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



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Eliche Moral, María del Carmen and González García, A. C. and Balcells, M. and Aguerri, J. A. L. and Gallego Maestro, Jesús and Zamorano Calvo, Jaime and Prieto, M. (2011) A minor merger origin for stellar inner discs and rings in spiral galaxies. Astronomy and astrophysics, 533 . ISSN 0004-6361

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Official URL: http://dx.doi.org/10.1051/0004-6361/201116509


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.

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© ESO 2011. We thank our anonymous referee whose suggestions helped us to improve the clarity and presentation of the results. We are also grateful to P. Erwin and L. Sparke for the permission to reproduce some figures from Erwin & Sparke (2003), and to the AAS for providing this permission too. Supported by the Spanish Ministry of Science and Innovation (MICINN) under projects AYA2009-10368, AYA2006-12955, and AYA2009-11137, and by the Madrid Regional Government through the AstroMadrid Project (CAM S2009/ESP-1496, http://www.laeff.cab.inta-csic.es/projects/astromadrid/main/index.php). Funded by the Spanish MICINN under the Consolider-Ingenio 2010 Program grant CSD2006-00070: "First Science with the GTC" (http://www.iac.es/consolider-ingenio-gtc/). A.C.G.G. is a Ramón y Cajal Fellow of the Spanish MICINN.

Uncontrolled Keywords:Sight velocity distributions; Double-barred galaxies; Integral-field absorption; Emission-line kinematics; Star-formation history; Elliptic galaxies; Sauron project; Nuclear rings; Lenticular galaxies; Central regions
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
ID Code:33732
Deposited On:28 Oct 2015 16:03
Last Modified:10 Dec 2018 15:05

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