Goz, DavidDavidGozMonaco, PierluigiPierluigiMonacoMURANTE, GiuseppeGiuseppeMURANTECURIR, AnnaAnnaCURIR2020-03-272020-03-2720150035-8711http://hdl.handle.net/20.500.12386/23645We thank Volker Springel who provided us with the non-public version of the gadget -3 code. We acknowledge useful discussions with Stefano Borgani, Gabriella De Lucia, Emiliano Munari and Marianna Annunziatella. The simulations were carried out at the ‘Centro Interuniversitario del Nord-Est per il Calcolo Elettronico’ (CINECA, Bologna), with CPU time assigned under University-of-Trieste/CINECA and ISCRA grants, and at the CASPUR computing centre with CPU time assigned under two standard grants. This work is supported by the PRIN MIUR 2010-2011 grant ‘The dark Universe and the cosmic evolution of baryons: from current surveys to Euclid’, by the PRIN-MIUR 2012 grant ‘Evolution of Cosmic Baryons’, by the PRIN-INAF 2012 grant ‘The Universe in a Box: Multi-scale Simulations of Cosmic Structures’, by the INFN ‘INDARK’ grant, by the European Com- missions FP7 Marie Curie Initial Training Network CosmoComp (PITN-GA-2009-238356), by the FRA2012 grant of the University of Trieste and by ‘Consorzio per la Fisica di Trieste’.We present a quantification of the properties of bars in two N-body+ smoothed particle hydrodynamics cosmological simulations of spiral galaxies, named GA and AqC. The initial conditions were obtained using the zoom-in technique and represent two dark matter haloes of 2-3 × 10<SUP>12</SUP> M<SUB>☉</SUB>, available at two different resolutions. The resulting galaxies are presented in the companion paper of Murante et al. We find that the GA galaxy has a bar of length 8.8 kpc, present at the two resolution levels even though with a slightly different strength. Classical bar signatures (e.g. pattern of streaming motions, high m = 2 Fourier mode with roughly constant phase) are consistently found at both resolutions. Though a close encounter with a merging satellite at z ̃ 0.6 (mass ratio 1: 50) causes a strong, transient spiral pattern and some heating of the disc, we find that bar instability is due to secular process, caused by a low Toomre parameter Q ≲ 1 due to accumulation of mass in the disc. The AqC galaxy has a slightly different history: it suffers a similar tidal disturbance due to a merging satellite at z ̃ 0.5 but with a mass ratio of 1: 32, that triggers a bar in the high-resolution simulation, while at low resolution the merging is found to take place at a later time, so that both secular evolution and merging are plausible triggers for bar instability.STAMPAenArticle10.1093/mnras/stu25572-s2.0-84922575880000350272900063https://academic.oup.com/mnras/article/447/2/1774/2593774?searchresult=1https://arxiv.org/abs/1412.28832015MNRAS.447.1774GFIS/05 - ASTRONOMIA E ASTROFISICA