Context. Satellite accretion events have been invoked for mimicking the internal secular evolutionary processes of bulge growth. However, N-body simulations of satellite accretions have paid little attention to the evolution of bulge photometric parameters, to the processes driving this evolution, and to the consistency of this evolution with observations. Aims. We want to investigate whether satellite accretions indeed drive the growth of bulges, and whether they are consistent with global scaling relations of bulges and discs. Methods. We perform N-body models of the accretion of satellites onto disc galaxies. A Tully-Fisher (M ∝ V α TF rot ) scaling between primary and satellite ensures that density ratios, critical to the outcome of the accretion, are realistic. We carry out a full structural, kinematic and dynamical analysis of the evolution of the bulge mass, bulge central concentration, and bulge-to-disc scaling relations. Results. The remnants of the accretion have bulge-disc structure. Both the bulge-to-disc ratio (B/D) and the Sérsic index (n) of the remnant bulge increase as a result of the accretion, with moderate final bulge Sérsic indices: n = 1.0 to 1.9. Bulge growth occurs no matter the fate of the secondary, which fully disrupts for α TF = 3 and partially survives to the remnant center for α TF = 3.5 or 4. Global structural parameters evolve following trends similar to observations. We show that the dominant mechanism for bulge growth is the inward flow of material from the disc to the bulge region during the satellite decay.Conclusions. The models confirm that the growth of the bulge out of disc material, a central ingredient of secular evolution models, may be triggered externally through satellite accretion.

Context. Early-type dwarf (dE) galaxies are the most common type of galaxies observed in the Universe. Their study has important cosmological implications because according to hierarchical galaxy evolution theories they are the progenitors of brighter galaxies. Nevertheless, the origin of this kind of system is still not well understood. Aims. The aim of the present work is to investigate whether the different locations of dwarf galaxies with respect to ellipticals in the face-on view of the fundamental plane could be due to the transformation of bright disc galaxies in low-mass systems by harassment. Methods. We have run high-resolution N-body numerical simulations to test the tidal stripping scenario of dE galaxies. The present simulations modelled several individual tidal stripping events in initial disc-like galaxy models with different bulge-to-disc mass ratios.Results. The models have shown that tidal stripping is a very efficient mechanism for removing stars and dark matter particles from galaxies, specially from their outer parts. The particles of the disc and halo components were easily stripped, while the bulge particles were not. Thus, the scale length of the discs were 40−50% shorter than the initial ones. Prograde tidal interactions create tidal features like stable bars in the discs of the galaxies. In contrast, bars are inhibited in retrograde encounters. After several tidal interactions the galaxy remnants looks like a dwarf spheroidal system. The final position of the low-mass systems in the face-on view of the fundamental plane (FP) depends on the initial conditions of the simulations. Thus, simulated galaxies with initial large B/D ratios are closer to the face-on view of the fundamental plane defined by bright E and bulges of early-type galaxies. Nevertheless, galaxies with initially small B/D ratio are located, after four fast tidal encounters, at the position of dE galaxies in the face-on view of the fundamental plane.The final position of the remnants in the FP do not depend on the orbital configuration of the encounters. Conclusions. We conclude that fast galaxy-galaxy interactions are efficient mechanisms of transforming bright galaxies into dwarf ones. Indeed, the different location observed between Es and dEs in the face-on view of the fundamental plane can be explained by the formation of dwarf galaxies by harassment of late-type bright ones.

Context. Observations have shown that inner discs and rings (IDs and IRs) are not preferably found in barred galaxies, which indicates that their formation may differ from that described by the traditional bar-origin scenario in many cases. In contrast, the role of minor mergers in producing these inner components (ICs), while often invoked, is still poorly understood. Aims. We investigate the capability of minor mergers to trigger the formation of IDs and IRs in spiral galaxies through collisionless N-body simulations. Methods. We run a battery of minor merger simulations in which both primary and secondary galaxies are modelled as disc-bulgehalo galaxies with realistic density ratios. Different orbits and mass ratios are considered, as well as two different models for the primary galaxy (a Sab or Sc). We then perform a detailed analysis of the morphology, structure, and kinematics of the ICs resulting from the minor merger. Results. All the simulated minor mergers develop thin ICs out of satellite material, supported by rotation. A wide morphological zoo of ICs are obtained (including IDs, IRs, pseudo-rings, nested IDs, spiral patterns, and combinations of them), but all have structural and kinematical properties similar to those observed. The sizes of the resulting ICs are comparable to those observed in real galaxies with the adequate scaling. The existence of the resulting ICs can be deduced from the features that they imprint in the isophotal profiles and kinemetric maps of the final remnant, as in many real galaxies. Weak transitory oval distortions appear in the remnant centre in many cases, but none of them develops a noticeable bar. The realistic density ratios used in the present models ensure that the satellites experience more efficient orbital circularization and disruption than in previous studies. Combined with the disc resonances induced by the encounter, these processes produce highly aligned co-and counter-rotating ICs at the remnant centre. Conclusions. Minor mergers are an efficient mechanism for forming rotationally-supported stellar ICs in spiral galaxies, without requiring either strong dissipation or the development of noticeable bars. The present models indicate that minor mergers can account for the existence of pure-stellar old ICs in unbarred galaxies, and suggest that their role must have been crucial in the formation of ICs and much more complex than just bar triggering.