Effects of galaxy–satellite interactions on bar formation

Abstract

Aims. We aim to show how encounters with low-mass satellite galaxies may alter the bar formation in a Milky Way-like disc galaxy. Methods. We use high-resolution N-body simulations of a disc galaxy prone to mild bar instability. For realistic initial conditions of satellites, we take advantage of cosmological simulations of Milky Way-like dark matter haloes. Results. The satellites may have a significant impact on the time of bar formation. Some runs with satellites demonstrate a delay, while others show an advancement in bar formation compared to the isolated run, with such time differences reaching ∼ 1 Gyr. Meanwhile, the final bar configuration, including its very appearance and the bar characteristics such as the pattern speed and the exponential growth rate of its amplitude are independent of the number of encounters and their orbits. The contribution of satellites with masses below 10 9 M ⊙ is insignificant, unless their pericentre distances are small. We suggest that the encounters act indirectly via inducing perturbations across the disc that evolve to delayed waves in the central part and interfere with an emerging seed bar. The predicted effect for the present-day host galaxy is expected to be even more significant at redshifts z 0.5.

External versus internal triggers of bar formation in cosmological zoom-in simulations

“…In agreement with our investigation, Moetazedian et al (2017) find that the only effect of the satellites is to either slightly anticipate or delay the bar growth (by at most ∼ 1 Gyr), whereas the main properties of the bar as well as its growth rate remain almost identical. We stress that our results and those discussed in Moetazedian et al (2017) complement each other. On one hand, our study takes into account the full assembly history of the main galaxy as well as the effect of gas, whereas both these aspects are not included in Moetazedian et al (2017).…”

“…We stress that our results and those discussed in Moetazedian et al (2017) complement each other. On one hand, our study takes into account the full assembly history of the main galaxy as well as the effect of gas, whereas both these aspects are not included in Moetazedian et al (2017). On the other hand, the idealised nature of Figure 11.…”

“…As mentioned above, some studies claim that the global effect of the gravitational perturbers could be summarised in a growth/formation inhibition (Li et al 2009;Lin et al 2014). It is interesting to compare our results to similar recent findings obtained by Moetazedian et al (2017), who detailed the effect of low-mass satellites on the bar growth in a barunstable galaxy. The masses, tidal radii, and impact parameters of the perturbers are inferred from the cosmological Aquarius-D simulation (Springel et al 2008).…”

“…the Moetazedian et al (2017) initial conditions results in an higher level of axisymmetry, which allows for a better characterization of the initial seeding of the bar. As an example, Moetazedian et al (2017) were able to follow the evolution of the bar strength parameter A 2 9 down to fluctuations of the order of 10 −3 , well below the physical noise due to the small substructures present in our study. The consistency of the findings in such different studies strongly supports the internal/secular origin of bars in field galaxies.…”

“…Indeed, in numerical experiments the whole 3D distribution of matter is completely characterized at any needed time and it is, in principle, possible to study the effect of every single interaction on every galaxy undergoing bar instability (e.g. Moetazedian et al 2017). Unfortunately, the number of studies that focus on the study of bars in a fully cosmological perspective, including the growth of the host galaxy through a sequence of mergers as well as accretion of diffuse gas, is still limited, as they require high spatial resolution ( ∼ < 100 pc, in order to properly resolve the stellar dynamics within the bar region) while evolving a large cosmological box (Romano-Díaz et al 2008;Kraljic et al 2012;Scannapieco & Athanassoula 2012;Goz et al 2015;Okamoto et al 2015;Spinoso et al 2017;Algorry et al 2017;Soko lowska et al 2017).…”