The rise and fall of bars in disc galaxies from z = 1 to z = 0

Abstract

Context. Stellar bars are non-axisymmetric structures found in over 30 per cent of massive disc galaxies in the local Universe. The environment could play a significant role in determining whether or not a spiral galaxy is likely to develop a bar. Aims. We investigate the influence of the environment on the evolution of barred and unbarred disc galaxies with a mass of larger than 1010 M⊙ from z = 1 down to z = 0, employing the TNG50 magnetic-hydrodynamical simulation. Methods. We determined the fraction of barred galaxies that conserve their bar and the fraction of those that lost it by z = 0. We also estimate the fraction of unbarred galaxies at z = 1 that develop a bar at later times. We study the merger histories and the distance of close companions for each category to understand the role of the environment in the evolution of these galaxies. Results. We find that 49 per cent of z = 1 disc galaxies undergo a morphological transformation, transitioning into either a lenticular or spheroidal galaxy, while the other 51 per cent retain the large disc shape. The morphological alteration is mostly influenced by the environment. Lenticular and spheroidal galaxies tend to exist in denser environments and have more frequent mergers compared to disc galaxies. We find that bars are stable after they have formed, as over half of the barred galaxies (60.2 per cent) retain the bar structure and have experienced fewer mergers compared to those galaxies that lose their bars (5.6 per cent). These latter galaxies start with weaker and shorter bars at z = 1, are influenced by tidal interactions, and are frequently observed in more populated areas. Additionally, our study reveals that less than 20 per cent of unbarred galaxies will never develop a bar and exhibit the quietest merger history. Unbarred galaxies that undergo bar formation after z = 1 more frequently experience a merger event. Furthermore, tidal interactions with a close companion may account for bar formation in at least one-third of these instances. Conclusions. Our findings highlight that stable bars are prevalent in disc galaxies. Bar evolution may nonetheless be affected by the environment. Interactions with nearby companions or tidal forces caused by mergers have the capacity to disrupt the disc. This perturbance may materialise as the dissolution of the bar, the formation of a bar, or, in its most severe form, the complete destruction of the disc, resulting in morphological transformation. Bars that are weak and short at z = 1 and undergo major or minor mergers may eventually dissolve, whereas unbarred galaxies that enter crowded environments or experience a merger may develop a bar.