A minor merger origin for stellar inner discs and rings in spiral galaxies

Eliche-Moral, M. C.; González-García, A. C.; Balcells, M.; Aguerri, J. A. L.; Gallego, J.; Zamorano, J.; Prieto, M.
Bibliographical reference

Astronomy & Astrophysics, Volume 533, id.A104

Advertised on:
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-bulge-halo 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. Figures 12-16 are available in electronic form at http://www.aanda.org
Related projects
Abell 370 is located approximately 4 billion light-years away in the constellation Cetus, the Sea Monster
Galaxy Evolution in Clusters of Galaxies

Galaxies in the universe can be located in different environments, some of them are isolated or in low density regions and they are usually called field galaxies. The others can be located in galaxy associations, going from loose groups to clusters or even superclusters of galaxies. One of the foremost challenges of the modern Astrophysics is to

Méndez Abreu
Group members
Traces of Galaxy Formation: Stellar populations, Dynamics and Morphology

We are a large, diverse, and very active research group aiming to provide a comprehensive picture for the formation of galaxies in the Universe. Rooted in detailed stellar population analysis, we are constantly exploring and developing new tools and ideas to understand how galaxies came to be what we now observe.

Martín Navarro