The morphology of galaxies gives essential constraints on the models of galaxy evolution. The morphology of the features in the low-surface-brightness regions of galaxies has not been fully explored yet because of observational difficulties. Here we present the results of our visual inspections of very deep images of a large volume-limited sample of 177 nearby massive early-type galaxies (ETGs) from the MATLAS survey. The images reach a surface-brightness limit of 28.5 − 29 mag arcsec−2 in the g′ band. Using a dedicated navigation tool and questionnaire, we looked for structures at the outskirts of the galaxies such as tidal shells, streams, tails, disturbed outer isophotes or peripheral star-forming disks, and simultaneously noted the presence of contaminating sources, such as Galactic cirrus. We also inspected internal sub-structures such as bars and dust lanes. We discuss the reliability of this visual classification investigating the variety of answers made by the participants. We present the incidence of these structures and the trends of the incidence with the mass of the host galaxy and the density of its environment. We find an incidence of shells, stream and tails of approximately 15%, about the same for each category. For galaxies with masses over 1011 M⊙, the incidence of shells and streams increases about 1.7 times. We also note a strong unexpected anticorrelation of the incidence of Galactic cirrus with the environment density of the target galaxy. Correlations with other properties of the galaxies, and comparisons to model predictions, will be presented in future papers.

Context. The Milky Way (MW) and Andromeda (M 31) galaxies possess rotating planes of satellites. Their formation has not been explained satisfactorily yet. It was suggested that the MW and M 31 satellites are ancient tidal dwarf galaxies, which could explain their configuration. This suggestion gained support by an analytic backward calculation of the relative MW-M 31 orbit in the MOND modified dynamics paradigm by Zhao et al. (2013) implying their close flyby 7-11 Gyr ago. Aims. Here we explore the Local Group history in MOND in more detail using a simplified first-ever self-consistent simulation. We note the features induced by the encounter in the simulation and identify their possible real counterparts. Methods. The initial conditions were set to eventually roughly reproduce the observed MW and M 31 masses, effective radii, separation, relative velocity and disk inclinations. We used the publicly available adaptive-mesh-refinement code Phantom of RAMSES. Results. Matter was transferred from the MW to M 31 along a tidal tail in the simulation. The encounter induced formation of several structures resembling the peculiarities of the Local Group. Most notably: 1) A rotating planar structure formed around M 31 from the transferred material. It had a size similar to the observed satellite plane and was oriented edge-on to the simulated MW, just as the real one. 2) The same structure also resembled the tidal features observed around M 31 by its size and morphology. 3) A warp in the MW developed with an amplitude and orientation similar to that observed. 4) A cloud of particles formed around the simulated MW, with the extent of the actual MW satellite system. The encounter did not end by merging in a Hubble time. The simulated stellar disks also thickened as a result of the encounter. Conclusions. The simulation demonstrated that MOND can possibly explain many peculiarities of the Local Group, which should be verified by future more elaborate simulations. The simulation moreover showed that tidal features observed in galaxies, usually interpreted as merger remnants, could have been formed by matter exchange during non-merging galactic flybys in some cases.