidal tails have a shorter lifetime. These estimates for the survival time of collisional debris provide clues for the interpretation of the shape and frequency of fine structures observed in deep images with regard to their mass assembly. We find that the detectability of stellar streams is most sensitive at the surface brightness limit, demonstrating greater visibility at the deepest surface brightness level used in our simulation. We see between two and three times more streams based on a surface brightness cut of 33 mag arcsec-2 than with 29 mag arcsec-2. We find that the detection of shells is strongly dependent upon the projection angle.